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diff --git a/old/67282-h/67282-h.htm b/old/67282-h/67282-h.htm deleted file mode 100644 index d64a863..0000000 --- a/old/67282-h/67282-h.htm +++ /dev/null @@ -1,31840 +0,0 @@ -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" - "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> -<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> - <head> - <meta http-equiv="Content-Type" content="text/html;charset=utf-8" /> - <meta http-equiv="Content-Style-Type" content="text/css" /> - <title> - The Principles of Biology, Vol. II, by Herbert Spencer—A Project Gutenberg eBook - </title> - <link rel="coverpage" href="images/cover.jpg" /> - <style type="text/css"> - -body { - margin-left: 10%; - margin-right: 10%; -} - - h1,h2,h3,h4 { - text-align: center; /* all headings centered */ - clear: both; - font-weight: normal; -} - -h2.smaller {font-size: 120%;} - -h4.smaller {font-size: 90%;} - -.subhed { display: block; margin-top: 1em; font-size: 80%; font-weight: normal; } - -.subhed1 { display: block; margin-top: 1em; font-size: 75%; font-weight: normal; } - -p { - margin-top: .51em; - text-align: justify; - margin-bottom: .49em; - text-indent: 1.2em; -} - -.p-left {text-indent: 0em; } - -.p0 {margin-top: 0em;} -.p2 {margin-top: 2em;} -.p4 {margin-top: 4em;} -.p6 {margin-top: 6em;} - -hr { - width: 33%; - margin-top: 2em; - margin-bottom: 2em; - margin-left: 33.5%; - margin-right: 33.5%; - clear: both; -} - -hr.tb {width: 45%; margin-left: 27.5%; margin-right: 27.5%;} -hr.chap {width: 65%; margin-left: 17.5%; margin-right: 17.5%;} -@media print { hr.chap {display: none; visibility: hidden;} } - -hr.full {width: 80%; margin-top: .2em; margin-bottom: 1em; margin-left: 10%; margin-right: 10%;} - -div.chapter {page-break-before: always;} - - -ul { list-style-type: none; } -li.i1 {text-indent: 1em;} - -table { -margin: auto; -width:auto; -border: 0; -border-spacing: 0; -border-collapse: collapse; } - -td { -padding: .05em .2em .2em 2.5em; -border: .1em none white; -text-align: left; -text-indent: -2em; } - -th.chap { -font-weight: normal; -font-size: x-small; -text-align: left; -padding-left: 1em; } - -th.pag { -font-weight: normal; -font-size: x-small; -text-align: right; -padding-left: 2em; } - -td.chn { -text-align: right; -vertical-align: top; -padding-right: 1em; } - -td.chn1 { -text-align: left; -vertical-align: top; -padding-right: 1em; } - -td.cht { -text-align: left; -vertical-align: top; -padding-left: 0em; -text-indent: -1em; -font-variant: small-caps;} - -td.cht1 { -text-align: left; -vertical-align: top; -padding-left: 0em; -text-indent: -1em;} - -td.pag { -text-align: right; -vertical-align: bottom; -padding-left: 4em;} - -td.header { -padding: 1.5em .2em .2em .2em; -text-align: center; -text-indent: 0em; -font-size: 100%; } - - - -.pagenum { /* uncomment the next line for invisible page numbers */ - /* visibility: hidden; */ - position: absolute; - left: 92%; - font-size: smaller; - text-align: right; - font-style: normal; - font-weight: normal; - font-variant: normal; -} /* page numbers */ - - -.blockquot { - margin-left: 5%; - margin-right: 10%; - font-size: 90%; -} - - -.center {text-align: center;} - -.left2 {text-align: left; - margin-left: 2em;} - -.smcap {font-variant: small-caps;} - -.xs { font-size: x-small;} - -.sm { font-size: small;} - -.smaller {font-size: 90%; } - -.hangingindent { - padding-left: 2em ; - text-indent: -2em ;} - -.hangingindent1 { - padding-left: 3em ; - text-indent: -2em ;} - - -/* Images */ - -img { - max-width: 100%; - height: auto; -} - -.figcenter { - margin: auto; - text-align: center; - page-break-inside: avoid; - max-width: 100%; -} - - -/* Footnotes */ -.footnotes {border: 1px dashed;} - -.footnote {margin-left: 10%; margin-right: 10%; font-size: 0.9em;} - -.footnote .label {position: absolute; right: 84%; text-align: right;} - -.fnanchor { - vertical-align: super; - font-size: .8em; - text-decoration: - none; -} - - -/* Transcriber's notes */ -.transnote {background-color: #E6E6FA; - color: black; - font-size:smaller; - padding:0.5em; - margin-bottom:5em; - font-family:sans-serif, serif; } - - </style> - </head> -<body> -<p style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of The Principles of Biology, Volume 2 (of 2), by Herbert Spencer</p> -<div style='display:block; margin:1em 0'> -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online -at <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you -are not located in the United States, you will have to check the laws of the -country where you are located before using this eBook. -</div> - -<p style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: The Principles of Biology, Volume 2 (of 2)</p> -<p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em'>Author: Herbert Spencer</p> -<p style='display:block; text-indent:0; margin:1em 0'>Release Date: January 30, 2022 [eBook #67282]</p> -<p style='display:block; text-indent:0; margin:1em 0'>Language: English</p> - <p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em; text-align:left'>Produced by: Karin Spence, Tim Lindell, Adrian Mastronardi, Josep Cols Canals and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/American Libraries.)</p> -<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK THE PRINCIPLES OF BIOLOGY, VOLUME 2 (OF 2) ***</div> - - - - -<h1>THE PRINCIPLES OF<br /> -BIOLOGY</h1> - - -<p class="center p-left sm p4 ">BY</p> - -<p class="center p-left">HERBERT SPENCER</p> - - -<p class="center p-left sm p4"><i>IN TWO VOLUMES</i><br /> -VOL. II</p> - -<p class="center p-left p2 xs">REVISED AND ENLARGED EDITION<br /> -1899</p> - -<p class="center p-left">NEW YORK<br /> -D. APPLETON AND COMPANY<br /> -1900</p> - -<div class="chapter"> - -<p class="center p-left xs p6"><span class="smcap">Copyright</span>, 1867, 1899,<br /> -<span class="smcap">By</span> D. APPLETON AND COMPANY.</p></div> - - -<div class="chapter"> -<p><span class="pagenum" id="Page_v">[v]</span></p> - -<h2 class="smaller">PREFACE<br /> -<span class="subhed">TO THE REVISED AND ENLARGED EDITION OF VOL. II.</span></h2></div> - -<p>To the statements made in the preface to the first volume of this -revised edition, there must here be added a few having special -reference to this second volume.</p> - -<p>One of them is that the revision has not been carried out in quite the -same way, but in a way somewhat less complete. When reviewing the first -volume a friendly critic, Prof. Lloyd Morgan, said:—</p> - -<div class="blockquot"> - -<p>“But though the intellectual weight has also been augmented, -it is an open question whether it would not have been wiser -to leave intact a treatise, &c... relegating corrections and -additions to notes and appendices.”</p> -</div> - -<p>I think that Prof. Morgan is right. Though at the close of the preface -to volume I, I wrote:—“in all sections not marked as new, the -essential ideas set forth are the same as they were in the original -edition of 1864,” yet the reader who has not read this statement, -or does not bear it in mind, will suppose that all or most of the -enunciated conceptions are of recent date, whereas only a small part of -them are. I have therefore decided to follow, in this second volume, a -course somewhat like that suggested by Prof. Morgan—somewhat like, I -say, because in sundry cases the amendments could not be satisfactorily -made by appended notes.</p> - -<p><span class="pagenum" id="Page_vi">[vi]</span></p> - -<p>But there has been a further reason for this change of method. An -invalid who is nearly eighty cannot with prudence enter upon work which -will take long to complete. Hence I have thought it better to make the -needful alterations and additions in ways requiring relatively moderate -time and labour.</p> - -<p>The additions made to this volume are less numerous and less important -than those made to the first volume. A new chapter ending Part V, on -“The Integration of the Organic World,” serves to round off the general -theory of Evolution in its application to living things. Beyond a new -section (<a href="#sect289">§ 289</a><i>a</i>) and the various foot-notes, serving chiefly the -purpose of elucidation, there are notes of some significance appended -to Chapters I, III, IV, and V, in Part IV, Chapters V and VIII, in Part -V, and Chapters IX, X, and XII in Part VI. Moreover there are three -further appendices, D<sup>2</sup>, F, and G, which have, I think, considerable -significance as serving to make clearer some of the views expressed in -the body of the work.</p> - -<p>Turning from the additions to the revisions, I have to say that the -aid needed for bringing up to date the contents of this volume, has -been given me by the gentlemen who gave me like aid in revising the -first volume: omitting Prof. Perkin, within whose province none of the -contents of this volume fall. Plant-Morphology and Plant-Physiology -have been overseen by Mr. A. G. Tansley. Criticisms upon parts dealing -with Animal Morphology I owe to Mr. J. T. Cunningham and Prof. E. W. -MacBride. And the statements included under Animal Physiology have been -checked by Mr. W. B. Hardy.</p> - -<p><span class="pagenum" id="Page_vii">[vii]</span></p> - -<p>For reasons like those named in the preface to the first volume, I -have not submitted the proofs of this revised second volume to these -gentlemen: a fact which it is needful to name, since one or other of -them might else be held responsible for some error which is not his but -mine. It is the more requisite to say this because while, in respect -of matters of fact, I have, save in one or two cases, accepted their -corrections as not to be questioned, I have not always done this in -respect of matters of inference, but in sundry places have adhered to -my own interpretations.</p> - -<p>Perhaps I may be excused for expressing some satisfaction that I -have not been obliged to relinquish the views set forth in 1864–7. -The hypothesis of physiological units—or, as I would now call them, -constitutional units—has been adopted by several zoologists under -modified forms. So far as I am aware, the alleged general law of -organic symmetry has not called forth any manifestations of dissent. -The suggested theory of vertebrate structure appears to have become -current; and from the investigations of the late Prof. Cope, has -received verification. The conclusions drawn in Part VI on “The Laws -of Multiplication,” have not, I believe, been controverted. And though -only some works on botany have given currency to the doctrine set forth -in Appendix C, “On Circulation and the Formation of Wood in Plants,” -yet I have met with no attempt to disprove it. The only views contested -by certain of the gentlemen above named, are those concerning the -origin of the two great phænogamic types of plants, and the origin of -the annulose type of animals. I have not, however,—perhaps because -of natural bias—found myself compelled<span class="pagenum" id="Page_viii">[viii]</span> to surrender these views. My -reasons for adhering to them will be found in notes to the ends of -Chapters III and IV in Part IV, and in Appendix D<sup>2</sup>.</p> - -<p>On now finally leaving biological studies, it remains only to say that -I am glad I have survived long enough to give this work its finished -form.</p> - -<p><span class="smcap">Brighton</span>,<br /> - -<span class="left2"><i>October, 1899</i>.</span></p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_ix">[ix]</span></p> - -<h2 class="smaller">PREFACE TO VOL. II.</h2> -</div> - - -<p>The proof sheets of this volume, like those of the last volume, have -been looked through by Dr. Hooker and Prof. Huxley; and I have, as -before, to thank them for their valuable criticisms, and for the -trouble they have taken in checking the numerous statements of fact on -which the arguments proceed. The consciousness that their many duties -render time extremely precious to them, makes me feel how heavy is my -obligation.</p> - -<p>Part IV., with which this volume commences, contains numerous figures. -Nearly one half of them are repetitions, mostly altered in scale and -simplified in execution, of figures, or parts of figures, contained -in the works of various Botanists and Zoologists. Among the authors -whom I have laid under contribution, I may name Berkeley, Carpenter, -Cuvier, Green, Harvey, Hooker, Huxley, Milne-Edwards, Ralfs, Smith. -The remaining figures, numbering 150, are from original sketches and -diagrams.</p> - -<p>The successive instalments which compose this volume, were issued -to the Subscribers at the following dates:—No. 13 (pp. 1–80) in -January, 1865; No. 14 (pp. 81–160) in June, 1865; No. 15 (pp. 161–240) -in December, 1865; No. 16 (pp. 241–320) in June, 1866; No. 17 (pp. -321–400) in November, 1866; and No. 18 (pp. 401–566) in March, 1867.</p> - -<p><span class="smcap">London</span>, <i>March 23rd, 1867</i>.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_xi">[xi]</span></p> - -<h2>CONTENTS OF VOL. II.</h2> -</div> - -<table summary="contents" class="smaller"> - <tr> - <td class="header" colspan="3">PART IV.—MORPHOLOGICAL DEVELOPMENT.</td> - </tr> - - <tr> - <th class="chap">CHAP.</th> - <th></th> - <th class="pag">PAGE</th> - </tr> - - <tr> - <td class="chn">I.—</td> - <td class="cht">The problems of morphology</td> - <td class="pag"><a href="#Page_3">3</a></td> - </tr> - - <tr> - <td class="chn">II.—</td> - <td class="cht">The morphological composition of plants</td> - <td class="pag"><a href="#Page_17">17</a></td> - </tr> - - <tr> - <td class="chn">III.—</td> - <td class="cht1"><span class="smcap">The morphological composition of plants</span>—<i>Continued</i></td> - <td class="pag"><a href="#Page_37">37</a></td> - </tr> - - - <tr> - <td class="chn">IV.—</td> - <td class="cht">The morphological composition of animals</td> - <td class="pag"><a href="#Page_85">85</a></td> - </tr> - - <tr> - <td class="chn">V.—</td> - <td class="cht1"><span class="smcap">The morphological composition of animals</span>—<i>Continued</i></td> - <td class="pag"><a href="#Page_111">111</a></td> - </tr> - - <tr> - <td class="chn">VI.—</td> - <td class="cht">Morphological differentiation in plants</td> - <td class="pag"><a href="#Page_128">128</a></td> - </tr> - - <tr> - <td class="chn">VII.—</td> - <td class="cht">The general shapes of plants</td> - <td class="pag"><a href="#Page_134">134</a></td> - </tr> - - <tr> - <td class="chn">VIII.—</td> - <td class="cht">The shapes of branches</td> - <td class="pag"><a href="#Page_145">145</a></td> - </tr> - - <tr> - <td class="chn">IX.—</td> - <td class="cht">The shapes of leaves</td> - <td class="pag"><a href="#Page_152">152</a></td> - </tr> - - <tr> - <td class="chn">X.—</td> - <td class="cht">The shapes of flowers</td> - <td class="pag"><a href="#Page_161">161</a></td> - </tr> - - <tr> - <td class="chn">XI.—</td> - <td class="cht">The shapes of vegetal cells</td> - <td class="pag"><a href="#Page_175">175</a></td> - </tr> - - <tr> - <td class="chn">XII.—</td> - <td class="cht">Changes of shape otherwise caused</td> - <td class="pag"><a href="#Page_178">178</a></td> - </tr> - - <tr> - <td class="chn">XIII.—</td> - <td class="cht">Morphological differentiation in animals</td> - <td class="pag"><a href="#Page_183">183</a></td> - </tr> - - <tr> - <td class="chn">XIV.—</td> - <td class="cht">The general shapes of animals</td> - <td class="pag"><a href="#Page_186">186</a></td> - </tr> - - <tr> - <td class="chn">XV.—</td> - <td class="cht">The shapes of vertebrate skeletons</td> - <td class="pag"><a href="#Page_209">209</a></td> - </tr> - - <tr> - <td class="chn">XVI.—</td> - <td class="cht">The shapes of animal cells</td> - <td class="pag"><a href="#Page_228">228</a></td> - </tr> - - <tr> - <td class="chn">XVII.—</td> - <td class="cht">Summary of morphological development</td> - <td class="pag"><a href="#Page_231">231</a></td> - </tr> - - <tr> - <td class="header" colspan="3">PART V.—PHYSIOLOGICAL DEVELOPMENT.</td> - </tr> - - <tr> - <td class="chn">I.—</td> - <td class="cht">The problems of physiology</td> - <td class="pag"><a href="#Page_239">239</a></td> - </tr> - - <tr> - <td class="chn">II.—</td> - <td class="cht">Differentiations between the outer and inner tissues of plants</td> - <td class="pag"><a href="#Page_244">244</a></td> - </tr> - - <tr> - <td class="chn">III.—</td> - <td class="cht">Differentiations among the outer tissues of plants</td> - <td class="pag"><a href="#Page_251">251</a><span class="pagenum" id="Page_xii">[xii]</span></td> - </tr> - - <tr> - <td class="chn">IV.—</td> - <td class="cht">Differentiations among the inner tissues of plants</td> - <td class="pag"><a href="#Page_272">272</a></td> - </tr> - - <tr> - <td class="chn">V.—</td> - <td class="cht">Physiological integration in Plants</td> - <td class="pag"><a href="#Page_292">292</a></td> - </tr> - - <tr> - <td class="chn">VI.—</td> - <td class="cht">Differentiations between the outer and inner tissues of animals</td> - <td class="pag"><a href="#Page_299">299</a></td> - </tr> - - <tr> - <td class="chn">VII.—</td> - <td class="cht">Differentiations among the outer tissues of animals</td> - <td class="pag"><a href="#Page_309">309</a></td> - </tr> - - <tr> - <td class="chn">VIII.—</td> - <td class="cht">Differentiations among the inner tissues of animals</td> - <td class="pag"><a href="#Page_323">323</a></td> - </tr> - - <tr> - <td class="chn">IX.—</td> - <td class="cht">Physiological integration in animals</td> - <td class="pag"><a href="#Page_373">373</a></td> - </tr> - - <tr> - <td class="chn">X.—</td> - <td class="cht">Summary of physiological development</td> - <td class="pag"><a href="#Page_384">384</a></td> - </tr> - - <tr> - <td class="chn">X<sup>A</sup>.—</td> - <td class="cht">The integration of the organic world</td> - <td class="pag"><a href="#Page_396">396</a></td> - </tr> - - <tr> - <td class="header" colspan="3">PART VI.—LAWS OF MULTIPLICATION.</td> - </tr> - - <tr> - <td class="chn">I.—</td> - <td class="cht">The factors</td> - <td class="pag"><a href="#Page_411">411</a></td> - </tr> - - <tr> - <td class="chn">II.—</td> - <td class="cht"><i>À PRIORI</i> principle</td> - <td class="pag"><a href="#Page_417">417</a></td> - </tr> - - <tr> - <td class="chn">III.—</td> - <td class="cht">Obverse <i>À PRIORI</i> principle</td> - <td class="pag"><a href="#Page_424">424</a></td> - </tr> - - <tr> - <td class="chn">IV.—</td> - <td class="cht">Difficulties of inductive verification</td> - <td class="pag"><a href="#Page_432">432</a></td> - </tr> - - <tr> - <td class="chn">V.—</td> - <td class="cht">Antagonism between growth and asexual genesis</td> - <td class="pag"><a href="#Page_439">439</a></td> - </tr> - - <tr> - <td class="chn">VI.—</td> - <td class="cht">Antagonism between growth and sexual genesis</td> - <td class="pag"><a href="#Page_448">448</a></td> - </tr> - - <tr> - <td class="chn">VII.—</td> - <td class="cht">The antagonism between development and genesis, asexual and sexual</td> - <td class="pag"><a href="#Page_461">461</a></td> - </tr> - - <tr> - <td class="chn">VIII.—</td> - <td class="cht">Antagonism between expenditure and genesis</td> - <td class="pag"><a href="#Page_467">467</a></td> - </tr> - - <tr> - <td class="chn">IX.—</td> - <td class="cht">Coincidence between high nutrition and genesis</td> - <td class="pag"><a href="#Page_475">475</a></td> - </tr> - - <tr> - <td class="chn">X.—</td> - <td class="cht">Specialities of these relations</td> - <td class="pag"><a href="#Page_486">486</a></td> - </tr> - - <tr> - <td class="chn">XI.—</td> - <td class="cht">Interpretation and qualification</td> - <td class="pag"><a href="#Page_497">497</a></td> - </tr> - - <tr> - <td class="chn">XII.—</td> - <td class="cht">Multiplication of the human race</td> - <td class="pag"><a href="#Page_506">506</a></td> - </tr> - - <tr> - <td class="chn">XIII.—</td> - <td class="cht">Human population in the future</td> - <td class="pag"><a href="#Page_522">522</a></td> - </tr> - - <tr> - <td class="header" colspan="3">APPENDICES.</td> - </tr> - - <tr> - <td class="chn1">A.—</td> - <td class="cht">Substitution of axial for foliar organs in plants</td> - <td class="pag"><a href="#Page_541">541</a></td> - </tr> - - <tr> - <td class="chn1">B.—</td> - <td class="cht">A criticism on Prof. Owen’s theory of the vertebrate skeleton</td> - <td class="pag"><a href="#Page_548">548</a></td> - </tr> - - <tr> - <td class="chn1">C.—</td> - <td class="cht">On circulation and the formation of wood in plants</td> - <td class="pag"><a href="#Page_567">567</a></td> - </tr> - - <tr> - <td class="chn1">D.—</td> - <td class="cht">On the origin of the vertebrate type</td> - <td class="pag"><a href="#Page_599">599</a></td> - </tr> - - <tr> - <td class="chn1">D<sup>2</sup>.—</td> - <td class="cht">The annulose type</td> - <td class="pag"><a href="#Page_602">602</a></td> - </tr> - - <tr> - <td class="chn1">E.—</td> - <td class="cht">The shapes and arrangements of flowers</td> - <td class="pag"><a href="#Page_608">608</a></td> - </tr> - - <tr> - <td class="chn1">F.—</td> - <td class="cht">Physiological (or constitutional) units</td> - <td class="pag"><a href="#Page_612">612</a></td> - </tr> - - <tr> - <td class="chn1">G.—</td> - <td class="cht">The inheritance of functionally-caused modifications</td> - <td class="pag"><a href="#Page_618">618</a></td> - </tr> -</table> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> - -<h2>PART IV.<br /> -<span class="subhed">MORPHOLOGICAL DEVELOPMENT.</span></h2></div> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_3">[3]</span></p> - -<h3>CHAPTER I.<br /> -<span class="subhed1">THE PROBLEMS OF MORPHOLOGY.</span></h3></div> - -<p class="p2">§ 175. The division of Morphology from Physiology, is one which may -be tolerably-well preserved so long as we do not carry our inquiries -beyond the empirical generalizations of their respective phenomena; but -it is one which becomes in great measure nominal, when the phenomena -are to be rationally interpreted. It would be possible, after analyzing -our Solar System, to set down certain general truths respecting the -sizes and distances of its primary and secondary members, omitting -all mention of their motions; and it would be possible to set down -certain other general truths respecting their motions, without -specifying their dimensions or positions, further than as greater -or less, nearer or more remote. But on seeking to account for these -general truths, arrived at by induction, we find ourselves obliged to -consider simultaneously the relative sizes and places of the masses, -and the relative amounts and directions of their motions. Similarly -with organisms. Though we may frame sundry comprehensive propositions -respecting the arrangements of their organs, considered as so many -inert parts; and though we may establish several wide conclusions -respecting the separate and combined actions of their organs, without -knowing anything definite respecting the forms and positions of these -organs; yet we cannot reach such a rationale of the facts as<span class="pagenum" id="Page_4">[4]</span> the -hypothesis of Evolution aims at, without contemplating structures and -functions in their mutual relations. Everywhere structures in great -measure determine functions; and everywhere functions are incessantly -modifying structures. In Nature the two are inseparable co-operators; -and Science can give no true interpretation of Nature without keeping -their co-operation constantly in view. An account of organic evolution, -in its more special aspects, must be essentially an account of the -interactions of structures and functions, as perpetually altered by -changes of conditions.</p> - -<p>Hence, when treating apart Morphological Development and Physiological -Development, all we can do is to direct our attention mainly to the -one or to the other, as the case may be. In dealing with the facts of -structure, we must consider the facts of function only in such general -way as is needful to explain the facts of structure; and conversely -when dealing with the facts of function.</p> - - -<p class="p2">§ 176. The problems of Morphology fall into two distinct classes, -answering respectively to the two leading aspects of Evolution. In -things which evolve there go on two processes—increase of mass -and increase of structure. Increase of mass is primary, and in -simple evolution takes place almost alone. Increase of structure is -secondary, accompanying or following increase of mass with more or -less regularity, wherever evolution rises above that form which small -inorganic bodies, such as crystals, present to us. As the fundamental -antagonism between Dissolution and Evolution consists in this, that -while the one is an integration of motion and disintegration of matter, -the other is an integration of matter and disintegration of motion; and -as this integration of matter accompanying disintegration of motion, -is a necessary antecedent to the differentiation of the matter so -integrated; it follows that questions concerning the mode in which the -parts are united into a whole, must be dealt with before<span class="pagenum" id="Page_5">[5]</span> questions -concerning the mode in which these parts become modified.<a id="FNanchor_1" href="#Footnote_1" class="fnanchor">[1]</a></p> - -<p>This is not obviously a morphological question. But an illustration or -two will make it manifest that fundamental differences may be produced -between aggregates by differences in the degrees of composition of the -increments: the ultimate units of the increments being the same. Thus -an accumulation of things of a given kind may be made by adding one -at a time. Or the things may be tied up into bundles of ten, and the -tens placed together. Or the tens may be united into hundreds, and a -pile of hundreds formed. Such unlikenesses in the structures of masses -are habitually seen in our mercantile transactions. Articles which -the consumer recognizes as single, the retailer keeps wrapped up in -dozens, the wholesaler sends in gross, and the manufacturer supplies -in packages of a hundred gross. That is, they severally increase -their stocks by units of simple, of compound, and of doubly-compound -kinds. Similarly result those differences of morphological composition -which we have first to consider. An organism consists of units. -These units may be aggregated into a mass by the addition of unit -to unit. Or they may be united into groups, and the groups joined -together. Or these groups of groups may be so combined as to form a -doubly-compound aggregate. Hence there arises respecting each organic -form the question—is its composition of the first, second, third, -or fourth order?—does it exhibit units of a singly-compounded kind -only, or are these consolidated into units of a doubly-compounded -kind, or a triply-compounded kind? And if it displays double or triple -composition,<span class="pagenum" id="Page_6">[6]</span> the homologies of its different parts become problems. -Under the disguises induced by the consolidation of primary, secondary, -and tertiary units, it has to be ascertained which answer to which, in -their degrees of composition.</p> - -<p>Such questions are more intricate than they at first appear; since, -besides the obscurities caused by progressive integration, and those -due to accompanying modifications of form, further obscurities -result from the variable growths of units of the different orders. -Just as an army may be augmented by recruiting each company, without -increasing the number of companies; or may be augmented by making up -the full complement of companies in each regiment, while the number -of regiments remains the same; or may be augmented by putting more -regiments into each division, other things being unchanged; or may be -augmented by adding to the number of its divisions without altering -the components of each division; or may be augmented by two or three -of these processes at once; so, in organisms, increase of mass may -result from additions of units of the first order, or those of the -second order, or those of still higher orders; or it may be due to -simultaneous additions to units of several orders. And this last mode -of integration being the general mode, puts difficulties in the way of -analysis. Just as the structure of an army would be made less easy to -understand if companies often outgrew regiments, or regiments became -larger than brigades; so these questions of morphological composition -are complicated by the indeterminate sizes of the units of each -kind: relatively-simple units frequently becoming more bulky than -relatively-compound units.</p> - - -<p class="p2">§ 177. The morphological problems of the second class are those having -for their subject-matter the changes of shape which accompany changes -of aggregation. The most general questions respecting the structure -of an organism, having been answered when it is ascertained of what -units it is composed as a whole, and in its several parts; there come -the more<span class="pagenum" id="Page_7">[7]</span> special questions concerning its form—form in the ordinary -sense. After the contrasts caused by variations in the process of -integration, we have to consider the contrasts caused by variations -in the process of differentiation. To speak specifically—the shape -of the organism as a whole, irrespective of its composition, has to -be accounted for. Reasons have to be found for the unlikeness between -its general outlines and the general outlines of allied organisms. And -there have to be answered kindred inquiries respecting the proportions -of its component parts:—Why, among such of these as are homologous -with one another, have there arisen the differences that exist? And how -have there been produced the contrasts between them and the homologous -parts of organisms of the same type?</p> - -<p>Very numerous are the heterogeneities of form presenting themselves -for interpretation under these heads. The ultimate morphological -units combined in any group, may be differentiated individually, or -collectively, or both: each of them may undergo changes of shape; -or some of them may be changed and others not; or the group may be -rendered multiform by the greater growth of some of its units than of -others. Similarly with the compound units arising by union of these -simple units. Aggregates of the second order may be made relatively -complex in form, by inequalities in the rates of multiplication of -their component units in diverse directions; and among a number of such -aggregates, numerous unlikenesses may be constituted by differences in -their degrees of growth, and by differences in their modes of growth. -Manifestly, at each higher stage of composition the possible sources of -divergence are multiplied still further.</p> - -<p>That facts of this order can be accounted for in detail is not to -be expected—the data are wanting. All that we may hope to do is to -ascertain their general laws. How this is to be attempted we will now -consider.</p> - - -<p class="p2">§ 178. The task before us is to trace throughout these<span class="pagenum" id="Page_8">[8]</span> phenomena -the process of evolution; and to show how, as displayed in them, it -conforms to those first principles which evolution in general conforms -to. Two sets of factors have to be taken into account. Let us look at -them.</p> - -<p>The factors of the first class are those which tend directly to -change an organic aggregate, in common with every other aggregate, -from that more simple form which is not in equilibrium with incident -forces, to that more complex form which is in equilibrium with them. -We have to mark how, in correspondence with the universal law that -the uniform lapses into the multiform, and the less multiform into -the more multiform, the parts of each organism are ever becoming -further differentiated; and we have to trace the varying relations -to incident forces by which further differentiations are entailed. -We have to observe, too, how each primary modification of structure, -induced by an altered distribution of forces, becomes a parent of -secondary modifications—how, through the necessary multiplication of -effects, change of form in one part brings about changes of form in -other parts. And then we have also to note the metamorphoses constantly -being induced by the process of segregation—by the gradual union -of like parts exposed to like forces, and the gradual separation of -like parts exposed to unlike forces. The factors of the second class -which we have to keep in view throughout our interpretations, are -the formative tendencies of organisms themselves—the proclivities -inherited by them from antecedent organisms, and which past processes -of evolution have bequeathed. We have seen it to be inferable from -various orders of facts (§§ <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect65">65</a>, <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect84">84</a>, <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect97">97–97<i>g</i></a>), that organisms are -built up of certain highly-complex molecules, which we distinguished as -physiological units [or constitutional units as they might otherwise -be called]—each kind of organism being built up of units peculiar to -itself. We recognized in these units, powers of arranging themselves -into the forms of the organisms to which they belong; analogous -to the powers which the molecules of inorganic substances have of -aggregating into specific crystalline<span class="pagenum" id="Page_9">[9]</span> forms. We have consequently -to regard this proclivity of the physiological units, as producing, -during the development of any organism, a combination of internal -forces that expend themselves in working out a structure in equilibrium -with the forces to which ancestral organisms were exposed; but not in -equilibrium with the forces to which the existing organism is exposed, -if the environment has been changed. Hence the problem in all cases is, -to ascertain the resultant of internal organizing forces, tending to -reproduce the ancestral form, and external modifying forces, tending -to cause deviations from that form. Moreover, we have to take into -account, not only the characters of immediately-preceding ancestors, -but also those of their ancestors, and ancestors of all degrees of -remoteness. Setting out with rudimentary types, we have to consider -how, in each successive stage of evolution, the structures acquired -during previous stages have been obscured by further integrations -and further differentiations; or, conversely, how the lineaments of -primitive organisms have all along continued to manifest themselves -under the superposed modifications.</p> - - -<p class="p2">§179. Two ways of carrying on the inquiry suggest themselves. We may -go through the several great groups of organisms, with the view of -reaching, by comparison of parts, certain general truths respecting -the homologies, the forms, and the relations of their parts; and then, -having dealt with the phenomena inductively, may retrace our steps with -the view of deductively interpreting the general truths reached. Or, -instead of thus separating the two investigations, we may carry them on -hand in hand—first establishing each general truth empirically, and -then proceeding to the rationale of it. This last method will, I think, -conduce to both brevity and clearness. Let us now thus deal with the -first class of morphological problems.</p> - - -<p>[<span class="smcap">Note.</span>—In preparation for treating of morphological -development,<span class="pagenum" id="Page_10">[10]</span> sundry other general considerations should have been -included in the foregoing chapter when originally published. This seems -the most appropriate place for now naming them. Some were implicitly -contained in the first volume, but it will be well definitely to state -these, as well as the others not yet implied.</p> - -<p>Interpretation of the forms of organisms and the forms of their parts, -must depend mainly on the conclusions previously drawn respecting -their phylogeny; and the drawing of such conclusions must be guided -by recognition of the various factors of Evolution, as well as by -recognition of certain extremely general results of Evolution and -certain concomitants of Evolution.</p> - -<p>A primary one among these is that no existing species can exhibit -more than approximately the ancestral structure of any other existing -species. As all ancestors have disappeared, so, in a greater or less -degree, the traits, specific, generic, or ordinal, which distinguished -the earlier of them have disappeared. Setting out with the familiar -symbol, a tree, let us regard its peripheral twigs as representing -extant species; let us assume that the interior of the tree is filled -up with some supporting substance, leaving only the ends of the -living twigs projecting; and let us suppose the trunk, main branches, -secondary branches, tertiary branches, &c., have decayed away. -Then if we take these decayed parts to stand for the divergent and -re-divergent lines of evolution which are represented by fossils in the -Earth’s crust, it will be manifest, first, that no one of the living -superficial twigs (or species) exhibits the ancestral organization -whence any other of the living superficial twigs (or species) has been -developed; it will be manifest, second, that the generic structure -inherited by any existing species must be a structure out of which -came sundry allied species—the fork, as it were, at which adjacent -twigs diverged; and third, that the ancestor of an order must, in like -manner, be sought at some point deeper down in the symbolic tree—a -place of divergence of<span class="pagenum" id="Page_11">[11]</span> the sub-branches representing allied genera. -Similarly with the ancestral types of classes, still deeper down in -the tree or further back in time. So that phylogeny becomes more and -more speculative as its questions become more and more radical. And -the difficulty is made greater by the deficiency of palæontological -evidence.</p> - -<p>One obvious corollary is that an ancestral type from which sundry -allied types now existing diverged, was, speaking generally, simpler -than these; since the divergent types became different by the -superposing of modifications, adding to their complexities. There is -a further reason for inferring that the least specialized member of -any group is more like the remote ancestor than any of the others; for -every adaptation stands in the way of subsequent re-adaptations: it -presents a greater amount of structure to be undone. To get some idea -of the ancestral type where no extant member of the group is manifestly -simpler than the rest, the method must be to take all its extant -members and, after letting their differences mutually cancel, observe -what remains common to them all.</p> - -<p>But there are difficulties standing in the way of phylogeny, and -consequently of morphology, much greater than these. Returning to -our symbolic tree, it is clear that it would be far from easy to say -of any one twig which extinct sub-branch, branch, and main branch it -belonged to, even supposing that the growths of all parts had been -uniformly outwards. Immensely more perplexing, then, must be the -affiliation if various of the branches, sub-branches, &c., have sent -out backward-growing shoots which have come to the surface only after -prolonged retrograde courses, and if other branches have sent shoots -into regions occupied by alien branches—shoots bearing twigs which -come to the surface along with those to which they are but remotely -allied. The problems of origin and of structure which organisms -present, are met by both of the difficulties thus symbolized.</p> - -<p>One of them arises from the prevalence of retrograde<span class="pagenum" id="Page_12">[12]</span> metamorphoses. -Throughout the animal world these are variously displayed by parasites, -multitudinous in their kinds; for most of them belong to types -much higher in organization. Changed habits and consequent changed -structures have so transferred them that only by study of their -embryonic stages can their kinships be made out. And these retrograde -metamorphoses, conspicuous among parasites, have, in the course of -evolution, affected some members of all groups; for in all groups the -struggle for existence has compelled some to adopt careers less trying -but less profitable.</p> - -<p>Not only by forcing on many kinds of organisms simpler ways of living, -and consequent degeneracy, has the universal competition caused -obscuring transformations. It has done this also by tempting many other -kinds of organisms to adopt ways of life not simpler than before but -merely different. Pressure continually prompts every type to intrude on -other types’ spheres of activity; and so causes it to assume certain -structural characters of the types whose spheres it invades, masking -its previous characters. Modifications hence arising have, in the great -mass of cases, been superposed one on another time after time. The -aquatic animal becomes through several transitions a land-animal, and -then the land-animal through other transitions becomes now an aërial -animal like the bat and now an aquatic animal like the whale. Certain -kinds of birds furnish extreme illustrations. There was the change from -the fish to the water-breathing amphibian and then to the air-breathing -amphibian; thence to the reptile living on the Earth’s surface; thence -to the flying reptile and the bird; then came the diving birds, joining -with their aërial life a life passed partly in the water; and finally -came a type like the penguin, in which the power of flight has been -lost and the water has again become the almost exclusive medium, except -for breathing. Of course the mouldings and re-mouldings of structure -resulting from these successive unlike modes of life, in many cases put -great difficulties in the way of ascertaining<span class="pagenum" id="Page_13">[13]</span> which are the original -corresponding parts. Some parts have become abnormally large; others -have dwindled or disappeared; and the relative positions of parts -have often been greatly changed. A bat’s wing and a bird’s wing are -analogous organs, but their frameworks are but partially homologous. -While in the bird the terminal parts of the fore-limb do little towards -supporting the wing, in the bat the wing is mainly supported by -enormously-developed terminal parts.</p> - -<p>The effects of the struggle to survive, which here prompts a simpler -life with resulting degeneracy and there a different life with -resulting new developments, are far from being the only causes of -morphological obscurations. Fulfilment of certain highly general -requirements gives certain common traits to plants of widely divergent -classes; and fulfilment of certain other highly general requirements -gives certain common traits to animals of widely divergent classes. -It was remarked in the first volume (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect54">§ 54<i>f</i></a>) that the cardinal -distinction between the characters of plants and animals arises from -the fact that while the chief food of plants is universally present the -food of animals is scattered. Here it has to be added that to utilize -the universally distributed food the ordinary plant needs the aid of -light, and has to acquire structures enabling it to get that aid; -while the ordinary animal, to utilize the scattered food, must acquire -the structures needful for locomotion. Let us contemplate separately -the traits hence resulting in the vegetal world and the traits hence -resulting in the animal world.</p> - -<p>The familiar plantain meets the requirement by growing stiff leaves -enabling it to press down the competing grasses around which would -else shade it; but the great majority of ordinary plants meet the -requirement by raising themselves into the air. Hence the need for a -stem, and hence the fact that plants of widely unlike natures similarly -form stems which, in achieving strength enough to support the foliage -and resist the wind, acquire certain adaptive structures having<span class="pagenum" id="Page_14">[14]</span> a -general similarity. Here from the edge of a pool is a reed, and here -from the adjacent copse is a hemlock: the one having grown tall in -escaping the shade of its companions and the other in escaping the -shade of the surrounding brushwood. On being cut across each discloses -a tube, and each exhibits septa dividing this tube into chambers. In -either case by the tubular structure is gained the greatest strength -with the least material; but there is no morphological kinship between -the tubes nor between the septa. Still more marked is the simulation -of homology by analogy in another plant which the adjacent ditch may -furnish—the common Horsetail. In this, again, we see an elongated -vertical-growing part, raising the foliage into the air; and, as -before, this is tubular and divided by septa. A type utterly alien from -the other two has, by survival of the fittest, been similarly moulded -to meet mechanical needs.</p> - -<p>Passing now to the obscurations in the animal world caused -by alterations favouring locomotion, we note first that the -locomotive power is at the outset very slight. Among many orders of -<i>Protozoa</i>, as also among many low types of <i>Metazoa</i>, -vibratile cilia are the most general agents of locomotion—necessarily -feeble locomotion. Regarded in the mass, the <i>Cœlenterata</i>, when -not stationary like the <i>Hydra</i> or higher types in the hydroid -stage, usually possess only such small self-mobility as the slow -rhythmical contractions of their umbrella-disks effect, or else such -as is effected by bands of cilia or of vibratile plates, as in the -<i>Beroe</i>. Even among these low tpes of <i>Metazoa</i>, however, in -which ordinarily the radial structure is conspicuous, or but slightly -obscured by an ovoid form as in the <i>Ctenophora</i>, we find, in the -<i>Cestus veneris</i>, extreme obscuration caused by an elongation -which facilitates movement through the water; alike by the actions of -its vibratile plates and by its undulations, which simulate those of -sundry higher animals.</p> - -<p>And here we come upon the essential fact to be recognized. Elongation -favours locomotion in various ways that are<span class="pagenum" id="Page_15">[15]</span> severally taken advantage -of by different types of creatures. (1) To a given mass of moving -matter the resistance of the medium decreases along with decrease -in the area of its transverse section, and this implies increase -of length: a given force will move the lengthened mass along with -greater facility. (2) Reaching a certain point the elongated form -enables an animal to progress by undulations, as in the water fish -do, and even some cœlenterates and turbellarians do, and as on land -snakes do: lateral resistances serving in either case as fulcra. (3) -Lengthening of the body serves otherwise to aid locomotion in the -creeping or burrowing worm, which, utilizing the statical resistance -of its hinder part thrusts onwards its fore part, and then, holding -fast its fore part by the aid of minute <i>setæ</i>, draws the hinder -part after it. But elongation, doubly advantageous at first, while -the body is itself the chief instrument of locomotion, gradually -loses its advantageousness as special instruments of locomotion are -developed. (4) This we see in that locomotive action effected by limbs, -which, many and small in the lower <i>Arthropoda</i> and becoming -few and larger in the higher, at length give great activity to a -shortened and consolidated body: a stage reached only through stages -of decreasing elongation accompanying increase of limb-power. (5) In -the <i>Vertebrata</i> locomotion by undulations comes, along certain -lines of evolution, to be replaced by that limb locomotion which -accompanies the rise from water-life to land-life: the evolution of -Amphibians exhibiting the transition. (6) Further, we see among mammals -that as limbs become efficient the elongated body ceases to be itself -instrumental in locomotion, but that still some elongation remains a -characteristic. (7) Finally, where limb locomotion reaches its highest -degree, as in birds, elongation disappears.</p> - -<p>These classes of familiar facts I have recalled to show that, in -the course of evolution, achievement by plants of the all-essential -elevation into the air and by animals of the all-essential power of -movement have developed this trait<span class="pagenum" id="Page_16">[16]</span> of elongation in various types; -and that in each kingdom acquisition of the common trait has had a -tendency now to obscure morphological equivalence, and now to give the -appearance of kinship where there is none. A further purpose has been -to prepare the way for a question hereafter to be discussed—whether, -in the various types of either kingdom, the elongation is effected -in the same ways or in different ways. We shall have to ask whether -the vertically-growing part is always, like that of <i>Lessonia</i>, -a simple individual, or whether, as possibly in Phænogams, it is a -united series of individuals; and similarly whether the elongated body -is always single, like that of a mollusc, or whether, as possibly in -annulose animals, it is a series of united individuals.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_17">[17]</span></p> - -<h3>CHAPTER II.<br /> -<span class="subhed1">THE MORPHOLOGICAL COMPOSITION OF PLANTS.</span></h3></div> - -<p id="sect180">§ 180. Evolution implies insensible modifications and gradual -transitions, which render definition difficult—which make it -impossible to separate absolutely the phases of organization from -one another. And this indefiniteness of distinction, to be expected -<i>à priori</i>, we are compelled to recognize <i>à posteriori</i>, -the moment we begin to group morphological phenomena into general -propositions. Thus, on inquiring what is the morphological unit, -whether of plants or of animals, we find that the facts refuse to be -included in any rigid formula. The doctrine that all organisms are -built up of cells, or that cells are the elements out of which every -tissue is developed, is but approximately true. There are living -forms of which cellular structure cannot be asserted; and in living -forms that are for the most part cellular, there are nevertheless -certain portions which are not produced by the metamorphosis of cells. -Supposing that clay were the only material available for building, -the proposition that all houses are built of bricks, would bear about -the same relation to the truth, as does the proposition that all -organisms are composed of cells. This generalization respecting houses -would be open to two criticisms:—first, that certain houses of a -primitive kind are formed, not of bricks, but out of unmoulded clay; -and second, that though other houses consist mainly of bricks, yet -their chimney-pots, drain-pipes, and<span class="pagenum" id="Page_18">[18]</span> ridge-tiles, do not result from -combination or metamorphosis of bricks, but are made directly out of -the original clay. And of like natures are the criticisms which must be -passed on the generalization, that cells are the morphological units -of organisms. To continue the simile, the truth turns out to be, that -the primitive clay or protoplasm out of which organisms are built, may -be moulded either directly, or with various degrees of indirectness, -into organic structures. The physiological units which we are obliged -to assume as the components of this protoplasm, must, as we have seen, -be the possessors of those proclivities which result in the structural -arrangements of the organism. The assumption of such structural -arrangements may go on, and in many cases does go on, by the shortest -route; without the passage through what we call metamorphoses. But -where such structural arrangements are reached by a circuitous route, -the first stage is the formation of these small aggregates which, under -the name of cells, are currently regarded as morphological units.</p> - -<p>The rationale of these truths appears to be furnished by the hypothesis -of evolution. We set out with molecules some degrees higher in -complexity than those molecules of nitrogenous colloidal substance -into which organic matter is resolvable; and we regard these very much -more complex molecules as having the implied greater instability, -greater sensitiveness to surrounding influences, and consequent -greater mobility of form. Such being the primitive physiological -units, organic evolution must begin with the formation of a minute -aggregate of them—an aggregate showing vitality by a higher degree -of that readiness to change its form of aggregation which colloidal -matter in general displays; and by its ability to unite the nitrogenous -molecules it meets with, into complex molecules like those of which -it is composed. Obviously, the earliest forms must have been minute; -since, in the absence of any but diffused organic matter, no form -but a minute one could find nutriment. Obviously, too,<span class="pagenum" id="Page_19">[19]</span> it must have -been structureless; since, as differentiations are producible only -by the unlike actions of incident forces, there could have been no -differentiations before such forces had had time to work. Hence, -distinctions of parts like those required to constitute a cell were -necessarily absent at first. And we need not therefore be surprised -to find, as we do find, specks of protoplasm manifesting life, and -yet showing no signs of organization. A further stage of evolution -is reached when the imperfectly integrated molecules forming one of -these minute aggregates, become more coherent; at the same time as -they pass into a state of heterogeneity, gradually increasing in its -definiteness. That is to say, we may look for the assumption by them, -of some distinctions of parts, such as we find in cells and in what -are called unicellular organisms. They cannot retain their primordial -uniformity; and while in a few cases they may depart from it but -slightly, they will, in the great majority of cases, acquire a decided -multiformity: there will result the comparatively integrated and -comparatively differentiated <i>Protophyta</i> and <i>Protozoa</i>. -The production of minute aggregates of physiological units being -the first step, and the passage of such minute aggregates into more -consolidated and more complex forms being the second step, it must -naturally happen that all higher organic types, subsequently arising -by further integrations and differentiations, will everywhere bear the -impress of this earliest phase of evolution. From the law of heredity, -considered as extending to the entire succession of living things -during the Earth’s past history, it follows that since the formation -of these small, simple organisms must have preceded the formation -of larger and more complex organisms, the larger and more complex -organisms must inherit their essential characters. We may anticipate -that the multiplication and combination of these minute aggregates or -cells, will be conspicuous in the early developmental stages of plants -and animals; and that throughout all subsequent stages, cell-production -and cell-differentiation<span class="pagenum" id="Page_20">[20]</span> will be dominant characteristics. The -physiological units peculiar to each higher species will, speaking -generally, pass through this form of aggregation on their way towards -the final arrangement they are to assume; because those primordial -physiological units from which they are remotely descended, aggregated -into this form. And yet, just as in other cases we found reasons for -inferring (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect">§ 131</a>) that the traits of ancestral organization may, -under certain conditions, be partially or wholly obliterated, and the -ultimate structure assumed without passing through them; so, here, -it is to be inferred that the process of cell-formation may, in some -cases, be passed over. Thus the hypothesis of evolution prepares us for -those two radical modifications of the cell-doctrine which the facts -oblige us to make. It leads us to expect that as structureless portions -of protoplasm must have preceded cells in the process of general -evolution; so, in the special evolution of each higher organism, there -will be an habitual production of cells out of structureless blastema. -And it leads us to expect that though, generally, the physiological -units composing a structureless blastema, will display their inherited -proclivities by cell-development and metamorphosis; there will -nevertheless occur cases in which the tissue to be formed, is formed by -direct transformation of the blastema.<a id="FNanchor_2" href="#Footnote_2" class="fnanchor">[2]</a></p> - -<p><span class="pagenum" id="Page_21">[21]</span></p> - -<p>Interpreting the facts in this manner, we may recognize that large -amount of truth which the cell-doctrine contains, without committing -ourselves to the errors involved by a sweeping assertion of it. We -are enabled to understand how it happens that organic structures are -usually cellular in their composition, at the same time that they are -not universally so. We are shown that while we may properly continue to -regard the cell as the morphological unit, we must constantly bear in -mind that it is such only in a qualified sense.</p> - - -<p class="p2">§ 181. These aggregates of the lowest order, each formed of -physiological units united into a group that is structurally single -and cannot be divided without destruction of its individuality, may, -as above implied, exist as independent organisms. The assumption to -which we are committed by the hypothesis of evolution, that such -so called unicellular plants were at first the only kinds of plants, -is in harmony with the fact that habitats not occupied by plants of -higher orders, commonly contain these protophytes in great abundance -and great variety. The various species of <i>Pleurococcaceæ</i>, -of <i>Desmidiaceæ</i>, and <i>Diatomaceæ</i>, supply examples of -morphological units living and propagating separately, under numerous -modifications of form and structure. Figures <a href="#i_022a">1, 2, and 3</a>, represent a -few of the commonest types.</p> - - <div class="figcenter" id="i_022a"> - <img - class="p2" - src="images/i_022a.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 1, 2, 3.</p> - </div> - - <div class="figcenter" id="i_022b"> - <img - class="p2" - src="images/i_022b.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 4, 5, 6.</p> - </div> - -<p class="p2">Mostly, simple plants are too small to be individually<span class="pagenum" id="Page_22">[22]</span> visible -without the microscope. But, in some cases, these vegetal aggregates -of the first order grow to appreciable sizes. In the mycelium of -some fungi, we have single cells developed into long branched -filaments, or ramified tubules, that are of considerable lengths. An -analogous structure characterizes certain tribes of <i>Algæ</i>, of -which <i>Codium adhærens</i>, Fig. <a href="#i_022b">4</a>, may serve as an example. In -<i>Botrydium</i>, another alga, Fig. <a href="#i_022b">5</a>, we have a structure which is -described as simulating a higher plant, with root, stem, bud, and -fruit, all produced by the branching of a single cell. And among -fungi the genus <i>Mucor</i>, Fig. <a href="#i_022b">6</a>, furnishes an example of allied -kind.<a id="FNanchor_3" href="#Footnote_3" class="fnanchor">[3]</a> Here, though the size attained is much greater than that of -many organisms which are morphologically compound, we are compelled to -consider the morphological composition as simple; since the whole can -no more be separated into minor wholes, than can the branched vascular<span class="pagenum" id="Page_23">[23]</span> -system of an animal. In these cases we have considerable bulk attained, -not by a number of aggregates of the first order being united into -an aggregate of the second order, but by the continuous growth of an -aggregate of the first order.</p> - - -<p class="p2" id="sect182">§ 182. The transition to higher forms begins in a very unobtrusive -manner. Among these aggregates of the first order, an approach towards -that union by which aggregates of the second order are produced, is -indicated by mere juxtaposition. Protophytes multiply rapidly; and -their rapid multiplication sometimes causes crowding. When, instead -of floating free in the water, they form a thin film on a moist -surface, or are imbedded in a common matrix of mucilage; the mechanical -obstacles to dispersion result in a kind of feeble integration, vaguely -shadowing forth a combined group. Somewhat more definite combination -is shown us by such plants as <i>Palmella botryoides</i>. Here the -members of a family of cells, arising by the spontaneous fission of -a parent-cell, remain united by slender threads of that jelly-like -substance which envelops their surfaces. In some <i>Diatomaceæ</i> -several individuals, instead of completely separating, hold together by -their angles; and in other <i>Diatomaceæ</i>, as the <i>Bacillaria</i>, -a variable number of units cohere so slightly, that they are -continually moving in relation to one another.</p> - -<p>This formation of aggregates of the second order, faintly indicated -in feeble and variable unions like the above, may be traced through -phases of increasing permanence and definiteness, as well as -increasing extent. In the yeast-plant, Fig. <a href="#i_024">7</a>, we have cells which -may exist singly, or joined into groups of several; and which have -their shapes scarcely at all modified by their connexion. Among the -<i>Desmidiaceæ</i>, it happens in many cases that the two individuals -produced by division of a parent-individual, part as soon as they are -fully formed; but in other cases, instead of parting they compose a -group of two. Allied kinds show us how, by subsequent fissions of the -adherent individuals and their progeny, there<span class="pagenum" id="Page_24">[24]</span> result longer groups; -and in some species, a continuous thread of them is thus produced. -Figs. <a href="#i_024">8, 9, 11</a>, exhibit these several stages. Fig. 10 represents a -<i>Scenedesmus</i> in which the individuation of the group is manifest. -Instead of linear aggregation, many protophytes illustrate central -aggregation; as shown in Figs. <a href="#i_024">12, 13, 14, 15</a>. Other instances are -furnished by such forms as the <i>Gonium pectorale</i>, Fig. <a href="#i_024">16</a> -(<i>a</i> being the front view, and <i>b</i> the edge view), and the -<i>Sarcina ventriculi</i>, Fig. <a href="#i_024">17</a>. Further, we have that spherical -mode of aggregation of which the <i>Volvox globator</i> furnishes a -familiar instance.</p> - - <div class="figcenter" id="i_024"> - <img - class="p2" - src="images/i_024.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 7–17.</p> - </div> - - <div class="figcenter" id="i_025"> - <img - class="p2" - src="images/i_025.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 18–23.</p> - </div> - -<p class="p2">Thus far, however, the individuality of the secondary aggregate is -feebly pronounced: not simply in the sense that it is small; but also -in the sense that the individualities of the primary aggregates are -very little subordinated. But on seeking further, we find transitions -towards forms in which the compound individuality is more dominant, -while the simple individualities are more obscured. Obscuration of one -kind accompanies mere increase of size in the secondary aggregate. -In proportion to the greater number of the morphological units held -together in one mass, becomes their relative insignificance as -individuals. We see this in the irregularly-spreading lichens that -form patches on rocks; and in such creeping fungi as grow in films -or laminæ on decaying wood and the bark of trees. In these cases, -however, the integration of the component cells is of an almost<span class="pagenum" id="Page_25">[25]</span> -mechanical kind. The aggregate of them is scarcely more individuated -than a lump of inorganic matter: as witness the way in which the lichen -extends its curved edges in this or that direction, as the surface -favours; or the way in which the fungus grows round and imbeds the -shoots and leaves that lie in its way, just as so much plastic clay -might do. Though here, in the augmentation of mass, we see a progress -towards the evolution of a higher type, we have as yet none of that -definiteness required to constitute a compound unit, or true aggregate -of the second order. Another kind of obscuration of the morphological -units, is brought about by their more complete coalescence into the -form of some structure made by their union. This is well exemplified -among the <i>Confervoideæ</i> and <i>Conjugatæ</i>. In Fig. <a href="#i_025">18</a>, there -are represented the stages of a growing <i>Mougeotia genuflexa</i>, -in which this merging of the simple individualities into the compound -individuality, is shown in the history of a single plant; and in Figs. -<a href="#i_025">19, 20, 21, 22, 23</a>, are represented a series of species from this -group, and that of <i>Cladophora</i>,<a id="FNanchor_4" href="#Footnote_4" class="fnanchor">[4]</a> in which we see a progressing -integration. While, in the lower types, the primitive spheroidal forms -of the cells are scarcely altered, in the higher types the cells are -so fused together as to constitute cylinders divided by septa. Here, -however,<span class="pagenum" id="Page_26">[26]</span> the indefiniteness is still great. There are no specific -limits to the length of any thread thus produced, and there is none of -that differentiation of parts required to give a decided individuality -to the whole.</p> - -<p>To constitute something like a true aggregate of the second order, -capable of serving as a compound unit that may be combined with others -like itself into still higher aggregates, there must exist both mass -and definiteness.</p> - - -<p class="p2">§ 183. An approach towards plants which unite these characters, may -be traced in such forms as <i>Bangia ciliaris</i>, Fig. <a href="#i_026">24</a>. The -multiplication of cells here takes place, not in a longitudinal -direction only, but also in a transverse direction; and the transverse -multiplication being greater towards the middle of the frond, there -results a difference between the middle and the two extremities—a -character which, in a feeble way, unites all the parts into a whole. -Even this slight individuation is, however, very indefinitely marked; -since, as shown by the figures, the lateral multiplication of cells -does not go on in a precise manner.</p> - - <div class="figcenter" id="i_026"> - <img - class="p2" - src="images/i_026.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 24.</p> - </div> - -<p class="p2">From some such type as this there appear to arise, through slight -differences in the modes of growth, two closely-allied groups of -plants, having individualities somewhat more pronounced. If, while -the cells multiply longitudinally, their lateral multiplication -goes on in one direction only, there results a flat surface, as in -the genus <i>Ulva</i> (Sea-lettuce) or in the upper part of the -thallus of <i>Enteromorpha Linza</i>, Fig. <a href="#i_027">25</a>; or where the lateral -multiplication is less uniform in its rate, in types like Fig. <a href="#i_027">26</a>. But -where the lateral multiplication occurs in two directions transverse -to one another, a hollow frond may be produced—sometimes irregularly -spheroidal, and sometimes<span class="pagenum" id="Page_27">[27]</span> irregularly tubular; as in <i>Enteromorpha -intestinalis</i>, Fig. <a href="#i_027">27</a>. And often, as in <i>Enteromorpha -compressa</i>, Fig. <a href="#i_027">28</a>, and other species, this tubular frond becomes -branched. Figs. <a href="#i_027">29</a> and <a href="#i_027">30</a> are magnified portions of such fronds, -showing the simple cellular aggregation which allies them with the -preceding forms.</p> - - <div class="figcenter" id="i_027"> - <img - class="p2" - src="images/i_027.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 25–30.</p> - </div> - -<p class="p2">In the common <i>Fuci</i> of our coasts, other and somewhat higher -stages of this integration are displayed. We have fronds preserving -something like constant breadths and dividing dichotomously with -approximate regularity. Though the subdivisions so produced are not -to be regarded as separate fronds, but only as extensions of one -frond, they foreshadow a higher degree of composition; and by the -comparatively methodic way in which they are united, give to the -aggregate a more definite, as well as a more complex, individuality. -Many of the higher lichens exhibit an analogous advance. While in the -lowest lichens, the different parts of the thallus are held together -only by being all attached to the supporting surface, in the higher -lichens the thallus is so far integrated that it can support itself by -attachment to such surface at one point only. And then, in still more -developed kinds, we find the thallus assuming a<span class="pagenum" id="Page_28">[28]</span> dichotomously-branched -form, and so gaining a more specific character as well as greater size.</p> - -<p>Where, as in types like these, the morphological units show an inherent -tendency to arrange themselves in a manner which is so far constant -as to give characteristic proportions, we may say that there is a -recognizable compound individuality. Considering the Thallophytes which -grow in this way apart from their kinships, and wholly with reference -to their morphological composition, we might not inaptly describe them -as pseudo-foliar.</p> - - -<p class="p2">§ 184. Another mode in which aggregation is so carried on as to produce -a compound individuality of considerable definiteness, is variously -displayed among other families of <i>Algæ</i>. When the cells, instead -of multiplying longitudinally alone, and instead of all multiplying -laterally as well as longitudinally, multiply laterally only at -particular places, they produce branched structures.</p> - -<p>Indications of this mode of aggregation occur among the -<i>Confervoideæ</i>, as shown in Figs. <a href="#i_025">22, 23</a>. Though, in some of the -more-developed <i>Algæ</i> which exhibit the ramified arrangement in -a higher degree, the component cells are, like those of the lower -<i>Algæ</i>, united together end to end, in such way as but little -to obscure their separate forms, as in <i>Cladophora Hutchinsiæ</i>, -Fig. <a href="#i_029">31</a>; they nevertheless evince greater subordination to the whole -of which they are parts, by arranging themselves more methodically. -Still further pronounced becomes the compound individuality when, while -the component cells of the branches unite completely into jointed -cylinders, the component cells of the stem form an axis distinguished -by its relative thickness and complexity. Such types of structures -are indicated by Figs. <a href="#i_029">32, 33</a>—figures representing small portions of -plants which are quite tree-like in their entire outlines. On examining -Figs. <a href="#i_029">34, 35, 36</a>, which show the structures of the stems in these -types, it will be seen, too, that the component cells in becoming -more<span class="pagenum" id="Page_29">[29]</span> coherent, have undergone changes of form which obscure their -individualities more than before. Not only are they much elongated, but -they are so compressed as to be prismatic rather than cylindrical. This -structure, besides displaying integration of the morphological units -carried on in two directions instead of one; and besides displaying -this higher integration in the greater merging of the individualities -of the morphological units in the general individuality; also displays -it in the more pronounced subordination of the branches and branchlets -to the main stem. This differentiation and consolidation of the stem, -brings all the secondary growths into more marked dependence; and so -renders the individuality of the aggregate more decided.</p> - - <div class="figcenter" id="i_029"> - <img - class="p2" - src="images/i_029.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 31–36.</p> - </div> - -<p class="p2">We might not inappropriately call this type of structure pseud-axial. -It simulates that of the higher plants in certain superficial -characters. We see in it a primary axis along which development may -continue indefinitely, and from which there bud out, laterally, -secondary axes of like nature, bearing like tertiary axes; and this is -a mode of growth with which Phænogams make us familiar.</p> - - -<p class="p2">§ 185. Some of the larger <i>Algæ</i> supply examples of an -integration still more advanced; not simply inasmuch as they unite -much greater numbers of morphological units<span class="pagenum" id="Page_30">[30]</span> into continuous masses, -but also inasmuch as they combine the pseudo-foliar structure with -the pseud-axial structure. Our own shores furnish an instance -of this in the common <i>Laminaria</i>; and certain gigantic -<i>Laminariaceæ</i> of the Antarctic seas, furnish yet better -instances. In <i>Necrocystis</i> the germ develops a very long -slender stem, which eventually expands into a large bladder-like -or cylindrical air-vessel; and the surface of this bears numerous -leaf-shaped expansions. Another kind, <i>Lessonia fuscescens</i>, -Fig. <a href="#i_030">37</a>, shows us a massive stem growing up through water many feet -deep—a stem which, bifurcating as it approaches the surface, flattens -out the ends of its subdivisions into fronds like ribands. These, -however, are not true foliar appendages, since they are merely expanded -continuations of the stem. In <i>Egregia</i> branches of the thallus -not only take the form of leaves, but these are differentiated into -several categories in accordance with a division of labour. In any of -these <i>Laminariaceæ</i> the whole plant, great as may be its size, -and made up though it seems to be of many groups of morphological -units, united into a compound group by their marked subordination to a -connecting mass, is nevertheless a single thallus, which is added to by -intercalary growth at the “transition place,” at the junction of the -stem-like and leaf-like portions. The aggregate is still an aggregate -of the second order.</p> - - <div class="figcenter" id="i_030"> - <img - class="p2" - src="images/i_030.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 37.</p> - </div> - - <div class="figcenter" id="i_031"> - <img - class="p2" - src="images/i_031.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 38–40.</p> - </div> - -<p class="p2">But among certain of the highest <i>Algæ</i>, we <i>do</i> find -something more than this union of the pseud-axial with the -pseudo-foliar structure. In addition to pseud-axes of comparative -complexity; and in addition to pseudo-folia that are like leaves, not -only in their general shapes but in having mid-ribs and even veins; -there are the beginnings of a higher stage of integration. Figs. <a href="#i_031">38, -39, and 40</a>, show some of the steps. In <i>Rhodymenia palmata</i>, -Fig. <a href="#i_031">38</a>, the<span class="pagenum" id="Page_31">[31]</span> parent-frond is comparatively irregular in form, and -without a mid-rib; and along with this very imperfect integration, we -see that the secondary fronds growing from the edges are distributed -very much at random, and are by no means specific in their shapes. A -considerable advance is displayed by <i>Phyllophora rubens</i>, Fig. -<a href="#i_031">39</a>. Here the frond, primary, secondary, or tertiary, betrays some -approach towards regularity in both form and size; by which, as also -by its partially-developed mid-rib, there is established a more marked -individuality; and at the same time, the growth of the secondary -fronds no longer occurs anywhere on the edge, in the same plane as the -parent-frond, but from the surface at specific places. <i>Delesseria -sanguinea</i>, Fig. <a href="#i_031">40</a>, illustrates a much more definite arrangement -of the same kind. The fronds of this plant, quite regularly shaped, -have their parts decidedly subordinated to the whole; and from their -mid-ribs grow other fronds which are just like them. Each of these -fronds is an organized group of those morphological units which we -distinguish as aggregates of the first order. And in this case, two or -more such aggregates of the second<span class="pagenum" id="Page_32">[32]</span> order, well individuated by their -forms and structures, are united together; and the plant composed of -them is thus rendered, in so far, an aggregate of the third order.</p> - -<p>Just noting that in certain of the most developed <i>Algæ</i>, as -the <i>Sargassum</i>, or common gulf-weed, this tertiary degree of -composition is far more completely displayed, so as to produce among -Thallophytes a type of structure closely simulating that of the higher -plants, let us now pass to the consideration of these higher plants.</p> - - -<p class="p2">§ 186. Having the surface of the soil for a support and the air for a -medium, terrestrial plants are mechanically circumstanced in a manner -widely different from that in which aquatic plants are circumstanced. -Instead of being buoyed up by a surrounding fluid of specific gravity -equal to their own, they have to erect themselves into a rare fluid -which yields no appreciable support. Further, they are dissimilarly -conditioned in having two sources of nutriment in place of one. Unlike -the <i>Algæ</i>, which derive all the materials for their tissues from -the water bathing their entire surfaces, and use their roots only -for attachment, most of the plants which cover the Earth’s surface, -absorb part of their food through their imbedded roots and part through -their exposed leaves. These two marked unlikenesses in the relations -to surrounding conditions, profoundly affect the respective modes of -growth. We must duly bear them in mind while studying the further -advance of composition.</p> - - <div class="figcenter" id="i_033"> - <img - class="p2" - src="images/i_033.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 41–44.</p> - </div> - - <div class="figcenter" id="i_034"> - <img - class="p2" - src="images/i_034.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 45–49.</p> - </div> - -<p class="p2">The class of plants to which we now turn—that of the -<i>Archegoniatæ</i>—is nearly related by its lower members to the -classes above dealt with: so much so, that some of the inferior -liverworts are quite licheniform, and are often mistaken for lichens. -Passing over these, let us recommence our synthesis with such members -of the class as repeat those indications of progress towards a higher -composition, which we have just observed among the more-developed -<i>Algæ</i>. The <i>Jungermanniaceæ</i> furnish us with a series of -types, clearly indicating the<span class="pagenum" id="Page_33">[33]</span> transition from an aggregate of the -second order to an aggregate of the third order. Figs. <a href="#i_033">41</a> and <a href="#i_033">42</a>, -indicate the structure among the lowest of this group. Here there is -but an incomplete development of the second order of aggregate. The -frond grows as irregularly as the thallus of a lichen: it is indefinite -in size and outline, spreading hither or thither as the conditions -favour. Moreover, it lacks the differentiations required to subordinate -its parts to the whole: it is uniformly cellular, having neither -mid-rib nor veins; and it puts out rootlets indifferently from all -parts of its under surface. In Fig. <a href="#i_033">43</a>, <i>Pellia epiphylla</i>, we -have an advance on this type. There is here, as shown in the transverse -section, Fig. <a href="#i_033">44</a>, a thickening of the frond along its central portion, -producing something like an approach towards a mid-rib; and from this -the rootlets are chiefly given off. The outline, too, is much less -irregular; whence results greater distinctness of the individuality. -A further step is displayed in <i>Metzgeria furcata</i>, Fig. <a href="#i_034">45</a>. -The frond of this plant, comparatively well integrated by the -distribution of its substance around a decided mid-rib, and by its -comparatively-definite outlines, produces secondary fronds. There is -what is called proliferous growth; and occasionally, as shown in Fig. -<a href="#i_034">46</a>, representing an enlarged portion, the growth is doubly-proliferous. -In these cases, however, the tertiary aggregate, so far as it is -formed, is but very feebly integrated; and its integration is but -temporary. For not only do these younger fronds that bud out from the -mid-ribs of older fronds, develop rootlets of their own; but as soon -as they are well grown and adequately rooted, they dissolve their -connexions with the parent-fronds,<span class="pagenum" id="Page_34">[34]</span> and become quite independent. From -these transitional forms we pass, in the higher <i>Jungermanniaceæ</i>, -to forms composed of many fronds that are permanently united by a -continuous stem. A more-developed aggregate of the third order is -thus produced. But though, along with increased definiteness in -the secondary aggregates, there is here an integration of them so -extensive and so regular, that they are visibly subordinated to the -whole they form; yet the subordination is really very incomplete. In -some instances, as in <i>Radula complanata</i>, Fig. <a href="#i_034">47</a>, the leaflets -develop roots from their under surfaces, just as the primitive frond -does; and in the majority of the group, as in <i>J. capitata</i>, Fig. -<a href="#i_034">48</a>, roots are given off all along the connecting stem, at the spots -where the leaflets or frondlets join it: the result being that though -the connected frondlets form a physical whole, they do not form, in any -decided manner, a physiological whole; since successive portions of -the united series, carry on their functions independently of the rest. -Finally, the most developed members of the group, whether lineally -descended from the less developed or from an early type common to the -two, present us with tertiary aggregates which are physiologically as -well as physically integrated.<a id="FNanchor_5" href="#Footnote_5" class="fnanchor">[5]</a> Not lying<span class="pagenum" id="Page_35">[35]</span> prone like the kinds thus -far described, but growing erect, the stem and attached leaflets become -dependent upon a single root or group of roots; and being so prevented -from carrying on their functions separately, are made members of a -compound individual: there arises a definitely-established aggregate of -the third degree of composition.</p> - -<p>The facts as arranged in the above order are suggestive. Minute -aggregates, or cells, the grouping of which we traced in <a href="#sect182">§ 182</a>, showed -us analogous phases of indefinite union, which appeared to lead the -way towards definite union. We see here among compound aggregates, as -we saw there among simple aggregates, the establishment of a specific -form, and a size that falls within moderate limits of variation. This -passage from less definite extension to more definite extension, -seems in the one case, as the other, to be accompanied by the result, -that growth exceeding a certain rate, ends in the formation of a new -aggregate, rather than an enlargement of the old. And on the higher -stage, as on the lower, this process, irregularly carried out in the -simpler types, produces in them unions that are but temporary; while in -the more-developed types, it proceeds in a systematic way, and ends in -the production of a permanent aggregate that is doubly compound.</p> - -<p><span class="pagenum" id="Page_36">[36]</span></p> - -<p>Must we then conclude that as cells, or morphological units, are -integrated into a unit of a higher order, which we call a thallus -or frond; so, by the integration of fronds, there is evolved a -structure such as the above-delineated species possess? Whether this -is the interpretation to be given of these plants, we shall best see -when considering whether it is the interpretation to be given of -plants which rank above them. Thus far we have dealt only with the -Cryptogamia. We have now to deal with the Phanerogamia or Phænogamia.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_37">[37]</span></p> - -<h3>CHAPTER III.<br /> -<span class="subhed1">THE MORPHOLOGICAL COMPOSITION OF PLANTS, <i>CONTINUED</i>.</span></h3></div> - -<p class="p2">§ 187. That advanced composition arrived at in the <i>Archegoniatæ</i>, -is carried still further in the Flowering Plants. In these -most-elevated vegetal forms, aggregation of the third order is always -distinctly displayed; and aggregates of the fourth, fifth, sixth, &c., -orders are very common.</p> - -<p>Our inquiry into the morphology of these flowering plants, may be -advantageously commenced by studying the development of simple leaves -into compound leaves. It is easy to trace the transition, as well as -the conditions under which it occurs; and tracing it will prepare us -for understanding how, and when, metamorphoses still greater in degree -take place.</p> - - -<p class="p2" id="sect188">§ 188. If we examine a branch of the common bramble, when in flower -or afterwards, we shall not unfrequently find a simple or undivided -leaf, at the insertion of one of the lateral flower-bearing axes, -composing the terminal cluster of flowers. Sometimes this leaf is -partially lobed; sometimes cleft into three small leaflets. Lower down -on the shoot, if it be a lateral one, occur larger leaves, composed -of three leaflets; and in some of these, two of the leaflets may be -lobed more or less deeply. On the main stem the leaves, usually still -larger, will be found to have five leaflets. Supposing the plant to be -a well-grown one, it will furnish all<span class="pagenum" id="Page_38">[38]</span> gradations between the simple, -very small leaf, and the large composite leaf, containing sometimes -even seven leaflets. Figs. <a href="#i_038">50 to 64</a>, represent leading stages of the -transition. What determines this transition? Observation shows that -the quintuple leaves occur where the materials for growth are supplied -in greatest abundance; that the leaves become<span class="pagenum" id="Page_39">[39]</span> less and less compound, -in proportion to their remoteness from the main currents of sap; and -that where an entire absence of divisions or lobes is observed, it is -on leaves within the flower-bunch: at the place, that is, where the -forces which cause growth are nearly equilibrated by the forces which -oppose growth; and where, as a consequence, gamogenesis is about to -be set in (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect78">§ 78</a>). Additional evidence that the degree of nutrition -determines the degree of composition of the leaf, is furnished by -the relative sizes of the leaves. Not only, on the average, is the -quintuple leaf much larger in its total area than the triple leaf; -but the component leaflets of the one, are usually much larger than -those of the other. The like contrasts are still more marked between -triple leaves and simple leaves. This connection of decreasing size -with decreasing composition, is conspicuous in the series of figures: -the differences shown being not nearly so great as may be frequently -observed. Confirmation may be drawn from the fact that when the leading -shoot is broken or arrested in its growth, the shoots it gives off -(provided they are given off after the injury), and into which its -checked currents of sap are thrown, produce leaves of five leaflets -where ordinarily leaves of three leaflets occur. Of course incidental -circumstances, as variations in the amounts of sunshine, or of rain, -or of matter supplied to the roots, are ever producing changes in the -state of the plant as a whole; and by thus affecting the nutrition of -its leaf-buds at the times of their formation, cause irregularities -in the relations of size and composition above described. But taking -these causes into account, it is abundantly manifest that a leaf-bud of -the bramble will develop into a simple leaf or into a leaf compounded -in different degrees, according to the quantity of assimilable matter -brought to it at the time when the rudiments of its structure are -being fixed. And on studying the habits of other plants—on observing -how annuals that have compound leaves usually bear simple leaves at -the outset, when the assimilating surface is but small; and how, when -compound-leaved<span class="pagenum" id="Page_40">[40]</span> plants in full growth bear simple leaves in the midst -of compound ones, the relative smallness of such simple leaves shows -that the buds from which they arose were ill-supplied with sap; it -will cease to be doubted that a foliar organ may be metamorphosed into -a group of foliar organs, if furnished, at the right time, with a -quantity of matter greater than can be readily organized round a single -centre of growth. An examination of the transitions through which -a compound leaf passes into a doubly-compound leaf, as seen in the -various intermediate forms of leaflets in Fig. <a href="#i_040">65</a>, will further enforce -this conclusion.</p> - - <div class="figcenter" id="i_038"> - <img - class="p2" - src="images/i_038.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 50–64.</p> - </div> - - <div class="figcenter" id="i_040"> - <img - class="p2" - src="images/i_040.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 65.</p> - </div> - -<p class="p2">Here we may advantageously note, too, how in such cases the leaf-stalk -undergoes concomitant changes of structure. In the bramble-leaves above -described, it becomes compound simultaneously with the leaf—the veins -become mid-ribs while the mid-ribs become petioles. Moreover, the -secondary stalks, and still more the main stalks, bear thorns similar -in their<span class="pagenum" id="Page_41">[41]</span> shapes, and approaching in their sizes, to those on the stem; -besides simulating the stem in colour and texture. In the petioles of -large compound leaves, like those of the common <i>Heracleum</i>, we -see still more distinctly both internal and external approximations -in character to axes. Nor are there wanting plants whose large, -though simple, leaves, are held out far from the stems by foot-stalks -that are, near the ends, sometimes so like axes that the transverse -sections of the two are indistinguishable; as instance the <i>Calla -palustris</i>.</p> - -<p>One other fact respecting the modifications which leaves undergo, -should be set down. Not only may leaf-stalks assume to a great degree -the characters of stems, when they have to discharge the functions -of stems, by supporting many leaves or very large leaves; but they -may assume the characters of leaves, when they have to undertake the -functions of leaves. The Australian Acacias furnish a remarkable -illustration of this. Acacias elsewhere found bear pinnate leaves; -but the majority of those found in Australia bear what appear to be -simple leaves. It turns out, however, that these are merely leaf-stalks -flattened out into foliar shapes: the laminæ of the leaves being -undeveloped. And the proof is that in young plants, showing their -kinships by their embryonic characters, these leaf-like petioles bear -true leaflets at their ends. A metamorphosis of like kind occurs in -<i>Oxalis bupleurifolia</i>, Fig. <a href="#i_041">66</a>. The fact most deserving of -notice, however, is that these leaf-stalks, in usurping the general -aspects and functions of leaf-blades, have, to some also usurped their -structures: though their venation is not like that of the leaf-blades -they replace, yet they have veins, and in some cases mid-ribs.</p> - - <div class="figcenter" id="i_041"> - <img - class="p2" - src="images/i_041.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 66.</p> - </div> - -<p class="p2">Reduced to their most general expression, the truths above shadowed -forth are these:—That group of morphological units, or cells, which -we see integrated into the compound<span class="pagenum" id="Page_42">[42]</span> unit called a leaf, has, in -each higher plant, a typical form, due to the special arrangement -of these cells around a mid-rib and veins. If the multiplication of -morphological units, at the time when the leaf-bud is taking on its -main outlines, exceeds a certain limit, these units begin to arrange -themselves round secondary centres, or lines of growth, in such ways as -to repeat, in part or wholly, the typical form: the larger veins become -transformed into imperfect mid-ribs of partially independent leaves; -or into complete mid-ribs of quite separate leaves. And as there goes -on this transition from a single aggregate of cells to a group of -such aggregates, there simultaneously arises, by similarly insensible -steps, a distinct structure which supports the several aggregates thus -produced, and unites them into a compound aggregate. These phenomena -should be carefully studied; since they give us a key to more involved -phenomena.<a id="FNanchor_6" href="#Footnote_6" class="fnanchor">[6]</a></p> - - -<p class="p2">§ 189. Thus far we have dealt with leaves ordinarily so-called: briefly -indicating the homologies between the parts of the simple and the -compound. Let us now turn to the homologies among foliar organs in -general. These have been<span class="pagenum" id="Page_43">[43]</span> made familiar to readers of natural history -by popularized outlines of <i>The Metamorphosis of Plants</i>—a title, -by the way, which is far too extensive; since the phenomena treated of -under it, form but a small portion of those it properly includes.</p> - -<p>Passing over certain vague anticipations which have been quoted from -ancient writers, and noting only that some clearer recognitions -were reached by Joachim Jung, a Hamburg professor, in the middle of -the 17th century; we come to the <i>Theoria Generationis</i>, which -Wolff published in 1759, and in which he gives definite forms to the -conceptions that have since become current. Specifying the views of -Wolff, Dr. Masters writes:—“After speaking of the homologous nature -of the leaves, the sepals and petals, an homology consequent on their -similarity of structure and identity of origin, he goes on to state -that the ‘pericarp is manifestly composed of several leaves, as in the -calyx, with this difference only, that the leaves which are merely -placed in close contact in the calyx, are here united together’; a -view which he corroborates by referring to the manner in which many -capsules open and separate ‘into their leaves.’ The seeds, too, he -looks upon as consisting of leaves in close combination. His reasons -for considering the petals and stamens as homologous with leaves, are -based upon the same facts as those which led Linnæus, and, many years -afterwards, Goethe, to the same conclusion. ‘In a word,’ says Wolff, -‘we see nothing in the whole plant, whose parts at first sight differ -so remarkably from each other, but leaves and stem, to which latter -the root is referrible.’” It appears that Wolff, too, enunciated the -now-accepted interpretation of compound fruits: basing it on the same -evidence as that since assigned. In the essay of Goethe, published -thirty years after, these relations among the parts of flowering plants -were traced out in greater detail, but not in so radical a way; for -Goethe did not, as did Wolff, verify his hypothesis by dissecting buds -in their early stages of development. Goethe appears to have<span class="pagenum" id="Page_44">[44]</span> arrived -at his conclusions independently. But that they were original with -him, and that he gave a more variously-illustrated exposition of them -than had been given by Wolff, does not entitle him to anything beyond -a secondary place, among those who have established this important -generalization.</p> - -<p>Were it not that these pages may be read by some to whom Biology, in -all its divisions, is a new subject of study, it would be needless to -name the evidence on which this now-familiar generalization rests. For -the information of such it will suffice to say, that the fundamental -kinship existing among all the foliar organs of a flowering plant, is -shown by the transitional forms which may be traced between them, and -by the occasional assumption of one another’s forms. “Floral leaves, or -bracts, are frequently only to be distinguished from ordinary leaves -by their position at the base of the flower; at other times the bracts -gradually assume more and more of the appearance of the sepals.” The -sepals, or divisions of the calyx, are not unlike undeveloped leaves: -sometimes assuming quite the structure of leaves. In other cases, they -acquire partially or wholly the colours of the petals—as, indeed, the -bracts and uppermost stem-leaves occasionally do. Similarly, the petals -show their alliances to the foliar organs lower down on the axis, and -to those higher up on the axis. On the one hand, they may develop into -ordinary leaves that are green and veined; and, on the other hand, as -so commonly seen in double flowers, they may bear anthers on their -edges. All varieties of gradation into neighbouring foliar organs may -be witnessed in stamens. Flattened and tinted in various degrees, they -pass insensibly into petals, and through them prove their homology with -leaves; into which, indeed, they are transformed in flowers that become -wholly foliaceous. The style, too, is occasionally changed into petals -or into green leaflets; and even the ovules are now and then seen to -take on leaf-like forms. Thus we have clear evidence that in Phænogams, -all the<span class="pagenum" id="Page_45">[45]</span> appendages of the axis are homologues: they are all modified -leaves.</p> - -<p>Wolff established, and Goethe further illustrated, another general law -of structure in flowering plants. Each leaf commonly contains in its -axil a bud, similar in structure to the terminal bud. This axillary bud -may remain undeveloped; or it may develop into a lateral shoot like -the main shoot; or it may develop into a flower. If a shoot bearing -lateral flowers be examined, it will be found that the internode, or -space which separates each leaf with its axillary flower from the leaf -and axillary flower above it, becomes gradually less towards the upper -end of the shoot. In some plants, as in the fox-glove, the internodes -constitute a regularly-diminishing series. In other plants, the series -they form suddenly begins to diminish so rapidly, as to bring the -flowers into a short spike: instance the common orchis. And again, by -still more sudden dwarfing of the internodes, the flowers are brought -into a cluster; as they are in the cowslip. On contemplating a clover -flower, in which this clustering has been carried so far as to produce -a compact head; and on considering what must happen if, by a further -arrest of axial development, the foot-stalks of the florets disappear; -it will be seen that there must result a crowd of flowers, seated -close together on the end of the axis. And if, at the same time, the -internodes of the upper stem-leaves also remain undeveloped, these -stem-leaves will be grouped into a common involucre: we shall have -a composite flower, such as the thistle. Hence, to modifications in -the developments of foliar organs, have to be added modifications in -the developments of axial organs. Comparisons disclose the gradations -through which axes, like their appendages, pass into all varieties -of size, proportion, and structure. And we learn that the occurrence -of these two kinds of metamorphosis, in all conceivable degrees -and combinations, furnishes us with a proximate interpretation of -morphological composition in Phænogams.</p> - -<p><span class="pagenum" id="Page_46">[46]</span></p> - -<p>I say a proximate interpretation, because there remain to be solved -certain deeper problems; one of which at once presents itself to be -dealt with under the present head. Leaves, petals, stamens, &c., being -shown to be homologous foliar organs; and the part to which they are -attached, proving to be an indefinitely-extended axis of growth, or -axial organ; we are met by the questions,—What is a foliar organ? and -What is an axial organ? The morphological composition of a Phænogam is -undetermined, so long as we cannot say to what lower structures leaves -and shoots are homologous; and how this integration of them originates. -To these questions let us now address ourselves.</p> - - -<p class="p2" id="sect190">§ 190–1. Already, in <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect78">§ 78</a>, reference has been made to the occasional -development of foliar organs into axial organs: the special case there -described being that of a fox-glove, in which some of the sepals were -replaced by flower-buds. The observation of these and some analogous -monstrosities, raising the suspicion that the distinction between -foliar organs and axial organs is not absolute, led me to examine into -the matter; and the result has been the deepening of this suspicion -into a conviction. Part of the evidence is given in Appendix A.</p> - -<p>Some time after having reached this conviction, I found on looking -into the literature of the subject, that analogous irregularities had -suggested to other observers, beliefs similarly at variance with the -current morphological creed. Difficulties in satisfactorily defining -these two elements, have served to shake this creed in some minds. -To others, the strange leaf-like developments which axes undergo in -certain plants, have afforded reasons for doubting the constancy of -this distinction which vegetal morphologists usually draw. And those -not otherwise rendered sceptical, have been made to hesitate by such -cases as that of the Nepaul-barley, in which the glume, a foliar -organ, becomes developed into an axis and bears flowers. In his -essay—“Vegetable Morphology:<span class="pagenum" id="Page_47">[47]</span> its History and Present Condition,”<a id="FNanchor_7" href="#Footnote_7" class="fnanchor">[7]</a> -whence I have already quoted, Dr. Masters indicates sundry of -the grounds for thinking that there is no impassable demarcation -between leaf and stem. Among other difficulties which meet us if -we assume that the distinction is absolute, one is implied by this -question:—“What shall we say to cases such as those afforded by the -leaves of <i>Guarea</i> and <i>Trichilia</i>, where the leaves after a -time assume the condition of branches and develop young leaflets from -their free extremities, a process less perfectly seen in some of the -pinnate-leaved kinds of <i>Berberis</i> or <i>Mahonia</i>, to be found -in almost every shrubbery?”</p> - -<p>A class of facts on which it will be desirable for us here to dwell -a moment, before proceeding to deal with the matter deductively, is -presented by the <i>Cactaceæ</i>. In this remarkable group of plants, -deviating in such varied ways from the ordinary phænogamic type, we -find many highly instructive modifications of form and structure. By -contemplating the changes here displayed within the limits of a single -order, we shall greatly widen our conception of the possibilities of -metamorphosis in the vegetal kingdom, taken as a whole. Two different, -but similarly-significant, truths are illustrated. First, we are shown -how, of these two components of a flowering plant, commonly regarded -as primordially distinguished, one may assume, throughout numerous -species, the functions, and to a great degree the appearance, of the -other. Second, we are shown how, in the same individual, there may -occur a re-metamorphosis: the usurped function and appearance being -maintained in one part of the plant, while in another part there is -a return to the ordinary appearance and function. We will consider -these two truths separately. Some of the <i>Euphorbiaceæ</i>, which -simulate Cactuses, show us the stages through which such abnormal -structures are arrived at. In <i>Euphorbia splendens</i>, the lateral -axes are considerably swollen at their distal ends, so as often to -be club-shaped: still, however, being covered with bark<span class="pagenum" id="Page_48">[48]</span> of the -ordinary colour, and still bearing leaves. But in kindred plants, -as <i>Euphorbia neriifolia</i>, this swelling of the lateral axes -is carried to a far greater extent; and, at the same time, a green -colour and a fleshy consistence have been acquired: the typical -relations nevertheless being still shown by the few leaves that grow -out of these soft and swollen axes. In the <i>Cactaceæ</i>, which -are thus resembled by plants not otherwise allied to them, we have -indications of a parallel transformation. Some kinds, not commonly -brought to England, bear leaves; but in the species most familiar to -us, the leaves are undeveloped and the axes assume their functions. -Passing over the many varieties of form and combination which these -green succulent growths display, we have to note that in some genera, -as in <i>Phyllocactus</i>, they become flattened out into foliaceous -shapes, having mid-ribs and something approaching to veins. So that -here, and in the genus <i>Epiphyllum</i>, which has this character -still more marked, the plant appears to be composed of fleshy leaves -growing one upon another. And then, in <i>Rhipsalis</i>, the same -parts are so leaf-like, that an uncritical observer would regard them -as leaves. These which are axial organs in their homologies, have -become foliar organs in their analogies. When, instead of comparing -these strangely-modified axes in different genera of Cactuses, we -compare them in the same individual, we meet with transformations no -less striking. Where a tree-like form is produced by the growth of -these foliaceous shoots, one on another; and where, as a consequence, -the first-formed of them become the main stem that acts as support -to secondary and tertiary stems; they lose their green, succulent -character, acquire bark, and become woody. In resuming the functions of -axes they resume the structures of axes, from which they had deviated. -In Fig. <a href="#i_049">71</a> are shown some of the leaf-like axes of <i>Rhipsalis -rhombea</i> in their young state; while Fig. <a href="#i_049">72</a> represents the oldest -portion of the same plant, in which the foliaceous characters are -quite obliterated, and there has resulted<span class="pagenum" id="Page_49">[49]</span> an ordinary stem-structure. -One further fact is to be noted. At the same time that their -leaf-like appearances are lost, the axes also lose their separate -individualities. As they become stem-like, they also become integrated; -and they do this so effectually that their original points of junction, -at first so strongly marked, are effaced, and a consolidated trunk is -produced.</p> - - <div class="figcenter" id="i_049"> - <img - class="p2" - src="images/i_049.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 71–72.</p> - </div> - -<p class="p2">Joined with the facts previously specified, these facts help us to -conceive how, in the evolution of flowering plants in general, the -morphological components that were once distinct, may become extremely -disguised. We may rationally expect that during so long a course of -modification, much greater changes of form, and much more decided -fusions of parts, have taken place. Seeing how, in an individual -plant, the single leaves pass into compound leaves, by the development -of their veins into mid-ribs while their petioles begin to simulate -axes; and seeing that leaves ordinarily exhibiting definitely-limited -developments, occasionally produce other leaves from their edges; we -are led to suspect the possibility of still greater changes in foliar -organs. When, further, we find that within the limits of one natural -order, petioles usurp the functions and appearances of leaves, at the -same time that in other orders, as in <i>Ruscus</i>, lateral axes so -simulate leaves that their axial nature would by most not be suspected, -did they not bear flowers on their mid-ribs or edges; and when, among -Cactuses, we perceive that such metamorphoses and re-metamorphoses -take place with great facility; our suspicion that the morphological -elements of Phænogams admit of profound transformations, is deepened. -And then, on discovering how frequent are the monstrosities which do -not seem satisfactorily explicable without admitting the development -of foliar organs into axial organs; we become<span class="pagenum" id="Page_50">[50]</span> ready to entertain -the hypothesis that during the evolution of the phænogamic type, the -distinction between leaves and axes has arisen by degrees.</p> - -<p>With our preconceptions loosened by such facts, and carrying with us -the general idea which such facts suggest, let us now consider in what -way the typical structure of a flowering plant may be interpreted.</p> - - -<p class="p2">§ 192. To proceed methodically, we must seek a clue to the structures -of Phanerogams, in the structures of those inferior plants that -approach to them—<i>Archegoniatæ</i>. The various divisions of this -class present, along with sundry characters which ally them with -Thallophytes, other characters by which the phænogamic structure -is shadowed forth. While some of the inferior <i>Hepaticæ</i> or -Liverworts, severally consist of little more than a thallus-like -frond, among the higher members of this group, and still more among -the Mosses and Ferns, we find a distinctly marked stem.<a id="FNanchor_8" href="#Footnote_8" class="fnanchor">[8]</a> Some -Archegoniates (or rather Rhizoids) have foliar expansions that are -indefinite in their forms; and some have quite definitely-shaped -leaves. Roots are possessed by all the more-developed genera of the -class; but there are other genera, as <i>Sphagnum</i>, which have no -roots. Here the fronds are formed of only a single layer of cells; -and there a double layer gives them a higher character—a difference<span class="pagenum" id="Page_51">[51]</span> -exhibited between closely-allied genera of one group, the Mosses. -Equally varied are the developments of the foliar organs in their -detailed structures: now being without mid-ribs or veins; now having -mid-ribs but no veins; now having both mid-ribs and veins. Nor must -we omit the similarly-significant circumstance, that whereas in the -lower Archegoniates the reproductive elements are immersed here and -there in the thallus-like frond, they are, in the higher orders, seated -in well-specialized and quite distinct fructifying organs, having -analogies with the flowers of Phænogams. Thus, many facts imply that if -the Phænogamic type is to be analyzed at all, we must look among the -Archegoniates for its morphological components, and the manner of their -integration.</p> - -<p>Already we have seen among the lower <i>Cryptogamia</i>, how, as they -became integrated and definitely limited, aggregates acquire the habit -of budding out other aggregates, on reaching certain stages of growth. -Cells produce other cells endogenously or exogenously; and fronds -give origin to other fronds from their edges or surfaces. We have -seen, too, that the new aggregates so produced, whether of the first -order or the second order, may either separate or remain connected. -Fissiparously-multiplying cells in some cases part company, while in -other cases they unite into threads or laminæ or masses; and fronds -originating proliferously from other fronds, sometimes when mature -disconnect themselves from their parents, and sometimes continue -attached to them. Whether they do or do not part, is clearly determined -by their nutrition. If the conditions are such that they can severally -thrive better by separating after a certain development is reached, -it will become their habit then to separate; since natural selection -will favour the propagation of those which separate most nearly at -that time. If, conversely, it profits the species for the cells or -fronds to continue longer attached, which it can only do if their -growths and subsequent powers of multiplication are thereby increased, -it must happen, through the continual survival of the fittest, that<span class="pagenum" id="Page_52">[52]</span> -longer attachment will become an established characteristic; and, -by persistence in this process, permanent attachment will result -when permanent attachment is advantageous. That disunion is really -a consequence of relative innutrition, and union a consequence of -relative nutrition, is clear <i>à posteriori</i>. On the one hand, the -separation of the new individuals, whether in germs or as developed -aggregates, is a dissolving away of the connecting substance; and -this implies that the connecting substance has ceased to perform its -function as a channel of nutriment. On the other hand, where, as -we see among Phænogams, there is about to take place a separation -of new individuals in the shape of germs, at the point where the -nutrition is the lowest, a sudden increase of nutrition will cause the -impending separation to be arrested; and the fructifying elements, -reverting towards the ordinary form, thereupon develop in connexion -with the parent. Turning to the Archegoniates, we find among them -many indications of this transition from discontinuous development -to continuous development. Thus the Liverworts give origin to new -plants by cells which they throw off from their surfaces; as, indeed, -we have seen that much higher plants do. “According to Bischoff,” -says Schleiden, “both the cells of the stem (<i>Jungermannia</i> [now -<i>Lophocolea</i>] <i>bidentata</i>) and those of the leaves (<i>J. -exsecta</i>) separate themselves as propagative cells from the plant, -and isolated cells shoot out and develop while still connected with the -parent plant into small cellular bodies (<i>Metzgeria furcata</i>), -which separate from the plant, and grow into new plants, as in <i>Mnium -androgynum</i> among the Mosses.” Now in the way above explained, -these propagative cells and proliferous buds, may continue developing -in connexion with the parent to various degrees before separating; or -the buds which are about to become fructifying organs may similarly, -under increased nutrition, develop into young fronds. As Sir W. Hooker -says of the male fructification in <i>Metzgeria furcata</i>,—“It -has the appearance of being a young shoot or innovation (for in -colour<span class="pagenum" id="Page_53">[53]</span> and texture I can perceive no difference) rolled up into a -spherical figure.” On finding in this same plant, that sometimes the -proliferously-produced frond buds out from itself another frond before -separating from the parent, as shown in Fig. <a href="#i_034">46</a>, it becomes clear -that this long-continued connexion may readily pass into permanent -connexion. And when we see how, even among Phænogams, buds may either -detach themselves as bulbils, or remain attached and become shoots; we -can scarcely doubt that among inferior plants, less definite in their -modes of organization, such transitions must continually occur.</p> - - <div class="figcenter" id="i_053"> - <img - class="p2" - src="images/i_053.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 73–76.</p> - </div> - -<p class="p2">Let us suppose, then, that Fig. <a href="#i_053">73</a> is the frond of some primitive -Archegoniate, similar in general characters to <i>Pellia epiphylla</i>, -Fig. <a href="#i_033">43</a>; bearing, like it, the fructifying buds on its upper surface, -and having a slightly-marked mid-rib and rootlets. And suppose -that, as shown, a secondary frond is proliferously produced from -the mid-rib, and continues attached to it. Evidently the ordinary -discontinuous development, can thus become a continuous development, -only on condition that there is an adequate supply, to the secondary -frond, of such materials as are furnished by the rootlets: the -remaining materials being obtainable by itself from the air. Hence, -that portion of the mid-rib lying between the secondary frond and -the chief rootlets, having its function increased, will increase in -bulk. An additional consequence will be a greater concentration of -the rootlets—there will be extra growth of those which are most -serviceably placed. Observe,<span class="pagenum" id="Page_54">[54]</span> next, that the structure so arising -is likely to be maintained. Such a variation implying, as it does, -circumstances especially favourable to the growth of the plant, will -give to the plant extra chances of leaving descendants; since the area -of frond supported by a given area of the soil, being greater than -in other individuals, there may be a greater production of spores. -And then, among the more numerous descendants thus secured by it, the -variation will give advantages to those in which it recurs. Such a -mode of growth having, in this manner, become established, let us ask -what is next likely to result. If it becomes the habit of the primary -frond to bear a secondary frond from its mid-rib, this secondary frond, -composed of physiological units of the same kind, will inherit the -habit; and supposing that the supply of mineral matters obtained by -the rootlets suffices for the full development of the secondary frond, -there is a likelihood that the growth from it of a tertiary frond, -will become an habitual characteristic of the variety. Along with the -establishment of such a tertiary frond, as shown in Fig. <a href="#i_053">74</a>, there -must arise a further development of mid-rib in the primary frond, as -well as in the secondary frond—a development which must bring with it -a greater integration of the two; while, simultaneously, extra growth -will take place in such of the rootlets as are most directly connected -with this main channel of circulation. Without further explanation it -will be seen, on inspecting Figs. <a href="#i_053">75 and 76</a>, that there may in this -manner result an integrated series of fronds, placed alternately on -opposite sides of a connecting vascular structure. That this connecting -vascular structure will, as shown in the figures, become more distinct -from the foliar surfaces as these multiply, is no unwarranted -assumption; for we have seen in compound-leaved plants, how, under -analogous conditions, mid-ribs become developed into separate -supporting parts, which acquire some of the characters of axes while -assuming their functions. And now mark how clearly the structure thus -built up by integration<span class="pagenum" id="Page_55">[55]</span> of proliferously-growing fronds, corresponds -with the structure of the more-developed <i>Jungermanniaceæ</i>. Each -of the fronds successively produced, repeating the characters of its -parent, will bear roots; and will bear them in homologous places, as -shown. Further, the united mid-ribs having but very little rigidity, -will be unable to maintain an erect position. Hence there will result -the recumbent, continuously-rooted stem, which these types exhibit: an -embryo phænogam having the weakness of an embryo.<a id="FNanchor_9" href="#Footnote_9" class="fnanchor">[9]</a></p> - -<p>A natural concomitant of the mode of growth here described, is that -the stem, while it increases longitudinally, increases scarcely at -all transversely: hence the old name Acrogens. Clearly the transverse -development of a stem is the correlative, partly of its function as -a channel of circulation, and partly of its function as a mechanical -support. That an axis may lift its attached leaves into the air, -implies thickness and solidity proportionate to the mass of such -leaves; and an increase of its sap-vessels, also proportionate to the -mass of such leaves, is necessitated when the roots are all at one end -and the leaves at the other. But in the generality of Acrogens, these -conditions, under which arises the necessity for transverse growth -of the axis, are absent wholly or in great part. The stem habitually -creeps below the surface, or lies prone upon the surface; and where -it grows in a vertical or inclined direction, does this by attaching -itself to a vertical or inclined object. Moreover, throwing out -rootlets, as it mostly does, at intervals throughout its length, it -is not called upon in any considerable degree, to transfer nutritive -materials from one of its ends to the other.<span class="pagenum" id="Page_56">[56]</span> Hence this peculiarity -which gives their name to the Acrogens, now called Archegoniates, is a -natural accompaniment of the low degree of specialization reached in -them. And that it is an incidental and not a necessary peculiarity, is -demonstrated by two converse facts. On the one hand, in those higher -Acrogens which, like the tree-ferns, lift large masses of foliage into -the air, there is just as decided a transverse expansion of the axis -as in dicotyledonous trees. On the other hand, in those Dicotyledons -which, like the common Dodder, gain support and nutriment from the -surfaces over which they creep, there is no more lateral expansion of -the axis than is habitual among Acrogens or Archegoniates. Concluding, -as we are thus fully justified in doing, that the lateral expansion -accompanying longitudinal extension, which is a general characteristic -of Phanerogams as distinguished from Archegoniates, is nothing more -than a concomitant of their usually-vertical growth;<a id="FNanchor_10" href="#Footnote_10" class="fnanchor">[10]</a> let us now -go on to consider how vertical growth originates, and what are the -structural changes it involves.</p> - - -<p class="p2">§ 193. Plants depend for their prosperity mainly on air and light: they -dwindle where they are smothered, and thrive where they can expand -their leaves into free space and sunshine. Those kinds which assume -prone positions, consequently labour under disadvantages in being -habitually interfered with by one another—they are mutually shaded -and<span class="pagenum" id="Page_57">[57]</span> mutually injured. Such of them, however, as happen, by variations -in mode of growth, to rise higher than others, are more likely to -flourish and leave offspring than others. That is to say, natural -selection will favour the more upright-growing forms. Individuals -with structures which lift them above the rest, are the fittest for -the conditions; and by the continual survival of the fittest, such -structures must become established. There are two essentially-different -ways in which the integrated series of fronds above described, may -be modified so as to acquire the stiffness needful for maintaining -perpendicularity. We will consider them separately.</p> - - <div class="figcenter" id="i_057"> - <img - class="p2" - src="images/i_057.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 77, 78.</p> - </div> - -<p class="p2">A thin layer of substance gains greatly in power of resisting a -transverse strain, if it is bent round so as to form a tube: witness -the difference between the pliability of a sheet of paper when -outspread, and the rigidity of the same sheet of paper when rolled up. -Engineers constantly recognize this truth, in devising appliances by -which the greatest strength shall be obtained at the smallest cost of -material; and among organisms, we see that natural selection habitually -establishes structures conforming to the same principle, wherever -lightness and stiffness are to be combined. The cylindrical bones of -mammals and birds, and the hollow shafts of feathers, are examples. -The lower plants, too, furnish cases where the strength needful for -maintaining an upright position, is acquired by this rolling up of -a flat thallus or frond. In Fig. <a href="#i_057">77</a> we have an <i>Alga</i> which -approaches towards a tubular distribution of substance; and which has a -consequent rigidity. Sundry common forms of lichen, having the thallus -folded into a branched tube, still more decidedly display the connexion -between this structural arrangement<span class="pagenum" id="Page_58">[58]</span> and this mechanical advantage. -And from the particular class of plants we are here dealing with—the -Archegoniates—a type is shown in Fig. <a href="#i_057">78</a>, <i>Riella helicophylla</i>, -similarly characterized by a thin frond that is made stiff enough to -stand, by an incurving which, though it does not produce a hollow -cylinder, produces a kindred form. If, then, as we have seen, natural -selection or survival of the fittest will favour such among these -recumbent Archegoniates as are enabled, by variations in their -structures, to maintain raised postures; it will favour the formation -of fronds that curve round upon themselves, and curve round upon the -fronds growing out of them. What, now, will be the result should such a -modification take place in the group of proliferous fronds represented -in Fig. <a href="#i_053">76</a>? Clearly, the result will be a structure like that shown -in Fig. <a href="#i_058">79</a>. And if this inrolling becomes more complete, a form like -<i>Jungermannia cordifolia</i>, represented in Fig. <a href="#i_058">80</a>, will be -produced.</p> - - <div class="figcenter" id="i_058"> - <img - class="p2" - src="images/i_058.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 79, 80.</p> - </div> - - <div class="figcenter" id="i_059"> - <img - class="p2" - src="images/i_059.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 81–89.</p> - </div> - - <div class="figcenter" id="i_060"> - <img - class="p2" - src="images/i_060.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 90, 91.</p> - </div> - -<p class="p2">When the successive fronds are thus folded round so completely that -their opposite edges meet, these opposite edges will be apt to unite: -not that they will grow together after being formed, but that they will -develop in connexion; or, in botanical language, will become “adnate.” -That foliar surfaces which, in their embryonic state, are in close -contact, often join into one, is a familiar fact. It is habitually so -with sepals or divisions of the calyx. In all campanulate flowers it is -so with petals. And in some tribes of plants it is so with stamens. We -are therefore well warranted in inferring that, under the conditions -above described, the successive fronds or leaflets will, by union of -their remote edges, first at their points of origin and afterwards -higher up,<span class="pagenum" id="Page_59">[59]</span> form sheaths inserted one within another, and including the -axis. This incurving of the successive fronds, ending in the formation -of sheaths, may be accompanied by different sets of modifications. -Supposing Fig. <a href="#i_059">81</a> to be a transverse section of such type (<i>a</i> -being the mid-rib, and <i>b</i> the expansion of an older frond; while -<i>c</i> is a younger frond proliferously developed within it), there -may begin two divergent kinds of changes, leading to two contrasted -structures. If, while frond continues to grow out of frond, the series -of united mid-ribs continues to be the channel of circulation between -the uppermost fronds and the roots—if, as a consequence, the compound -mid-rib, or rudimentary axis, continues to increase in size laterally; -there will arise the series of transitional forms represented by the -transverse sections 82, 83, 84, 85; ending in the production of a solid -axis, everywhere wrapped round by the foliar surface of the frond, as -an outer layer or sheath. But if, on the other hand, circumstances -favour a form of plant which maintains its uprightness at the smallest -cost of substance—if the vascular bundles of each succeeding mid-rib, -instead of remaining concentrated, become distributed all round the -tube<span class="pagenum" id="Page_60">[60]</span> formed by the infolded frond; then the structure eventually -reached, through the transitional forms 86, 87, 88, 89, will be a -hollow cylinder.<a id="FNanchor_11" href="#Footnote_11" class="fnanchor">[11]</a> And now observe how the two structures thus -produced, correspond with two kinds of Monocotyledons. Fig. <a href="#i_060">90</a> -represents a species of <i>Dendrobium</i>, in which we see clearly -how each leaf is but a continuation of the external layer of a solid -axis—a sheath such as would result from the infolded edges of a frond -becoming adnate; and on examining how the sheath of each leaf includes -the one above it, and how the successive sheaths include the axis, it -will be manifest that the relations of parts are just such as exist -in the united series of fronds shown in Fig. <a href="#i_058">79</a>—the successive nodes -answering to the successive points of origin of the fronds. Conversely, -the stem of a grass, Fig. <a href="#i_060">91</a>, displays just such relations of parts, -as would result from the development of the type shown in Fig. <a href="#i_058">79</a>, -if instead of the mid-ribs thickening into a solid axis, the matter -composing them became evenly distributed round the foliar surfaces, -at the same time that the incurved edges of the foliar surfaces -united. The arrangements of the tubular axis and its appendages, -thus resulting, are still more instructive than those<span class="pagenum" id="Page_61">[61]</span> of the solid -axis. For while, even more clearly than in the <i>Dendrobium</i>, -we see at the point <i>b</i>, a continuity of structure between the -substance of the axis below the node, and the substance of the sheath -above the node: we see that this sheath, instead of having its edges -united as in <i>Dendrobium</i>, has them simply overlapping, so as -to form an incomplete hollow cylinder which may be taken off and -unrolled; and we see that were the overlapping edges of this sheath -united all the way from the node <i>a</i> to the node <i>b</i>, it -would constitute a tubular axis, like that which precedes it or like -that which it includes. And then, giving an unexpected conclusiveness -to the argument, it turns out that in one family of grasses, the -overlapping edges of the sheaths <i>do</i> unite: thus furnishing us -with a demonstration that tubular structures <i>are</i> produced by -the incurving and joining of foliar surfaces; and that so, hollow axes -may be interpreted as above, without making any assumption unwarranted -by fact. One further correspondence between the type thus ideally -constructed, and the monocotyledonous type, must be noted. If, as -already pointed out, the transverse growth of an axis arises when the -axis comes to be a channel of circulation between all the roots at one -of its extremities and all the leaves at the other; and if this lateral -bulging must increase as fast as the quantity of foliage to be brought -in communication with the roots increases—especially if such foliage -has at the same time to be raised high above the earth’s surface; what -must happen to a plant constructed in the manner just described? The -elder fronds or foliar organs, ensheathing the younger ones, as well -as the incipient axis serving as a bond of union, are at first of such -circumference only as suffices to inclose these undeveloped parts. -What, then, will take place when the inclosed parts grow—when the axis -thickens while it elongates? Evidently the earliest-formed sheaths, not -being large enough for the swelling axis, must burst; and evidently -each of the later-formed sheaths must, in its turn, do the like. There -must<span class="pagenum" id="Page_62">[62]</span> result a gradual exfoliation of the successive sheaths, like that -indicated as beginning in the above figure of <i>Dendrobium</i>; which, -at <i>a</i>, shows the bud of the undeveloped parts just visible above -the enwrapping sheaths, while at <i>b</i>, and <i>c</i>, it shows the -older sheaths in process of being split open. That is to say, there -must result the mode of growth which helped to give the name Endogens -to this class.</p> - - <div class="figcenter" id="i_063"> - <img - class="p2" - src="images/i_063.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 92–94.</p> - </div> - - <div class="figcenter" id="i_064"> - <img - class="p2" - src="images/i_064.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 95–99.</p> - </div> - -<p class="p2">The other way in which an integrated series of fronds may acquire -the rigidity needful for maintaining an erect position, has next to -be considered. If the successive fronds do not acquire such habit -of curling as may be taken advantage of by natural selection, so as -to produce the requisite stiffness; then, the only way in which the -requisite stiffness appears producible, is by the thickening and -hardening of the fused series of mid-ribs. The incipient axis will not, -in this case, be inclosed by the rolled-up fronds; but will continue -exposed. Survival of the fittest will favour the genesis of a type, in -which those portions of the successive mid-ribs that enter into the -continuous bond, become more bulky than the disengaged portions of the -mid-ribs: the individuals which thrive and have the best chances of -leaving offspring, being, by the hypothesis, individuals having axes -stiff enough to raise their foliage above that of their fellows. At -the same time, under the same influences, there will tend to result -an elongation of those portions of the mid-ribs, which become parts -of the incipient axis; seeing that it will profit the plant to have -its leaves so far removed from one another, as to prevent mutual -interferences. Hence, from the recumbent type there will evolve, by -indirect equilibration (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect167">§ 167</a>), such modifications as are shown in -Figs. <a href="#i_063">92, 93, 94</a>; the first of which is a slight advance on the ideal -type represented in Fig. <a href="#i_053">76</a>, arising in the way described; and the -others of which are actual plants—<i>Haplomitrium Hookeri</i>, and -<i>Plagiochila decipiens</i>. Thus the higher Archegoniates show us -how, along with an assumption of the upright attitude, there does go -on, as we see there must go on, a separation<span class="pagenum" id="Page_63">[63]</span> of the leaf-producing -parts from the root-producing parts; a greater development of that -connecting portion of the successive fronds, by which they are kept -in communication with the roots, and raised above the ground; and -a consequent increased differentiation of such connecting portion -from the parts attached to it. And this lateral bulging of the axis, -directly or indirectly consequent on its functions as a support and -a channel, being here unrestrained by the early-formed fronds folded -round it, goes on without the bursting of these. Hence arises a -leading character of what is called exogenous growth—a growth which -is, however, still habitually accompanied by exfoliation, in flasks, -of the outermost layers, continually being cracked and split by the -accumulation of layers within them. And now if we examine plants of -the exogenous type, we find among them many displaying the stages of -this metamorphosis. In Fig. <a href="#i_064">95</a>, is shown a form in which the continuity -of the axis with the mid-rib of the leaf, is manifest—a continuity -that is conspicuous in the common thistle. Here the foliar expansion, -running some distance down the axis, makes the included portion of the -axis a part of its mid-rib; just as in the ideal types above drawn. -By the greater growth of the internodes,<span class="pagenum" id="Page_64">[64]</span> which are very variable, -not only in different plants but in the same plant, there results a -modification like that delineated in Fig. <a href="#i_064">96</a>. And then, in such forms -as Fig. <a href="#i_064">97</a>, there is shown the arrangement that arises when, by more -rapid development of the proximal end of the mid-rib, the distal part -of the foliar surface is separated from the part which embraces the -axis: the wings of the mid-rib still serving, however, to connect the -two portions of the foliar surface. Such a separation is, as pointed -out in <a href="#sect188">§ 188</a>, an habitual occurrence; and in some compound leaves, an -actual tearing of the inter-venous tissue is caused by extra growth -of the mid-rib. Modifications like this, and the further one in Fig. -<a href="#i_064">98</a>, we may expect to be established by survival of the fittest, among -those plants which produce considerable masses of leaves; since the -development of mid-ribs into foot-stalks, by throwing the leaves -further away from the axes, will diminish the shading of the leaves, -one by another. And then, among plants of bushy growth, in which -the assimilating surfaces become still more liable to intercept one -another’s light, natural selection will continue to give an advantage -to those which carry their assimilating surfaces at the ends of the -petioles, and do not develop assimilating surfaces close to the -axis, where they are most shaded. Whence will result a disappearance -of the stipules and the foliar fringes of the mid-ribs; ending in -the production of the ordinary stalked leaf, Fig. <a href="#i_064">99</a>, which is -characteristic of trees. Meanwhile, the axis thickens in proportion to -the number of leaves it has to carry, and to put in communication with -the roots; and so<span class="pagenum" id="Page_65">[65]</span> there comes to be a more marked contrast between it -and the petioles, severally carrying a leaf each.<a id="FNanchor_12" href="#Footnote_12" class="fnanchor">[12]</a></p> - - -<p class="p2">§ 194. When, in the course of the process above sketched out, there has -arisen such community of nutrition among the fronds thus integrated -into a series, that the younger ones are aided by materials which the -older ones have elaborated; the younger fronds will begin to show, at -earlier and earlier periods of development, the structures about to -originate from them. Abundant nutrition will abbreviate the intervals -between the successive prolifications; so that eventually, while each -frond is yet imperfectly formed, the rudiment of the next will begin to -show itself. All embryology justifies this inference. The analogies it -furnishes lead us to expect that when this serial arrangement becomes -organic, the growing part of the series will show the general relations -of the forthcoming parts, while they are very small and unspecialized. -What will in such case be the appearances they assume? We shall have -no difficulty in perceiving what it will be, if we take a form like -that shown in Fig. <a href="#i_063">92</a>, and dwarf its several parts at the same time -that we generalize them. Figs. <a href="#i_065">100, 101, 102, and 103</a>, will show the -result; and in Fig. <a href="#i_065">104</a>, which is the bud of a dicotyledon, we see how -clear is the morphological correspondence: <i>a</i> being the rudiment -of a foliar organ beginning to take shape; <i>b</i> being the almost -formless rudiment of the next foliar organ; and<span class="pagenum" id="Page_66">[66]</span> <i>c</i> being the -quite-undifferentiated part whence the rudiments of subsequent foliar -organs are to arise.</p> - - <div class="figcenter" id="i_065"> - <img - class="p2" - src="images/i_065.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 100–104.</p> - </div> - - <div class="figcenter" id="i_066"> - <img - class="p2" - src="images/i_066.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 105–106.</p> - </div> - -<p class="p2">And now we are prepared for entering on a still-remaining question -respecting the structure of Phænogams—what is the origin of axillary -buds? As the synthesis at present stands, it does not account for -these; but on looking a little more closely into the matter, we shall -find that the axillary buds are interpretable in the same manner as the -terminal buds. So to interpret them, however, we must return to that -process of proliferous growth with which we set out, for the purpose of -observing some facts not before named. <i>Delesseria hypoglossum</i>, -Fig. <a href="#i_066">105</a>, represents a seaweed of the same genus as one outlined in -Fig. <a href="#i_031">40</a>; but of a species in which proliferous growth is carried much -further. Here, not only does the primary frond bud out many secondary -fronds from its mid-rib; but most of the secondary fronds similarly -bud out several tertiary fronds; and even by some of the tertiary -fronds, this prolification is repeated. Besides being shown that the -budding out of several fronds from one frond, may become habitual; we -are also shown that it may become a<span class="pagenum" id="Page_67">[67]</span> habit inherited by the fronds -so produced, and also by the fronds they produce: the manifestation -of the tendency being probably limited only by failure of nutrition. -That under fit conditions an analogous mode of growth will occur in -fronds of the acrogenic type, like those we set out with, is shown -by the case of <i>Metzgeria furcata</i>, Figs. <a href="#i_034">45, 46,</a> in which such -compound prolification is partially displayed. Let us suppose, then, -that the frond <i>a</i>, Fig. <a href="#i_066">106</a>, produces not only a single secondary -frond <i>b</i>, but also another such secondary frond <i>b’</i>. Let -us suppose, further, that the frond <i>b</i> is in like manner doubly -proliferous: producing both <i>c</i> and <i>c’</i>. Lastly, let us -suppose that in the second frond <i>b’</i> which <i>a</i> produces, -as well as in the second frond <i>c’</i> which <i>b</i> produces, the -doubly-proliferous habit is manifested. If, now, this habit grows -organic—if it becomes, as it naturally will become, the characteristic -of a plant of luxuriant growth, the unfolding parts of which can be -fed by the unfolded parts; it will happen with each lateral series, -as with the main series, that its successive components will begin to -show themselves at earlier and earlier stages of development. And in -the same way that, by dwarfing and generalizing the original series, we -arrive at a structure like that of the terminal bud; by dwarfing and -generalizing a lateral series, as shown in Figs. <a href="#i_067">107–110</a>, we arrive at -a structure answering in nature and position to the axillary bud.</p> - - <div class="figcenter" id="i_067"> - <img - class="p2" - src="images/i_067.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 107–110.</p> - </div> - -<p class="p2">Facts confirming these interpretations are afforded by the structure -and distribution of buds. The phænogamic axis in its primordial form, -being an integrated series of folia; and the development of that part -by which these folia are held together at considerable distances -from one another, taking place afterwards; it is inferable from the -general<span class="pagenum" id="Page_68">[68]</span> principles of embryology, that in its rudimentary stages, the -phænogamic shoot will have its foliar parts more clearly marked out -than its axial parts. This we see in every bud. Every bud consists -of the rudiments of leaves packed together without any appreciable -internodal spaces; and the internodal spaces begin to increase with -rapidity, only when the foliar organs have been considerably developed. -Moreover, where nutrition falls short, and arrest of development -takes place—that is, where a flower is formed—the internodes remain -undeveloped: the unfolding ceases before the later-acquired characters -of the phænogamic shoot are assumed. Lastly, as the hypothesis leads us -to expect, axillary buds make their appearances later than the foliar -organs which they accompany; and where, as at the ends of shoots, these -foliar organs show failure of chlorophyll, the axillary buds are not -produced at all. That these are inferable traits of structure, will be -manifest on inspecting Figs. <a href="#i_066">106</a>–<a href="#i_067">110</a>; and on observing, first, that -the doubly-proliferous tendency of which the axillary bud is a result, -implies abundant nutrition; and on observing, next, that the original -place of secondary prolification, is such that the foliar surface on -which it occurs, must grow to some extent before the bud appears.</p> - -<p>On thus looking at the matter—on contemplating afresh the ideal type -shown in Fig. <a href="#i_066">106</a>, and noting how, by the conditions of the case, the -secondary prolifications must cease before that primary prolification -which produces the main axis; we are enabled to reconcile all the -phenomena of axillary gemmation. We see harmony among the several -facts—first, that the axillary bud becomes a lateral, leaf-bearing -axis if there is abundant material for growth; second, that its -development is arrested, or it becomes a flower-bearing axis, if the -supply of sap is but moderate; third, that it is absent when the -nutrition is failing. We are no longer committed to the gratuitous -assumption that, in the phænogamic type, there must exist an axillary -bud to each foliar<span class="pagenum" id="Page_69">[69]</span> organ; but we are led to conclude, <i>à priori</i>, -that which we find, <i>à posteriori</i>, that axillary buds are as -normally absent in flowers as they are normally present lower down -the axis. And then, to complete the argument, we are prepared for the -corollary that axillary prolification may naturally arise even at the -ends of axes, should the failing nutrition which causes the dwarfing of -the foliar organs to form a flower, be suddenly changed into such high -nutrition as to transform the components of the flower into appendages -that are green, if not otherwise leaf-like—a condition under which -only, this phenomenon is proved to occur.</p> - - -<p class="p2">§ 195. One more question presents itself, when we contrast the -early stages of development in the two classes of Phænogams; and a -further answer, supplied by the hypothesis, gives to the hypothesis -a further probability. It is characteristic of a monocotyledon, to -have a single seed-leaf or cotyledon; and it is characteristic of a -dicotyledon, to have at least two cotyledons, if not more than two. -That is to say, the monocotyledonous mode of germination everywhere -co-exists with the endogenous mode of growth; and along with the -exogenous mode of growth, there always goes either a dicotyledonous or -polycotyledonous germination. Why is this? Such correlations cannot -be accidental—cannot be meaningless. A true theory of the phænogamic -types in their origin and divergence, should account for the connexion -of these traits. Let us see whether the foregoing theory does this.</p> - -<p>The higher plants, like the higher animals, bequeath to their offspring -more or less of nutriment and structure. Superior organisms of either -kingdom do not, as do all inferior organisms, cast off their progeny -in the shape of minute portions of protoplasm, unorganized and without -stocks of material for them to organize; but they either deposit -along with the germs they cast off, certain quantities of albuminoid -substance to be appropriated by them while they<span class="pagenum" id="Page_70">[70]</span> develop themselves, -or else they continue to supply such substance while the germs -partially develop themselves before their detachment. Among plants -this constitutes one distinction between seeds and spores. Every seed -contains a store of food to serve the young plant during the first -stages of its independent life; and usually, too, before the seed is -detached, the young plant is so far advanced in structure, that it -bears to the attached stock of nutriment much the same relation that -the young fish bears to the appended yelk-bag at the time of leaving -the egg. Sometimes, indeed, the development of chlorophyll gives the -seed-leaves a bright green, while the seed is still contained in the -parent-pod. This early organization of the phænogam must be supposed -rudely to indicate the type out of which the phænogamic type arose. -On the foregoing hypothesis, the seed-leaves therefore represent the -primordial fronds; which, indeed, they simulate in their simple, -cellular, unveined structures. And the question here to be asked is—do -the different relations of the parts in young monocotyledons and -dicotyledons correspond with the different relations of the primordial -fronds, implied by the endogenous and the exogenous modes of growth? We -shall find that they do.</p> - - <div class="figcenter" id="i_071"> - <img - class="p2" - src="images/i_071.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 111–122.</p> - </div> - -<p class="p2">Starting, as before, with the proliferous form shown in Fig. <a href="#i_071">111</a>, it -is clear that if the strength required for maintaining the vertical -attitude, is obtained by the rolling up of the fronds, the primary -frond will more and more conceal the secondary frond within it. At the -same time, the secondary frond must continue to be dependent on the -first for its nutrition; and, being produced within the first, must -be prevented by defective supply of light and air, from ever becoming -synchronous in its development with the first. Hence, this infolding -which leads to the endogenous mode of growth, implies that there must -always continue such pre-eminence of the first-formed frond or its -representative, as to make the germination monocotyledonous. Figs. -<a href="#i_071">111 to 115</a>, show the transitional forms that would result from the -infolding of<span class="pagenum" id="Page_71">[71]</span> the fronds. In Fig. <a href="#i_071">116</a> (a vertical section of the form -represented in Fig. <a href="#i_071">115</a>) are exhibited the relations of the successive -fronds to each other. The modified relations that would result, if -the nutrition of the embryo admitted of anticipatory development of -the successive fronds, are shown in Fig. <a href="#i_071">117</a>. And how readily the -structure may pass into that of the monocotyledonous germ, will be -seen on inspecting Fig. <a href="#i_071">118</a>; which is a vertical section of an actual -monocotyledon at an early stage—the incomplete lines at the left of -its root, indicating its connexion with the seed.<a id="FNanchor_13" href="#Footnote_13" class="fnanchor">[13]</a> Contrariwise,<span class="pagenum" id="Page_72">[72]</span> -where the strength required for maintaining an upright attitude is not -obtained by the rolling up of the fronds, but by the strengthening -of the continuous mid-rib, the second frond, so far from being less -favourably circumstanced than the first, becomes in some respects even -more favourably circumstanced: being above the other, it gets a greater -share of light, and it is less restricted by surrounding obstacles. -There is nothing, therefore, to prevent it from rapidly gaining an -equality with the first. And if we assume, as the truths of embryology -entitle us to do, an increasing tendency towards anticipation in the -development of subsequent fronds—if we assume that here, as in other -cases, structures which were originally produced in succession will, -if the nutrition allows and no mechanical dependence hinders, come to -be produced simultaneously; there is nothing to prevent the passage of -the type represented in Fig. <a href="#i_071">111</a>, into that represented in Fig. <a href="#i_071">122</a>. -Or rather, there is everything to facilitate it; seeing that natural -selection will continually favour the production of a form in which the -second frond grows in such way as not to shade the first, and in such -way as allows the axis readily to assume a vertical position.</p> - -<p>Thus, then, is interpretable the universal connexion between -monocotyledonous germination and endogenous growth; as well as -the similarly-universal connexion between exogenous growth and -the development of two or more cotyledons. That it explains these -fundamental relations, adds very greatly to the probability of the -hypothesis.</p> - - -<p class="p2" id="sect196">§ 196. While we are in this manner enabled to discern the kinship that -exists between the higher vegetal types themselves, as well as between -them and the lower types; we<span class="pagenum" id="Page_73">[73]</span> are at the same time supplied with a -rationale of those truths which vegetal morphologists have established. -Those homologies which Wolff indicated in their chief outlines and -Goethe followed out in detail, have a new meaning given to them when we -regard the phænogamic axis as having been evolved in the way described. -Forming the modified conception which we are here led to do, respecting -the units of which a flowering plant is composed, we are no longer -left without an answer to the question—What is an axis? And we are -helped to understand the naturalness of those correspondences which the -successive members of each shoot display. Let us glance at the facts -from our present standpoint.</p> - - <div class="figcenter" id="i_074"> - <img - class="p2" - src="images/i_074.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 123–129.</p> - </div> - -<p class="p2">The unit of composition of a Phænogam, is such portion of a shoot as -answers to one of the primordial fronds. This portion is neither one -of the foliar appendages nor one of the internodes; but it consists of -a foliar appendage together with the preceding internode, including -the axillary bud where this is developed. The parts intercepted by -the dotted lines in Fig. <a href="#i_074">123</a>, constitute such a segment; and the true -homology is between this and any other foliar organ with the portion -of the axis below it. And now observe how, when we take this for the -unit of composition, the metamorphoses which the phænogamic axis -displays, are inferable from known laws of development. Embryology -teaches us that arrest of development shows itself first in the absence -of those parts that have arisen latest in the course of evolution; -that if defect of nutrition causes an earlier arrest, parts that are -of more ancient origin abort; and that the part alone produced when -the supply of materials fails near the outset, is the primordial -part. We must infer, therefore, that in each segment of a Phænogam, -the foliar organ, which answers to the primordial frond, will be the -most constant element; and that the internode and the axillary bud, -will be successively less constant. This we find. Along with a smaller -size of foliar surface implying lower nutrition, it is usual to see a<span class="pagenum" id="Page_74">[74]</span> -much-diminished internode and a less-pronounced axillary bud, as in -Fig. <a href="#i_074">124</a>. On approaching the flower, the axillary bud disappears; and -the segment is reduced to a small foliar surface, with an internode -which is in most cases very short if not absent, as in 125 and 126. -In the flower itself, axillary buds and internodes are both wanting: -there remains only a foliar surface (127), which, though often larger -than the immediately-preceding foliar surface, shows failing nutrition -by absence of chlorophyll. And then, in the quite terminal organs of -fructification (129), we have the foliar part itself reduced to a -mere rudiment. Though these progressive degenerations are by no means -regular, being in many cases varied by adaptations to particular -requirements, yet it cannot, I think, be questioned, that the general -relations are as described, and that they are such as the hypothesis -leads us to expect. Nor are we without a kindred explanation of certain -remaining traits of foliar organs in their least-developed forms. -Petals, stamens, pistils, &c., besides reminding us of the primordial -fronds by their diminished sizes, and by the want of those several -supplementary parts which the preceding segments possess, also remind -us of them by their histological characters: they consist of simple -cellular tissue, scarcely at all differentiated. The fructifying cells, -too, which here make their appearance, are borne in ways like those in -which the lower Acrogens bear them—at the edge of the frond, or at the -end of a peduncle, or immersed in the general substance; as in Figs. -<a href="#i_074">128 and 129</a>. Nay, it might even be said that<span class="pagenum" id="Page_75">[75]</span> the colours assumed by -these terminal folia, call to mind the plants out of which we conclude -that Phænogams have been evolved; for it is said of the fronds of the -<i>Jungermanniaceæ</i>, that, “though under certain circumstances of a -pure green, they are inclined to be shaded with red, purple, chocolate, -or other tints.”</p> - -<p>As thus understood, then, the homologies among the parts of the -phænogamic axis are interpretable, not as due to a needless adhesion -to some typical form or fulfilment of a predetermined plan; but as -the inevitable consequences of the mode in which the phænogamic axis -originates.</p> - - -<p class="p2">§ 197. And now it remains only to observe, in confirmation of -the foregoing synthesis, that it at once explains for us various -irregularities. When we see leaves sometimes producing leaflets from -their edges or extremities, we recognize in the anomaly a resumption -of an original mode of growth: fronds frequently do this. When we -learn that a flowering plant, as the <i>Drosera intermedia</i>, -has been known to develop a young plant from the surface of one of -its leaves, we are at once reminded of the proliferous growths and -fructifying organs in the Liverworts. The occasional production of -bulbils by Phænogams, ceases to be so surprising when we find it to -be habitual among the inferior Acrogens, and when we see that it is -but a repetition, on a higher stage, of that self-detachment which -is common among proliferously-produced fronds. Nor are we any longer -without a solution of that transformation of foliar organs into axial -organs, which not uncommonly takes place. How this last irregularity -of development is to be accounted for, we will here pause a moment to -consider. Let us first glance at our data.</p> - -<p>The form of every organism, we have seen, must depend on the structures -of its physiological [or constitutional] units. Any group of such -units will tend to arrange itself into the complete organism, if -uncontrolled and placed in fit conditions. Hence the development of -fertilized germs; and<span class="pagenum" id="Page_76">[76]</span> hence the development of those self-detached -cells which characterize some plants. Conversely, physiological units -which form a small group involved in a larger group, and are subject to -all the forces of the larger group, will become subordinate in their -structural arrangements to the larger group—will be co-ordinated into -a part of the major whole, instead of co-ordinating themselves into a -minor whole. This antithesis will be clearly understood on remembering -how, on the one hand, a small detached part of a hydra soon moulds -itself into the shape of an entire hydra; and how, on the other hand, -the cellular mass that buds out in place of a lobster’s lost claw, -gradually assumes the form of a claw—has its parts so moulded as to -complete the structure of the organism: a result which we cannot but -ascribe to the forces which the rest of the organism exerts upon it. -Consequently, among plants, we may expect that whether any portion of -protoplasm moulds itself into the typical form around an axis of its -own, or is moulded into a part subordinate to another axis, will depend -on the relative mass of its physiological units—the accumulation of -them that has taken place before the assumption of any structural -arrangement. A few illustrations will make clear the validity of this -inference. In the compound leaf, Fig. <a href="#i_040">65</a>, the several lateral growths -<i>a</i>, <i>b</i>, <i>c</i>, <i>d</i>, are manifestly homologous; -and on comparing a number of such leaves together, it will be seen -that one of these lateral growths may assume any degree of complexity, -according to the degree of its nutrition. Every fern-leaf exemplifies -the same general truth still better. Whether each sub-frond remains -an undeveloped wing of the main frond, or whether it organizes itself -into a group of frondlets borne by a secondary rib, or whether, going -further, as it often does, it gives rise to tertiary ribs bearing -frondlets, is determined by the supply of materials for growth; since -such higher developments are most marked at points where the nutrition -is greatest; namely, next the stem. But the clearest evidence is -afforded among the <i>Algæ</i>,<span class="pagenum" id="Page_77">[77]</span> which, not drawing nutriment from -roots, have their parts much less mutually dependent; and are therefore -capable of showing more clearly, how any part may remain an appendage -or may become the parent of appendages, according to circumstances. In -the annexed Fig. <a href="#i_077">130</a>, representing a branch of <i>Ptilota plumosa</i>, -we see how a wing grows into a wing-bearing branch if its nutrition -passes a certain point. This form, so strikingly like that of the -feathery crystallizations of many inorganic substances, implies that, -as in such crystallizations, the simplicity or complexity of structure -at any place depends on the quantity of matter that has to be arranged -at that place in a given time.<a id="FNanchor_14" href="#Footnote_14" class="fnanchor">[14]</a></p> - - <div class="figcenter" id="i_077"> - <img - class="p2" - src="images/i_077.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 130.</p> - </div> - -<p class="p2">Hence, then, we are not without an interpretation of those -over-developments which the phænogamic axis occasionally undergoes. -Fig. <a href="#i_065">104</a>, represents the phænogamic bud in its rudimentary state. The -lateral process <i>b</i>, which ordinarily becomes a foliar appendage, -differs very little from the terminal process <i>c</i>, which is to -become an axis—differs mainly in having, at this period when its form -is being determined, a smaller bulk. If while thus undifferentiated, -its nutrition remains inferior to that of the terminal process, it -becomes moulded into a part that is subordinate to the general axis. -But if, as sometimes happens, there is supplied to it such an abundance -of the materials needful for growth, that it becomes as large as the -terminal process; then we<span class="pagenum" id="Page_78">[78]</span> may naturally expect it to begin moulding -itself round an axis of its own: a foliar organ will be replaced by -an axial organ. And this result will be especially liable to occur, -when the growth of the axis has been previously undergoing that arrest -which leads to the formation of a flower; that is when, from defect -of materials, the terminal process has almost ceased to increase, and -when some concurrence of favourable causes brings a sudden access of -sap which reaches the lateral processes before it reaches the terminal -process.<a id="FNanchor_15" href="#Footnote_15" class="fnanchor">[15]</a></p> - - -<p class="p2">§198. The general conclusion to which these various lines of evidence -converge, is, then, that the shoot of a flowering plant is an aggregate -of the third degree of composition. Taking as aggregates of the first -order, those small portions of protoplasm which ordinarily assume -the forms under which they are known as cells; and considering as -aggregates of the second order, those assemblages of such cells which, -in the lower cryptogams, compose the various kinds of thallus; then -that structure, common to the higher cryptogams and to phænogams, -in which we find a series of such groups of cells bound up into a -continuous whole, must be regarded as an aggregate of the third -order. The inference drawn from analysis, and verified by a synthesis -which corresponds in a remarkable manner with the facts, is that -those compound parts which, in Monocotyledons and Dicotyledons are -called axes, have really arisen by integration of such simple parts -as in lower plants are called fronds. Here, on a higher<span class="pagenum" id="Page_79">[79]</span> level, -appears to have taken place a repetition of the process already -observed on lower levels. The formation of those small groups of -physiological units which compose the lowest protophytes, is itself -a process of integration; and the consolidation of such groups into -definitely-circumscribed and coherent cells or morphological units, is -a completing of the process. In those coalescences by which many such -cells are joined into threads, and discs, and solid or flattened-out -masses, we see these morphological units aggregating into units of a -compound kind: the different phases of the transition being exemplified -by groups of various sizes, various degrees of cohesion, and various -degrees of definiteness. And now we find evidences of a like process -on a larger scale: the compound groups are again compounded. Moreover, -as before, there are not wanting types of organization by which the -stages of this higher integration are shadowed forth. From fronds that -occasionally produce other fronds from their surfaces, we pass to those -that habitually produce them; from those that do so in an indefinite -manner, to those that do so in a definite manner; and from those that -do so singly, to those that do so doubly and triply through successive -generations of fronds. Even within the limits of a sub-class, we find -gradations between fronds irregularly proliferous, and groups of such -fronds united into a regular series.</p> - -<p>Nor does the process end here. The flowering plant is rarely -uniaxial—it is nearly always multiaxial. From its primary shoot there -grow out secondary shoots of like kind. Though occasionally among -Phænogams, and frequently among the higher Cryptogams, the germs of -new axes detach themselves under the form of bulbils, and develop -separately instead of in connexion with the parent axis; yet in most -Phænogams the germ of each new axis maintains its connexion with the -parent axis: whence results a group of axes—an aggregate of the fourth -order. Every tree, by the production<span class="pagenum" id="Page_80">[80]</span> of branch out of branch, shows -us this integration repeated over and over again; forming an aggregate -having a degree of composition too complex to be any longer defined.</p> - -<hr class="tb" /> - -<p>[<span class="smcap">Note.</span>—A criticism passed on the general argument set -forth in the foregoing sections, runs as follows:—“I have already -pointed out that the process of evolution by which you believe the -Liverworts with a distinct axis and appendages to have been produced -from the thalloid forms is not founded on sound evidence either in -comparative morphology or development. But even if we admit that such -an integration of a proliferously-produced colony might have given -rise to the leafy <i>Jungermanniaceæ</i>, there are even more weighty -objections to the supposition that the same process produced the shoot -structures of the flowering plants. In the first place the flowering -plant-body is <i>not homologous with the liverwort plant-body</i>, -since they represent different generations. The liverwort plant-body or -<i>gametophyte</i>, <i>i.e.</i>, the generation bearing sexual organs, -is homologous with the prothallus of ferns and other Pteridophytes, -and in the Flowering Plants with reduced structures contained within -the spores (embryo-sac and pollen-grain) but still giving rise to -sexual cells. The liverwort spore-capsule and its accessory parts -(in fact everything produced from the fertilized egg) is homologous -with the sporogonium of the mosses, and, as most botanists think, -with the leafy plant-body of Pteridophytes and Phanerogams. This -generation is called the <i>sporophyte</i> and from the spores which -it produces are developed the gametophytes of the next generation. -These generalizations were first established by Hofmeister, and all -subsequent work has tended to establish them more firmly. The only -doubtful question is (and the doubt is mainly, I think, peculiar to -myself, certainly not being shared by the majority of botanists) -whether the sporophyte of Mosses and Liverworts is really homologous -with that of Pteridophytes and<span class="pagenum" id="Page_81">[81]</span> Phanerogams, whether it may not rather -be regarded as a parallel development along another line of descent -from the Green Algæ.</p> - -<p>“Hence we must look for the origin of the shoot-structure of flowering -plants in the sporophytes of the Pteridophytes, from which group there -is no reason to doubt that the phanerogams have arisen in descent. -The various groups of Pteridophytes vary much in the organization -of these shoot-systems, as a mental glance at the types exhibited -by the Ferns, Horse-tails, Club-mosses, <i>Ophioglossaceæ</i>, and -the isolated Isoetes will convince you at once. It may be that some -of these groups are independent in descent, <i>i.e.</i>, that the -<i>Pteridophyta</i> are polyphyletic, and the current hypothesis with -regard to the phanerogams is that they have arisen by two, if not -three, separate lines of descent from different groups of Pteridophytes -(this is indicated in the classificatory diagram on p. 377 of vol. I). -I should not, however, care to pin my faith to these or to any such -lines of ancestry. Still I think we must look for the ancestors of the -Flowering Plants among the Pteridophytes, and the latter always have -a good distinction between axis and appendages. The problem of the -evolution of these differentiated sporophytic shoots is undoubtedly the -great outstanding problem of morphology. Various attempts have been -made to solve it, of which probably the most important is the theory -of Profs. Bown and Campbell, who derive the Pteridophytes from some -Liverwort like <i>Anthoceros</i>, but the sporophyte of course from the -sporophytic portion of the plant (not much more than a spore-capsule), -the prothallus of the Fern representing the vegetative thallus of -Anthoceros. I am not wholly convinced by these undoubtedly ingenious -hypotheses, in support of which an immense amount of facts have been -collected; but my position would, I know, simply ‘put us to ignorance -again’ on this question.</p> - -<p>“I have discussed this at some length in order to bring out clearly -the immense difficulty of constructing a wellgrounded<span class="pagenum" id="Page_82">[82]</span> theory of -the origin of the differentiated shoot-system of the higher plant. -I confess I don’t think it can be done at all with the materials at -present at our disposal. Of course it is just possible to suppose that -some ancestral sporophyte had the structure of a proliferous thalloid -liverwort gametophyte, and that from it was evolved the phanerogamic -shoot in the ways you suggest. This gives us absolutely no clue, -however, to any Pteridophytic shoot, which ought to be intermediate -(more or less) between the hypothetical ancestor and the Phanerogam, -and is furthermore, as far as I can see, not supported by an atom of -evidence of any kind. It is true that your theory fits in well with the -phenomena exhibited by phanerogamic shoots themselves, but this fact -you will see must lose much of its significance if the hypothesis lacks -foundation.</p> - -<p>“With regard to your method of explaining the fundamental characters -of ‘Exogens’ and ‘Endogens,’ this of course is part of the same -hypothesis; but I may point out that since Von Mohl and Sanio, between -1855 and 1865, showed (1) that the growth at the stem apex of a -monocotyledon was <i>not</i> endogenous, and (2) that the ‘thickening -ring’ near the apex of a dicotyledon was not to be confused, as had -been done up till then, with the ring of <i>secondary meristem</i> -or <i>true cambium</i>, which arose lower down, and only in woody -or practically woody stem, the terms ‘Exogen’ and ‘Endogen’ have -necessarily fallen into disuse, since they imply a false conception of -what happens. Both monocotyledons and dicotyledons have a ‘thickening -ring,’ which gives rise to the primary vascular cylinder of the stem. -When the stem is of considerable thickness, as in Palms, &c., it grows -by the active cell-division of its outer layers, so that both classes -are ‘exogenous’ in this sense; while the addition of a centrifugal zone -of secondary wood is confined to certain Dicotyledons (Trees, shrubs, -&c.).</p> - -<p>“The distinction between the embryos, moreover, is not absolute. The -single cotyledon is usually terminal in monocotyledons,<span class="pagenum" id="Page_83">[83]</span> but not always -(<i>Dioscoraceæ</i> have lateral cotyledons), but the plumule may push -through it (Grasses) or make its exit sideways (Palms), or be formed at -the side (<i>Alisma</i>); and Dicotyledons very similarly.</p> - -<p>“The occurrence of completely sheathing leaves in grasses is perhaps -correlated with the absence of cambium, but grasses are an aberrant -type among monocotyledons, and secondary thickening is only found in -very few genera of this class, so that the correlation is, so to speak, -negative and indirect.... It is clear that the greater part of the -discussion will have to be re-written.”</p> - -<p>For the reasons assigned in the preface I cannot undertake to re-write -the discussion, as suggested. It must stand for what it is worth. All I -can do is here to include along with it the foregoing criticisms.</p> - -<p>I may, however, indicate the line of defence I should take were I to -go again into the matter. The objections are based on the structure of -existing Liverworts and Phænogams. But I have already referred to the -probability—or, indeed, the certainty—that in conformity with the -general principle set forth in the note to Chapter I, we must conclude -that the early types of Liverworts out of which the Phænogams are -supposed to have evolved, as well as the early types of Phænogams in -which the stages of evolution were presented, no longer exist. We must -infer that forms simpler than any now known, and more intermediate in -their traits, were the forms concerned; and if so, it may be held that -the incongruities with the hypothesis which are presented by existing -forms, do not negative it. The scepticism my critic himself expresses -respecting the current interpretation is a partial justification of -this view. Moreover, his admission that the theory set forth “fits in -well with the phenomena exhibited by phanerogamic shoots,” must, I -think, be regarded as weighty evidence. On the Evolution hypothesis -we are obliged to suppose that the Monocotyledons and Dicotyledons -respectively arose by integration of fronds; and if to the<span class="pagenum" id="Page_84">[84]</span> question -after what manner the integration took place, there is an hypothesis -which renders it comprehensible, and agrees both with the structures of -the two kinds of shoots and the structures of the two kinds of seeds, -as well as with various of the other phenomena the two types present, -it has strong claims for acceptance.</p> - -<p>Reconsideration suggests the following remarks.</p> - -<p>1. Alternation of generations is a means of furthering multiplication. -To be effective each member of either generation must be a -self-supporting centre of growth or diffusion or both. Hence if, as in -the Liverworts, one of the so-called alternating generations is not -independent, but a permanent growth on the other—a parasite—it is a -misuse of words to call the arrangement Alternation of generations. -(Since this was written I have found that Sir Edward Fry takes the -same view. He approvingly quotes Professor Bower, who says that “the -alternation of generations is not an accurate statement of facts or a -useful analogy.”)</p> - -<p>2. The alternating of sexual and non-sexual processes is not -fundamentally distinctive; for, as shown by sundry Archegoniates, -it is an inconstant trait, and as shown by Klebs’ experiments on -<i>Vaucheria</i>, the conditions may be varied so as to determine its -occurrence or non-occurrence. Nay, the same individual may reproduce in -either way.</p> - -<p>3. Still more significant is the fact that in some of the marine -Thallophytes, there is a process like that which in a moss or a fern -is considered an alternation of generations, whereas in others, as -the Brown Wrack (<i>Fucus</i>), each generation is sexual. Thus the -presence or absence of this mode of genesis cannot be a cardinal -distinction.</p> - -<p>4. With these facts before us, it is not only a reasonable supposition -but a highly probable supposition, that there have existed plants of -the Liverwort type in which the so-called alternation of generations -did not take place. If so, nearly all the foregoing objections to my -hypothesis fall to the ground.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_85">[85]</span></p> - -<h3>CHAPTER IV.<br /> -<span class="subhed1">THE MORPHOLOGICAL COMPOSITION OF ANIMALS.</span></h3></div> - -<p>§ 199. What was said in <a href="#sect180">§ 180</a>, respecting the ultimate structure of -organisms, holds more manifestly of animals than of plants. That -throughout the vegetal kingdom the cell is the morphological unit, is -a proposition admitting of a better defence, than the proposition that -the cell is the morphological unit throughout the animal kingdom. The -qualifications with which, as we saw, the cell-doctrine must be taken, -are qualifications thrust upon us more especially by the facts which -zoologists have brought to light. It is among the <i>Protozoa</i> that -there occur numerous cases of vital activity displayed by specks of -protoplasm; and from the minute anatomy of all creatures above these, -are drawn the numerous proofs that non-cellular tissues may arise by -direct metamorphosis of mixed colloidal substances.<a id="FNanchor_16" href="#Footnote_16" class="fnanchor">[16]</a></p> - -<p><span class="pagenum" id="Page_86">[86]</span></p> - -<p>Our survey of morphological composition throughout the animal kingdom, -must therefore begin with those undifferentiated aggregates of -physiological units [or constitutional units], out of which are formed -what we call, with considerable license, morphological units.</p> - - -<p class="p2">§ 200. In that division of the <i>Protozoa</i> distinguished as -<i>Rhizopoda</i>, are presented, under various modifications, these -minute portions of living organic matter, so little differentiated, -if not positively undifferentiated, that animal individuality can -scarcely be claimed for them. Figs. <a href="#i_086">131, 132, and 133</a>, represent -certain nearly-allied types of these—<i>Amœba</i>, <i>Actinophrys</i>, -and <i>Lieberkühnia</i>. The viscid jelly or sarcode, comparable in -its physical properties to white of egg, out of which one of these -creatures is mainly formed, shows us in various ways, the feebleness -with which the component physiological units are integrated—shows us -this by its very slight cohesion, by the extreme indefiniteness and -mutability of its form, and by the absence of a limiting membrane. It -is no longer held even by unqualified adherents of the cell-doctrine -that the <i>Amœba</i> has an investment. Its outer surface, compared -to the film which forms on the surface of paste, does not prevent the -taking of solid particles into the mass of the body, and does not, in -such kindred forms as Fig. <a href="#i_086">133</a>, prevent the pseudopodia from coalescing -when they meet. Hence it cannot properly have the name of a cell-wall. -A considerable portion of the body, however, in <i>Difflugia</i>,<span class="pagenum" id="Page_87">[87]</span> Fig. -<a href="#i_086">134</a>, has a denser coating formed of agglutinated foreign particles; -so that the protrusion of the pseudopodia is limited to one part of -it. And in the solitary <i>Foraminifera</i>, like <i>Gromia</i>, -the sarcode is covered over most of its surface by a delicate -calcareous shell, pierced with minute holes, through which the slender -pseudopodia are thrust. The <i>Gregarina</i> exhibits an advance in -integration, and a consequent greater definiteness. Figs. <a href="#i_086">135 and -136</a>, exemplifying this type, show the complete membrane in which the -substance of the creature is contained. Here there has arisen what -may be properly called a cell: under its solitary form this animal is -truly unicellular. Its embryology has considerable significance. After -passing through a certain quiescent, “encysted” state, its interior -breaks up into small portions, which, after their exit, assume forms -like that of the <i>Amœba</i>; and from this young condition in -which they are undifferentiated, they pass into that adult condition -in which they have limiting membranes. If this development of the -individual <i>Gregarina</i> typifies the mode of evolution of the -species, it yields further support to the belief, that fragments of -sarcode existed earlier than any of the structures which are called -cells. Among aggregates of the first order, there are some much more -highly developed. These are the <i>Infusoria</i>, constituting the -most numerous of the <i>Protozoa</i>, in species as in individuals. -Figs. <a href="#i_086">137, 138, and 139</a>, are examples. In them we find, along with -greater definiteness, a considerable heterogeneity. The sarcode of -which the body consists, has an indurated outer layer, bearing cilia -and sometimes spines; there is an opening serving as mouth, a permanent -œsophagus, and a cavity or cavities, temporarily formed in the interior -of the sarcode, to serve as one or more stomachs; and there is a -comparatively specific arrangement of these and various minor parts.</p> - - <div class="figcenter" id="i_086"> - <img - class="p2" - src="images/i_086.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 131–139.</p> - </div> - -<p class="p2">Thus in the animal kingdom, as in the vegetal kingdom, there exists -a class of minute forms having this peculiarity, that no one of them -is separable into a number of visible<span class="pagenum" id="Page_88">[88]</span> components homologous with one -another—no one of them can be resolved into minor individualities. -Its proximate units are those physiological units of which we conclude -every organism consists. The aggregate is an aggregate of the first -order.</p> - - -<p class="p2" id="sect201">§ 201. Among plants are found types indicating a transition from -aggregates of the first order to aggregates of the second order; and -among animals we find analogous types. But the stages of progressing -integration are not here so distinct. The reason probably is, that -the simplest animals, having individualities much less marked than -those of the simplest plants, do not afford us the same facilities for -observation. In proportion as the limits of the minor individualities -are indefinite, the formation of major individualities out of them, -naturally leaves less conspicuous traces.</p> - - <div class="figcenter" id="i_088"> - <img - class="p2" - src="images/i_088.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 140–145.</p> - </div> - -<p class="p2">Be this as it may, however, in such types of <i>Protozoa</i> as the -compound <i>Radiolaria</i>, we find that though there is reason to -regard the aggregate as an aggregate of the second order, yet its -divisibility into minor individualities like those just described, -is less manifest. Fig. <a href="#i_088">140</a> representing <i>Sphærozoum punctatum</i>, -one of the group, illustrates this. The sceptically-minded may -perhaps doubt whether we can regard the “cellæform bodies” contained -in it, as the morphological units of the animal. The jelly-like -mass in which they are imbedded, is but indefinitely divisible into -portions having each a cell or nucleus for its centre.<a id="FNanchor_17" href="#Footnote_17" class="fnanchor">[17]</a> Among -the<span class="pagenum" id="Page_89">[89]</span> <i>Foraminifera</i>, we find only indefinite evidence of the -coalescence of aggregates of the first order, into aggregates of the -second order. There are solitary Foraminifers, allied to the creature -represented in Fig. <a href="#i_086">134</a>. Certain ideal types of combination among -them, are shown in Fig. <a href="#i_088">141</a>. And setting out from these, we may ascend -in various directions to kinds compounded to an immense variety of -degrees in an immense variety of ways. In all of them, however, the -separability of the major individuality into minor individualities, -is very incomplete. The portion of sarcode contained in one of these -calcareous chambers, gives origin to an external bud; and this -presently becomes covered, like its parent, with calcareous matter: the -position in which each successive chamber is so produced, determining -the form of the compound shell. But the portions of sarcode thus budded -out one from another, do not become distinctly individualized. Fig. -<a href="#i_088">142</a>, representing the living network which remains when the shell of -an Orbitolite has been dissolved, shows the continuity that exists -among the occupants of its aggregated chambers.<a id="FNanchor_18" href="#Footnote_18" class="fnanchor">[18]</a> In the compound -<i>Infusoria</i>, the component units remain quite distinct. Being, -as aggregates of the first order, much more definitely organized, -their union into aggregates of the second order does<span class="pagenum" id="Page_90">[90]</span> not destroy -their original individualities. Among the <i>Vorticellæ</i>, of which -two kinds are delineated in Figs. <a href="#i_088">144 and 145</a>, there are various -illustrations of this: the members of the community being sometimes -appended to a single stem; sometimes attached by long separate stems to -a common base; and sometimes massed together.</p> - - <div class="figcenter" id="i_090"> - <img - class="p2" - src="images/i_090.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 146–147.</p> - </div> - -<p class="p2">Thus far, these aggregates of the second order exhibit but indefinite -individualities. The integration is physical; but not physiological. -Though, in the <i>Polycytharia</i>, there is a shape that has some -symmetry; and though, in the <i>Foraminifera</i>, the formation of -successive chambers proceeds in such methodic ways as to produce -quite-regular and tolerably-specific shells; yet no more in these than -in the Sponges or the compound <i>Vorticellæ</i>, do we find such -co-ordination as gives the whole a life predominating over the lives of -its parts. We have not yet reached an aggregate of the second order, -so individuated as to be capable of serving as a unit in still higher -combinations. But in the class <i>Cœlenterata</i>, this advance is -displayed. The common <i>Hydra</i>, habitually taken as the type of -the lowest division of this class, has specialized parts performing -mutually-subservient functions, and thus exhibiting a total life -distinct from the lives of the units. Fig. <a href="#i_090">146</a> represents one of these -creatures in its contracted state and in its expanded state; while -Fig. <a href="#i_090">147</a> is a diagram showing the wall of this creature’s sac-like -body as seen in section under the microscope: <i>a</i> and <i>b</i> -being the outer and inner cellular layers; while between them is the -“mesoglœa” or “structureless lamella,” the supporting or skeletal -layer. But this lowly-organized tissue of the Hydra, illustrates -a phase of integration in which the lives of the minor aggregates -are only partially-subordinated to the life of the major aggregate -formed by them. For a <i>Hydra’s</i> substance is separable<span class="pagenum" id="Page_91">[91]</span> into -<i>Amœba</i>-like portions, capable of moving about independently. -If we bear in mind how analogous are the extreme extensibility and -contractility of a <i>Hydra’s</i> body and tentacles, to the properties -displayed by the sarcode among Rhizopods; we may infer that probably -the movements and other actions of a <i>Hydra</i>, are due to the -half-independent co-operation of the <i>Amœba</i>-like individuals -composing it.</p> - - -<p class="p2">§ 202. A truth which we before saw among plants, we here see repeated -among animals—the truth that as soon as the integration of aggregates -of the first order into aggregates of the second order, produces -compound wholes so specific in their shapes and sizes, and so mutually -dependent in their parts, as to have distinct individualities; there -simultaneously arises the tendency in them to produce, by gemmation, -other such aggregates of the second order. The approach towards -definite limitation in an organism, is, by implication, an approach -towards a state in which growth passing a certain point, results, not -in the increase of the old individual, but in the formation of a new -individual. Thus it happens that the common polype buds out other -polypes, some of which very shortly do the like, as shown in Fig. <a href="#i_091">148</a>: -a process paralleled by the fronds of sundry <i>Algæ</i>, and by those -of the lower <i>Jungermanniaceæ</i>. And just as, among these last -plants, the proliferously-produced fronds, after growing to certain -sizes and developing rootlets, detach themselves from their parent -fronds; so among these animals, separation of the young ones from -the bodies of their parents ensues when they have acquired tolerably -complete organizations.</p> - - <div class="figcenter" id="i_091"> - <img - class="p2" - src="images/i_091.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 148–150.</p> - </div> - -<p class="p2">There is reason to think that the parallel holds still further.<span class="pagenum" id="Page_92">[92]</span> Within -the limits of the <i>Jungermanniaceæ</i>, we found that while some -genera exhibit this discontinuous development, other genera exhibit a -development that is similar to it in all essential respects, save that -it is continuous. And here within the limits of the <i>Hydrozoa</i>, -we find, along with this genus in which the gemmiparous individuals -are presently cast off, other genera in which they are not cast off, -but form a permanent aggregate of the third order. Figs. <a href="#i_091">149 and -150</a>, exemplify these compound <i>Hydrozoa</i>—one of them showing -this mode of growth so carried out as to produce a single axis; and -the other showing how, by repetitions of the process, lateral axes -are produced. Integrations characterizing certain higher genera of -the <i>Hydrozoa</i> which swim or float instead of being fixed, are -indicated by Figs. <a href="#i_092">151 and 152</a>: the first of them representing the type -of a group in which the polypes growing from an axis, or cœnosarc, -are drawn through the water by the rhythmical contractions of the -organs from which they hang; and the second of them representing a -<i>Physalia</i> the component polypes of which are united into a -cluster, attached to an air-vessel.</p> - - <div class="figcenter" id="i_092"> - <img - class="p2" - src="images/i_092.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 151–152.</p> - </div> - -<p class="p2">A parallel series of illustrations might be drawn from that second -division of the <i>Cœlenterata</i>, known as the <i>Actinozoa</i>. -Here, too, we have a group of species—the Sea-anemones—the -individuals of which are solitary. Here, too, we have agamogenetic -multiplication: occasionally by gemmation, but more frequently by that -modified process called spontaneous fission. And here, too, we have -compound forms resulting from the arrest of this spontaneous fission -before it is complete. To give examples is needless; since they would -but show, in more varied ways, the truth already made sufficiently<span class="pagenum" id="Page_93">[93]</span> -clear, that the compound <i>Cœlenterata</i> are aggregates of the third -order, produced by integration of aggregates of the second order such -as we have in the <i>Hydra</i>. As before, it is manifest that on the -hypothesis of evolution, these higher integrations will insensibly -arise, if the separation of the gemmiparous polypes is longer and -longer postponed; and that an increasing postponement will result by -survival of the fittest, if it profits the group of individuals to -remain united instead of dispersing.<a id="FNanchor_19" href="#Footnote_19" class="fnanchor">[19]</a></p> - - -<p class="p2">§ 203. The like relations exist, and imply that the like processes have -been gone through, among those more highly organized animals called -<i>Polyzoa</i> and <i>Tunicata</i>. We have solitary individuals, -and we have variously-integrated groups of individuals: the chief -difference between the evidence here furnished, and that furnished -in the last case, being the absence of a type obviously linking the -solitary state with the aggregated state.</p> - - <div class="figcenter" id="i_093"> - <img - class="p2" - src="images/i_093.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 153–155.</p> - </div> - -<p class="p2">This integration of aggregates of the second order, is carried on -among the <i>Polyzoa</i> in divers ways, and with different degrees of -completeness. The little patches of minute cells, shown as magnified -in Fig. <a href="#i_093">153</a>, so common on the fronds of sea-weeds and the surfaces of -rocks at low-water mark, display little beyond mechanical combination. -The adjacent individuals,<span class="pagenum" id="Page_94">[94]</span> though severally originated by gemmation -from the same germ, have but little physiological dependence. In -kindred kinds, however, as shown in Figs. <a href="#i_093">154 and 155</a>, one of which -is a magnified portion of the other, the integration is somewhat -greater: the co-operation of the united individuals being shown in the -production of those tubular branches which form their common support, -and establish among them a more decided community of nutrition.</p> - - <div class="figcenter" id="i_094"> - <img - class="p2" - src="images/i_094.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 156–159.</p> - </div> - -<p class="p2">Among the Ascidians this general law of morphological composition is -once more displayed. Each of these creatures subsists on the nutritive -particles contained in the water which it draws in through one orifice -and sends out through another; and it may thus subsist either alone, or -in connexion with others that are in some cases loosely aggregated and -in other cases closely aggregated. Fig. <a href="#i_094">156</a>, <i>Phallusia mentula</i>, -is one of the solitary forms. A type in which the individuals are -united by a stolon that gives origin to them by successive buds, is -shown in <i>Perophora</i>, Fig. <a href="#i_094">157</a>. Among the <i>Botryllidæ</i>, of -which one kind is drawn on a small scale in Fig. <a href="#i_094">159</a>, and a portion of -the same on a larger scale in Fig. <a href="#i_094">158</a>, there is a combination of the -individuals into annular clusters, which are themselves imbedded in a -common gelatinous matrix. And in this group there are integrations even -a stage higher, in which several such clusters of clusters grow from -a single base. Here the compounding and recompounding appears to be -carried further than anywhere else in the animal kingdom.</p> - -<p>Thus far, however, among these aggregates of the third order, we see -what we before saw among the simpler aggregates of the second order—we -see that the component individualities are but to a very small extent -subordinated to<span class="pagenum" id="Page_95">[95]</span> the individuality made up of them. In nearly all the -forms indicated, the mutual dependence of the united animals is so -slight, that they are more fitly comparable to societies, of which -the members co-operate in securing certain common benefits. There is -scarcely any specialization of functions among them. Only in the last -type described do we see a number of individuals so completely combined -as to simulate a single individual. And even here, though there appears -to be an intimate community of nutrition, there is no physiological -integration beyond that implied in several mouths and stomachs having a -common vent.<a id="FNanchor_20" href="#Footnote_20" class="fnanchor">[20]</a></p> - - -<p class="p2">§ 204. We come now to an extremely interesting question. Does there -exist in other sub-kingdoms composition of the third degree, analogous -to that which we have found so prevalent among the <i>Cœlenterata</i> -and the <i>Polyzoa</i> and <i>Tunicata</i>? The question is not -whether elsewhere there are tertiary aggregates produced by the -branching or clustering of secondary aggregates, in ways like those -above traced; but whether elsewhere there are aggregates which, though -otherwise unlike in the arrangement of their parts, nevertheless -consist of parts so similar to one another that we may suspect them -to be united secondary aggregates. The various compound types above -described, in which the united animals maintain their individualities -so distinctly that the individuality of the aggregate remains vague, -are constructed in such ways that the united animals carry on their -several activities with scarcely any mutual hindrance. The members of -a branched <i>Hydrozoon</i>, such as is shown in Fig. <a href="#i_091">149</a> or Fig. <a href="#i_091">150</a>, -are so placed that they can all spread their tentacles and catch their -prey as well as though separately attached to stones or weeds. Packed -side by side on a flat surface or<span class="pagenum" id="Page_96">[96]</span> forming a tree-like assemblage, -the associated individuals among the <i>Polyzoa</i> are not unequally -conditioned: or if one has some advantage over another in a particular -case, the mode of growth and the relations to surrounding objects are -so irregular as to prevent this advantage re-appearing with constancy -in successive generations. Similarly with the Ascidians growing from -a stolon or those forming an annular cluster: each of them is as well -placed as every other for drawing in the currents of sea-water from -which it selects its food. In these cases the mode of aggregation -does not expose the united individuals to multiform circumstances; -and therefore is not calculated to produce among them any structural -multiformity. For the same reason no marked physiological division -of labour arises among them; and consequently no combination close -enough to disguise their several individualities. But under converse -conditions we may expect converse results. If there is a mode of -integration which necessarily subjects the united individuals -to unlike sets of incident forces, and does this with complete -uniformity from generation to generation, it is to be inferred that -the united individuals will become unlike. They will severally assume -such different functions as their different positions enable them -respectively to carry on with the greatest advantage to the assemblage. -This heterogeneity of function arising among them, will be followed by -heterogeneity of structure; as also by that closer combination which -the better enables them to utilize one another’s functions. And hence, -while the originally-like individuals are rendered unlike, they will -have their homologies further obscured by their progressing fusion into -an aggregate individual of a higher order.</p> - -<p>These converse conditions are in nearly all cases fulfilled where -the successive individuals arising by continuous development are so -budded-off as to form a linear series. I say in nearly all cases, -because there are some types in which the associated individuals, -though joined in single file, are<span class="pagenum" id="Page_97">[97]</span> not thereby rendered very unlike -in their relations to the environment; and therefore do not become -differentiated and integrated to any considerable extent. I refer to -such Ascidians as the <i>Salpidæ</i>. These creatures float passively -in the sea, attached together in strings. Being placed side by side -and having mouths and vents that open laterally, each of them is as -well circumstanced as its neighbours for absorbing and emitting the -surrounding water; nor have the individuals at the two extremities -any marked advantages over the rest in these respects. Hence in this -type, and in the allied type <i>Pyrosoma</i>, which has its component -individuals built into a hollow cylinder, linear aggregation may exist -without the minor individualities becoming obscured and the major -individuality marked: the conditions under which a differentiation -and integration of the component individuals may be expected, are not -fulfilled. But where the chain of individuals produced by gemmation, is -either habitually fixed to some solid body by one of its extremities or -moves actively through the water or over submerged stones and weeds, -the several members of the chain become differently conditioned in the -way above described; and may therefore be expected to become unlike -while they become united. A clear idea of the contrast between these -two linear arrangements and their two diverse results, will be obtained -by considering what happens to a row of soldiers, when changed from -the ordinary position of a single rank to the position of Indian file. -So long as the men stand shoulder to shoulder, they are severally able -to use their weapons in like ways with like efficiency; and could, -if called on, similarly perform various manual processes directly -or indirectly conducive to their welfare. But when, on the word of -command “right face,” they so place themselves that each has one of -his neighbours before him and another behind him, nearly all of them -become incapacitated for fighting and for many other actions. They can -walk or run one after another, so as to produce movement of the file -in<span class="pagenum" id="Page_98">[98]</span> the direction of its length; but if the file has to oppose an enemy -or remove an obstacle lying in the line of its march, the front man -is the only one able to use his weapons or hands to much purpose. And -manifestly such an arrangement could become advantageous only if the -front man possessed powers peculiarly adapted to his position, while -those behind him facilitated his actions by carrying supplies, &c. This -simile, grotesque as it seems, serves to convey better perhaps than -any other could do, a clear idea of the relations that must arise in a -chain of individuals arising by gemmation, and continuing permanently -united end to end. Such a chain can arise only on condition that -combination is more advantageous than separation; and for it to be more -advantageous, the anterior members of the series must become adapted to -functions facilitated by their positions, while the posterior members -become adapted to functions which their positions permit. Hence, direct -or indirect equilibration or both, must tend continually to establish -types in which the connected individuals are more and more unlike -one another, at the same time that their several individualities are -more and more disguised by the integration consequent on their mutual -dependence.</p> - -<p>Such being the anticipations warranted by the general laws of -evolution, we have now to inquire whether there are any animals which -fulfil them. Very little search suffices; for structures of the kind -to be expected are abundant. In that great division of the animal -kingdom at one time called <i>Annulosa</i>, but now grouped into -<i>Annelida</i> and <i>Arthropoda</i>, we find a variety of types -having the looked-for characters. Let us contemplate some of them.</p> - - -<p class="p2" id="sect205">§ 205. An adult Chætopod is composed of segments which repeat one -another in their details as well as in their general shapes. Dissecting -one of the lower orders, such as is shown in Fig. <a href="#i_099">160</a>, proves that -the successive segments, besides having like locomotive appendages, -like branchiæ, and<span class="pagenum" id="Page_99">[99]</span> sometimes even like pairs of eyes, also have like -internal organs. Each has its enlargement of the alimentary canal; -each its contractile dilatation of the great blood-vessel; each its -portion of the double nervous cord, with ganglia when these exist; -each its branches from the nervous and vascular trunks answering to -those of its neighbours; each its similarly answering set of muscles; -each its pair of openings through the body-wall; and so on throughout, -even to the organs of reproduction. That is to say, every segment is -in great measure a physiological whole—every segment contains most -of the organs essential to individual life and multiplication: such -essential organs as it does not contain, being those which its position -as one in the midst of a chain, prevents it from having or needing. If -we ask what is the meaning of these homologies, no adequate answer is -supplied by any current hypothesis. That this “vegetative repetition” -is carried out to fulfil a predetermined plan, was shown to be quite -an untenable notion (§§ <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect133">133</a>, <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect134">134</a>). On the one hand, we found nothing -satisfactory in the conception of a Creator who prescribed to himself -a certain unit of composition for all creatures of a particular class, -and then displayed his ingenuity in building up a great variety of -forms without departing from the “archetypal idea.” On the other hand, -examination made it manifest that even were such a conception worthy -of being entertained, it would have to be relinquished; since in each -class there are numerous deviations from the supposed “archetypal -idea.” Still less can these traits of structure be accounted<span class="pagenum" id="Page_100">[100]</span> for -teleologically. That certain organs of nutrition and respiration and -locomotion are repeated in each segment of a dorsibranchiate annelid, -may be regarded as functionally advantageous for a creature following -its mode of life. But why should there be a hundred or even two -hundred pairs of ovaries? This is an arrangement at variance with that -physiological division of labour which every organism profits by—is -a less advantageous arrangement than might have been adopted. That -is to say, the hypothesis of a designed adaptation fails to explain -the facts. Contrariwise, these structural traits are just such as -might naturally be looked for, if these annulose forms have arisen by -the integration of simpler forms. Among the various compound animals -already glanced at, it is very general for the united individuals to -repeat one another in all their parts—reproductive organs included. -Hence if, instead of a clustered or branched integration, such as -the <i>Cœlenterata</i>, <i>Polyzoa</i> and <i>Tunicata</i> exhibit, -there occurs a longitudinal integration; we may expect that the united -individuals will habitually indicate their original independence by -severally bearing germ-producing or sperm-producing organs.</p> - - <div class="figcenter" id="i_099"> - <img - class="p2" - src="images/i_099.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 160–161.</p> - </div> - -<p class="p2">The reasons for believing one of these creatures to be an aggregate of -the third order, are greatly strengthened when we turn from the adult -structure to the mode of development. Among the <i>Dorsibranchiata</i> -and <i>Tubicolæ</i>, the embryo leaves the egg in the shape of a -ciliated gemmule, not much more differentiated than that of a polype. -As shown in Fig. <a href="#i_101">162</a>, it is a nearly globular mass; and its interior -consists of untransformed cells. The first appreciable change is -an elongation and a simultaneous commencement of segmentation. The -segments multiply by a modified gemmation, which takes place from the -hinder end of the penultimate segment. And considerable progress in -marking out these divisions is made before the internal organization -begins. Figs. <a href="#i_101">163, 164, 165</a>, represent some of these early stages. In -annelids of other orders, the embryo assumes the segmented<span class="pagenum" id="Page_101">[101]</span> form while -still in the egg. But it does this in just the same manner as before. -Indeed, the essential identity of the two modes of development is shown -by the fact that the segmentation within the egg is only partially -carried out: in all these types the segments continue to increase in -number for some time after hatching. Now this process is as like that -by which compound animals in general are formed, as the different -conditions of the case permit. When new individuals are budded-out -laterally, their unfolding is not hindered—there is nothing to -disguise either the process or the product. But gemmæ produced one from -another in the same straight line, and remaining connected, restrict -one another’s developments; and that the resulting segments are so many -gemmiparously-produced individuals, is necessarily less obvious.</p> - - <div class="figcenter" id="i_101"> - <img - class="p2" - src="images/i_101.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 162–165.</p> - </div> - -<p class="p2" id="sect206">§ 206. Evidence remains which adds very greatly to the weight of -that already assigned. Thus far we have studied only the individual -segmented animal; considering what may be inferred from its mode of -evolution and final organization. We have now to study segmented -animals in general. Comparison of different groups of them and of -kinds within each group, will disclose various phases of progressive -integration of the nature to be anticipated.</p> - - <div class="figcenter" id="i_103"> - <img - class="p2" - src="images/i_103.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 166–169.</p> - </div> - -<p class="p2">Among the simpler <i>Platyhelminthes</i>, as in some kinds of -<i>Planaria</i>, transverse fission occurs. A portion of a -<i>Planaria</i> separated by spontaneous constriction, becomes -an independent<span class="pagenum" id="Page_102">[102]</span> individual. Sir J. G. Dalyell found that in some -cases numerous fragments artificially separated, grew into perfect -animals.<a id="FNanchor_21" href="#Footnote_21" class="fnanchor">[21]</a> In these creatures which thus remind us of the lowest -<i>Hydrozoa</i> in their powers of agamogenetic multiplication, the -individuals produced one from another do not continue connected. As -the young ones laterally budded-off by the <i>Hydra</i> separate -when complete, so do the young ones longitudinally budded-off by the -<i>Planaria</i>. Fig. <a href="#i_103">166</a> indicates this. But there are allied types -which show us a more or less persistent union of homologous parts, -or individuals, similarly arising by longitudinal gemmation.<a id="FNanchor_22" href="#Footnote_22" class="fnanchor">[22]</a> -The cestoid <i>Entozoa</i> furnish illustrations. Without dwelling -on the fact that each segment of a <i>Tænia</i>, like each separate -<i>Planaria</i>, is an independent hermaphrodite; and without -specifying the sundry common structural traits which add probability to -the suspicion that there is some kinship between the individuals of the -one order and the segments of the other; it will suffice to point out -that the two types are so far allied as to demand their union under the -same sub-class title. And recognizing this kinship, we see significance -in the fact that in the one case the longitudinally-produced gemmæ -separate as complete individuals, and in the other continue united -as segments in smaller or larger numbers and for shorter or longer -periods. In <i>Tænia echinococcus</i>,<span class="pagenum" id="Page_103">[103]</span> represented in Fig. <a href="#i_103">167</a>, we -have a species in which the number of segments thus united does not -exceed four. In <i>Echinobothrium typus</i> there are eight or ten; -and in cestoids generally they are numerous.<a id="FNanchor_23" href="#Footnote_23" class="fnanchor">[23]</a> A considerable hiatus -occurs between this phase of integration and the next higher phase -which we meet with; but it is not greater than the hiatus between the -types of the <i>Platyhelminthes</i> and the <i>Chætopoda</i>, which -present the two phases. Though it is doubtful whether separation of -single segments occurs among the Annelida,<a id="FNanchor_24" href="#Footnote_24" class="fnanchor">[24]</a> yet very often we -find strings of segments,<span class="pagenum" id="Page_104">[104]</span> arising by repeated longitudinal budding, -which after reaching certain lengths undergo spontaneous fission: in -some cases doing this so as to form two or more similar strings of -segments constituting independent individuals; and in other cases -doing it so that the segments spontaneously separated are but a small -part of the string. Thus a <i>Syllis</i>, Fig. <a href="#i_103">168</a>, after reaching -a certain length, begins to transform itself into two individuals: -one of the posterior segments develops into an imperfect head, and -simultaneously narrows its connexion with the preceding segments, from -which it eventually separates. Still more remarkable is the extent to -which this process is carried in certain kindred types; which exhibit -to us several individuals thus being simultaneously formed out of -groups of segments. Fig. <a href="#i_103">169</a>, copied (omitting the appendages) from -one contained in a memoir by M. Milne-Edwards, represents six worms of -different ages in course of development: the terminal one being the -eldest, the one having the greatest number of segments, and the one -that will first detach itself; and the successively anterior ones, with -their successively smaller numbers of segments, being successively -less advanced towards fitness for separation and independence. Here -among groups of segments we see repeated what in the previous cases -occurs with single segments. And then in other annelids we find that -the string of segments arising by gemmation from a single germ becomes -a permanently united whole: the tendency to any more complete fission -than that which marks out the segments, being lost; or, in other words, -the integration having become relatively complete. Leaving out of sight -the question of alliance among the types above grouped together, that -which it here concerns us to notice is, that longitudinal gemmation -does go on; that it is displayed in that primitive form in which the -gemmæ separate as soon as produced; that we have types in which such -gemmæ hang together in groups of four, or in groups of eight and ten, -from which however the gemmæ successively separate as individuals;<span class="pagenum" id="Page_105">[105]</span> -that among higher types we have long strings of similarly-formed -gemmæ which do not become individually independent, but separate into -organized groups; and that from these we advance to forms in which all -the gemmæ remain parts of a single individual. One other significant -fact must be added. There are cases in which annelids multiply by -lateral gemmation.<a id="FNanchor_25" href="#Footnote_25" class="fnanchor">[25]</a> That the longitudinally-produced gemmæ which -compose an annelid, should thus have, one of them or several of them, -the power of laterally budding-off gemmæ, from which other annelids -arise, gives further support to the hypothesis that, primordially, the -segments were independent individuals. And it suggests this belief -the more strongly because, in certain types of <i>Cœlenterata</i>, we -see that longitudinal and lateral gemmation <i>do</i> occur together, -where the longitudinally-united gemmæ are demonstrably independent -individuals.</p> - - -<p class="p2" id="sect207">§ 207. Though it seems next to impossible that we shall ever be able -to find a type such as that which is here supposed to be the unit of -composition of the annulose type, since we must assume such a type -to have been long since extinct, yet the foregoing evidence goes -far towards showing that an annulose animal is an aggregate of the -third order. This repetition of segments, sometimes numbering several -hundreds, like one another in all their organs even down to those of -reproduction, while it is otherwise unaccountable, is fully accounted -for if these segments are homologous with the separate individuals of -some lower type. The gemmation by which these segments are produced, is -as similar as the conditions allow, to the gemmation by which compound<span class="pagenum" id="Page_106">[106]</span> -animals in general are produced. As among plants, and as among -demonstrably-compound animals, we see that the only thing required -for the formation of a permanent chain of gemmiparously-produced -individuals, is that by remaining associated such individuals will -have advantages greater than are to be gained by separation. Further, -comparisons of the annuloid and lower annulose forms, disclose -a number of those transitional phases of integration which the -hypothesis leads us to expect. And, lastly, the differences among these -united individuals or successive segments, are not greater than the -differences in their positions and functions explain—not greater than -such differences are known to produce among other united individuals: -witness sundry compound <i>Hydrozoa</i>.</p> - -<p>Indirect evidence of much weight has still to be given. Thus far we -have considered only the less developed <i>Annulosa</i>. The more -integrated and more differentiated types of the class remain. If in -them we find a carrying further of the processes by which the lower -types are here supposed to have been evolved, we shall have additional -reason for believing them to have been so evolved. If we find that in -these superior orders, the individualities of the united segments are -much less pronounced than in the inferior, we shall have grounds for -suspecting that in the inferior the individualities of the segments are -less pronounced than in those lost forms which initiated the annulose -sub-kingdom.</p> - -<hr class="tb" /> - -<p>[<span class="smcap">Note.</span>—Partly from the wish to incorporate further evidence, -and partly from the wish to present the evidence, old and new, in a -more effective order, I decide here to recast the foregoing exposition.</p> - -<p>Significant traits of development are exhibited in common by two -groups otherwise unallied—certain of the <i>Platyhelminthes</i> and -certain of the lower <i>Annulosa</i>. Of the <i>Platyhelminthes</i> the -ordinary type is an unsegmented creature: a<span class="pagenum" id="Page_107">[107]</span> Planarian or a Trematode -exemplifying it. Among the free forms, as in some Planarians, there -occurs transverse fission, and prompt separation of the segments; -while among some other free forms, as the <i>Microstomida</i>, the -two segments first produced, themselves become segmented while -still adherent, and this process is repeated until a string is -formed. Another group of the <i>Platyhelminthes</i>, the Cestoid -<i>Entozoa</i>, exhibit analogous processes. There are unsegmented -forms, as the <i>Caryophyllæus</i>, and there are forms in which the -segments, now few now many, adhere together in chains; the terminal -members of which, however, eventually separate, and having before -separation approached the trematode structure, become independent -individuals which grow, creep about, and continue the race. In both -of these types the condition under which the gemmiparously-produced -members remain connected, is that they shall be able to feed -individually: in the one case by lateral mouths, in the other case by -absorption through the integument. It is further observable that in -both cases separation of the component individuals occurs at sexual -maturity, when advantage in nutrition has ceased to be the dominant -need and dispersion of the species has taken its place in degree of -importance. Among Annelids, higher though they are in type, we find -parallelisms. Usually in its first stage an annelid is unsegmented, -but as fast as it elongates lines of segmentation indent its surface. -This segmentation proceeds in various ways, and the segments exhibit -various degrees of dependence. In some low types, spontaneous fission -goes on to the extent of producing single segments, each of which has -such vitality that it buds out anterior and posterior parts at its two -ends. Thus alike in the simple form which exists before segmentation -and in the form exhibited by a detached segment, we have a unit -analogous to each of the units which are joined together in certain -free <i>Turbellaria</i> and in the Cestoids: the difference being that -in the Annelids the sexually mature units do not individually disunite. -But though there does<span class="pagenum" id="Page_108">[108]</span> not take place separation of single completed -segments, there takes place separation of groups of segments, which -are either sexually mature at the time they drop off or presently -become so. And the groups of segments which have become sexually mature -before they drop off, have simultaneously acquired swimming organs and -developed eyes, enabling them to spread and diffuse the species. Sundry -biologists recognize a parallelism between that detachment of developed -segments which goes on in the cestoid <i>Entozoa</i>, and that which -goes on in the <i>Scyphomedusæ</i>. The successively detached members -of the strobila are sexually matured or maturing individuals which, -as medusæ, are fitted for swimming about, multiplying, and reaching -other habitats; while each detached proglottis of the cestoid is, -by the nature of its medium, limited to creeping about. Clearly -this fissiparous process in such Annelids as the <i>Syllidæ</i>, -which has similarly been compared to the strobilization of the -<i>Scyphomedusæ</i>, differs simply in the respect that single segments -are not adapted for locomotion, and it therefore profits the species -to separate in groups. All these facts and analogies point to the -conclusion that the remote ancestor of the Annelids was an unsegmented -creature homologous with each of the segments of an existing Annelid.</p> - -<p>This conclusion is supported by other kinds of evidence here to -be added. The larvæ of Annelids are very various; but amid their -differences there is a recognizable type. “The Trochophore is the -typical larval form of the Annelid stem”: a trochophore being a -curious spheroidal ciliated structure suggestive of cœlenterate -affinities. And this unsegmented larva, representing the remote -ancestor from which the many Annelid types diverged, is similar to the -larvæ of the <i>Rotifera</i> and the <i>Mollusca</i>: a trochophore -is common to all these great classes. Moreover since, among the -<i>Rhizota</i> (a sub-class of the <i>Rotiferæ</i>), there is a -species, <i>Trochosphæra</i>, solitary and free-swimming, resembling -in form and structure a trochophore, though it is not a larva but an -adult, we get further<span class="pagenum" id="Page_109">[109]</span> evidence that there was a primitive creature of -this general character, of which the trochophores of <i>Mollusca</i>, -<i>Rotifera</i>, and <i>Annelida</i> are divergent modifications, and -which was unsegmented: the implication being that the segmentation of -the <i>Annelida</i> was superinduced. That this segmentation resulted -from gemmation is implied by what are called polytrochal larvæ. These -“sometimes appear as a stage succeeding other larval types. Thus -those of <i>Arenicola marina</i> arise from larvæ which at first were -monotrochal, later became telotrochal, and finally, by the appearance -of new ciliated rings between those already present, assumed the -stage of polytrochal larvæ.... This condition warrants the assumption -that the segmented forms are to be looked upon as the younger, the -unsegmented, on the other hand, as the phylogenetically older.” -(Korschelt and Heider, i, 278.) And that the above-described rings -of cilia mark off segments is shown by the case of <i>Ophryotrocha -puerilis</i>, which “remains, as it were, in a larval condition, since -the segments retain their ciliation throughout life.” (<i>Ib.</i>, -277.) Yet one more significant fact must be named. In early stages -of development each segment of an archiannelidan has cœlomic spaces -separate from those of neighbouring segments, but in the adult the -septa “generally break down either partially or completely, so that -the peri-visceral cavity becomes a continuous space from end to end -of the animal.” (Sedgwick, <i>Text Book</i>, 449.) While this fact is -congruous with the hypothesis here maintained, it is incongruous with -the hypothesis that the annelid was originally an elongated creature -which afterwards became segmented; since in that case the implication -would be that the cœlomic septa, not arising from recapitulation of an -ancestral structure, but originated by the process of segmentation, -were first superfluously formed and then destroyed.</p> - -<p>Various lines of evidence thus converge to the conclusion that an -annulose animal is an aggregate of the third order.</p> - -<p>In June, 1865, when No. 14 of my serial containing the<span class="pagenum" id="Page_110">[110]</span> foregoing -chapter was issued, I supposed myself to be alone in holding this -belief respecting the annulose type, and long continued to suppose -so. Over thirty years later, however, in M. Edmond Perrier’s work, -<i>La Philosophie Zoologique avant Darwin</i>, I found mention of a -lecture delivered by M. Lacaze-Duthiers at the École Normale Supérieure -in Paris, and reported in the <i>Revue des Cours Scientifiques</i> -for January 28, 1865, in which he enunciated a like belief. Judging, -however, by the account of this lecture which M. Perrier gives (he was -present), it appears that M. Lacaze-Duthiers simply contended that this -view of the annulose structure as arising by union of once-independent -units, is suggested by certain <i>à priori</i> considerations. There is -no indication that he assigned any of the classes of facts above given, -which go to show that it <i>has</i> thus arisen.</p> - -<p>For further facts and arguments concerning the genesis of the annulose -type, see <a href="#Page_602">Appendix D 2.</a>]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_111">[111]</span></p> - -<h3>CHAPTER V.<br /> -<span class="subhed1">THE MORPHOLOGICAL COMPOSITION OF ANIMALS, <i>CONTINUED</i>.</span></h3></div> - -<p id="sect208">§ 208. Insects, Arachnids, Crustaceans, and Myriapods, are all -members of that higher division of the <i>Annulosa</i><a id="FNanchor_26" href="#Footnote_26" class="fnanchor">[26]</a> called -<i>Articulata</i> or now more generally <i>Arthropoda</i>. Though -in these creatures the formation of segments may be interpreted as -a disguised gemmation; and though, in some of them, the number of -segments increases by this modified budding after leaving the egg, -as it does among the Annelids; yet the process is not nearly so -dominant: the segments are usually much less numerous than we find -them in the types last considered. In most cases, too, the segments -are in a greater degree differentiated one from another, at the same -time that they are severally more differentiated within themselves. -Nor is there any instance of spontaneous fission taking place in the -series of segments composing an articulate animal. On the contrary, -the integration, always great enough permanently to unite the -segments, is frequently carried so far as to hide very completely the -individualities of some or many of them; and occasionally, as among -the Acari, the consolidation, or the arrest of segmentation, is so<span class="pagenum" id="Page_112">[112]</span> -decided as to leave scarcely a trace of the articulate structure: -the type being in these cases indicated chiefly by the presence of -those characteristically-formed limbs, which give the alternative -name <i>Arthropoda</i> to all the higher <i>Annulosa</i>. Omitting -the parasitic orders, which, as in other cases, are aberrant members -of their sub-kingdom, comparisons between the different orders prove -that the higher are strongly distinguished from the lower, by the much -greater degree in which the individuality of the tertiary aggregate -dominates over the individualities of those secondary aggregates called -segments or “somites,” of which it is composed. The successive Figs. -<a href="#i_112">170–176</a>, representing (without their limbs) a Julus, a Scolopendra, -an isopodous Crustacean, and four kinds of decapodous Crustaceans, -ending with a Crab, will convey at a glance an idea of the way in -which that greater size and heterogeneity reached by the higher -types, is accompanied by an integration which, in the extreme cases, -nearly obliterates all traces of composite structure. In the Crab the -posterior segments, usually folded underneath the shell, alone preserve -their primitive distinctness. So completely confluent are the rest, -that it seems absurd to say that a Crab’s carapace is composed of as -many segments as there are pairs of limbs, foot-jaws, and antennæ -attached to it; and were it not that during early stages of the Crab’s -development<span class="pagenum" id="Page_113">[113]</span> the segmentation is faintly marked, the assertion might be -considered illegitimate.</p> - - <div class="figcenter" id="i_112"> - <img - class="p2" - src="images/i_112.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 170–176.</p> - </div> - -<p class="p2">That all articulate animals are thus composed from end to end -of homologous segments, is, however, an accepted doctrine among -naturalists. It is a doctrine that rests on careful observation of -three classes of facts—the correspondences of parts in the successive -“somites” of an adult articulate animal; the still more marked -correspondences of such parts as they exist in the embryonic or larval -articulate animal; and the maintenance of such correspondences in some -types, which are absent in types otherwise near akin to them. The -nature of the conclusion which these evidences unite in supporting, -will best be shown by the annexed copies from the lecture-diagrams -of Prof. Huxley; exhibiting the typical structures of a Myriapod, an -Insect, a Spider, and a Crustacean, with their relations to a common -plan, as interpreted by him.</p> - - <div class="figcenter" id="i_113"> - <img - class="p2" - src="images/i_113.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 177–186.</p> - </div> - -<p class="p2">Treating of these homologies, Prof. Huxley says “that a striking -uniformity of composition is to be found in the heads of, at any rate, -the more highly organized members of these four classes; and that, -typically, the head of a Crustacean, an Arachnid, a Myriapod, or an -Insect, is composed of six<span class="pagenum" id="Page_114">[114]</span> somites (or segments corresponding with -those of the body) and their appendages, the latter being modified so -as to serve the purpose of sensory and manducatory organs.”<a id="FNanchor_27" href="#Footnote_27" class="fnanchor">[27]</a></p> - -<p>Thus even in the higher <i>Arthropoda</i>, the much greater -consolidation and much greater heterogeneity do not obliterate all -evidence of the fact, that the organism is an aggregate of the third -order. Comparisons show that it is divisible into a number of proximate -units, each of which is akin in certain fundamental traits to its -neighbours, and each of which is an aggregate of the second order, in -so far as it is an organized combination of those aggregates of the -first order which we call morphological units or cells. And that these -segments or somites, which make up an annulose animal, were originally -aggregates of the second order having independent individualities, -is an hypothesis which gathers further support from the contrast -between the higher and the lower Arthropods, as well as from the -contrast between the Arthropods<span class="pagenum" id="Page_115">[115]</span> in general and the Annelids. For if -that masking of the individualities of the segments which we find -distinguishes the higher forms from the lower, has been going on from -the beginning, as we may fairly assume; it is to be inferred that the -individualities of the segments in the lower forms, were originally -more marked than they now are. Reversing those processes of change by -which the most developed <i>Annulosa</i> have arisen from the least -developed; and applying in thought this reversed process to the least -developed, as they were described in the last Chapter; we are brought -to the conception of attached segments that are all completely alike, -and have their individualities in no appreciable degree subordinated to -that of the chain they compose. From which there is but one step to the -conception of gemmiparously-produced individuals which severally part -one from another as soon as they are formed.</p> - - -<p class="p2">§ 209. We must now return to a junction whence we diverged some time -ago. As before explained under the head of Classification, organisms -do not admit of uniserial arrangement, either in general or in detail; -but everywhere form groups within groups. Hence, having traced the -phases of morphological composition up to the highest forms in any -sub-kingdom, we find ourselves at the extremity of a great branch, from -which there is no access to another great branch, except by going back -to some place of bifurcation low down in the tree.</p> - -<p>There exist such similarities of shape and structure between the larval -forms of low Molluscs and those of Annelids and Rotifers, as to show -that there was an early type common to them all; and its probable -characters, suggested by comparison, seem to imply that it had arisen -from some cœlenterate type, intermediate between the <i>Cnidaria</i> -and the <i>Ctenophora</i>. But there is this noteworthy difference -between the molluscan larva and the allied larvæ, that it gives -origin to only one animal and not to a group of animals, united or<span class="pagenum" id="Page_116">[116]</span> -disunited. No true Mollusc multiplies by gemmation, either continuous -or discontinuous; but the product of every fertilized germ is a single -individual.</p> - -<p>It is a significant fact that here, where for the first time we have -homogenesis holding throughout an entire sub-kingdom, we have also -throughout an entire sub-kingdom no case in which the organism is -divisible into two, three, or more, like parts. There is neither any -such clustering or branching as a cœlenterate or molluscoid animal -usually displays; nor is there any trace of that segmentation which -characterizes the <i>Annulosa</i>. Among these animals in which no -single egg produces several individuals, no individual is separable -into several homologous divisions. This connexion will be seen to have -a probable meaning, on remembering that it is the converse of the -connexion which obtains among the <i>Annulosa</i>, considered as a -group.</p> - -<p>A Mollusc, then, is an aggregate of the second order. Not only in the -adult animal is there no sign of a multiplicity of like parts that -have become obscured by integration; but there is no sign of such -multiplicity in the embryo. And this unity is just as conspicuous in -the lowest Lamellibranch as in the highest Cephalopod.</p> - - <div class="figcenter" id="i_116"> - <img - class="p2" - src="images/i_116.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 188–190.</p> - </div> - -<p class="p2">It may be well to note, however, more especially because it illustrates -a danger of misinterpretation presently to be guarded against, that -there are certain Molluscs which simulate the segmented structure. -Externally a <i>Chiton</i>, Fig. <a href="#i_116">188</a>, appears to be made up of -divisions substantially like those of the creature Fig. <a href="#i_116">189</a>; and -one who judged only by externals, would say that the creature Fig. -<a href="#i_116">190</a> differs as much from the creature Fig. 189, as this does from -the preceding one. But the truth is, that while <a href="#i_116">190</a> and <a href="#i_116">189</a> are -closely-allied types, <a href="#i_116">189</a> differs from <a href="#i_116">188</a><span class="pagenum" id="Page_117">[117]</span> much more widely than -a man does from a fish. And the radical distinction between them -is this:—Whereas in the Crustacean the segmentation is carried -transversely through the whole mass of the body, so as to render the -body more or less clearly divisible into a series of parts which are -similarly composed; in the Mollusc the segmentation is limited to the -shell carried on its upper surface, and leaves its body as completely -undivided as is that of a common slug.<a id="FNanchor_28" href="#Footnote_28" class="fnanchor">[28]</a> Were the body cut through at -each of the divisions, the section of it attached to each portion of -the shell would be unlike all the other sections. Here the segmentation -has a purely functional derivation—is adaptive instead of genetic. The -similarly-formed and similarly-placed parts, are not homologous in the -same sense as are the appendages of a phænogamic axis or the limbs of -an insect.</p> - - -<p class="p2" id="sect210">§ 210. In studying the remaining and highest sub-kingdom of animals, it -is important to recognize this radical difference in meaning between -that likeness of parts which is produced by likeness of modifying -forces, and that likeness of parts which is due to primordial identity -of origin. On our recognition of this difference depends the view we -take of certain doctrines that have long been dominant, and have still -a wide currency.</p> - -<p>Among the <i>Vertebrata</i>, as among the <i>Mollusca</i>, homogenesis -is universal. The two sub-kingdoms are like one another and unlike the -remaining sub-kingdoms in this, that in all the types they severally -include, a single fertilized ovum produces only a single individual. It -is true that as the eggs of certain gasteropods occasionally exhibit -spontaneous fission<span class="pagenum" id="Page_118">[118]</span> of the vitelline mass, which may or may not result -in the formation of two individuals; so among vertebrate animals we -now and then meet with double monsters, which appear to imply such a -spontaneous fission imperfectly carried out. But these anomalies serve -to render conspicuous the fact, that in both these sub-kingdoms the -normal process is the integration of the whole germ-mass into a single -organism, which at no phase of its development displays any tendency to -separate into two or more parts.</p> - -<p>Equally as throughout the <i>Mollusca</i>, there holds throughout the -<i>Vertebrata</i> the correlative fact, that not even in its lowest any -more than in its highest types, is the body divisible into homologous -segments. The vertebrate animal, under its simplest as under its most -complex form, is like the molluscous animal in this, that you cannot -cut it into transverse slices, each of which contains a digestive -organ, a respiratory organ, a reproductive organ, &c. The organs of the -least-developed fish as well as those of the most developed mammal, -form but a single physiological whole; and they show not the remotest -trace of having ever been divisible into two or more physiological -wholes. That segmentation which the vertebrate animal usually exhibits -throughout part of its organization, is the same in origin and -meaning as the segmentation of a <i>Chiton’s</i> shell; and no more -implies in the vertebrate animal a composite structure, than do the -successive pairs of branchiæ of the <i>Doto</i>, or the transverse -rows of branchiæ in the <i>Eolis</i>, imply composite structure in -the molluscous animal. To some this will seem a very questionable -proposition; and had we no evidence beyond that which adult vertebrate -animals of developed types supply, it would be a proposition not easy -to substantiate. But abundant support for it is to be found in the -structure of the vertebrate embryo, and in the comparative morphology -of the <i>Vertebrata</i> in general.</p> - -<p>Embryologists teach us that the primordial relations of parts are most -clearly displayed in the early stages of evolution;<span class="pagenum" id="Page_119">[119]</span> and that they -generally become partially or completely disguised in its later stages. -Hence, were the vertebrate animal on the same level as the annulose -animal in degree of composition—did it similarly consist of segments -which are homologous in the sense that they are the proximate units -of composition; we ought to find this fundamental fact most strongly -marked at the outset. As in the annelid-embryo the first conspicuous -change is the elongation and division into segments, by constrictions -that encircle the whole body; and as in the arthropod embryo the -blastoderm becomes marked out transversely into pieces which extend -themselves round the yelk before the internal organization has made -any appreciable progress; so in the embryo of every vertebrate animal, -had it an analogous composition, the first decided change should be -a segmentation implicating the entire mass. But it is not so. Sundry -important differentiations occur before any divisions begin to show -themselves. There is the defining of that elongated, elevated area with -its longitudinal groove, which becomes the seat of subsequent changes; -there is the formation of the notochord lying beneath this groove; -there is the growth upwards of the boundaries of the groove into the -dorsal laminæ, which rapidly develop and fold over in the region of -the head. Rathke, as quoted and indorsed by Prof. Huxley, describes -the subsequent changes as follows:—“The gelatinous investing mass, -which, at first, seems only to constitute a band to the right and to -the left of the notochord forms around it, in the further course of -development, a sheath, which ends in a point posteriorly. Anteriorly, -it sends out two processes which underlie the lateral parts of the -skull, but very soon coalesce for a longer or shorter distance. -Posteriorly, the sheath projects but little beyond the notochord; but, -anteriorly, for a considerable distance, as far as the infundibulum. -It sends upwards two plates, which embrace the future central parts -of the nervous system laterally, probably throughout their entire -length.” That is to say, in the<span class="pagenum" id="Page_120">[120]</span> <i>Vertebrata</i> the first step is -the marking out on the blastoderm of an integrated structure, within -which segments subsequently appear. When these do appear, they are -for some time limited to the middle region of the spinal axis; and no -more then than ever after, do they implicate the general mass of the -body in their transverse divisions. On the contrary, before vertebral -segmentation has made much progress, the rudiments of the vascular -system are laid down in a manner showing no trace of any primordial -correspondence of its parts with the divisions of the axis. Equally -at variance with the belief that the vertebrate animal is essentially -a series of homologous parts, is the heterogeneity which exists among -these parts on their first appearance. Though in the head of an adult -articulate animal there is little sign of divisibility into segments -like those of the body; yet such segments, with their appropriate -ganglia and appendages, are easily identifiable in the articulate -embryo. But in the <i>Vertebrata</i> this antithesis is reversed. At -the time when segmentation has become decided in the dorsal region of -the spine, there is no trace of segments in the parts which are to form -the skull—nothing whatever to suggest that the skull is being formed -out of divisions homologous with vertebræ.<a id="FNanchor_29" href="#Footnote_29" class="fnanchor">[29]</a> And minute observation -no more discloses any such homology than does general appearance. -“Remak,” says Prof. Huxley, “has more fully proved than any other -observer, the segmentation into ‘urwirbel,’ or proto-vertebræ, which is -characteristic of the vertebral column, stops at the occipital margin -of the skull—the base of which, before ossification, presents no trace -of that segmentation which occurs throughout the vertebral column.”</p> - - <div class="figcenter" id="i_121"> - <img - class="p2" - src="images/i_121.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 191.</p> - </div> - -<p class="p2">Consider next the evidence supplied by comparative morphology. In -preceding sections (<a href="#sect206">§§ 206</a>, <a href="#sect208">208</a>) it has been<span class="pagenum" id="Page_121">[121]</span> shown that among annulose -animals, the divisibility into homologous parts is most clearly -demonstrable in the lowest types. Though in decapodous Crustaceans, in -Insects, in Arachnids, there is difficulty in identifying some or many -of the component somites; and though, when identified, they display -only partial correspondences; yet on descending to Annelids, the -composition of the entire body out of such somites becomes conspicuous, -and the homology between each somite and its neighbours is shown by the -repetition of one another’s structural details, as well as by their -common gemmiparous origin: indeed, in some cases we have the homology -directly demonstrated by seeing a somite of the body transformed into -a head. If, then, a vertebrate animal had a segmental composition of -kindred nature, we ought to find it most clearly marked in the lowest -<i>Vertebrata</i> and most disguised in the highest <i>Vertebrata</i>. -But here, as before, the fact is just the reverse. Among the -<i>Vertebrata</i> of developed type, such segmentation as really exists -remains conspicuous—is but little obscured even in parts of the spinal -column formed out of integrated vertebræ. Whereas in the undeveloped -vertebrate type, segmentation is scarcely at all traceable.<a id="FNanchor_30" href="#Footnote_30" class="fnanchor">[30]</a> The -<i>Amphioxus</i>, Fig. <a href="#i_121">191</a>, is not only without ossified vertebræ; not -only is it without cartilaginous representatives of them; but it is -even without anything like distinct membranous divisions. The spinal -column exists as a continuous notochord: the only signs of incipient -segmentation being given by its membranous sheath, in the upper part -of which “quadrate masses of somewhat denser<span class="pagenum" id="Page_122">[122]</span> tissue seem faintly to -represent neural spines.” Moreover, throughout sundry groups of fishes -and amphibians, the segmentation remains very imperfect: only certain -peripheral appendages of the vertebræ becoming defined and solidified, -while in place of the bodies of the vertebræ there still continues the -undivided notochord. Thus, instead of being morphologically composed -of vertebral segments, the vertebrate animal in its primitive form is -entirely without vertebral segments; and vertebral segments begin to -appear only as we advance towards developed forms. Once more, evidence -equally adverse to the current hypothesis meets us on observing that -the differences between the parts supposed to be homologous, are as -great at first as at last. Did the vertebrate animal primordially -consist of homologous segments from snout to tail; then the segments -said to compose the skull ought, in the lowest <i>Vertebrata</i>, to -show themselves much more like the remaining segments than they do in -the highest <i>Vertebrata</i>. But they do not. Fishes have crania -made up of bones that are no more clearly arrangeable into segments -like vertebræ, than are the cranial bones of the highest mammal. Nay, -indeed, the case is much stronger. The simplest fish possessing a -skeleton, has a cranium composed of cartilage that is not segmented at -all!</p> - -<p>Besides being inconsistent with the leading truths of Embryology -and Comparative Morphology, the hypothesis of Goethe and Oken is -inconsistent with itself. The facts brought forward to show that there -exists an archetypal vertebra, and that the vertebrate animal is -composed of archetypal vertebræ arranged in a series, and severally -modified to fit their positions—these facts, I say, so far from -proving as much, suffice, when impartially considered, to disprove it. -No assigned, nor any conceivable, attribute of the supposed archetypal -vertebra is uniformly maintained. The parts composing it are constant -neither in their number, nor in their relative positions, nor in their -modes of ossification,<span class="pagenum" id="Page_123">[123]</span> nor in the separateness of their several -individualities when present. There is no fixity of any one element, -or connexion, or mode of development, which justifies even a suspicion -that vertebræ are modelled after an ideal pattern. To substantiate -these assertions here would require too much space, and an amount of -technical detail wearisome to the general reader. The warrant for them -will be found in a criticism on the osteological works of Prof. Owen, -originally published in the <i>British and Foreign Medico-Chirurgical -Review</i> for Oct. 1858. This criticism I add in the Appendices, for -the convenience of those who may wish to study the question more fully. -(See Appendix B.)</p> - -<p>Everything, then, goes to show that the segmental composition -which characterises the apparatus of external relation in most -<i>Vertebrata</i>, is not primordial or genetic, but functionally -determined or adaptive. Our inference must be that the vertebrate -animal is an aggregate of the second order, in which a relatively -superficial segmentation has been produced by mechanical intercourse -with the environment. We shall hereafter see that this conception leads -us to a consistent interpretation of the facts—shows us why there has -arisen such unity in variety as exists in every vertebral column, and -why this unity in variety is displayed under countless modifications in -different skeletons.<a id="FNanchor_31" href="#Footnote_31" class="fnanchor">[31]</a></p> - - -<p class="p2">§ 211. On glancing back at the facts brought together in these two -chapters, we see it to be probable that there has gone on among animals -a process like that which we saw reason to think has gone on among -plants. Minute aggregates of those physiological units which compose -living protoplasm,<span class="pagenum" id="Page_124">[124]</span> exist as <i>Protozoa</i>: some of them incoherent, -indefinite, and almost homogeneous, and others of them more coherent, -definite, and heterogeneous. By union of these nucleated particles -of sarcode, are produced various indefinite aggregates of the second -order—Sponges, <i>Polycytharia</i>, Foraminifers, &c.; in which the -compound individuality is scarcely enough marked to subordinate the -primitive individualities. But in other types, as in <i>Hydra</i>, the -lives of the morphological units are in a considerable degree, though -not wholly, merged in the life of the integrated body they form. As the -primary aggregate, when it passes a certain size, undergoes fission or -gemmation; so does the secondary aggregate. And as on the lower stage -so on the higher, we see cases in which the gemmiparously-produced -individuals part as soon as formed, and other cases in which they -continue united, though in great measure independent. This massing -of secondary aggregates into tertiary aggregates, is variously -carried on among the <i>Hydrozoa</i>, the <i>Actinozoa</i>, the -<i>Polyzoa</i>, and the <i>Tunicata</i>. In most of the types so -produced, the component individualities are very little subordinated -to the individuality of the composite mass—there is only physical -unity and not physiological unity; but in certain of the oceanic -<i>Hydrozoa</i>, the individuals are so far differentiated and combined -as very much to mask them. Forms showing us clearly the transition to -well-developed individuals of the third order, are not to be found. -Nevertheless, in the great sub-kingdom <i>Annulosa</i>, there are -traits of structure, development, and mode of multiplication, which go -far to show that its members are such individuals of the third order; -and in the relations to external conditions involved by the mode of -union, we find an adequate cause for that obscuration of the secondary -individualities which we must suppose has taken place. The two other -great subdivisions, <i>Mollusca</i> and <i>Vertebrata</i>, between -the lower members of which there are suggestive points of community, -present us only with aggregates of the second order, that have in many -cases become very large and<span class="pagenum" id="Page_125">[125]</span> very complex. We find in them no trace of -the union of gemmiparously-produced individuals. Neither the molluscous -nor the vertebrate animal shows the faintest trace of a segmentation -affecting the totality of its structure; and we see good grounds for -concluding that such segmentation as exceptionally occurs in the one -and usually occurs in the other, is superinduced.</p> - -<hr class="tb" /> - -<p>[<span class="smcap">Note</span>:—A critic calls in question the statement on p. 121 -respecting the <i>Amphioxus</i>. At the outset, however, he admits -that in the <i>Amphioxus</i> “the central nervous system and the -notochord are not segmented.” In the Annelid, however, the central -nervous system is segmented, and there is segmentation of the part -which, as a supporting structure, is analogous to the notochord in -respect of function—the outer part which represents the exo-skeleton -in contrast to the endo-skeleton. He goes on to say that “the gut is -not involved [in the segmentation] and exhibits in <i>Amphioxus</i> -just as it does in worms differentiations entirely independent of the -segmentation of the mesoblast.” Part of this statement is, I think, -not congruous with all the facts. In <i>Protodrilus</i>, one of the -lowest of the <i>Archiannelida</i>, “the intestine is moniliform, there -being a constriction between each segment” and the next. (Shipley.) -Complete segmentation of the intestine is obviously impossible, -since, were the canal divided into portions by septa, no food could -pass. But the fact that the gut has these successive expansions and -constrictions, corresponding to the successive segments, and giving -to each segment a partially-separate stomach, shows that segmentation -has gone as far as consists with the carrying on of the lives of the -segments. No such partial segmentation exists in the <i>Amphioxus</i>. -Thus, then, three fundamental structures—the directive structure, the -supporting structure, and the alimentary structure—are respectively -simple in the lowest vertebrate and segmented, or<span class="pagenum" id="Page_126">[126]</span> partially segmented, -in the lowest Annelid. Again, while it is said that the gill-clefts -exhibit segmentation, it is admitted that this has no relevance to -any constitutional segmentation: “they are segmented on a plan of -their own” irrespective of other organs. Another allegation is that -the ovaries of <i>Amphioxus</i> are segmented. Their segmentation, -however, like that of the gills, is isolated, and may be considered -as illustrating those repetitions of like parts seen in supernumerary -vertebræ in various creatures—a repetition which becomes habitual -if the resulting structure is advantageous to the species. On the -statement that while the <i>Amphioxus</i> has no rudiments of a -renal system the Elasmobranch embryo has such rudiments, which are -as distinctly segmented as the nephridia of a worm, two comments may -be made. The first is that if in these Vertebrates the nephridia -bear a relation to the general structure like that which they do in -Annelids, then one would expect to find the segmental arrangement -shown in the lowest type, as in Annelids, rather than in a type -considerably advanced in development. Should it be replied that in the -<i>Amphioxus</i> an excretory system had not yet arisen, though one -is required for the higher organization of an Elasmobranch, then the -answer may be that since the segmental arrangement in the Elasmobranch -corresponds with that of the myotomes, it has no reference to any -primordial segmentation, since the myotomes have been functionally -generated. The second comment is that whereas the nephridia of the -Annelid have independent external openings, the nephridia in the -Elasmobranch have not. These discharge their secretions into certain -general tubes of exit common to them all; showing that each of them, -instead of being a member of a partially independent structure, is -united with others in subordination to a general structure. That -is to say, the segmentations are far from being parallel in their -essential natures. The assertion accompanying these criticisms, that -there is “no difference <i>in principle</i> between the segmentation -of <i>Amphioxus</i><span class="pagenum" id="Page_127">[127]</span> and Annelid” is difficult to reconcile with the -visible contrast between the two. Whatever local segmentations there -are in an <i>Amphioxus</i> appear to me quite unlike “in principle” -to those which an Annelid exhibits. Could its portion of gut be duly -supplied with nutriment, the segment of a low Annelid could carry on -its vital functions independently. In the parts of the <i>Amphioxus</i> -we see nothing approaching to this. Cut it into transverse sections -and no one of them contains anything like the assemblage of structures -required for living. The <i>Amphioxus</i> is a physiological whole, and -in that respect differs radically from the Annelid, each segment of -which is in chief measure a physiological whole. No occurrence of local -segmentation in the <i>Amphioxus</i> can obliterate this fundamental -contrast.</p> - -<p>An accompanying contrast tells the same story. On ascending from the -lowest to the highest annulose types we see a progressing integration, -morphological and physiological; so that whereas in a low annelid -the successive parts are in large measure independent in their -structures and in their lives, in a high arthropod, as a crab, most -of the parts have lost their individualities and have become merged -in a consolidated organism with a single life. Quite otherwise is it -in the vertebrate series. Its lowest member is at the very outset a -complete morphological and physiological whole, and the formation of -those serial parts which some think analogous to the serial parts of an -Annelid, begins at a later stage and becomes gradually pronounced. That -is to say, the course of transformation is reversed.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_128">[128]</span></p> - -<h3>CHAPTER VI.<br /> -<span class="subhed1">MORPHOLOGICAL DIFFERENTIATION IN PLANTS.</span></h3></div> - -<p>§ 212. While, in the course of their evolution, plants and animals -have displayed progressive integrations, there have at the same time -gone on progressive differentiations of the resulting aggregates, -both as wholes and in their parts. These differentiations and the -interpretations of them, form the second class of morphological -problems.</p> - -<p>We commence as before with plants. We have to consider, first, the -several kinds of modification in shape they have undergone; and, -second, the relations between these kinds of modification and their -factors. Let us glance at the leading questions that have to be -answered.</p> - - -<p class="p2">§ 213. Irrespective of their degrees of composition, plants may, and -do, become changed in their general forms. Are their changes capable of -being formulated? The inquiry which meets us at the outset is—does a -plant’s shape admit of being expressed in any universal terms?—terms -that remain the same for all genera, orders, and classes.</p> - -<p>After plants considered as wholes, have to be considered their -proximate components, which vary with their degrees of composition, -and in the highest plants are what we call branches. Is there any law -traceable among the contrasted shapes of different branches in the same -plant? Do the relative developments of parts in the same branch conform -to any law? And are these laws, if they exist, allied with one<span class="pagenum" id="Page_129">[129]</span> another -and with that to which the shape of the whole plant conforms?</p> - -<p>Descending to the components of these components, which in developed -plants we distinguish as leaves, there meet us kindred questions -respecting their relative sizes, their relative shapes, and their -shapes as compared with those of foliar organs in general. Of their -morphological differentiations, also, it has to be asked whether they -exemplify any truth that is exemplified by the entire plant and by its -larger parts.</p> - -<p>Then, a step lower, we come down to those morphological units of -which leaves and fronds consist; and concerning these arise parallel -inquiries touching their divergences from one another and from cells in -general.</p> - -<p>The problems thus put together in several groups cannot of course be -rigorously separated. Evolution presupposes transitions which make all -such classings more or less conventional; and adherence to them must be -subordinate to the needs of the occasion.</p> - - -<p class="p2">§ 214. In studying the causes of the morphological differentiations -thus divided out and prospectively generalized, we shall have to bear -in mind several orders of forces which it will be well briefly to -specify.</p> - -<p>Growth tends inevitably to initiate changes in the shape of any -aggregate, by altering both the amounts of the incident forces and -the forces which the parts exert on one another. With the mechanical -actions this is obvious. Matter that is sensibly plastic cannot be -increased in mass without undergoing a change in its proportions, -consequent on the diminished ratio of its cohesive force to the force -of gravitation. With the physiological actions it is equally obvious. -Increase of size, other things equal, alters the relations of the parts -to the material and dynamical factors of nutrition; and by so affecting -differently the nutrition of different parts, initiates further changes -of proportions.</p> - -<p><span class="pagenum" id="Page_130">[130]</span></p> - -<p>In plants of the third order it is thus with the proximate components: -they are subject to mutual influences that are unlike one another and -are continually changing. The earlier-formed units become mechanical -supporters of the later-formed units, and so experience modifying -forces from which the later-formed units are exempt. Further, these -elder units simultaneously begin to serve as channels through which -materials are carried to and from the younger units—another cause -of differentiation that goes on increasing in intensity. Once more, -there arise ever-strengthening contrasts between the amounts of light -which fall upon the youngest or outermost units and the eldest or -innermost units; whence result structural contrasts of yet another -kind. Evidently, then, along with the progressive integration of cells -into fronds, of fronds into axes, and of axes into plants still more -composite, there come into play sundry causes of differentiation which -act on the whole and on each of its parts, whatever their grade. The -forces to be overcome, the forces to be utilized, and the matters to -be appropriated, do not remain the same in their proportions and modes -of action for any two members of the aggregate: be they members of the -first, second, third, or any other order.</p> - - -<p class="p2">§ 215. Nor are these the only kinds and causes of heterogeneity which -we have to consider. Beyond the more general changes produced in the -relative sizes and shapes of plants and their parts by progressive -aggregation, there are the more particular changes determined by the -more particular conditions.</p> - -<p>Plants as wholes assume unlike attitudes towards their environments; -they have many ways of articulating their parts with one another; they -have many ways of adjusting their parts towards surrounding agencies. -These are causes of special differentiations additional to those -general differentiations that result from increase of mass and increase -of composition. In each part considered individually, there arises<span class="pagenum" id="Page_131">[131]</span> -a characteristic shape consequent on that relative position towards -external and internal forces, which the mode of growth entails. Every -member of the aggregate presents itself in a more or less peculiar way -towards the light, towards the air, and towards its point of support; -and according to the relative homogeneity or heterogeneity in the -incidence of the agencies thus brought to bear on it, will be the -relative homogeneity or heterogeneity of its shape.</p> - - -<p class="p2">§ 216. Before passing from this <i>à priori</i> view of the -morphological differentiations which necessarily accompany -morphological integrations, to an <i>à posteriori</i> view of them, it -seems needful to specify the meanings of certain descriptive terms we -shall have to employ.</p> - -<p>Taking for our broadest division among forms, the regular and the -irregular, we may divide the latter into those which are wholly -irregular and those which, being but partially irregular, suggest -some regular form to which they approach. By slightly straining the -difference between them, two current words may be conveniently used to -describe these subdivisions. The entirely irregular forms we may class -as <i>asymmetrical</i>—literally as forms without any equalities of -dimensions. The forms which approximate towards regularity without -reaching it, we may distinguish as <i>unsymmetrical</i>: a word which, -though it asserts inequality of dimensions, has been associated by -use rather with such slight inequality as constitutes an observable -departure from equality.</p> - -<p>Of the regular forms there are several classes, differing in the number -of directions in which equality of dimensions is repeated. Hence -results the need for names by which symmetry of several kinds may be -expressed.</p> - -<p>The most regular of figures is the sphere: its dimensions are the same -from centre to surface in all directions; and if cut by any plane -through the centre, the separated parts are equal and similar. This is -a kind of symmetry which stands alone, and will be hereafter spoken of -as <i>spherical symmetry</i>.</p> - -<p><span class="pagenum" id="Page_132">[132]</span></p> - -<p>When a sphere passes into a spheroid, either prolate or oblate, there -remains but one set of planes that will divide it into halves, which -are in all respects alike; namely, the planes in which its axis lies, -or which have its axis for their line of intersection. Prolate and -oblate spheroids may severally pass into various forms without losing -this property. The prolate spheroid may become egg-shaped or pyriform, -and it will still continue capable of being divided into two equal -and similar parts by any plane cutting it down its axis; nor will the -making of constrictions deprive it of this property. Similarly with the -oblate spheroid. The transition from a slight oblateness, like that of -an orange, to an oblateness reducing it nearly to a flat disc, does -not alter its divisibility into like halves by every plane passing -through its axis. And clearly the moulding of any such flattened oblate -spheroid into the shape of a plate, leaves it as before, symmetrically -divisible by all planes at right angles to its surface and passing -through its centre. This species of symmetry is called <i>radial -symmetry</i>. It is familiarly exemplified in such flowers as the -daisy, the tulip, and the dahlia.</p> - -<p>From spherical symmetry, in which we have an infinite number of axes -through each of which may pass an infinite number of planes severally -dividing the aggregate into equal and similar parts; and from radial -symmetry, in which we have a single axis through which may pass an -infinite number of planes severally dividing the aggregate into -equal and similar parts; we now turn to <i>bilateral symmetry</i>, -in which the divisibility into equal and similar parts becomes much -restricted. Noting, for the sake of completeness, that there is a -sextuple bilateralness in the cube and its derivative forms which admit -of division into equal and similar parts by planes passing through -the three diagonal axes and by planes passing through the three axes -that join the centres of the surfaces, let us limit our attention to -the three kinds of bilateralness which here concern us. The first of -these is <i>triple<span class="pagenum" id="Page_133">[133]</span> bilateral symmetry</i>. This is the symmetry of -a figure having three axes at right angles to one another, through -each of which there passes a single plane that divides the aggregate -into corresponding halves. A common brick will serve as an example; -and of objects not quite so simple, the most familiar is that modern -kind of spectacle-case which is open at both ends. This may be divided -into corresponding halves along its longitudinal axis by cutting it -through in the direction of its thickness, or by cutting it through in -the direction of its breadth; or it may be divided into corresponding -halves by cutting it across the middle. Of objects which illustrate -<i>double bilateral symmetry</i>, may be named one of those boats built -for moving with equal facility in either direction, and therefore -made alike at stem and stern. Obviously such a boat is separable into -equal and similar parts by a vertical plane passing through stem and -stern; and it is also separable into equal and similar parts by a -vertical plane cutting it amidships. To exemplify <i>single bilateral -symmetry</i> it needs but to turn to the ordinary boat of which the -two ends are unlike. Here there remains but the one plane passing -vertically through stem and stern, on the opposite sides of which the -parts are symmetrically disposed.</p> - -<p>These several kinds of symmetry as placed in the foregoing order, imply -increasing heterogeneity. The greatest uniformity in shape is shown -by the divisibility into like parts in an infinite number of infinite -series of ways; and the greatest degree of multiformity consistent -with any regularity, is shown by the divisibility into like parts in -only a single way. Hence, in tracing up organic evolution as displayed -in morphological differentiations, we may expect to pass from the one -extreme of spherical symmetry, to the other extreme of single bilateral -symmetry. This expectation we shall find to be completely fulfilled.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_134">[134]</span></p> - -<h3>CHAPTER VII.<br /> -<span class="subhed1">THE GENERAL SHAPES OF PLANTS.</span></h3></div> - -<p id="sect217">§ 217. Among protophytes those exemplified by <i>Pleurococcus -vulgaris</i> are by general consent considered the simplest. As -shown in Fig. <a href="#i_022a">1</a>, they are globular cells presenting no obvious -differentiation save that between inner and outer parts. Their -uniformity of figure co-exists with a mode of life involving the -uniform exposure of all their sides to incident forces. For though -each individual may have its external parts differently related to -environing agencies, yet the new individuals produced by spontaneous -fission, whether they part company or whether they form clusters and -are made polyhedral by mutual pressure, have no means of maintaining -parallel relations of position among their parts. On the contrary, -the indefiniteness of the attitudes into which successive generations -fall, must prevent the rise of any unlikeness between one portion of -the surface and another. Spherical symmetry continues because, on the -average of cases, incident forces are equal in all directions.</p> - - <div class="figcenter" id="i_135"> - <img - class="p2" - src="images/i_135.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 1, 2, 3.</p> - </div> - -<p class="p2">Other orders of <i>Protophyta</i> have much more special forms, along -with much more special attitudes: their homologous parts maintaining, -from generation to generation, unlike relations to incident forces. The -<i>Desmidiaceæ</i> and <i>Diatomaceæ</i>, of which Figs.<a href="#i_135"> 2 and 3</a> show -examples, severally include genera characterized by triple bilateral -symmetry. A <i>Navicula</i> is divisible into corresponding halves -by a transverse<span class="pagenum" id="Page_135">[135]</span> plane and by two longitudinal planes—one cutting -its valves at right angles and the other passing between its valves. -The like is true of those numerous transversely-constricted forms -of <i>Desmidiaceæ</i>, exemplified by the second of the individuals -represented in Fig. <a href="#i_135">2</a>. If now we ask how a <i>Navicula</i> is related -to its environment, we see that its mode of life exposes it to three -different sets of forces: each set being resolvable into two equal and -opposite sets. A <i>Navicula</i> moves in the direction of its length, -with either end foremost. Hence, on the average, its ends are subject -to like actions from the agencies to which its motions subject it. -Further, either end while moving exposes its right and left sides to -amounts of influence which in the long run must be equal. If, then, -the two ends are not only like one another, but have corresponding -right and left sides, the symmetrical distribution of parts answers to -the symmetrical distribution of forces. Passing to the two edges and -the two flat surfaces, we similarly find a clue to their likenesses -and differences in their respective relations to the things around -them. These locomotive protophytes move through the entangled masses -of fragments and fibres produced by decaying organisms and confervoid -growths. The interstices in such matted accumulations are nearly all -of them much longer in one dimension than in the rest—form crevices -rather than regular meshes. Hence, a small organism will have much -greater facility of insinuating itself through this <i>débris</i>, -in which it finds nutriment, if its transverse section is flattened -instead of square or circular. And while we see how, by survival of the -fittest, a flattened form is likely to be acquired by diatoms having -this habit; we also see that likeness will be maintained between the -two flat surfaces and between the two edges. For, on the average, -the relations of the two flat surfaces to the sides of the openings -through which the<span class="pagenum" id="Page_136">[136]</span> diatom passes, will be alike; and so, too, on the -average, will be the relations of the two edges. In desmids of the type -exemplified by the second individual in Fig. <a href="#i_135">2</a>, a kindred equalization -of dimensions is otherwise insured. There is nothing to keep one of the -two surfaces uppermost rather than the other; and hence, in the long -succession of individuals, the two surfaces are sure to be similarly -exposed to light and agencies in general. When to this is added the -fact that spontaneous fission occurs transversely in a constant way, -it becomes manifest that the two ends, while they are maintained in -conditions like one another, are maintained in conditions unlike those -of the two edges. Here then, as before, triple bilateral symmetry -in form, co-exists with a triple bilateral symmetry in the average -distribution of actions.</p> - - <div class="figcenter" id="i_136"> - <img - class="p2" - src="images/i_136.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 4, 5, 6.</p> - </div> - -<p class="p2">Still confining our attention to aggregates of the first order, let us -next note what results when the two ends are permanently subject to -different conditions. The fixed unicellular plants, of which examples -are given in Figs. <a href="#i_136">4, 5, and 6</a>, severally illustrate the contrast -in shape arising between the part that is applied to the supporting -surface and the part that extends into the surrounding medium. These -two parts which are the most unlike in their relations to incident -forces, are the most unlike in the forms. Observe, next, that the part -which lifts itself into the water or air, is more or less decidedly -radial. Each outward-growing tubule of <i>Codium adhærens</i>, Fig. <a href="#i_136">4</a>, -has its parts disposed with some regularity around its axis; the upper -stem and spore-vessel<span class="pagenum" id="Page_137">[137]</span> of <i>Botrydium</i>, Fig. <a href="#i_136">5</a>, display a lateral -growth that is approximately equal in every direction; and the stems -of the <i>Mucor</i>, Fig. <a href="#i_136">6</a>, shoot up with an approach to evenness on -all sides. Plants of this low type are naturally very variable in their -modes of growth: each individual being greatly modified in form by its -special circumstances. But they nevertheless show us a general likeness -between parts exposed to like forces, as well as a general unlikeness -between parts exposed to unlike forces.</p> - -<p>Respecting the forms of these aggregates of the first order, it has -only to be added that they are asymmetrical where there is total -irregularity in the incidence of forces. We have an example in the -indefinitely contorted and branched shape of a fungus-cell, growing as -a mycelium among the particles of soil or through the interstices of -organic tissue.</p> - - -<p class="p2" id="sect218">§ 218. Re-illustrations of the general truths which the forms of -these vegetal aggregates of the first order display, are furnished by -vegetal aggregates of the second order. The equalities and inequalities -of growth in different directions, prove to be similarly related to -the equalities and inequalities of environing actions in different -directions.</p> - -<p>Of spherical symmetry an instance occurs in <i>Eudorina elegans</i>. -The ciliated cells are here so united as to produce a small, -mulberry-shaped, hollow ball which, being similarly conditioned -on all sides, shows no unlikenesses of structure. An allied form, -however, <i>Volvox globator</i>, presents a highly instructive, -though very trifling, modification. It is not absolutely homogeneous -in its structure and is not absolutely homogeneous in its motions. -The waving cilia of its component cells have fallen into such slight -heterogeneities of action as to cause rotation in a constant direction; -and along with a fixed axis of rotation there has arisen a fixed axis -of progression. A concomitant fact is that the cells of the colony -exhibit an appreciable differentiation in relation to the fixed axis. -There is an incipient divergence from<span class="pagenum" id="Page_138">[138]</span> spherical uniformity along with -this slight divergence from uniformity of conditions.</p> - -<p>Vegetal aggregates of the second order are usually fixed: locomotion -is exceptional. Fixity implies that the surface of attachment is -differently circumstanced from the free surface. Hence we may expect -to find, as we do find, that among these rooted aggregates of the -second order, as among those of the first order, the primary contrast -of shape is between the adherent part and the loose part. Sea-weeds -variously exemplify this. In some the fronds are very irregular and -in some tolerably regular; in some the form is pseudo-foliar and in -some pseud-axial; but differing though they do in these respects, -they agree in having the end which is attached to a solid body unlike -the other end. The same truth is seen in such secondary aggregates -as the common Agarics, or rather in their immensely-developed organs -of fructification. A puff-ball, Fig. <a href="#i_138">192</a>, presents no other obvious -unlikeness of parts than that between its under and upper surfaces. So -too with the stalked kinds that frequent our woods and pastures. In the -types which Figs. <a href="#i_138">193, 194, 195</a>, delineate, the unlikenesses between -the rooted ends and the expanded ends, as well as between the under -and upper surfaces of the expanded ends, are obviously related to this -fundamental contrast of conditions. Nor is this relation less clearly -displayed in the sessile fungi which grow out from the sides of trees, -as shown at <i>a</i>, <i>b</i>, Fig. <a href="#i_138">196</a>. That which is common to this -and the preceding types, is the contrast between the attached end and -the free end.</p> - - <div class="figcenter" id="i_138"> - <img - class="p2" - src="images/i_138.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 192–196.</p> - </div> - -<p><span class="pagenum" id="Page_139">[139]</span></p> - -<p class="p2">From what these forms have in common, let us turn to that which they -have not in common, and observe the causes of the want of community. -A puff-ball shows us in the simplest way, the likeness of parts -accompanying likeness of conditions, along with the unlikeness of parts -accompanying unlikeness of conditions. For while, if we cut vertically -through its centre, we find a difference between top and bottom, if -we cut horizontally through its centre, we find no differences among -its several sides. Being, on the average of cases, similarly related -to the environment all round, it remains the same all round. The -radial symmetry of the mushroom and other vertically-growing fungi, -illustrates this connexion of cause and effect still better. But -now mark what happens in the group of <i>Agaricus noli-tangere</i>, -shown in Fig. <a href="#i_138">195</a>. Radially-symmetrical as is the type, and radially -symmetrical as are those centrally-placed individuals which are equally -crowded all round, we see that the peripheral individuals, dissimilarly -circumstanced on their outer sides and on their sides next the group, -have partially changed their radial symmetry into bilateral symmetry. -It is no longer possible to make two corresponding halves by <i>any</i> -vertical plane cutting down through the pileus and the stem; but there -is only <i>one</i> vertical plane that will thus produce corresponding -halves—the plane on the opposite sides of which the relations to the -environment are alike. And then mark that the divergence from all-sided -symmetry towards two-sided symmetry, here caused in the individual by -special circumstances, is characteristic of the race where the habits -of the race constantly involve two-sidedness of conditions. Besides -being exemplified by such comparatively undifferentiated types as -certain <i>Polypori</i>, Fig. <a href="#i_138">196</a>, <i>a</i>, <i>b</i>, this truth -is exemplified by members of the genus just named. In <i>Agaricus -horizontalis</i>, Fig. <a href="#i_138">196</a>, <i>c</i>, we have a departure from radial -symmetry that is conspicuous only in the form of the stem. A more -decided bilateralness exists in <i>A. subpalmatus</i>, shown in -elevation at <i>d</i> and in section at <i>d´</i>. And<span class="pagenum" id="Page_140">[140]</span> <i>Lentinus -flabelliformis</i>, of which <i>e</i> and <i>e´</i> are different -views, exhibits complete bilateralness—a bilateralness in which -there is the greatest likeness of the parts that are most similarly -conditioned, and the greatest unlikeness of the parts that are most -dissimilarly conditioned.</p> - -<p>Among plants of the second order of composition, it will suffice -to note one further class of facts which are the converse of the -foregoing and have the same implications. These are the facts showing -that along with habitual irregularity in the relations to external -forces, there is habitual irregularity in the mode of growth. Besides -finding such facts among Thallophytes, as in the tubers of underground -fungi and in the creeping films of sessile lichens, which severally -show us variations of proportions obviously caused by variations in -the amounts of the influences on their different sides, we also, -among Archegoniates of inferior types, find irregularities of form -along with irregularities in environing actions. The fronds of the -<i>Marchantiaceæ</i> or such <i>Jungermanniaceæ</i> as are shown in -Figs. <a href="#i_033">41, 42, 43</a>, illustrate the way in which each lowly-organized -aggregate of the second order, not individuated by the mutual -dependence of its parts, has its form determined by the balance of -facilities and resistances which each side of the frond meets with as -it spreads.</p> - - -<p class="p2">§ 219. Among plants displaying integration of the third degree, and -among plants still further compounded, these same truths are equally -manifest. In the forms of such plants we see primary contrasts and -secondary contrasts which, no less clearly than the foregoing, are -related to contrasts of conditions.</p> - -<p>That flowering plants from the daisy up to the oak, have in common the -fundamental unlikeness between the upward growing part and the downward -growing part; and that this most marked unlikeness corresponds with the -most marked unlikeness between the two parts of their environment, soil -and air; are facts too conspicuous to be named<span class="pagenum" id="Page_141">[141]</span> were they not important -items in the argument. More instructive perhaps, because less familiar, -is the fact that we miss this extreme contrast in flowering plants -which have not their higher and lower portions exposed to conditions -thus extremely contrasted. A parasite like the Dodder, growing in -entangled masses upon other plants, from which it sucks the juices, is -not thus divisible into two strongly-distinguished halves.</p> - -<p>Leaving out of consideration the difference between the supporting -part and the supported part in phænogams, and looking at the supported -part only, we observe between its form and the habitual incidence of -forces, a relation like that which we observed in the simpler plants. -Phænogams that are practically if not literally uniaxial, and those -which develop their lateral axes only in the shape of axillary flowers, -when uninterfered with commonly send up vertical stems round which the -leaves and flowers are disposed with a more or less decided radial -symmetry. Gardens and fields supply us with such instances as the Tulip -and the Orchis; and, on a larger scale, the Palms and the Aloes are -fertile in examples. The exceptions, too, are instructive. Besides the -individual divergences arising from special interferences, there are -to be traced general divergences where the habits of the plants expose -them to general interferences in anything approaching to constant ways. -Plants which, like the Foxglove, have spikes of flowers that are borne -on flexible foot-stalks, have their flowers habitually bent round to -one face of the stem: an unlikeness of distribution probably caused -by unlikeness in the relation to the Sun’s rays. The wild Hyacinth, -too, with stem so flexible that its upper part droops, shows us how a -consequent difference in the action of gravity on the flowers, causes -them to deviate from their typically-radial arrangement towards a -bilateral arrangement.</p> - - <div class="figcenter" id="i_142"> - <img - class="p2" - src="images/i_142.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 197–199.</p> - </div> - -<p class="p2">Much more conspicuous are these general and special relations of form -to general and special actions in the environment, among phænogams -that are multiaxial. That when<span class="pagenum" id="Page_142">[142]</span> standing alone, and in places where -the winds do not injure them nor adjacent things shade them, shrubs -and trees develop with tolerable evenness on all sides, is an obvious -truth. Equally obvious is the truth that, when growing together in -a wood, and mutually interfered with on all sides, trees still show -obscurely radial distributions of parts; though, under such conditions, -they have tall taper stems with branches directed upwards—a difference -of shape clearly due to the different incidence of forces. And almost -equally obvious is the truth, that a tree of this same kind growing -at the edge of the wood, has its outer branches well developed and -its inner branches comparatively ill-developed. Fig. <a href="#i_142">197</a>, which -inaccurately represents this difference, will serve to make it manifest -that while one of the peripheral trees can be cut into something like -two similar halves by a vertical plane directed towards the centre of -the wood—a plane on each side of which the conditions are alike—it -cannot be cut into similar halves by any other plane. A like divergence -from an indefinitely-radial symmetry towards an indefinitely-bilateral -symmetry, occurs in trees that have their conditions made bilateral -by growing on inclined surfaces. Two of the common forms observable -in such cases are given in Fig. <a href="#i_142">198</a>. Here there is divisibility into -parts that are tolerably similar, by a vertical plane running directly -down the hill; but not by any other plane. Then, further, there is the -bilateralness, similar in general meaning though differently caused, -often seen in trees exposed to strong prevailing winds. Almost<span class="pagenum" id="Page_143">[143]</span> every -sea-coast has abundant examples of stunted trees which, like the one -shown in Fig. <a href="#i_142">199</a>, have been made to deviate from their ordinary equal -growth on all sides of a vertical axis, to a growth that is equal only -on the opposite sides of a vertical plane directed towards the wind’s -eye.</p> - -<p>From among vegetal aggregates of the third order, we have now only to -add examples of the entirely asymmetrical form which accompanies an -entirely irregular distribution of incident forces. Creeping plants -furnish such examples. They show, both when climbing up vertical or -inclined surfaces and when trailing on the ground, that their branches -grow hither and thither as the balance of forces aids or opposes; -and the general outline is without symmetry of any kind, because the -environing influences have no kind of regularity in their arrangement.</p> - - -<p class="p2">§ 220. Along with some unfamiliar facts, I have here set down facts -which are so familiar as to seem scarcely worth noting. It is because -these facts have become meaningless to perceptions deadened by infinite -repetitions of them, that it is needful here to point out their -meanings. Not alone for its intrinsic importance has the unlikeness -between the attached ends and the free ends been traced among plants -of all degrees of integration. Nor is it simply because of the -significance they have in themselves, that instances have been given -of those varieties of symmetry and asymmetry which the free ends of -plants equally display: be they plants of the first, second, third, -or any higher order. Neither has the only other purpose been that of -showing how, in the radial symmetry of some vegetal aggregates and -the single bilateral symmetry of others, there are traceable the same -ultimate principles as in the spherical symmetry and triple bilateral -symmetry of certain minute plants first described. But the main object -has been to present, under their simplest aspects, those general laws -of morphological differentiation which are fulfilled by the component -parts of each plant.</p> - -<p><span class="pagenum" id="Page_144">[144]</span></p> - -<p>If organic form is determined by the distribution of forces, and the -approach in every case towards an equilibrium of inner actions with -outer actions; then this relation between forms and forces must hold -alike in the organism as a whole in its proximate units, and in its -units of lower orders. Formulas which express the shapes of entire -plants in terms of surrounding conditions, must be formulas which also -express the shapes of their several parts in terms of surrounding -conditions. If, therefore, we find that a plant as a whole is radially -symmetrical or bilaterally symmetrical or asymmetrical, according as -the incident forces affect it equally on all sides of an axis, or -affect it equally only on the opposite sides of one plane, or affect -it equally in no two directions; then, we may expect that, in like -manner, each member of a plant will display radial symmetry where -environing influences are alike along many radii, bilateral symmetry -where there is bilateralness of environing influences, and unsymmetry -or asymmetry where there is partial or entire departure from a balance -of surrounding actions.</p> - -<p>To show that this expectation is borne out by the facts, will be the -object of the following four chapters. Let us begin with the largest -parts into which plants are divisible; and proceed to the successively -smaller parts.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_145">[145]</span></p> - -<h3>CHAPTER VIII.<br /> -<span class="subhed1">THE SHAPES OF BRANCHES.</span></h3></div> - - -<p>§ 221. Aggregates of the first order supply a few examples of forms -ramified in an approximately-regular manner, under conditions which -subject their parts to approximately-regular distributions of forces. -Some unicellular <i>Algæ</i>, becoming elaborately branched, assume -very much the aspects of small trees; and show us in their branches -analogous relations of forms to forces. <i>Bryopsis plumosa</i> may -be instanced. Fig. <a href="#i_145a">200</a> represents the end of one of its lateral -ramifications, above and beneath which come others of like characters. -Here it will be seen that the attached and free ends differ; that the -two sides are much alike; and that they are unlike the upper and under -surfaces, which resemble one another. The more highly developed members -of the same group of <i>Algæ</i>, the <i>Siphoneæ</i>, show a marked -radial symmetry co-existing with very elaborate branching, <i>e.g.</i>, -<i>Neomeris</i>, <i>Cymopolia</i>, and others.</p> - - <div class="figcenter" id="i_145a"> - <img - class="p2" - src="images/i_145a.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 200.</p> - </div> - - -<p class="p2">§ 222. Fig. <a href="#i_145b">201</a> shows us how, in an aggregate of the second order, -each proximate component is modified by its relations to the rest; -just as we before saw a whole fungus of the same type modified<span class="pagenum" id="Page_146">[146]</span> by -its relations to environing objects. If a branch of the fungus here -figured, be compared with one of the fungi clustered together in Fig. -195, or, still better, with one of the laterally-growing fungi shown -in Fig. <a href="#i_138">196</a>, there will be perceived a kindred transition from radial -to bilateral symmetry, occurring under kindred conditions. The portion -of the pileus next to the side of attachment is undeveloped in this -branched form as in the simpler form; and in the one case as in the -other, the stem is modified towards the side of attachment. A division -into similar halves, which, as shown in Fig. <a href="#i_138">196</a> <i>e</i>, might be -made of the whole fungus by a vertical plane passing through the centre -of the pileus and the axis of the supporting body, might here be made -of the branch, by a vertical plane passing through the centre of its -pileus and the axis of the main stem. Among aggregates of this order, -the <i>Algæ</i> furnish cases of kindred nature. In the branches of -<i>Lessonia</i>, Fig. <a href="#i_030">37</a>, may be observed a substantially-similar -relationship. As their inner parts are less developed than their outer -parts, while their two sides are developed in approximately equal -degrees, they are rendered bilateral.</p> - - <div class="figcenter" id="i_145b"> - <img - class="p2" - src="images/i_145b.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 201.</p> - </div> - - -<p class="p2">§ 223. These few cases introduce us to the more familiar but more -complex cases which plants of the third degree of aggregation -present. At <i>a</i>, <i>b</i>, <i>c</i>, Fig. <a href="#i_146">202</a>, are sketched -three homologous parts of the same tree: <i>a</i> being the leading<span class="pagenum" id="Page_147">[147]</span> -shoot; <i>b</i> a lateral branch near the top, and <i>c</i> a lateral -branch lower down. There is here a double exemplification. While -the branch <i>a</i>, as a whole, has its branchlets arranged with -tolerable regularity all round, in correspondence with its equal -exposure on all sides, each branchlet shows by its curve as much -bilateral symmetry as its simple form permits. The branch <i>b</i>, -dissimilarly circumstanced on the side next the main stem and on the -side away from it, has an approximate bilateralness as a whole, while -the bilateralness of its branchlets varies with their respective -positions. And in the branch <i>c</i>, having its parts still more -differently conditioned, these traits of structure are still more -marked. Extremely strong contrasts of this kind occur in trees having -very regular modes of growth. The uppermost branches of a Spruce-fir -have radially-arranged branchlets: each of them, if growing vigorously, -repeats the type of the leading shoot, as shown in Fig. <a href="#i_146">203</a>, <i>a</i>, -<i>b</i>. But if we examine branches lower and lower down the tree, we -find the vertically-growing branchlets bear a less and less ratio to -the horizontally-growing ones; until, towards the bottom, the radial -arrangement has wholly merged into the bilateral. Shaded and confined -by the branches above them, these eldest branches develop their -offshoots in those directions where there is most space and light: -becoming finally quite flattened and fan-shaped, as shown at Fig. <a href="#i_146">203</a>, -<i>c</i>. And on remembering that each of these eldest branches, when -first it diverged from the main stem, was radial, we see not only that -between the upper and lower branches does this contrast in structure -hold, but also that each branch is transformed from the radial to -the bilateral by the progressive change in its environment. Other -forces besides those which aid or hinder growth, conspire to produce -this two-sided character in lateral branches. The annexed Fig. <a href="#i_146">204</a>, -sketched from an example of the <i>Pinus Coulterii</i> at Kew, shows -very clearly how, by mere gravitation, the once radially-arranged -branchlets may be so bent as to produce in the branch as a whole a<span class="pagenum" id="Page_148">[148]</span> -decided bilateralness. A full-grown <i>Araucaria</i>, too, exhibits -in its lower branches modifications similarly caused; and in each -of such branches there may be remarked the further fact, that its -upward-bending termination has a partially-modified radialness, at the -same time that its drooping lateral branchlets give to the part nearer -the trunk a completely bilateral character.</p> - - <div class="figcenter" id="i_146"> - <img - class="p2" - src="images/i_146.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 202–204.</p> - </div> - -<p class="p2">Now in these few instances, typical of countless instances which might -be given, we see, as we saw in the case of the fungi, that the same -thing is true of the parts in their relations to the whole and to one -another, which is true of the whole in its relations to the environment -at large. Entire trees become bilateral instead of radial, when exposed -to forces that are equal only on opposite sides of one plane; and in -their branches, parallel changes of form occur under parallel changes -of conditions.</p> - - -<p class="p2">§ 224. There remains to be said something respecting the distribution -of leaves. How a branch carries its leaves constitutes one of -its characters as a branch, and is to be considered apart from -the characters of the leaves themselves. The principles hitherto -illustrated we shall here find illustrated still further.</p> - -<p>The leading shoot and all the upper twigs of a fir-tree, have their -pin-shaped leaves evenly distributed all round, or placed radially;<a id="FNanchor_32" href="#Footnote_32" class="fnanchor">[32]</a> -but as we descend we find them beginning to assume a bilateral -distribution; and on the lower, horizontally-growing branches, their -distribution is quite bilateral.<a id="FNanchor_33" href="#Footnote_33" class="fnanchor">[33]</a> Between the Irish and English -kinds of Yew, there is a contrast of like significance. The branches -of the one, shooting up as they do almost vertically, are clothed with -leaves<span class="pagenum" id="Page_149">[149]</span> all round; while those of the other, which spread laterally, -bear their leaves on the two sides. In trees with better-developed -leaves, the same principle is more or less manifest in proportion as -the leaves are more or less enabled by their structures to maintain -fixed positions. Where the foot-stalks are long and slender, and where, -consequently, each leaf, according to its weight, the flexibility and -twist of its foot-stalk, and the direction of the branch it grows from, -falls into some indefinite attitude, the relations are obscured. But -where the foot-stalks are stiff, as in the Laurel, it will be found, as -before, that from the topmost and upward growing branches the leaves -diverge on all sides; while the undermost branches, growing out from -the shade of those above, have their leaves so turned as to bring them -into rows horizontally spread out on the two sides of each branch.</p> - - <div class="figcenter" id="i_149"> - <img - class="p2" - src="images/i_149.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 205.</p> - </div> - -<p class="p2">A kindred truth, having like implications, comes into view when we -observe the relative sizes of leaves on the same branch, where their -sizes differ. Fig. <a href="#i_149">205</a> represents a branch of a Horse-chestnut, taken -from the lowermost fringe of the tree, where the light has been to -a great extent intercepted from all but the most protruded parts. -Beyond the fact that the leaves become by appropriate growths of their -foot-stalks bilaterally distributed on this drooping branch, instead of -being distributed symmetrically all round, as on one of the ascending -shoots, we have here to note the fact that there is unequal development -on the upper and lower sides. Each of the compound leaves acquires a -foot-stalk and leaflets that are large in proportion to the supply -of light; and hence, as we descend towards the bottom of the tree, -the clusters of leaves display increasing contrasts. How marked these -contrasts become will be seen on comparing <i>a</i> and <i>b</i>, which -form one pair of leaves that<span class="pagenum" id="Page_150">[150]</span> are normally equal, or <i>c</i> and -<i>d</i>, which form another pair normally equal.</p> - -<p>Let us not omit to note, while we have this case before us, the proof -it affords that these differences of development are in a considerable -degree determined by the different conditions of the parts after they -have been unfolded. Though those inequalities of dimensions whence -the differentiations of form result, may be in many cases largely due -to the inequalities in the circumstances of the parts while in the -bud (which are, however, representative of inequalities in ancestral -circumstances); yet these are clearly not the sole causes of the -unlikenesses which eventually arise. This bilateralness resulting from -the unequal sizes of the leaves, must be considered as due to the -differential actions that come into play after the leaves have assumed -their typical structures.</p> - - -<p class="p2">§ 225. How, in the arrangement of their twigs and leaves, branches tend -to lapse from forms that are approximately symmetrical to forms that -are quite asymmetrical, need not be demonstrated: it is sufficiently -conspicuous. But it may be well to point out how the tendency to -do this further enforces our argument. The comparatively regular -budding out of secondary axes and tertiary axes, does not usually -produce an aggregate which maintains its regularity, for the simple -reason that many of the axes abort. Terminal buds are some of them -destroyed by birds; others are burrowed into by insects; others are -nipped by frost; others are broken off or injured during gales of wind. -The environment of each branch and its branchlets is thus ever being -varied on all sides: here, space being left vacant by the death of some -shoot that would ordinarily have occupied it; and there, space being -trenched on by the lateral growth of some adjacent branch that has had -its main axis broken. Hence the asymmetry, or heterogeneity of form, -assumed by the branch, is caused by the asymmetrical distribution<span class="pagenum" id="Page_151">[151]</span> of -incident forces—a result and a cause which go on ever complicating.</p> - - -<p class="p2">§ 226. One conspicuous trait in the shapes of branches has still to be -named. Their proximal or attached ends differ from their distal or free -ends, in the same way that the lower ends of trees differ from their -upper ends. This fact, like the fact to which it is here paralleled, -has had its significance obscured by its extreme familiarity. But -it shows in a striking way how the most differently conditioned -parts become the most strongly contrasted in their structures. A -phænogamic axis is made up of homologous segments, marked off from -one another by the nodes; and a compound branch consists of groups of -such segments. The earliest-formed segments, alike of the tree and of -each branch, serve as mechanical supports and channels for sap to the -successive generations of segments that grow out of them; and become -more and more shaded by their progeny as these increase. Hence the -progressively-increasing contrasts which, while mainly due to the -unlikenesses of bulk accompanying differences of age, are in part due -to the unlikenesses of structure which differences of relation to the -environment have caused.</p> - - -<p class="p2">§ 227. Thus, then, it is with the proximate parts of plants as it is -with plants as wholes. The radial symmetry, the bilateral symmetry, and -the asymmetry, which branches display in different trees, in different -parts of the same tree, and at different stages of their own growths, -prove to be all consequent on the ways in which they stand towards the -entire plexus of surrounding actions. The principle that the growths -are unequal in proportion as the relations of parts to the environment -are unequal, serves to explain all the leading traits of structure.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_152">[152]</span></p> - -<h3>CHAPTER IX.<br /> -<span class="subhed1">THE SHAPES OF LEAVES.</span></h3></div> - - -<p>§ 228. Next in the descending order of composition come compound -leaves. The relative sizes and distributions of their leaflets, as -affecting their forms as wholes, have to be considered in their -relations to conditions. Figs. <a href="#i_153">206, 207</a>, represent leaves of the common -<i>Oxalis</i> and of the <i>Marsilea</i>, in which radial symmetry -is as completely displayed as the small number of leaflets permits. -This equal development of the leaflets on all sides, occurs where -the foot-stalks, growing up vertically from creeping or underground -stems, are so long that the leaves either do not interfere with one -another or do it in an inconstant way: the leaflets are not differently -conditioned on different sides, as they are where the foot-stalks grow -out in the ordinary manner. How unlikeness of position influences the -leaflets is clearly shown in a Clover-leaf, Fig. <a href="#i_153">208</a>, which deviates -from the Oxalis-leaf but slightly towards bilateralness, as it deviates -from it but slightly in the attitude of its petiole; which is a little -inclined away from the others borne by the same procumbent axis. A -familiar example of an almost radial symmetry along with almost equal -relations to surrounding conditions, occurs in the root-leaves of -the Lupin, Fig. <a href="#i_153">209</a> <i>b</i>. Here though we have lateral divergence -from a vertical axis, yet the long foot-stalks preserve nearly erect -positions, and carry their leaves to such distances from the axis, -that the development of the leaflets on the side next it is not much<span class="pagenum" id="Page_153">[153]</span> -hindered. Still the interference of the leaves with one another is, -on the average, somewhat greater on the proximal side than on the -distal side; and hence the interior leaflets are rather less than the -exterior leaflets. In further proof of which influence, let it be added -that, as shown in the figure, at <i>a</i>, the leaves growing out of -the flowering stem deviate towards the two-sided form more decidedly. -Two-sidedness is much greater where there is a greater relative -proximity of the inner leaflets to the axis, or where the foot-stalk -approaches towards a horizontal position. The Horse-chestnut, Fig. <a href="#i_149">205</a>, -already instanced as showing how the arrangements and sizes of leaflets -are determined by the incidence of forces, serves also to show how the -incidence of forces determines the relative sizes and arrangements of -leaflets. Fig. <a href="#i_153">210</a>, which shows a leaf of the <i>Bombax</i>, further -illustrates this relation of structure to conditions.</p> - - <div class="figcenter" id="i_153"> - <img - class="p2" - src="images/i_153.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 206–210.</p> - </div> - - <div class="figcenter" id="i_154"> - <img - class="p2" - src="images/i_154.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 211, 212.</p> - </div> - -<p class="p2">Compound leaves that are completely bilateral, present us with -modifications of form exemplifying the same general truth in another -way. In them the proximal and distal parts have none of that -resemblance which we see in those intermediate forms just described. -The portion next the axis and the portion furthest from the axis -are entirely different; and the only likeness is between the wings -or leaflets on opposite sides of the main foot-stalk or mid-rib. -On turning back to Fig. <a href="#i_040">65</a>, it will be seen that the compound leaf -there<span class="pagenum" id="Page_154">[154]</span> drawn to exemplify another truth, serves also to exemplify this -truth: the homologous parts <i>a</i>, <i>b</i>, <i>c</i>, <i>d</i>, -while they are unlike one another, are, in their main proportions, -severally like the parts with which they are paired. And here let us -not overlook a characteristic which is less conspicuous but not less -significant. Each of the lateral wings has winglets that are larger -on the one side than on the other; and in each case the two sides -are dissimilarly conditioned. Even in the several components of each -wing may be traced a like divergence from symmetry, along with a like -inequality in the relations to the rest: the proximal half of each -leaflet is habitually larger than the distal half. In the leaves of -the Bramble, previously figured, kindred facts are presented. How far -such differences of development are due to the positions of the parts -in the bud; how far the respective spaces available for the parts -when unfolded affect them; and how far the parts are rendered unlike -by unlikenesses in their relations to light; it is difficult to say. -Probably these several factors operate in all varieties of proportion. -That the habitual shading of some parts by others largely aids in -causing these divergences from symmetry, is very instructively shown -by the compound leaves of the Cow-parsnip. Fig. <a href="#i_154">211</a> represents one -of these. While the leaf as a whole is bilaterally symmetrical, each -of the wings has an unsymmetrical bilateralness: the side next the -axis being larger than the remoter side. How does this happen? Fig. -<a href="#i_154">212</a>, which is a diagrammatic section down the mid-rib of the leaf, -showing its inclined attitude and the positions of the<span class="pagenum" id="Page_155">[155]</span> wings <i>a</i>, -<i>b</i>, <i>c</i>, will make the cause clear. As the wings overlap, -like the bars of a Venetian blind, each intercepts some light from the -one below it; and the one below it thus suffers more on its distal -side than on its proximal side. Hence the smaller development of the -distal side. That this is the cause is further shown by the proportion -that is maintained between the degree of obscuration and the degree of -non-development; for this unlikeness is greater between the two sides -<i>a</i> and <i>a´</i>, than between <i>b</i> and <i>b´</i> or <i>c</i> -and <i>c´</i>, at the same time that the interference is greater in -the lower wings than in the upper. Of course in this case and in the -kindred cases hereafter similarly interpreted, it is not meant that -this differentiation is consequent solely, or even chiefly, on the -differential actions experienced by the individual plant. Though there -is good reason to believe that the rate of growth in each part of each -leaf is affected by the incidence of light, yet contrasts so marked and -so systematic as these are not explicable without taking into account -the inheritance of modifications either functionally caused or caused -by spontaneous variation. Clearly, the tendency will be towards the -preservation of a plant which distributes its chlorophyll in the most -advantageous way; and hence there will always be a gravitation towards -a form in which shaded parts of leaves are undeveloped.</p> - - -<p class="p2">§ 229. From compound leaves to simple ones, we find transitions in -leaves of which the divisions are partial instead of total; and in -these we see, with equal clearness, the relations between forms and -positions that have been traced thus far. Fig. <a href="#i_156a">213</a> is the leaf of a -Winter-aconite in which, round a vertical petiole, there is a radial -distribution of half-separated leaflets. The <i>Cecropia</i>-leaf, -Fig. <a href="#i_156a">214</a>, shows us a two-sided development of the parts beginning to -modify, but not obliterating, the all-sided arrangement; and this mixed -symmetry occurs under conditions that are intermediate. A more marked -degree of the same relation is presented<span class="pagenum" id="Page_156">[156]</span> in the leaf of the Lady’s -Mantle, Fig. <a href="#i_156a">215</a>. And then in the Sycamore and the Vine, we have a -cleft type of leaf in which a decided bilateralness of form co-exists -with a decided bilateralness of conditions.</p> - - <div class="figcenter" id="i_156a"> - <img - class="p2" - src="images/i_156a.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 213–215.</p> - </div> - - <div class="figcenter" id="i_156b"> - <img - class="p2" - src="images/i_156b.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 216–218.</p> - </div> - -<p class="p2">The quite simple leaves to which we now descend, exhibit, very -distinctly, a parallel series of facts. Where they grow up on long and -completely-independent foot-stalks, without definite subordination -to some central vertical axis, the leaves of water-plants are -symmetrically peltate. Of this the sacred Indian-bean, Fig. <a href="#i_156b">216</a>, -furnishes an example. Here there is only a trace of bilateralness in -the venation of the leaf, corresponding to the very small difference -of the conditions on the proximal and distal sides. In the <i>Victoria -regia</i>, Fig. <a href="#i_156b">217</a>, the foot-stalks, though radiating almost -horizontally from a centre, are so long as to keep the leaves quite -remote from one another; and in it each leaf is almost symmetrically -peltate, with a bilateralness indicated only by a seam over the -line of the foot-stalk. The leaves of the <i>Nymphæa</i>, Fig. <a href="#i_156b">218</a>, -more closely clustered, and having less room transversely than -longitudinally, exhibit a marked advance to the two-sided form; not -only in the excess of the length over the breadth, but in the existence -of a cleft,<span class="pagenum" id="Page_157">[157]</span> where in the <i>Victoria regia</i> there is merely a seam. -Among land-plants similar forms are found under analogous conditions. -The common <i>Hydrocotyle</i>, Fig. <a href="#i_157">219</a>, which sends up direct from its -roots a few almost upright leaf-stalks, has these surmounted by peltate -leaves; which leaves, however, diverge slightly from radial symmetry in -correspondence with the slight contrast of circumstances which their -grouping involves. Another case is supplied by the Nasturtium, Fig. -<a href="#i_157">220</a>, which combines the characters—a creeping stem, long leaf-stalks -growing up at right angles to it, and unsymmetrically peltate leaves, -of which the least dimension is, on the average, towards the stem. -But perhaps the most striking illustration is that furnished by the -<i>Cotyledon umbilicus</i>, Fig. <a href="#i_157">221</a>, in which different kinds of -symmetry occur in the leaves of the same plant, along with differences -in their relations to conditions. The root-leaves, <i>a</i>, growing up -on vertical petioles before the flower-stalk makes its appearance, are -symmetrically peltate; while the leaves which subsequently grow out of -the flower-stalk, <i>b</i>, are at the bottom transitionally bilateral, -and higher up completely bilateral.</p> - - <div class="figcenter" id="i_157"> - <img - class="p2" - src="images/i_157.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 219–221.</p> - </div> - -<p class="p2">That the bilateral form of leaf is the ordinary form, corresponds with -the fact that, ordinarily, the circumstances of the leaf are different -in the direction of the plant’s axis from what they are in the opposite -direction, while<span class="pagenum" id="Page_158">[158]</span> transversely the circumstances are alike. It is -needless to give diagrams to illustrate this extremely familiar truth. -Whether they are broad or long, oval or heart-shaped, pointed or -obtuse, the leaves of most trees and plants will be remembered by all -as having the ends by which they are attached unlike the free ends, -while the two sides are alike. And it will also be remembered that -these equalities and inequalities of development correspond with the -equalities and inequalities in the incidence of forces.</p> - - -<p class="p2">§ 230. A confirmation that is interesting and important, is furnished -by the cases in which leaves present unsymmetrical forms in positions -where their parts are unsymmetrically related to the environment. A -considerable deviation from bilateral symmetry may be seen in a leaf -which habitually so carries itself, that the half on the one side of -the mid-rib is more shaded than the other half. The drooping branches -of the Lime, delineated in Fig. <a href="#i_158">222</a>, show us leaves so arranged and -so modified. On examining their attitudes and their relations one to -another, it will be found that each leaf is so inclined that the half -of it next to the shoot grows over the shoot and gets plenty of light; -while the other half so hangs down that it comes a good deal into the -shade of the preceding leaf. The result is that having leaves which -fall into these positions, the species profits by a large development -of the exposed halves; and by survival of the fittest, acting along -with the direct effect of extra exposure, this modification becomes -established. How unquestionable is the connexion between the relative -positions of the halves and their relative developments, will be -admitted on observing a<span class="pagenum" id="Page_159">[159]</span> converse case. Fig. <a href="#i_158">223</a> represents a shoot of -<i>Strobilanthes glomeratus</i>. Here the leaves are so set on the stem -that the inner half of each leaf is shaded by the subsequently-formed -leaf, while its outer half is not thus shaded; and here we find -the inner half less developed than the outer half. But the most -conclusive evidence of this relation between unsymmetrical form and -unsymmetrical distribution of surrounding forces, is supplied by the -genus <i>Begonia</i>; for in it we have a manifest proportion between -the degree of the alleged effect and the degree of the alleged cause. -These plants produce their leaves in pairs, in such ways that the -connate leaves interfere with one another, much or little according -as the foot-stalks are short or long; and the result is a correlative -divergence from symmetry. In <i>Begonia nelumbiifolia</i>, which has -petioles so long that the connate leaves are not kept close together, -there is but little deviation from a bilaterally-peltate form; whereas, -accompanying the comparatively marked and constant proximity in <i>B. -pruinata</i>, Fig. <a href="#i_158">224</a>, we see a more decidedly unsymmetrical shape; -and in <i>B. mahringii</i>, Fig. <a href="#i_158">225</a>, the modification thus caused is -pushed so far as to destroy the peltate structure.<a id="FNanchor_34" href="#Footnote_34" class="fnanchor">[34]</a></p> - - <div class="figcenter" id="i_158"> - <img - class="p2" - src="images/i_158.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 222–225.</p> - </div> - - -<p class="p2">§ 231. Again, then, we are taught the same truth. Here, as before, -we see that homologous units of any order become<span class="pagenum" id="Page_160">[160]</span> differentiated in -proportion as their relations to incident forces become different. And -here, as before, we see that in each unit, considered by itself, the -differences of dimension are greatest in those directions in which the -parts are most differently conditioned; while there are no differences -between the dimensions of the parts that are not differently -conditioned.<a id="FNanchor_35" href="#Footnote_35" class="fnanchor">[35]</a></p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_161">[161]</span></p> - -<h3>CHAPTER X.<br /> -<span class="subhed1">THE SHAPES OF FLOWERS.</span></h3></div> - - -<p class="p2">§ 232. Following an order like that of preceding chapters, let us first -note a few typical facts respecting the forms of clusters of flowers, -apart from the forms of the flowers themselves. Two kindred kinds -of <i>Leguminosæ</i> serve to show how the members of clusters are -distributed in an all-sided manner or in a two-sided manner, according -as the circumstances are alike on all sides or alike on only two sides. -In <i>Hippocrepis</i>, represented in Fig. <a href="#i_161">226</a>, the flowers growing at -the end of a vertical stem, are arranged round it in radial symmetry. -Contrariwise in <i>Melilotus</i>, Fig. <a href="#i_161">227</a>, where the axillary stem -bearing the flowers is so placed in relation to the main stem, that its -outer and inner faces are differently conditioned, the flowers are all -on the outer face: the cluster is bilaterally symmetrical, since it may -be cut into approximately equal and similar groups by a vertical plane -passing through the main axis.</p> - - <div class="figcenter" id="i_161"> - <img - class="p2" - src="images/i_161.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 226, 227.</p> - </div> - -<p class="p2">Plants of this same tribe furnish clusters of intermediate characters -having intermediate conditions. Among these, as among the clusters -which other types present, may be<span class="pagenum" id="Page_162">[162]</span> found some in which conformity -to the general law is not obvious. The discussion of these apparent -anomalies would carry us too much out of our course. A clue to the -explanation of them will, I believe, be found in the explanation -presently to be given of certain kindred anomalies in the forms of -individual flowers.</p> - - -<p class="p2" id="sect233">§ 233. The radially-symmetrical form is common to all individual -flowers that have vertical axes. In plants which are practically if -not literally uniaxial, and bear their flowers at the ends of upright -stalks, so that the faces open horizontally, the petals are disposed -in an all-sided way. Crocuses, Tulips, and Poppies are familiar -examples of this structure occurring under these conditions. A -Ranunculus flower, Fig. <a href="#i_162">228</a>, will serve as a typical one. Similarly, -flowers which have peduncles flexible enough to let them hang directly -downwards, and are not laterally incommoded, are also radial; as in -the <i>Fuchsia</i>, Fig. <a href="#i_162">229</a>, as in <i>Cyclamen</i>, <i>Hyacinth</i>, -&c. These relations of form to position are, I believe, uniform. -Though some flowers carried at the ends of upright or downright stems -have oblique shapes, it is only when they have inclined axes or are -not equally conditioned all round. No solitary flower having an axis -habitually vertical, presents a bilateral form. This is as we should -expect; since flowers which open out their faces horizontally, whether -facing upwards or downwards, are, on the average, similarly affected on -all sides.</p> - - <div class="figcenter" id="i_162"> - <img - class="p2" - src="images/i_162.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 228, 229.</p> - </div> - - <div class="figcenter" id="i_163"> - <img - class="p2" - src="images/i_163.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 230, 231.</p> - </div> - -<p class="p2">At first it seems that flowers thus placed should alone be radial; -but further consideration discloses conditions under which this -type of symmetry may exist in flowers otherwise placed. Remembering -that the radial form is the primitive form—that, morphologically -speaking, it results from the contraction into a whorl, of parts that -are originally arranged in the same spiral succession as the leaves; -we must expect<span class="pagenum" id="Page_163">[163]</span> it to continue wherever there are no forces tending -to change it. What now must be the forces tending to change it? They -must be forces which do not simply affect differently the different -parts of an individual flower. They must be forces which affect in -like contrasted ways the homologous parts of other individual flowers, -both on the same plant and on surrounding plants of the same species. -A permanent modification can be expected only in cases where, by -inheritance, the effects of the modifying causes accumulate. That -they may accumulate the flowers must keep themselves so related to -the environment, that the homologous parts may, generation after -generation, be subjected to like differentiating forces. Hence, among -a plant’s flowers which maintain no uniformity in the relations of -their parts to surrounding influences, the radial form will continue. -Let us glance at the several causes which entail this variability. -When flowers are borne on many branches, which have all inclinations -from the vertical to the horizontal—as are the flowers of the Apple, -the Plum, the Hawthorn—they are placed in countless different -attitudes. Consequently, any spontaneous variation in shape which -might be advantageous were the attitude constant, is not likely to -be advantageous; and any functionally-produced modification in one -flower, is likely to be neutralized in offspring by some opposite -functionally-produced modification in another flower. It is quite -comprehensible, therefore, that irregularly-branched plants should -thus preserve their laterally-borne flowers from undergoing permanent -deviations from their primitive radial symmetry. Fig. <a href="#i_163">230</a>, representing -a blossoming twig of the Blackthorn, illustrates this. Again, upright -panicles, such as those of the Saxifrage exemplified in Fig. <a href="#i_163">231</a>, -and irregular terminal groups of flowers otherwise<span class="pagenum" id="Page_164">[164]</span> named, furnish -conditions under which there is similarly an absence of determinate -relations between the parts of the flowers and the incident forces; -and hence an absence of bilateralness. This inconstancy of relative -position is produced in various other ways—by extreme flexibility -of the stems, as in the Blue-bell; by the tendency of the peduncles -to curl to a greater or less extent in diverse directions, as in -<i>Pyrola</i>; by special twistings of the peduncles, differing in -degree in different individuals, as in <i>Convolvulus</i>; by unusual -laxity of the petals, as in <i>Lythrum</i>. Elsewhere the like -general result arises from a progressive change of attitude, as in -<i>Myosotis</i>, the stem of which as it unfolds causes each flower to -undergo a transition from an upward position of the mouth to a lateral -position; or as in most <i>Cruciferæ</i>, where the like effect follows -from an altered direction of the peduncle.</p> - -<p>There are, however, certain seemingly-anomalous cases where radial -symmetry is maintained by laterally-placed flowers, which keep -their parts in relative positions that are tolerably constant. The -explanation of these exceptions is not manifest. It is only when -we take into account certain incident actions liable to be left -unremembered, that we find a probable solution. It will be most -convenient to postpone the consideration of these cases until we have -reached the general rule to which they are exceptions.</p> - - -<p class="p2" id="sect234">§ 234. Transitions varying in degree from the radial towards the -bilateral, are common in flowers that are borne at the ends of branches -or axes which are inclined in tolerably constant ways. We may see -this in sundry garden flowers such as <i>Petunia</i>, or such as -<i>Isoloma</i> and <i>Achimenes</i>, shown in Figs. <a href="#i_164">232 and 233</a>. If -these plants be examined, it will be perceived that the mode of growth -makes the flower unfold in a partially one-sided<span class="pagenum" id="Page_165">[165]</span> position; that its -parts of attachment have rigidity sufficient to prevent this attitude -from being very much interfered with; and that though the individual -flowers vary somewhat in their attitudes, they do not vary to the -extent of neutralizing the differentiating conditions—there remains -an average divergence from a horizontal unfolding of the flower, to -account for its divergence from radial symmetry.</p> - - <div class="figcenter" id="i_164"> - <img - class="p2" - src="images/i_164.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 232, 233.</p> - </div> - -<p class="p2">We pass insensibly from forms like these, to forms having bilateral -symmetry strongly pronounced. Some such forms occur among flowers -that grow at the ends of upright stems; as in <i>Pinguicula</i>, -and in the Violet tribe. But this happens only where, in successive -generations, the flower unfolds its parts sideways in constant -relative positions. And in the immense majority of flowers -having well-marked two-sided forms, the habitual exposure of -the different parts to different sets of forces, is effectually -secured by the mode of placing. As illustrations, I may name the -genera—<i>Orchis</i>, <i>Utricularia</i>, <i>Salvia</i>, <i>Salix</i>, -<i>Delphinium</i>, <i>Mentha</i>, <i>Teucrium</i>, <i>Ajuga</i>, -<i>Ballota</i>, <i>Galeopsis</i>, <i>Lamium</i>, <i>Stachys</i>, -<i>Nepeta</i>, <i>Marrubium</i>, <i>Calamintha</i>, <i>Melittis</i>, -<i>Prunella</i>, <i>Scutellaria</i>, <i>Bartsia</i>, <i>Euphrasia</i>, -<i>Rhinanthus</i>, <i>Melampyrum</i>, <i>Pedicularis</i>, -<i>Linaria</i>, <i>Digitalis</i>, <i>Orobanche</i>, <i>Fumaria</i>, -<i>&c.</i>; to which may be added all the Grasses and all the -<i>Papilionaceæ</i>. In most of these cases the flowers, being sessile -on the sides of upright stems, are kept in quite fixed attitudes; and -in the other cases the peduncles are very short, or else stiff enough -to secure general uniformity in the positions. A few of the more marked -types are shown in Figs. <a href="#i_165">234 to 241</a>.</p> - - <div class="figcenter" id="i_165"> - <img - class="p2" - src="images/i_165.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 234–241.</p> - </div> - - <div class="figcenter" id="i_166a"> - <img - class="p2" - src="images/i_166a.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 242–246.</p> - </div> - - <div class="figcenter" id="i_166b"> - <img - class="p2" - src="images/i_166b.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 247, 248.</p> - </div> - -<p class="p2">Very instructive evidences here meet us. Sometimes within the limits -of one genus we find radial flowers, bilateral flowers, and flowers of -intermediate characters. The genus</p> - -<p><span class="pagenum" id="Page_166">[166]</span></p> - -<p><i>Begonia</i> may be instanced. In <i>B. rigida</i> the flowers, -various in their attitudes, are in their more conspicuous characters -radial: though there is a certain bilateralness in the calyx, the five -petals are symmetrically disposed all round. <i>B. Wageneriana</i> -furnishes two forms of flowers. On the same individual plant may be -found radial flowers like Fig. <a href="#i_166a">242</a>, and others, like Fig. <a href="#i_166a">243</a>, which -are merging into the bilateral. More decided is the bilateralness in -<i>B. albo-coccinea</i>, Fig. <a href="#i_166a">244</a>; and still more in <i>B. nitida</i>, -Fig. <a href="#i_166a">245</a>. While in <i>B. heracleifolia</i>, Fig. <a href="#i_166a">246</a>, the change -reaches its extreme by the disappearance of the lateral petals. -On examining the modes of growth in these several species, they -will be seen to explain these changes in the manner alleged. Even -more conclusive are the nearly-allied transformations occurring in -artificially-produced varieties of the same species. <i>Gloxinia</i> -may be named in illustration. In Fig. <a href="#i_166b">247</a> is represented one of the -ordinary forms, which shows us bilateralness of shape along with a -mode of growth that renders the conditions alike on the two sides -while different above and below. But in <i>G. erecta</i>, Fig. <a href="#i_166b">248</a>, -we have the flower assuming an upright attitude, and at the same time -assuming the radial type. This is not to be interpreted as a production -of radial symmetry out of bilateral symmetry, under the action of the -appropriate conditions. It is rather to be taken as a case of what is -termed “peloria”—a reversion to the primitive radial type, from which -the bilateral modification had been derived. The significant inference -to be drawn from it is,<span class="pagenum" id="Page_167">[167]</span> that this primitive radial type had an upright -attitude; and that the derivation of a bilateral type from it, occurred -along with the assumption of an inclined attitude.</p> - -<p>We come now to a group of cases above referred to, in which radial -symmetry continues to co-exist with that constant lateral attitude -ordinarily accompanied by the two-sided form. Two examples will -suffice: one a very large flower, the Hollyhock, and the other a very -small flower, the Agrimony. Why does the radial form here remain -unchanged? and how does its continuance consist with the alleged -general law?</p> - -<p>Until quite recently I have been unable to find any probable answers -to these questions. When the difficulty first presented itself, I -could think of no other possible cause for the anomaly, than that the -parts of the Hollyhock-flower, unfolding spirally as they do, might -have different degrees of spiral twist in different flowers, and might -thus not be unfolded in sufficiently-constant positions. But this -seemed a questionable interpretation; and one which did not obviously -apply to the case of the Agrimony. It was only on inquiring what are -the special causes of modifications in the forms of flowers, that a -more feasible explanation suggested itself; and this would probably -never have suggested itself, had not Mr. Darwin’s investigations into -the fertilization of Orchids led me to take into account an unnoticed -agency.</p> - - <div class="figcenter" id="i_168"> - <img - class="p2" - src="images/i_168.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 249.</p> - </div> - -<p class="p2">The actions which affect the forms of leaves, affect much less -decidedly the forms of flowers; and the forms of flowers are influenced -by actions which do not influence the forms of leaves. Partly through -the direct action of incident forces and partly through the indirect -action of natural selection, leaves get their parts distributed in -ways that most facilitate their assimilative functions, under the -circumstances in which they are placed; and their several types -of symmetry are thus explicable. But in flowers, the petals and -fructifying organs of which do not contain chlorophyll, the tendency -to grow most where the supply of light is greatest, is less decided, -if<span class="pagenum" id="Page_168">[168]</span> not absent; and a shape otherwise determined is hence less liable -to alter in consequence of altered relations to sun and air. Gravity, -too, must be comparatively ineffective in causing modifications: the -smaller sizes of the parts, as well as their modes of attachment, -giving them greater relative rigidity. Not, indeed, that these -incident forces of the inorganic world are here quite inoperative. -Fig. <a href="#i_168">249</a>, representing a species of <i>Campanula</i>, shows that -the developments of individual flowers are somewhat modified by the -relations of their parts to general conditions. But the fact to be -observed is, that the extreme transformations which flowers undergo are -not likely to be thus caused: some further cause must be sought. And -if we bear in mind the functions of flowers, we shall find in their -adaptations to these functions, under conditions that are extremely -varied, an adequate cause for the different types of symmetry, as -well as for the exceptions to them. Flowers are parts in which -fertilization is effected; and the active agents of this fertilization -are insects—bees, moths, butterflies, &c. Mr. Darwin has shown in -many cases, that the forms and positions of the essential organs of -fructification, are such as to facilitate the actions of insects in -transferring pollen from the anthers of one flower to the pistil of -another—an arrangement produced by natural selection. And here we -shall find reason for concluding, that the forms and positions of -those subsidiary parts which give their shapes to flowers, similarly -arise by the survival of individuals which have the subsidiary parts -so adjusted as to aid this fertilizing process—the deviations from -radial symmetry being among such adjustments. The reasoning is as -follows. So long as the axis of a flower is vertical and the conditions -are similar all round, a bee or butterfly alighting on it, will be as -likely to come from one side as from another; and hence, hindrance -rather than facilitation would<span class="pagenum" id="Page_169">[169]</span> result if the several sides of the -flower did not afford it equally free access. In like manner, flowers -which are distributed over a plant in such ways that their discs open -out on planes of all directions and inclinations, will have no tendency -to lose their radial symmetry; since, on the average, no part of the -periphery is differently related to insect-agency from any other part. -But flowers so fixed as to open out sideways in tolerably-constant -attitudes, have their petals differently related to insect-agency. A -bee or butterfly coming to a laterally-growing flower, does not settle -on it in one way as readily as in another; but almost of necessity -settles with the axis of its body inclined upwards towards the stem of -the plant. Hence the side-petals of a flower so fixed, habitually stand -to the alighting insect in relations different from those in which the -upper and lower petals stand; and the upper and lower petals differ -from one another in their relations to it. If, then, there so arises -an habitual attitude of the insect towards the petals, there is likely -to be some arrangement of the petals that will be most convenient to -the insect—will most facilitate its entrance into the flower. Thus -we see in many cases, that a long undermost petal or lip, by enabling -the insect to settle in such way as to bring its head opposite to the -opening of the tube, aids its fertilizing agency. But whatever be the -special modifications of the corolla which facilitate the actions of -the particular insects concerned, all of them will conduce to bilateral -symmetry; since they will be alike for the two sides but unlike for -the top and bottom. And now we are prepared for understanding the -exceptions. Flowers growing sideways can become thus adapted by -survival of the fittest, only if they are of such sizes and structures -that insect-agency can affect them in the way described. But in the -plants named above, this condition is not fulfilled. A Hollyhock-flower -is so open, as well as so large, that its petals are not in any -appreciable degree differently related to the insects which visit -it. On the other hand, the flower of the<span class="pagenum" id="Page_170">[170]</span> Agrimony is so small, that -unless visited by insects of a corresponding size which settle as bees -and butterflies settle, its parts will not be affected in the alleged -manner. That all anomalies of this kind can at once be satisfactorily -explained, is scarcely to be expected: the circumstances of each case -have to be studied. But it seems not improbable that they are due to -causes of the kind indicated.<a id="FNanchor_36" href="#Footnote_36" class="fnanchor">[36]</a></p> - - -<p class="p2">§ 235. We have already glanced at clusters of flowers for the purpose -of considering their shapes as clusters. We must now return to them to -observe the modifications undergone by their component flowers. Among -these occur illustrations of great significance.</p> - -<p>An example of transition from the radial to the bilateral form in -clustered flowers of the same species, is furnished by the cultivated -<i>Geraniums</i>, called by florists <i>Pelargoniums</i>. Some of -these, bearing somewhat small terminal clusters of flowers, which -are closely packed together with their faces almost upwards, have -radially-symmetrical flowers. But among other varieties having terminal -clusters of which the members are mutually thrust on one side by -crowding, the flowers depart very considerably from the radial shape<span class="pagenum" id="Page_171">[171]</span> -towards the bilateral shape. A like result occurs under like conditions -in Rhododendrons and Azaleas. The <i>Verbena</i>, too, furnishes -an illustration of radial flowers rendered slightly two-sided by -the slight two-sidedness of their relations to other flowers in the -cluster. And among the <i>Cruciferæ</i> a kindred case occurs in the -cultivated Candytuft.</p> - -<p>Evidence of a somewhat different kind is offered us by clustered -flowers in which the peripheral members of the clusters differ from the -central members; and this evidence is especially significant where we -find allied species that do not exhibit the deviation, at the same time -that they do not fulfil the conditions under which it may be expected. -Thus, in <i>Scabiosa succisa</i>, Fig. <a href="#i_171">250</a>, which bears its numerous -small flowers in a hemispherical knob, the component flowers, similarly -circumstanced, are all equal and all radial; but in <i>Scabiosa -arvensis</i>, Fig. <a href="#i_171">251</a>, in which the numerous small flowers form a -flattened disk only the confined central ones are radial: round the -edge the flowers are much larger and conspicuously bilateral.</p> - - <div class="figcenter" id="i_171"> - <img - class="p2" - src="images/i_171.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 250, 251.</p> - </div> - - <div class="figcenter" id="i_172"> - <img - class="p2" - src="images/i_172.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 252.</p> - </div> - -<p class="p2">But the most remarkable and most conclusive proofs of these relations -between forms and positions, are those given by the clustered flowers -called <i>Umbelliferæ</i>. In some cases, as where the component -flowers have all plenty of room, or where the surface of the umbel -is more or less globular, the modifications are not conspicuous; but -where, as in <i>Viburnum</i>, <i>Chærophyllum</i>, <i>Anthriscus</i>, -<i>Torilis</i>, <i>Caucalis</i>, <i>Daucus</i>, <i>Tordylium</i>, -&c., we have flowers clustered in such ways as to be differently -conditioned, we find a number of modifications that are marked and -varied in proportion as the differences of conditions are marked and -varied. In <i>Chærophyllum</i>, where the flowers of each umbellule are -closely placed so as to form a flat surface, but where the umbellules -are wide apart and form a dispersed umbel, the umbellules do not -differ from one another; though among the<span class="pagenum" id="Page_172">[172]</span> flowers of each umbellule -there are decided differences: the central flowers being small and -radial, while the peripheral ones are large and bilateral. But in -other genera, where not only the flowers of each umbellule but also -the umbellules themselves, are closely clustered into a flat surface, -the umbellules themselves become contrasted; and many remarkable -secondary modifications arise. In an umbel of <i>Heracleum</i>, for -instance, there are to be noted the facts;—first, that the external -umbellules are larger than the internal ones; second, that in each -umbellule the central flowers are less developed than the peripheral -ones; third, that this greater development of the peripheral flowers -is most marked in the outer umbellules; fourth, that it is most -marked on the outer sides of the outer umbellules; fifth, that while -the interior flowers of each umbellule are radial, the exterior ones -are bilateral; sixth, that this bilateralness is most marked in the -peripheral flowers of the peripheral umbellules; seventh, that the -flowers on the outer sides of these peripheral umbellules are those in -which the bilateralness reaches a maximum; and eighth, that where the -outer umbellules touch one another, the flowers, being unsymmetrically -placed, are unsymmetrically bilateral.<a id="FNanchor_37" href="#Footnote_37" class="fnanchor">[37]</a> The like modifications -are displayed, though not in so clearly-traceable a way, in an umbel -of <i>Tordylium</i>, Fig. <a href="#i_172">252</a>. Considering how obviously these -various forms are related to the various conditions, we should be -scarcely able, even in the<span class="pagenum" id="Page_173">[173]</span> absence of all other facts, to resist the -conclusion that the differences in the conditions are the causes of the -differences in the forms.</p> - - <div class="figcenter" id="i_173"> - <img - class="p2" - src="images/i_173.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 253.</p> - </div> - -<p class="p2">Composite flowers furnish evidence so nearly allied to that which -clustered flowers furnish, that we may fitly glance at them under -the same head. Such a common type of this order as the Sun-flower, -exemplifies the extremely marked difference which arises in many -of these plants between the closely-packed internal florets, each -similarly circumstanced on all sides, and the external florets, not -similarly circumstanced on all sides. In Fig. <a href="#i_173">253</a>, representing the -inner and outer florets of a Daisy, the contrast is marked between the -small radial corolla of the one and the larger bilateral corolla of the -other. In many cases, however, this contrast is less marked: the inner -florets also having their outward-growing prolongations—a difference -possibly related to some difference in the habits of the insects that -fertilize them. Nevertheless, these composite flowers which have -inner florets with strap-shaped corollas outwardly directed, equally -conform to the general principle; both in the radial arrangement of -the assemblage of florets, and in the bilateral shape of each floret; -which has its parts alike on the two sides of a line passing from the -centre of the assemblage to the circumference. Certain other members of -this order fulfil the law somewhat differently. In <i>Centaurea</i>, -for instance, the inner florets are small and vertical in direction, -while the outer florets are large and lateral in direction. And here -may be remarked, in passing, a clear indication of the effect which -great flexibility of the petals has in preventing a flower from losing -its original radiate form; for while in <i>C. cyanus</i>, the large -outward-growing florets, having short, stiff divisions of the corolla, -are decidedly bilateral, in <i>C. scabiosa</i>, where the divisions of -the<span class="pagenum" id="Page_174">[174]</span> corolla are long and flexible, the radial form is scarcely at all -modified. On bearing in mind the probable relations of the forms to -insect-agency, the meaning of this difference will not be difficult to -understand.<a id="FNanchor_38" href="#Footnote_38" class="fnanchor">[38]</a></p> - - -<p class="p2">§ 236. In extremely-varied ways there are thus re-illustrated among -flowers, the general laws of form which leaves and branches and -entire plants disclose to us. Composed as each cluster of flowers -is of individuals that are originally similar; and composed as each -flower is of homologous foliar organs; we see both that the like -flowers become unlike and the like parts of each flower become unlike, -where the positions involve unlike incidence of forces. The symmetry -remains radial where the conditions are equal all round; shows -deviation towards two-sidedness where there is slight two-sidedness -of conditions; becomes decidedly bilateral where the conditions are -decidedly bilateral; and passes into an unsymmetrical form where the -relations to the environment are unsymmetrical.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_175">[175]</span></p> - -<h3>CHAPTER XI.<br /> -<span class="subhed1">THE SHAPES OF VEGETAL CELLS.</span></h3></div> - - -<p>§ 237. We come now to aggregates of the lowest order. Already something -has been said (<a href="#sect217">§ 217</a>) concerning the forms of those morphological units -which exist as independent plants. But it is here requisite briefly to -note the modifications undergone by them where they become components -of larger plants.</p> - - <div class="figcenter" id="i_175"> - <img - class="p2" - src="images/i_175.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 254.</p> - </div> - -<p class="p2">Of the numerous cell-forms which are found in the tissues of the higher -plants, it will suffice to give, in Fig. <a href="#i_175">254</a>, representing a section -of a leaf, a single example. In this it will be seen that the cells -forming the upper and lower surfaces, <i>a</i> and <i>b</i>, have -differences of shape related to differences in the incidence of forces: -they are more or less flattened in relation to the environment. The -underneath cells at <i>c</i>, form a class which, similarly exposed to -light at their outer ends, and, as we may assume, largely developed -in adjustment to their active assimilative functions, are, by mutual -pressure, made to grow more in the direction of their lengths than in -the direction of their breadths. Then on the other side we see that -the cells <i>d</i>, next above the outer layer, while approximately -similar, become more and more dissimilar as they diverge from the -surface, and are quite<span class="pagenum" id="Page_176">[176]</span> irregular in the interior <i>e</i>, where there -is no definiteness in the conditions to which they are exposed. Thus -the divergences of these cells from primordial sphericity are such as -correspond with unlikenesses in their circumstances. And throughout the -more complex modifications which the cells of other tissues exhibit, -the like correspondences hold.</p> - - <div class="figcenter" id="i_176a"> - <img - class="p2" - src="images/i_176a.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 32–35.</p> - </div> - -<p class="p2">Among plants of a lower order of aggregation, we have already seen how -cells become metamorphosed as they become integrated into masses having -definite organizations. The higher <i>Algæ</i>, exemplified in Figs. -<a href="#i_176a">32, 34, 35</a>, show this very clearly. Here the departure from the simple -cell-form to the form of an elongated prism, is manifestly subordinated -to the contrasts in the relations of the parts. And it is interesting -to observe how, in one of the branches of Fig. <a href="#i_176a">32</a>, we pass from the -small, almost-spherical cells which terminate the branchlets, to the -large, much-modified cells which join the main stem, through gradations -obviously related in their changed forms to the altered actions their -positions expose them to.</p> - - <div class="figcenter" id="i_176b"> - <img - class="p2" - src="images/i_176b.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 19–23.</p> - </div> - -<p class="p2">More simply, but quite as conclusively, do the inferior <i>Algæ</i>, -of which Figs. <a href="#i_176b">19–23</a> are examples, show us how cells pass from their -original spherical symmetry into radial symmetry, as they pass from a -state in which they are similarly-conditioned<span class="pagenum" id="Page_177">[177]</span> on all sides, to a state -in which two of their opposite sides or ends are conditioned in ways -that are like one another, but unlike the ways in which all other sides -are conditioned.</p> - -<p>Still more instructive are the morphological differentiations of -those protophytes in which the first steps towards a higher degree of -integration are shown. In Fig. <a href="#i_177">10</a>, representing one of the transitional -forms of <i>Desmidiaceæ</i>, it is to be noted that besides the -difference between the transverse and longitudinal dimensions, which -the component units display in common, the two end-units differ from -the rest: they have appendages which the rest have not. Once more, -where the integration is carried on in such ways as to produce not -strings but clusters, there arise contrasts and correspondences just -such as might be looked for. All the four members of the group shown in -Fig. <a href="#i_177">12</a>, are similarly conditioned; and each of them has a bilateral -shape answering to its bilateral relations. In Fig. <a href="#i_177">14</a> we have a number -of similarly-bilateral individuals on the circumference, including a -central individual differing from the rest by having the bilateral -character nearly obliterated. And then, in Fig. <a href="#i_177">15</a>, we have two central -components of the group, deviating more decidedly from those that -surround them.<a id="FNanchor_39" href="#Footnote_39" class="fnanchor">[39]</a></p> - - <div class="figcenter" id="i_177"> - <img - class="p2" - src="images/i_177.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 7–17.</p> - </div> - - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_178">[178]</span></p> - -<h3>CHAPTER XII.<br /> -<span class="subhed1">CHANGES OF SHAPE OTHERWISE CAUSED.</span></h3></div> - - -<p>§ 238. Besides the more special causes of modification in the shapes of -plants and of their parts, certain more general causes must be briefly -noticed. These may be described as consequences of variations in the -total quantities of the matters and forces furnished to plants by their -environments. Some of the changes of form so produced are displayed by -plants as wholes, and others only by their parts. We will glance at -them in this order.</p> - - -<p class="p2">§ 239. It is a familiar fact that luxuriant shoots have relatively-long -internodes; and, conversely, that a shoot dwarfed from lack of sap, -has its nodes closely clustered: a concomitant result being that the -lateral axes, where these are developed, become in the one case far -apart and in the other case near together. Fig. <a href="#i_178">255</a> represents a branch -to the parts of which the longer and shorter internodes so resulting -give differential characters. A whole tree being in many cases -simultaneously thus affected by states of the earth or the air, all -parts of it may have such variations impressed on them; and, indeed, -such variations, following more or less regularly the changes of the -seasons, give to many trees manifest<span class="pagenum" id="Page_179">[179]</span> traits of structure. In Fig. <a href="#i_178">256</a>, -a shoot of <i>Phyllocactus crenatus</i>, we have an interesting example -of a variation essentially of the same nature, little as it appears -to be so. For each of the lateral indentations is here the seat of -an axillary bud; and these we see are separated by internodes which, -becoming broader as they become longer, and narrower as they become -shorter, produce changes of form that correspond with changes in the -luxuriance of growth.</p> - - <div class="figcenter" id="i_178"> - <img - class="p2" - src="images/i_178.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 255, 256.</p> - </div> - -<p class="p2">To complete the statement it must be added that these variations of -nutrition often determine the development or non-development of lateral -axes; and by so doing cause still more marked structural differences. -The Foxglove may be named as a plant which illustrates this truth.<a id="FNanchor_40" href="#Footnote_40" class="fnanchor">[40]</a></p> - - -<p class="p2">§ 240. From the morphological differentiations caused by unlikenesses -of nutrition felt by the whole plant, we pass now to those which are -thus caused in some of its parts and not in others. Among such are -the contrasts between flowering axes, and the axes that bear leaves -only. It has already been shown in <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect78">§ 78</a>, that the belief expressed by -Wolff in a direct connexion between fructification and innutrition, -is justified inductively by many facts of many kinds. Deductively -too, in <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect79">§ 79</a>, we saw reason to conclude that such a relation would be -established by survival of the fittest; seeing that it would profit -a species for its members to begin sending off migrating germs from -the ends of those axes which innutrition prevented from further -agamogenetic multiplication. Once more, when considering the nature of -the phænogamic axis, we found support for this belief in the fact<span class="pagenum" id="Page_180">[180]</span> that -the components of a flower exhibit a reversion to that type from which -the phænogamic type has probably arisen—a reversion which the laws of -embryology would lead us to look for where innutrition had arrested -development.</p> - -<p>Hence, then, we may properly count those deviations of structure -which constitute inflorescence, as among the morphological -differentiations produced by local innutrition. I do not mean that the -detailed modifications which the essential and subservient organs of -fructification display, are thus accounted for: we have seen reason -to think them otherwise caused. But I mean that the morphological -characters which distinguish gamogenetic axes in general from -agamogenetic axes, such as non-development of the internodes and -dwarfing of the foliar organs, are primarily results of failure in the -supply of some material required for further growth.<a id="FNanchor_41" href="#Footnote_41" class="fnanchor">[41]</a></p> - - -<p class="p2">§ 241. Another trait which has to be noticed under this head, is the -spiral, or rather the helical, arrangement of parts. The successive -nodes of a phænogam habitually bear their appendages in ways implying -more or less twist in the substance of the axis; and in climbing plants -the twist is such<span class="pagenum" id="Page_181">[181]</span> as to produce a corkscrew shape. This structure is -ascribable to differences of interstitial nutrition. Take a shoot which -is growing vertically. It is clear that if the molecules are added -with perfect equality on all sides, there will be no tendency towards -any kind of lateral deviation; and the successively-produced parts -will be perpendicularly over one another. But any inequality in the -rate of growth on the different sides of the shoot, will destroy this -straightness in the lines of growth. If the greatest and least rates -of molecular increase happen to be on opposite sides, the shoot must -assume a curve of single curvature; but in every other case of unequal -molecular increase, a curve of double curvature must result. Now it is -a corollary from the instability of the homogeneous, that the rates of -growth on all sides of a shoot can never be exactly alike; and it is -also to be inferred from the same general law, that the greatest and -least rates of growth will not occur on exactly opposite sides of the -shoot, at the same time that equal rates of growth are preserved by the -two other sides. Hence, there must almost inevitably arise more or less -of twist; and the appendages of the internodes will so be prevented -from occurring perpendicularly one over another.</p> - -<p>A deviation of this kind, necessarily initiated by physical causes -in conformity with the general laws of evolution, is likely to be -made regular and decided by natural selection. For under ordinary -circumstances, a plant profits by having its axis so twisted as to -bring the appended leaves into positions which prevent them from -shading one another. And, manifestly, modifications in the forms, -sizes, and insertions of the leaves, may, under the same agency, lead -to adapted modifications of the twist. We must therefore ascribe this -common characteristic of phænogams, primarily to local differences of -nutrition, and secondarily to survival of the fittest.</p> - -<p><span class="pagenum" id="Page_182">[182]</span></p> - -<p>It is proper to add that there are some Monocotyledons, as <i>Ravenala -madagascariensis</i>, in which this character does not occur. What -conditions of existence they are that here hold this natural tendency -in check, it is not easy to see.<a id="FNanchor_42" href="#Footnote_42" class="fnanchor">[42]</a></p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_183">[183]</span></p> - -<h3>CHAPTER XIII.<br /> -<span class="subhed1">MORPHOLOGICAL DIFFERENTIATION IN ANIMALS.</span></h3></div> - - -<p>§ 242. The general considerations which preluded our inquiry into the -shapes of plants and their parts, equally serve, so far as they go, to -prelude an inquiry into the shapes of animals and their parts. Among -animals, as among plants, the formation of aggregates greater in bulk -or higher in degree of composition, or both, is accompanied by changes -of form in the aggregates as wholes as well as by changes of form in -their parts; and the processes of morphological differentiation conform -to the same general laws in the one kingdom as in the other.</p> - -<p>It is needless to recapitulate the several kinds of modification to be -explained, and the several factors that co-operate in working them. -In so far as these are common to plants and animals, the preceding -chapters have sufficiently familiarized them. Nor is it needful to -specify afresh the several types of symmetry and their descriptive -names; for what is true of them in the one case is true of them in the -other. There is, however, one new and all-important factor which we -shall have now to take into account; and about this a few preliminary -remarks are requisite.</p> - - -<p class="p2">§ 243. This new factor is motion—motion of the organism in relation -to surrounding objects, or of the parts of the<span class="pagenum" id="Page_184">[184]</span> organism in relation -to one another, or both. Though there are plants, especially of the -simpler kinds, which move, and though a few of the simpler animals do -not move; yet movements are so exceptional and unobtrusive in the one -kingdom, while they are so general and conspicuous in the other, that -the broad distinction commonly made is well warranted. What, among -plants, is an inappreciable cause of morphological differentiation, -becomes, among animals, the chief cause of morphological -differentiation.</p> - -<p>Rooted animals or animals otherwise fixed, of course present traits -of structure nearest akin to those we have lately been studying. The -motions of parts in relation to one another and to the environment, -being governed by the mode of aggregation and mode of fixing, we are -presented with morphological differentiations similar in their general -characters to those of plants, and showing us parallel kinds of -symmetry under parallel conditions. But animals which move from place -to place are subject to an additional class of actions and reactions. -These actions and reactions affect them in various ways according to -their various modes of movement. Let us glance at the several leading -relations between shape and motion which we may expect to find.</p> - -<p>If an organism advances through a homogeneous medium with one end -always foremost, that end, being exposed to forces unlike those to -which the other end is exposed, may be expected to become unlike it; -and supposing this to be the only constant contrast of conditions, -we may expect an equal distribution of the parts round the axis -of movement—a radial symmetry. If, in addition to this habitual -attitude of the ends, one surface of the body is always uppermost -and another always lowermost, there arise between the top and bottom -dissimilarities of conditions, while the two sides remain similarly -conditioned. Hence it is inferable that such an organism will be -divisible into similar halves by a vertical plane passing through -its axis of motion—will have a bilateral symmetry. We may presume -that this<span class="pagenum" id="Page_185">[185]</span> symmetry will deviate but little from double bilateralness -where the upper and under parts are not exposed to strongly-contrasted -influences; while we may rationally look for single bilateral symmetry -of a decided kind, in creatures having dorsal and ventral parts -conversant with very unlike regions of the environment: as in all cases -where the movement is over a solid surface. If the movement, though -over a solid surface, is not constant in direction, but takes place as -often on one side as on another, radial symmetry may be again looked -for; and if the motions are still more variously directed—if they are -not limited to approximately-plane surfaces, but extend to surfaces -that are distributed all around with a regular irregularity—an -approach of the radial towards the spherical symmetry is to be -anticipated. Where the habits are such that the intercourse between the -organism and its environment, does not involve an average equality of -actions and reactions on any two or more sides, there may be expected -either total irregularity or some divergence from regularity.</p> - -<p>The like general relations between forms and incident forces are -inferable in the component parts of animals, as well as in the animals -as wholes. It is needless, however, to occupy space by descriptions of -these. Let us now pass to the facts, and see how they confirm, <i>à -posteriori</i>, the conclusions here reached <i>à priori</i>.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_186">[186]</span></p> - -<h3>CHAPTER XIV.<br /> -<span class="subhed1">THE GENERAL SHAPES OF ANIMALS.</span></h3></div> - - -<p>§ 244. Certain of the <i>Protozoa</i> are quite indefinite in their -shapes, and quite inconstant in those indefinite shapes which they -have—the relations of their parts are indeterminate both in space and -time. In one of the simpler Rhizopods, at least during the active stage -of its existence, no permanent distinction of inside and outside is -established; and hence there can arise no established correspondence -between the shape of the outside and the distribution of environing -actions. But when the relation of inner and outer becomes fixed, -either over part of the mass or over the whole of it, we have kinds -of symmetry that correspond with the habitual incidence of forces. -An <i>Amœba</i> in becoming encysted, passes from an indefinite, -ever-changing form into a spherical form; and the order of symmetry -which it thus assumes, is in harmony with the average equality of the -actions on all its sides. In <i>Difflugia</i>, Fig. <a href="#i_187">134</a>, and still -better in <i>Arcella</i>, we have an indefinitely-radial symmetry -occurring where the conditions are different above and below but alike -all around. Among the <i>Gregarinida</i> the spherical symmetry and -symmetry passing from that into the radial, are such as appear to be -congruous with the simple circumstances of these creatures in the -intestines of insects. But the relations of these lowest types to their -environments are comparatively so indeterminate, and our knowledge of -their actions so<span class="pagenum" id="Page_187">[187]</span> scanty, that little beyond negative evidence can be -expected from the study of them.</p> - - <div class="figcenter" id="i_187"> - <img - class="p2" - src="images/i_187.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 131–139.</p> - </div> - -<p class="p2">The like may be said of the <i>Infusoria</i>. These are more or -less irregular. In some cases, where the line of movement through -the water is tolerably definite and constant, we have a form that -is approximately radial—externally at least. But usually, as shown -in Figs. <a href="#i_187">137, 138, 139</a>, there is either an unsymmetrical or an -asymmetrical shape. And when one of these creatures is watched under -the microscope, the congruity of this shape with the incidence of -forces is manifest. For the movements are conspicuously varied and -indeterminate—movements which do not expose any two or more sides of -the mass to approximately equal sets of actions.<a id="FNanchor_43" href="#Footnote_43" class="fnanchor">[43]</a></p> - - -<p class="p2">§ 245. Among aggregates of the second order, as among aggregates -of the first order, we find that of those possessing any definite -shapes the lowest are spherical or spheroidal. Such are some of the -<i>Radiolaria</i>, as <i>Collozoum inerme</i>. These bodies which float -passively in the sea, and present in turn all their sides to the same -influences, have their parts disposed with approximate regularity round -a centre—approximate, because in the absence of locomotion a slight -irregularity of growth, almost certain to take place, may cause a -fixed attitude and a resulting deviation from spherical symmetry. The -best cases in illustration of the truth here named, are furnished by -rotating and locomotive organisms respecting which there is a dispute -whether they are animal or vegetal—the <i>Volvocineæ</i>. These, -already instanced under<span class="pagenum" id="Page_188">[188]</span> the one head in <a href="#sect218">§ 218</a>, may here be instanced -afresh under the other. Further, among these secondary aggregates -in which the units, only physically integrated, have not had their -individualities merged into an individuality of a higher order, must be -named the compound <i>Infusoria</i>. The cluster of <i>Vorticellæ</i> -in Fig. <a href="#i_088">144</a>, will sufficiently exemplify them; and the striking -resemblance borne by its individuals to those of a radially-arranged -cluster of flowers, will show how, under analogous conditions, the -general principles of morphological differentiation are similarly -illustrated in the two kingdoms.</p> - - -<p class="p2">§ 246. Radial symmetry is usual in low aggregates of the second order -which have their parts sufficiently differentiated and integrated -to give individualities to them as wholes. The <i>Cœlenterata</i> -offer numerous examples of this. Solitary polypes—hydroid or -helianthoid—mostly stationary, and when they move, moving with any -side foremost, do not by locomotion subject their bodies to habitual -contrasts of conditions. Seated with their mouths upwards or downwards, -or else at all degrees of inclination, the individuals of a species -taken together, are subject to no mechanical actions affecting some -parts of their discs more than other parts. And this indeterminateness -of attitude similarly prevents their relations to prey from being such -as subject some of their prehensile organs to forces unlike those to -which the rest are subject. The fixed end is differently conditioned -from the free end, and the two are therefore different; but around the -axis running from the fixed to the free end the conditions are alike -in all directions, and the form therefore is radial. Again, among many -of the simple free-swimming <i>Hydrozoa</i>, the same general truth -is exemplified under other circumstances. In a common <i>Medusa</i>, -advancing through the water by the rhythmical contractions of its -disc, the mechanical reactions are the same on all sides; and as, from -accidental causes, every part of the edge of the disc<span class="pagenum" id="Page_189">[189]</span> comes uppermost -in its turn, no part is permanently affected in a different way from -the rest. Hence the radial form continues.</p> - - <div class="figcenter" id="i_189"> - <img - class="p2" - src="images/i_189.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 257, 258.</p> - </div> - -<p class="p2">In others of this same group, however, there occur forms which show -us an incipient bilateralness; and help us to see how a more decided -bilateralness may arise. Sundry of the <i>Medusidæ</i> are proliferous, -giving origin to gemmæ from the body of the central polypite or from -certain points on the edge of the disc; and this budding, unless it -occurs equally on all sides, which it does not and is unlikely to -do, must tend to destroy the balance of the disc, and to make its -attitude less changeable. In other cases the growth of a large process -[a much-developed tentacle] from the edge of the disc on one side, as -in <i>Steenstrupia</i>, Fig. <a href="#i_189">257</a>, constitutes a similar modification, -and a cause of further modification. The animal is no longer divisible -into any two quite similar halves, except those formed by a plane -passing through the process; and unless the process is of the same -specific gravity as the disc, it must tend towards either the lowest -or the highest point, and must so serve to increase the bilateralness, -by keeping the two sides of the disc similarly conditioned while -the top and bottom are differently conditioned. Fig. <a href="#i_189">258</a> represents -the underside of another <i>Medusa</i>, in which a more decided -bilateralness is produced by the presence of two such processes. Among -the simple free-swimming <i>Actinozoa</i>, occur like deviations -from radial symmetry, along with like motions through the water in -bilateral attitudes. Of this a <i>Cydippe</i> is a familiar example. -Though radial in some of its characters, as in the distribution of -its meridional bands of locomotive paddles with their accompanying -canals, this creature has a two-sided distribution of tentacles<span class="pagenum" id="Page_190">[190]</span> and -various other parts, corresponding with its two-sided attitude in -moving through the water. And in other genera of this group, as in -<i>Cestum</i>, <i>Eurhamphæa</i>, and <i>Callianira</i>, that almost -equal distribution of parts which characterizes the <i>Beroe</i> is -quite lost.</p> - -<p>Here seems a fit place to meet the objection which some may feel to -this and other such illustrations, that they amount very much to -physical truisms. If the parts of a <i>Medusa</i> are disposed in -radial symmetry round the axis of motion through the water, there will -of course be no means of maintaining one part of its edge uppermost -more than another; and the equality of conditions may be ascribed -to the radiateness, as much as the radiateness to the equality of -conditions. Conversely, when the parts are not radially arranged -around the axis of motion, they must gravitate towards some one -attitude, implying a balance on the two sides of a vertical plane—a -bilateralness; and the two-sided conditions so necessitated, may be -as much ascribed to the bilateralness as the bilateralness to the -two-sided conditions. Doubtless the form and the conditions are, in -the way alleged, necessary correlates; and in so far as it asserts -this, the objection harmonizes with the argument. To the difficulty -which it at the same time raises by the implied question—Why make -the form the result of the conditions, rather than the conditions -the result of the form? the reply is this:—The radial type, both as -being the least differentiated type and as being the most obviously -related to lower types, must be taken as antecedent to the bilateral -type. The individual variations which incidental circumstances produce -in the radial type, will not cause divergence of a species from the -radial type, unless such variations give advantages to the individuals -displaying them; which there is no reason to suppose they will always -do. Those occasional deviations from the radial type, which the law of -the instability of the homogeneous warrants us in expecting to take -place, will, however, in some cases be beneficial; and will then be -likely to establish<span class="pagenum" id="Page_191">[191]</span> themselves. Such deviations must tend to destroy -the original indefiniteness and variability of attitude—must cause -gravitation towards an habitual attitude. And gravitation towards an -habitual attitude having once commenced, will continually increase, -where increase of it is not negatived by adverse agencies: each further -degree of bilateralness rendering more decided the actions that conduce -to bilateralness. If this reply be thought insufficient, it may be -enforced by the further one, that as, among plants, the incident forces -are the antecedents and the forms the consequents (changes of forces -being in many cases visibly followed by changes of forms) we are -warranted in concluding that the like order of cause and effect holds -among animals.<a id="FNanchor_44" href="#Footnote_44" class="fnanchor">[44]</a></p> - - -<p class="p2">§ 247. Keeping to the same type but passing to a higher degree of -composition, we meet more complex and varied illustrations of the same -general laws. In the compound<span class="pagenum" id="Page_192">[192]</span> <i>Cœlenterata</i>, presenting clusters -of individuals which are severally homologous with the solitary -individuals last dealt with, we have to note both the shapes of the -individuals thus united, and the shapes of the aggregates made up of -them.</p> - - <div class="figcenter" id="i_192"> - <img - class="p2" - src="images/i_192.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 149, 150.</p> - </div> - -<p class="p2">Such of the fixed <i>Hydrozoa</i> and <i>Actinozoa</i> as form branched -societies, continue radial; both because their varied attitudes do not -expose them to appreciable differences in their relations to those -surrounding actions which chiefly concern them (the actions of prey), -and because such differences, even if they were appreciable, would -be so averaged in their effects on the dissimilarly-placed members -of each group as to be neutralized in the race. Among the tree-like -coral-polypedoms, as well as in such ramified assemblages of simpler -polypes as are shown in Figs. <a href="#i_192">149, 150</a>, we have, indeed, cases in many -respects parallel to the cases of scattered flowers (<a href="#sect233">§ 233</a>), which -though placed laterally remain radial, because no differentiating -agency can act uniformly on all of them. Meanwhile, in the groups which -these united individuals compose, we see the shapes of plants further -simulated under a further parallelism of conditions. The attached ends -differ from the free ends as they do in plants; and the regular or -irregular branches obviously stand to environing actions in relations -analogous to those in which the branches of plants stand.</p> - -<p>The members of those compound <i>Cœlenterata</i> which move -through the water by their own actions, in attitudes that are -approximately constant, show us a more or less distinct two-sidedness. -<i>Diphyes</i>, Fig. <a href="#i_193a">259</a>, furnishes an example. Each of the -largely-developed and modified polypites forming its swimming sacs is -bilateral, in correspondence with the bilateralness of its conditions; -and in each of the appended polypites the insertion of the solitary -tentacle produces a kindred divergence from the primitive radial type. -The aggregate, too, which here very much subordinates its members,<span class="pagenum" id="Page_193">[193]</span> -exhibits the same conformity of structure to circumstances. It admits -of symmetrical bisection by a plane passing through its two contractile -sacs, or nectocalyces, but not by any other plane; and the plane which -thus symmetrically bisects it, is the vertical plane on the two sides -of which its parts are similarly conditioned as it propels itself -through the water.</p> - - <div class="figcenter" id="i_193a"> - <img - class="p2" - src="images/i_193a.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 259.</p> - </div> - -<p class="p2">Another group of the oceanic <i>Hydrozoa</i>, the <i>Physophoridæ</i>, -furnishes interesting evidence—not so much in respect of the forms of -the united individuals, which we may pass over, as in respect of the -forms of the aggregates. Some of these are without swimming organs, -and have their parts suspended from air-vessels which habitually float -on the surface of the water. Hence the distribution of their parts is -asymmetrical. The <i>Physalia</i>, Fig. <a href="#i_193b">152</a>, is an example. Here the -relations of the integrated group of individuals to the environment -are indefinite; and there is thus no agency tending to change that -comparatively irregular mode of growth which is probably derived from a -primordial type of the branched <i>Hydrozoa</i>.</p> - - <div class="figcenter" id="i_193b"> - <img - class="p2" - src="images/i_193b.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 152.</p> - </div> - -<p class="p2">So various are the modes of union among the compound -<i>Cœlenterata</i>, that it is out of the question to deal with them -all. Even did space permit, it would be impracticable for any one but -a professed naturalist, to trace throughout<span class="pagenum" id="Page_194">[194]</span> this group the relations -between shapes and conditions of existence. The above must be taken -simply as a few of the most significant and easily-interpretable cases.</p> - - -<p class="p2">§ 248. In the sub-kingdoms <i>Polyzoa</i> and <i>Tunicata</i> we -meet with examples not wholly unlike the foregoing. Among the types -assembled under these names there are simple individuals or aggregates -of the second order, and societies or tertiary aggregates produced by -their union. The relations of forms to forces have to be traced in both.</p> - -<p>Solitary Ascidians, fixed or floating, carry on an inactive and -indefinite converse with the actions in the environment. Without -power to move about vivaciously, and unable to catch any prey but -that contained in the currents of water they absorb and expel, these -creatures are not exposed to sets of forces which are equal on two -or more sides; and their shapes consequently remain vague. Though -internally their parts have a partially-symmetrical arrangement, due -to their derivation, yet they are substantially unsymmetrical in that -part of the body which is concerned with the environment. Fig. <a href="#i_094">156</a> is -an example.<a id="FNanchor_45" href="#Footnote_45" class="fnanchor">[45]</a> Among the composite Ascidians, floating and fixed, -the shape of the aggregate, partly determined by the habitual mode of -gemmation and partly by the surrounding conditions in each case, is in -great measure indefinite. We can say no more about it than that it is -not obviously at variance with the laws alleged.</p> - -<p>Evidence of a more positive kind occurs among those compound -<i>Molluscoida</i> which are most like the compound <i>Cœlenterata</i> -in their modes of union—the <i>Polyzoa</i>. Many of these form -groups that are more or less irregular—spreading as films over -solid surfaces, combining into seaweed-like fronds, budding out from -creeping stolons, or growing up into tree-shaped societies; and besides -aggregating<span class="pagenum" id="Page_195">[195]</span> irregularly they are irregularly placed on surfaces -inclined in all directions. Merely noting that this asymmetrical -distribution of the united individuals is explained by the absence of -definiteness in the relations of the aggregate to incident forces, it -concerns us chiefly to observe that the united individuals severally -exemplify the same truth as do similarly-united individuals among -the <i>Cœlenterata</i>. Averaging the members of each society, the -ciliated tentacles they protrude are similarly related to prey on all -sides; and therefore remain the same on all sides. This distribution -of tentacles is not, however, without exception. Among the fresh-water -<i>Polyzoa</i> there are some genera, as <i>Plumatella</i> and -<i>Crystatella</i>, in which the arrangement of these parts is very -decidedly bilateral. Some species of them show us such relations of the -individuals to one another and to their surface of attachment, as give -a clue to the modification; but in other species the meaning of this -deviation from the radial type is not obvious.</p> - - -<p class="p2">§ 249. In the <i>Platyhelminthes</i> good examples of the connexions -between forms and forces occur. The <i>Planaria</i> exemplifies -the single bilateral symmetry which, even in very inferior forms, -accompanies the habit of moving in one direction over a solid -surface. Humbly organized as are these creatures and their allies the -<i>Nemertidæ</i>, we see in them, just as clearly as in the highest -animals, that where the movements subject the body to different forces -at its two ends, different forces on its under and upper surfaces, and -like forces along its two sides, there arises a corresponding form, -unlike at its extremities, unlike above and below, but having its two -sides alike.</p> - -<p>The <i>Echinodermata</i> furnish us with instructive -illustrations—instructive because among types that are nearly allied, -we meet with wide deviations of form answering to marked contrasts in -the relations to the environment. The facts fall into four groups. The -<i>Crinoidea</i>, once so abundant<span class="pagenum" id="Page_196">[196]</span> and now so rare, present a radial -symmetry answering to an incidence of forces that are equal on all -sides. In the general attitudes of their parts towards surrounding -actions, they are like uniaxial plants or like polypes; and show, as -those do, marked differences between the attached ends and the free -ends, along with even distributions of parts all round their axes. In -the <i>Ophiuridea</i>, and in the Star-fishes, we have radial symmetry -co-existing with very different habits; but habits which nevertheless -account for the maintenance of the form. Holding on to rocks and weeds -by its simple or branched arms, or by the suckers borne on the under -surface of its rays, one of these creatures moves about not always with -one side foremost, but with any side foremost. Consequently, averaging -its movements, its arms or rays are equally affected, and therefore -remain the same on all sides. On watching the ways of the common -Sea-urchin, we are similarly furnished with an explanation of its -spherical, or rather its spheroidal, figure. Here the habit is not to -move over any one approximately-flat surface; but the habit is to hold -on by several surfaces on different sides at the same time. Frequenting -crevices and the interstices among stones and weeds, the Sea-urchin -protrudes the suckers arranged in meridional bands over its shell, -laying hold of objects now on this side and now on that, now above and -now below: the result being that it does not move in all directions -over one plane but in all directions through space. Hence the approach -in general form towards spherical symmetry—an approach which is, -however, restrained by the relations of the parts to the mouth and -vent: the conditions not being exactly the same at the two poles as at -other parts of the surface. Still more significant is that deviation -from this shape which occurs among such of the <i>Echinidea</i> as -have habitats of a different kind, and consequently, different habits. -The genera <i>Echinocyamus</i>, <i>Spatangus</i>, <i>Brissus</i>, and -<i>Amphidotus</i>, diverge markedly towards a bilateral structure. -These creatures are found not on rocky<span class="pagenum" id="Page_197">[197]</span> shores but on flat sea-bottoms, -and some of them only on bottoms of sand or mud. Here, there is none of -that distribution of surfaces on all sides which makes the spheroidal -form congruous with the conditions. Having to move about over an -approximately-horizontal plane, any deviation of structure arising -accidentally which leads to one side being kept always foremost, will -be an advantage: greater fitness to function becoming possible in -proportion as function becomes fixed. Survival of the fittest will -therefore tend to establish, under such conditions, a form that keeps -the same part in advance—a form in which, consequently, the original -radial symmetry diverges more and more towards bilateral symmetry.</p> - - -<p class="p2">§ 250. Very definite and comparatively uniform, are the relations -between shapes and circumstances among the <i>Annulosa</i>: including -under that title the <i>Annelida</i> and the <i>Arthropoda</i>. The -agreements and the disagreements are equally instructive.</p> - -<p>At one time or other of its life, if not throughout its life, every -annulose animal is locomotive; and its temporary or permanent -locomotion, being carried on with one end habitually foremost and -one surface habitually uppermost, it fulfils those conditions under -which bilateral symmetry arises. Accordingly, bilateral symmetry -is traceable throughout the whole of this sub-kingdom. Traceable, -we must say, because, though it is extremely conspicuous in the -immense majority of annulose types, it is to a considerable extent -obscured where obscuration is to be expected. The embryos of the -<i>Tubicolæ</i>, after swimming about a while, settle down and build -themselves tubes, from which they protrude their heads; and in them, -or in some of them, the bilateral symmetry is disguised by the -development of head-appendages in an all-sided manner. The tentacles -of <i>Terebella</i> are distributed much in the same way as those of -a polype. The breathing organs in <i>Sabella unispira</i>, Fig. <a href="#i_198">260</a>, -do not correspond<span class="pagenum" id="Page_198">[198]</span> on opposite sides of a median plane. Even here, -however, the body retains its primitive bilateralness; and it is -further to be remarked that this loss of bilateralness in the external -appendages, does not occur where the relations to external conditions -continue bilateral: witness the <i>Serpula</i>, Fig. <a href="#i_198">261</a>, which has -its respiratory tufts arranged in a two-sided way, under the two-sided -conditions involved by the habitual position of its tube.</p> - - <div class="figcenter" id="i_198"> - <img - class="p2" - src="images/i_198.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 260–261.</p> - </div> - -<p class="p2">The community of symmetry among the higher <i>Annulosa</i>, has an -unobserved significance. That Flies, Beetles, Lobsters, Centipedes, -Spiders, Mites, have in common the characters, that the end which moves -in advance differs from the hinder end, that the upper surface differs -from the under surface, and that the two sides are alike, is a truth -received as a matter of course. After all that has been said above, -however, it will be seen to have a meaning not to be overlooked; since -it supplies a million-fold illustration of the laws which have been set -forth. It is needless to give diagrams. Every reader can call to mind -the unity indicated.</p> - - <div class="figcenter" id="i_199"> - <img - class="p2" - src="images/i_199.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 263–270.</p> - </div> - -<p class="p2">While, however, annulose animals repeat so uniformly these traits of -structure, there are certain other traits in which they are variously -contrasted; and their contrasts have to be here noted, as serving -further to build up the general argument. In them we see the stages -through which<span class="pagenum" id="Page_199">[199]</span> bilateral symmetry becomes gradually more marked, as -the conditions it responds to become more decided. A common Earth-worm -may be instanced as a member of this sub-kingdom that is among the -least-conspicuously bilateral. Though internally its parts have a -two-sided arrangement; and though the positions of its orifices give -it an external two-sidedness, at the same time that they establish -a difference between the two ends; yet its two-sidedness is not -strongly-marked. The form deviates but little from what we have -distinguished as triple bilateral symmetry: if the creature is cut -across the middle, the head and tail ends are very much alike; if -cut in two along its axis by a horizontal plane, the under and upper -halves are very much alike, externally if not internally; and if cut -in two along its axis by a vertical plane, the two sides are quite -alike. Figs. <a href="#i_199">263 and 264</a> will make this clear. Such creatures as the -<i>Julus</i> and the Centipede, may be taken as showing a transition -to double bilateral symmetry. Besides being divisible into exactly -similar halves by a vertical plane passing through its axis, one of -these animals may be bisected transversely into parts that differ only -slightly; but if cut in two by a horizontal plane passing through its -axis, the under and upper halves are decidedly unlike. Figs. <a href="#i_199">265, 266</a>, -exhibit these traits. Among the isopodous crustaceans, the departure -from these low types of symmetry is more<span class="pagenum" id="Page_200">[200]</span> marked. As shown in Figs.<a href="#i_199"> 267</a> -and 268, the contrast between the upper and under parts is greater, -and the head and tail ends differ more obviously. In all the higher -<i>Arthropoda</i>, the unlikeness between the front half and the hind -half has become conspicuous. There is in them single bilateral symmetry -of so pronounced a kind, that no other resemblance is suggested than -that between the two sides. By Figs. <a href="#i_199">269 and 270</a>, representing a -decapodous crustacean divided longitudinally and transversely, this -truth is made manifest. On calling to mind the habits of the creatures -here drawn and described, it will be seen that they explain these -forms. The incidence of forces is the same all around the Earth-worm -as it burrows through the compact ground. The Centipede, creeping -amid loose soil or <i>débris</i> or beneath stones, insinuates itself -between solid surfaces—the interstices being mostly greater in one -dimension than in others. And all the higher <i>Annulosa</i>, moving -about as they do over exposed objects, have their dorsal and ventral -parts as dissimilarly acted upon as are their two ends.</p> - - <div class="figcenter" id="i_200"> - <img - class="p2" - src="images/i_200.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 271.</p> - </div> - -<p class="p2">One other fact only respecting annulose animals needs to be noticed -under this head—the fact, namely, that they become unsymmetrical -where their parts are unsymmetrically related to the environment. -The common Hermit-crab serves as an instance. Here, in addition -to the unlikeness of the two sides implied by that curvature of -the body which fits the creature to the shell it inhabits, there -is an unlikeness due to the greater development of the limbs, and -especially the claws, on the outer side. As in the embryo of the -Hermit-crab the two sides are alike; and as both the embryo and the -ancestor lived in such a way, being free, that the conditions were -alike on the two sides; and as the embryo may be taken to represent -the type from which the Hermit-crab has been derived; we have in -this case evidence that a symmetrically-bilateral form has been -moulded into an unsymmetrically-bilateral<span class="pagenum" id="Page_201">[201]</span> form, by the action of -unsymmetrically-bilateral conditions. A further illustration is -supplied by <i>Bopyrus</i>, Fig. <a href="#i_200">271</a>: a parasite which lives in the -branchial chamber of prawns, and whose habits similarly account for its -distorted shape.</p> - - -<p class="p2">§ 251. Among the <i>Mollusca</i> we find more varied relations -between shapes and circumstances. Some of these relations are highly -instructive.</p> - -<p>Mollusks of one order, the <i>Pteropoda</i>, swim in the sea much in -the same way that butterflies fly in the air, and have shapes not -altogether unlike those of butterflies. Fig. <a href="#i_201">272</a> represents one of -these creatures. That its bilaterally-symmetrical shape harmonizes with -its bilaterally-symmetrical conditions is sufficiently obvious.</p> - - - <div class="figcenter" id="i_201"> - <img - class="p2" - src="images/i_201.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 272.</p> - </div> - -<p class="p2">Among the <i>Lamellibranchiata</i>, we have diverse forms accompanying -diverse modes of life. Such of them as frequently move about, like -the fresh-water Mussel, have their two valves and the contained parts -alike on the opposite sides of a vertical plane: they are bilaterally -symmetrical in conformity with their mode of movement. The marine -Mussel, too, though habitually fixed, and though not usually so fixed -that its two valves are similarly conditioned, still retains that -bilateral symmetry which is characteristic of the order; and it does -this because in the species considered as a whole, the two valves -are not dissimilarly conditioned. If the positions of the various -individuals are averaged, it will be seen that the differentiating -actions neutralize one another. In certain other fixed Lamellibranchs, -however, there is a considerable deviation from bilateral symmetry; -and it is a deviation of the kind to be anticipated under the -circumstances. Where one valve is always downwards, or next to the -surface of attachment, while the other valve is always upwards, or next -to the environing water, we may expect to find the two<span class="pagenum" id="Page_202">[202]</span> valves become -unlike. This we do find: witness the Oyster. In the Oyster, too, we see -a further irregularity. There is a great indefiniteness of outline, -both in the shell and in the animal—an indefiniteness made manifest by -comparing different individuals. We have but to remember that growing -clustered together, as Oysters do, they must interfere with one another -in various ways and degrees, to see how the indeterminateness of form -and the variety of form are accounted for.</p> - -<p>Among the Gasteropods modifications of a more definite kind occur. “In -all Mollusks,” says Professor Huxley, “the axis of the body is at first -straight, and its parts are arranged symmetrically with regard to a -longitudinal vertical plane, just as in a vertebrate or an articulate -embryo.” In some Gasteropods, as the <i>Chiton</i>, this bilateral -symmetry is retained—the relations of the body to surrounding actions -not being such as to disturb it. But in those more numerous types -which have spiral shells, there is a marked deviation from bilateral -symmetry, as might be expected. “This asymmetrical over-development -never affects the head or foot of the mollusk”: only those parts -which, by inclosure in a shell, are protected from environing actions, -lose their bilateralness; while the external parts, subjected by the -movements of the creatures to bilateral conditions, remain bilateral. -Here, however, a difficulty meets us. Why is it that the naked -Gasteropods, such as our common slugs, deviate from bilateral symmetry, -though their modes of movement are those along with which complete -bilateral symmetry usually occurs? The reply is that their deviations -from bilateral symmetry are probably inherited, and that they are -maintained in such parts of their organization as are not exposed to -bilaterally-symmetrical conditions. There is reason to believe that the -naked Gasteropods are descended from Gasteropods which had shells: the -evidence being that the naked Gasteropods have shells during the early -stages of their development, and that some of them<span class="pagenum" id="Page_203">[203]</span> retain rudimentary -shells throughout life. Now the shelled Gasteropods deviate from -bilateral symmetry in the disposition of both the alimentary system -and the reproductive system. The naked Gasteropods, in losing their -shells, have lost that immense one-sided development of the alimentary -system which fitted them to their shells, and have acquired that -bilateral symmetry of external figure which fits them for their habits -of locomotion; but the reproductive system remains one-sided, because, -in respect to it, the relations to external conditions remain one-sided.</p> - -<p>The Cephalopods show us bilaterally-symmetrical external forms along -with habits of movement through the water in two-sided attitudes. At -the same time, in the radial distribution of the arms, enabling one -of these creatures to take an all-sided grasp of its prey, we see how -readily upon one kind of symmetry there may be partially developed -another kind of symmetry, where the relations to conditions favour it.</p> - - -<p class="p2">§ 252. The <i>Vertebrata</i> illustrate afresh the truths which we -have already traced among the <i>Annulosa</i>. Flying through the air, -swimming through the water, and running over the earth as vertebrate -animals do, in common with annulose animals, they are, in common with -annulose animals, different at their anterior and posterior ends, -different at their dorsal and ventral surfaces, but alike along their -two sides. This single bilateral symmetry remains constant under the -extremest modifications of form. Among fish we see it alike in the -horizontally-flattened Skate, in the vertically-flattened Bream, in -the almost-spherical <i>Diodon</i>, and in the greatly-elongated -<i>Syngnathus</i>. Among reptiles the Turtle, the Snake, and the -Crocodile all display it. And under the countless modifications of -structure displayed by birds and mammals, it remains conspicuous.</p> - - - <div class="figcenter" id="i_204"> - <img - class="p2" - src="images/i_204.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 273–280.</p> - </div> - -<p class="p2">A less obvious fact which it concerns us to note among the -<i>Vertebrata</i>, parallel to one which we noted among the -<i>Annulosa</i>, is that whereas the lower vertebrate forms deviate<span class="pagenum" id="Page_204">[204]</span> -but little from triple bilateral symmetry, the deviation becomes great -as we ascend. Figs. <a href="#i_204">273 and 274</a> show how, besides being divisible into -similar halves by a vertical plane passing through its axis, a Fish -is divisible into halves that are not very dissimilar by a horizontal -plane passing through its axis, and also into other not very dissimilar -halves by a plane cutting it transversely. If, as shown in Figs. <a href="#i_204">275 -and 276</a>, analogous sections be made of a superior Reptile, the divided -parts differ more decidedly. When a Mammal and a Bird are treated in -the same way, as shown in Figs. <a href="#i_204">277, 278</a>, and Figs. <a href="#i_204">279, 280</a>, the parts -marked off by the dividing planes are unlike in far greater degrees. On -considering<span class="pagenum" id="Page_205">[205]</span> the mechanical converse between organisms of these several -types and their environments—on remembering that the fish habitually -moves through a homogeneous medium of nearly the same specific gravity -as itself, that the terrestrial reptile either crawls on the surface or -raises itself very incompletely above it, that the more active mammal, -having its supporting parts more fully developed, thereby has the under -half of its body made more different from the upper half, and that the -bird is subject by its mode of life to yet another set of actions and -reactions; we shall see that these facts are quite congruous with the -general doctrine, and furnish further support to it.</p> - -<p>One other significant piece of evidence must be named. Among the -<i>Annulosa</i> we found unsymmetrical bilateralness in creatures -having habits exposing them to unlike conditions on their two sides; -and among the <i>Vertebrata</i> we find parallel cases. They are -presented by the <i>Pleuronectidæ</i>—the order of distorted flat -fishes to which the Sole and the Flounder belong. On the hypothesis of -evolution, we must conclude that fishes of this order have arisen from -an ordinary bilaterally-symmetrical type of fish, which, feeding at the -bottom of the sea, gained some advantage by placing itself with one -of its sides downwards, instead of maintaining the vertical attitude. -Besides the general reason there are special reasons for concluding -this. In the first place, the young Sole or Flounder is bilaterally -symmetrical—has its eyes on opposite sides of its head and swims in -the usual way. In the second place, the metamorphosis which produces -the unsymmetrical structure sometimes does not take place—there are -abnormal Flounders that swim vertically, like other fishes. In the -third place, the transition from the symmetrical structure to the -unsymmetrical structure may be traced. Almost incredible though it -seems, one of the eyes is transferred from the underside of the head to -the upper side: the transfer being effected by a distorted development -of the cranial bones—atrophy of some and hypertrophy of others,<span class="pagenum" id="Page_206">[206]</span> -along with a general twist. This metamorphosis furnishes several -remarkable illustrations of the way in which forms become moulded -into harmony with incident forces. For besides the divergence from -bilateral symmetry involved by presence of both eyes upon the upper -side, there is a further divergence from bilateral symmetry involved by -differentiation of the two sides in respect to the contours of their -surfaces and the sizes of their fins. And then, what is still more -significant, there is a near approach to likeness between the halves -that were originally unlike, but are, under the new circumstances, -exposed to like conditions. The body is divisible into similarly-shaped -parts by a plane cutting it along the side from head to tail: “the -dorsal and ventral instead of the lateral halves become symmetrical in -outline and are equipoised.”</p> - - -<p class="p2">§ 253. Thus, little as there seems in common between the shapes of -plants and the shapes of animals, we yet find, on analysis, that the -same general truths are displayed by both. The one ultimate principle -that in any organism equal amounts of growth take place in those -directions in which the incident forces are equal, serves as a key to -the phenomena of morphological differentiation. By it we are furnished -with interpretations of those likenesses and unlikenesses of parts, -which are exhibited in the several kinds of symmetry; and when we take -into account inherited effects, wrought under ancestral conditions -contrasted in various ways with present conditions, we are enabled to -comprehend, in a general way, the actions by which animals have been -moulded into the shapes they possess.</p> - -<p>To fill up the outline of the argument, so as to make it correspond -throughout with the argument respecting vegetal forms, it would be -proper here to devote a chapter to the differentiations of those -homologous segments out of which animals of certain types are composed. -Though, among most animals of the third degree of composition, -such as the<span class="pagenum" id="Page_207">[207]</span> rooted <i>Hydrozoa</i>, the <i>Polyzoa</i>, and the -<i>Ascidioida</i>, the united individuals are not reduced to the -condition of segments of a composite individual, and do not display -any marked differentiations; yet there are some animals in which such -subordinations, and consequent heterogeneities, occur. The oceanic -<i>Hydrozoa</i> form one group of them; and we have seen reason to -conclude that the <i>Annulosa</i> form another group. It is not worth -while, however, to occupy space in detailing these unlikenesses of -homologous segments, and seeking specific explanations of them. -Among the oceanic <i>Hydrozoa</i> they are extremely varied; and the -habits and derivations of these creatures are so little known, that -there are no adequate data for interpreting the forms of the parts in -terms of their relations to the environment. Conversely, among the -<i>Annulosa</i> those differentiations of the homologous segments -which accompany their progressing integration, have so much in common, -and have general causes which are so obvious, that it is needless to -deal with them at any length. They are all explicable as due to the -exposure of different parts of the chain of segments to different sets -of actions and reactions: the most general contrast being that between -the anterior segments and the posterior segments, answering to the most -general contrast of conditions to which annulose animals subject their -segments; and the more special contrasts answering to the contrasts of -conditions entailed by their more special habits.</p> - -<p>Were an exhaustive treatment of the subject practicable, there should -here, also, come a chapter devoted to the internal structures of -animals—meaning, more especially, the shapes and arrangements of the -viscera. The relations between forms and forces among these inclosed -parts are, however, mostly too obscure to allow of interpretation. -Protected as the viscera are in great measure from the incidence of -external forces, we are not likely to find much correspondence between -their distribution and the distribution of external forces. In this -case the influences, partly<span class="pagenum" id="Page_208">[208]</span> mechanical, partly physiological, which -the organs exercise on one another, become the chief causes of their -changes of figure and arrangement; and these influences are complex and -indefinite. One general fact may, indeed, be noted—the fact, namely, -that the divergence towards asymmetry which generally characterizes -the viscera, is marked among those of them which are most removed -from mechanical converse with the environment, but not so marked -among those of them which are less removed from such converse. Thus -while, throughout the <i>Vertebrata</i>, the alimentary system, with -the exception of its two extremities, is asymmetrically arranged, the -respiratory system, which occupies one end of the body, generally -deviates but little from bilateral symmetry, and the reproductive -system, partly occupying the other end of the body, is in the main -bilaterally symmetrical: such deviation from bilateral symmetry as -occurs, being found in its most interiorly-placed parts, the ovaries. -Just indicating these facts as having a certain significance, it will -be best to leave this part of the subject as too involved for detailed -treatment.</p> - -<p>Internal structures of one class, however, not included among -the viscera, admit of general interpretation—structures which, -though internal, are brought into tolerably-direct relations with -environing forces, and are therefore subordinate in their forms to -the distribution of those forces. These internal structures it will -be desirable to deal with at some length; both because they furnish -important illustrations enforcing the general argument, and because an -interpretation of them which we have seen reason to reject, cannot be -rejected without raising the demand for some other interpretation.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_209">[209]</span></p> - -<h3>CHAPTER XV.<br /> -<span class="subhed1">THE SHAPES OF VERTEBRATE SKELETONS.</span></h3></div> - - -<p id="sect254">§ 254. When an elongated mass of any substance is transversely -strained, different parts of the mass are exposed to forces of opposite -kinds. If, for example, a bar of metal or wood is supported at its two -ends, as shown in Fig. <a href="#i_209">281</a>, and has to bear a weight on its centre, its -lower part is thrown into a state of tension, while its upper part is -thrown into a state of compression. As will be manifest to any one who -observes what happens on breaking a stick across his knee, the greatest -degree of tension falls on the fibres forming the convex surface, while -the fibres forming the concave surface are subject to the greatest -degree of compression. Between these extremes the fibres at different -depths are subject to different forces. Progressing upwards from the -under surface of the bar shown in Fig. <a href="#i_209">281</a>, the tension of the fibres -becomes less; and progressing downwards from the upper surface, the -compression of the fibres becomes less; until, at a certain distance -between the two surfaces, there is a place at which the fibres are -neither extended nor compressed. This, shown by the dotted line in<span class="pagenum" id="Page_210">[210]</span> the -figure, is called in mechanical language the “neutral axis.” It varies -in position with the nature of the substance strained: being, in common -pine-wood, at a distance of about five-eighths of the depth from the -upper surface, or three-eighths from the under surface. Clearly, if -such a piece of wood, instead of being subject to a downward force, is -secured at its ends and subject to an upward force, the distribution -of the compressions and tensions will be reversed, and the neutral -axis will be nearest to the upper surface. Fig. <a href="#i_210">282</a> represents these -opposite attitudes of the bar and the changed position of its neutral -axis: the arrow indicating the direction of the force producing the -upward bend, and the faint dotted line <i>a</i>, showing the previous -position of the neutral axis. Between the two neutral axes will be seen -a central space; and it is obvious that when the bar has its strain -from time to time reversed, the repeated changes of its molecular -condition must affect the central space in a way different from that -in which they affect the two outer spaces. Fig. <a href="#i_211">283</a> is a diagram -conveying some idea of these contrasts in molecular condition. If A B C -D be the middle part of a bar thus treated, while G H and K L are the -alternating neutral axes; then the forces to which the bar is in each -case subject, may be readily shown. Supposing the deflecting force to -be acting in the direction of the arrow E, then the tensions to which -the fibres between G and F are exposed, will be represented by a series -of lines increasing in length as the distance from G increases; so that -the triangle G F M, will express the amount and distribution of all -the molecular tensions. But the molecular compressions throughout the -space from G to E, must balance the molecular tensions; and hence, if -the triangle G E N be made equal to the triangle<span class="pagenum" id="Page_211">[211]</span> G F M, the parallel -lines of which it is composed (here dotted for the sake of distinction) -will express the amount and distribution of the compressions between -E and G. Similarly, when the deflecting force is in the direction of -the arrow F, the compressions and tensions will be quantitatively -symbolized by the triangles K F O, and K E P. And thus the several -spaces occupied by full lines and by dotted lines and by the two -together, will represent the different actions to which different -parts of the transverse section are subject by alternating transverse -strains. Here, then, it is made manifest to the eye that the central -space between G and K, is differently conditioned from the spaces above -and below it; and that the difference of condition is sharply marked -off. The fibres forming the outer surface C D, are subject to violent -tensions and violent compressions. Progressing inwards the tensions and -compressions decrease—the tensions the more rapidly. As we approach -the point G, the tensions to which the fibres are alternately subject, -bear smaller and smaller ratios to the compressions, and disappear -at the point G. Thence to the centre occur compressions only, of -alternating intensities, becoming at the centre small<span class="pagenum" id="Page_212">[212]</span> and equal; and -from the centre we advance, through a reverse series of changes, to the -other side.</p> - - <div class="figcenter" id="i_209"> - <img - class="p2" - src="images/i_209.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 281.</p> - </div> - - <div class="figcenter" id="i_210"> - <img - class="p2" - src="images/i_210.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 282.</p> - </div> - - <div class="figcenter" id="i_211"> - <img - class="p2" - src="images/i_211.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 283.</p> - </div> - -<p class="p2">Thus it is demonstrable that any substance in which the power of -resisting compression is unequal to the power of resisting tension, -cannot be subject to alternating transverse strains, without having -a central portion differentiated in its conditions from the outer -portions, and consequently differentiated in its structure. This -conclusion may easily be verified by experiment. If something having -a certain toughness but not difficult to break, as a thick piece of -sheet lead, be bent from side to side till it is broken, the surface of -fracture will exhibit an unlikeness of texture between the inner and -outer parts.</p> - - -<p class="p2" id="sect255">§ 255. And now for the application of this seemingly-irrelevant -truth. Though it has no obvious connection with the interpretation of -vertebral structure, we shall soon see that it fundamentally concerns -us.</p> - - <div class="figcenter" id="i_212"> - <img - class="p2" - src="images/i_212.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 284.</p> - </div> - -<p class="p2">The simplest type of vertebrate animal, the fish, has a mode of -locomotion which involves alternating transverse strains. It is not, -indeed, subjected to alternating transverse strains by some outer -agency, as in the case we have been investigating: it subjects itself -to them. But though the strains are here internally produced instead -of externally produced, the case is not therefore removed into a -wholly different category. For supposing Fig. <a href="#i_212">284</a> to represent the -outline of a fish when bent on one side (the dotted lines representing -its outline when the bend is reversed), it is clear that part of the -substance forming the convex half must be in a state of tension. This -state of tension implies the existence in the other half of some -counter-balancing compression. And between the two there must be a -neutral axis. The way in which this conclusion is reconcilable with the -fact that there is tension somewhere in the concave side of a fish, -since the curve is<span class="pagenum" id="Page_213">[213]</span> caused by muscular contractions on the concave -side, will be made clear by the rude illustration which a bow supplies. -A bow may be bent by a thrust against its middle (the two ends being -held back), or it may be bent by contracting a string that unites its -ends; but the distributions of mechanical forces within the wood of the -bow, though not quite alike in the two cases, will be very similar. -Now while the muscular action on the concave side of a fish differs -from that represented by the tightened string of a bow, the difference -is not such as to destroy the applicability of the illustration: the -parallel holds so far as this, that within that portion of the fish’s -body which is passively bent by the contracting muscles, there must be, -as in a strung bow, a part in compression, a part in tension, and an -intermediate part which is neutral.</p> - -<p>After thus seeing that even in the developed fish with its complex -locomotive apparatus, this law of the transverse strain holds in a -qualified way, we shall understand how much more it must hold in any -form that may be supposed to initiate the vertebrate type—a form -devoid of that segmentation by which the vertebrate type is more or -less characterized. We shall see that assuming a rudimentary animal, -still simpler than the <i>Amphioxus</i>, to have a feeble power of -moving itself through the water by the undulations of its body, or -some part of its body, there will necessarily come into play certain -reactions which must affect the median portion of the undulating mass -in a way unlike that in which they affect its lateral portions. And if -there exists in this median portion a tissue which keeps its place with -any constancy, we may expect that the differential conditions produced -in it by the transverse strain, will initiate a differentiation. It -is true that the distribution of the viscera in the <i>Amphioxus</i>, -Fig. <a href="#i_214">191</a>, and in the type from which we may suppose it to have arisen, -is such as to interfere with this process. It is also true that the -actions and reactions described would not of themselves give to the -median portion<span class="pagenum" id="Page_214">[214]</span> a cylindrical shape, like that of the cartilaginous rod -running along the back of the <i>Amphioxus</i>. But what we have here -to note in the first place is, that these habitual alternate flexions -have a tendency to mark off from the outer parts an unlike inner part, -which may be seized hold of, maintained, and further modified, by -natural selection, should any advantage thereby result. And we have to -note in the second place, that an advantage <i>is</i> likely to result. -The contractions cannot be effective in producing undulations, unless -the general shape of the body is maintained. External muscular fibres -unopposed by an internal resistant mass, would cause collapse of the -body. To meet the requirements there must be a means of maintaining -longitudinal rigidity without preventing bends from side to side; -and such a means is presented by a structure initiated as described. -In brief, whether we have or have not the actual cause, we have here -at any rate “a true cause.” Though there are difficulties in tracing -out the process in a definite way, it may at least be said that the -mechanical genesis of this rudimentary vertebrate axis is quite -conceivable. And even the difficulties may, I think, be more fully met -than at first sight seems possible.</p> - - <div class="figcenter" id="i_214"> - <img - class="p2" - src="images/i_214.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 191.</p> - </div> - -<p class="p2">What is to be said of the other leading trait which the simplest -vertebrate animal has in common with all higher vertebrate animals—the -segmentation of its lateral muscular masses? Is this, too, explicable -on the mechanical hypothesis? Have we, in the alternating transverse -strains, a cause for the fact that while the rudimentary vertebrate -axis<span class="pagenum" id="Page_215">[215]</span> is without any divisions, there are definite divisions of the -substance forming the animal’s sides? I think we have. A glance at the -distribution of forces under the transverse strain, as represented in -the foregoing diagrams, will show how much more severe is the strain -on the outer parts than on the inner parts; and how, consequently, -any modifications of structure eventually necessitated, will arise -peripherally before they arise centrally. The perception of this may be -enforced by a simple experiment. Take a stick of sealing-wax and warm -it slowly and moderately before the fire, so as to give it a little -flexibility. Then bend it gently until it is curved into a semi-circle. -On the convex surface small cracks will be seen, and on the concave -surface wrinkles; while between the two the substance remains -undistorted. If the bend be reversed and re-reversed, time after time, -these cracks and wrinkles will become fissures which gradually deepen. -But now, if changes of this class, entailed by alternating transverse -strains, commence superficially, as they manifestly must; there arise -the further questions—What will be the special modifications produced -under these special conditions? and through what stages will these -modifications progress? Every one has literally at hand an example -of the way in which a flexible external layer that is now extended -and now compressed, by the bending of the mass it covers, becomes -creased; and a glance at the palms and the fingers will show that the -creases are near one another where the skin is thin, and far apart -where the skin is thick. Between this familiar case and the case of -the rhinoceros-hide, in which there are but a few large folds, various -gradations may be traced. Now the like must happen with the increasing -layers of contractile fibres forming the sides of the muscular tunic -in such a type as that supposed. The bendings will produce in them -small wrinkles while they are thin, but more decided and comparatively -distant fissures as they become thick. Fig. <a href="#i_216">289</a>, which is a horizontal -longitudinal section, shows how these thickening layers will<span class="pagenum" id="Page_216">[216]</span> adjust -themselves on the convex and the concave surfaces, supposing the fibres -of which they are composed to be oblique, as their function requires; -and it is not difficult to see that when once definite divisions have -been established, they will advance inwards as the layers develop; -and will so produce a series of muscular bundles. Here then we have -something like the <i>myocommata</i> [or myotomes as now called] which -are traceable in the <i>Amphioxus</i>, and are conspicuous in all -superior fishes.</p> - - <div class="figcenter" id="i_216"> - <img - class="p2" - src="images/i_216.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 289.</p> - </div> - - -<p class="p2" id="sect256">§ 256. These are highly speculative conceptions. I have ventured to -present them with the view of implying that the hypothesis of the -mechanical genesis of vertebrate structure is not wholly at fault when -applied to the most rudimentary vertebrate animal. Lest it should be -alleged that the question is begged if we set out with a type which, -like the <i>Amphioxus</i>, already displays segmentation throughout -its muscular system, it seemed needful to indicate conceivable modes -in which there may have been mechanically produced those leading -traits that distinguish the <i>Amphioxus</i>. All I intend to suggest -is that mechanical actions have been at work, and that probably they -have operated in the manner alleged: so preparing the way for natural -selection.</p> - -<p>But now let us return to the region of established fact, and consider -whether such actions and reactions as we actually witness, are adequate -causes of those observed differentiations and integrations which -distinguish the more-developed vertebrate animals. Let us see whether -the theory of mechanical genesis affords us a deductive interpretation -of the inductive generalizations.</p> - -<p>Before proceeding, we must note a process of functional adaptation -which here co-operates with natural selection. I refer to the usual -formation of denser tissues at those parts of an organism which are -exposed to the greatest<span class="pagenum" id="Page_217">[217]</span> strains—either compressions or tensions. -Instances of hardening under compression are made familiar to us by -the skin. We have the general contrast between the soft skin covering -the body at large, and the indurated skin covering the inner surfaces -of the hands and the soles of the feet. We have the fact that even -within these areas the parts on which the pressure is habitually -greatest have the skin always thickest; and that in each person special -points exposed to special pressures become specially dense—often as -dense as horn. Further, we have the converse fact that the skin of -little-used hands becomes abnormally thin—even losing, in places, that -ribbed structure which distinguishes skin subject to rough usage. Of -increased density directly following increased tension, the skeletons, -whether of men or animals, furnish abundant evidence. Anatomists easily -discriminate between the bones of a strong man and those of a weak -man, by the greater development of those ridges and crests to which -the muscles are attached; and naturalists, on comparing the remains of -domesticated animals with those of wild animals of the same species, -find kindred differences. The first of these facts shows unmistakably -the immediate effect of function on structure, and by obvious alliance -with it the second may be held to do the same: both implying that the -deposit of dense substance capable of great resistance, constantly -takes place at points where the tension is excessive.</p> - -<p>Taking into account, then, this adaptive process, continually aided -by the survival of individuals in which it has taken place most -rapidly, we may expect, on tracing up the evolution of the vertebrate -axis, to find that as the muscular power becomes greater there arise -larger and harder masses of tissue, serving the muscles as <i>points -d’appui</i>; and that these arise first in those places where the -strains are greatest. Now this is just what we <i>do</i> find. The -<i>myocommata</i> are so placed that their actions are likely to -affect first that upper coat of the notochord, where there are found<span class="pagenum" id="Page_218">[218]</span> -“quadrate masses of somewhat denser tissue,” which “seem faintly to -represent neural spines,” even in the <i>Amphioxus</i>. It is by the -development of the neural spines, and after them of the hæmal spines, -that the segments of the vertebral column are first marked out; and -under the increasing strains of more-developed <i>myocommata</i>, -it is just these peripheral appendages of the vertebral segments -that must be most subject to the forces which cause the formation of -denser tissue. It follows from the mechanical hypothesis that as the -muscular segmentation must begin externally and progress inwards, so, -too, must the vertebral segmentation. Besides thus finding reason -for the fact that in fishes with wholly cartilaginous skeletons, the -vertebral segments are indicated by these processes, while yet the -notochord is unsegmented; we find a like reason for the fact that -the transition from the less-dense cartilaginous skeleton to the -more-dense osseous skeleton, pursues a parallel course. In the existing -<i>Lepidosiren</i>, which by uniting certain piscine and amphibian -characters betrays its close alliance with primitive types, the axial -part of the vertebral column is unossified, while there is ossification -of the peripheral parts. Similarly with numerous genera of fishes -classed as palæozoic. The fossil remains of them show that while the -neural and hæmal spines consisted of bone, the central parts of the -vertebræ were not bony. It may in some cases be noted, too, both in -extant and in fossil forms, that while the ossification is complete at -the outer extremities of the spines it is incomplete at their inner -extremities—thus similarly implying centripetal development.</p> - - -<p class="p2" id="sect257">§ 257. After these explanations the process of eventual segmentation -in the spinal axis itself, will be readily understood. The original -cartilaginous rod has to maintain longitudinal rigidity while -permitting lateral flexion. As fast as it becomes definitely marked -out, it will begin to concentrate within itself a great part of those -pressures and tensions<span class="pagenum" id="Page_219">[219]</span> caused by transverse strains. As already said, -it must be acted upon much in the same manner as a bow, though it is -bent by forces acting in a more indirect way; and like a bow, it must, -at each bend, have the substance of its convex side extended and the -substance of its concave side compressed. So long as the vertebrate -animal is small or inert, such a cartilaginous rod may have sufficient -strength to withstand the muscular strains; but, other things equal, -the evolution of an animal that is large, or active, or both, implies -muscular strains which must tend to cause modification in such a -cartilaginous rod. The results of greater bulk and of greater vivacity -may be best dealt with separately. As the animal increases in size, -the rod will grow both longer and thicker. On looking back at the -diagrams of forces caused by transverse strains, it will be seen that -as the rod grows thicker, its outer parts must be exposed to more -severe tensions and pressures if the degree of bend is the same. It is -doubtless true that when the fish, advancing by lateral undulations, -becomes longer, the curvature assumed by the body at each movement -becomes less; and that from this cause the outer parts of the notochord -are, other things equal, less strained—the two changes thus partially -neutralizing one another. But other things are <i>not</i> equal. For -while, supposing the shape of the body to remain constant, the force -exerted in moving the body increases as the cubes of its dimensions, -the sectional area of the notochord, on which fall the reactions of -this exerted force, increases only as the squares of the dimensions: -whence results a greater stress upon its substance. This, however, -will not be very decided where there is no considerable activity. It -is clear that augmenting bulk, taken alone, involves but a moderate -residuary increase of strain on each portion of the notochord; and this -is probably the reason why it is possible for a large <i>sluggish</i> -fish like the Sturgeon, to retain the notochordal structure. But now, -passing to the effects of greater activity, a like dynamical inquiry at -once shows us how rapidly<span class="pagenum" id="Page_220">[220]</span> the violence of the actions and reactions -rises as the movements become more vivacious. In the first place, the -resistance of a medium such as water increases as the square of the -velocity of the body moving through it; so that to <i>maintain</i> -double the speed, a fish has to expend four times the energy. But the -fish has to do more than this—it has to <i>initiate</i> this speed, or -to impress on its mass the force implied by this speed. Now the <i>vis -viva</i> of a moving body varies as the square of the velocity; whence -it follows that the energy required to generate that <i>vis viva</i> is -measured by the square of the velocity it produces. Consequently, did -the fish put itself in motion <i>instantaneously</i>, the expenditure -of energy in generating its own <i>vis viva</i> and simultaneously -overcoming the resistance of the water, would vary as the fourth -power of the velocity. But the fish cannot put itself in motion -instantaneously—it must do it by increments; and thus it results that -the amounts of the forces expended to give itself different velocities -must be represented by some series of numbers falling between the -squares and the fourth powers of those velocities. Were the increments -slowly accumulated, the ratios of increasing effort would but little -exceed the ratios of the squares; but whoever observes the sudden, -convulsive action with which an alarmed fish darts out of a shallow -into deep water, will see that the velocity is rapidly generated, -and that therefore the ratios of increasing effort probably exceed -the ratios of the squares very considerably. At any rate it will be -clear that the efforts made by fishes in rushing upon prey or escaping -enemies (and it is these extreme efforts which here concern us) must, -as fishes become more active, rapidly exalt the strains to be borne -by their motor organs; and that of these strains, those which fall -upon the notochord must be exalted in proportion to the rest. Thus the -development of locomotive power, which survival of the fittest must -tend in most cases to favour, involves such increase of stress on the -primitive cartilaginous rod as will tend, other things equal, to cause -its modification.</p> - -<p><span class="pagenum" id="Page_221">[221]</span></p> - - <div class="figcenter" id="i_221"> - <img - class="p2" - src="images/i_221.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 291–293.</p> - </div> - -<p class="p2">What must its modification be? Considering the complication of the -influences at work, conspiring, as above indicated, in various ways and -degrees, we cannot expect to do more than form an idea of its average -character. The nature of the changes which the notochord is likely -to undergo, where greater bulk is accompanied by higher activity, is -rudely indicated by Figs. <a href="#i_221">291, 292, and 293</a>. The successively thicker -lines represent the successively greater strains to which the outer -layers of tissue are exposed; and the widening interspaces represent -the greater extensions which they have to bear when they become convex, -or else the greater gaps that must be formed in them. Had these outer -layers to undergo extension only, as on the convex side, continued -natural selection might result in the formation of a tissue elastic -enough to admit of the requisite stretching. But at each alternate -bend these outer layers, becoming concave, are subject to increased -compression—a compression which they cannot withstand if they have -become simply more extensible. To withstand this greater compression -they must become harder as well as more extensible. How are these two -requirements to be reconciled? If, as facts warrant us in supposing, a -formation of denser substance occurs at those parts of the notochord -where the strain is greatest; it is clear that this formation cannot -so go on as to produce a continuous mass: the perpetual flexions must -prevent this. If matter that will not yield at each bend, is deposited -while the bendings are continually taking place, the bendings will -maintain certain places of discontinuity in the deposit—places at -which the whole of the stretching consequent on each bend will be -concentrated. And thus the tendency will be to form segments of hard -tissue capable of great resistance<span class="pagenum" id="Page_222">[222]</span> to compression, with intervals -filled by elastic tissue capable of great resistance to extension—a -vertebral column.</p> - -<p>And now observe how the progress of ossification is just such as -conforms to this view. That centripetal development of segments which -holds of the vertebrate animal as a whole, as, if caused by transverse -strains, it ought to do, and which holds of the vertebral column as -a whole, as it ought to do, holds also of the central axis. On the -mechanical hypothesis, the outer surface of the notochord should be -the first part to undergo induration, and that division into segments -which must accompany induration. And accordingly, in a vertebral column -of which the axis is beginning to ossify, the centrums consist of bony -rings inclosing a still-continuous rod of cartilage.</p> - - -<p class="p2">§ 258. Sundry other general facts disclosed by the comparative -morphology of the <i>Vertebrata</i>, supply further confirmation. Let -us take first the structure of the skull.</p> - -<p>On considering the arrangement of the muscular flakes, or -<i>myocommata</i>, in any ordinary fish which comes to table—an -arrangement already sketched out in the <i>Amphioxus</i>—it is not -difficult to see that that portion of the body out of which the head -of the vertebrate animal becomes developed, is a portion which cannot -subject itself to bendings in the same degree as the rest of the -body. The muscles developed there must be comparatively short, and -much interfered with by the pre-existing orifices. Hence the cephalic -part will not partake in any considerable degree of the lateral -undulations; and there will not tend to arise in it any such distinct -segmentation as arises elsewhere. We have here, then, an explanation of -the fact, that from the beginning the development of the head follows -a course unlike that of the spinal column; and of the fact that the -segmentation, so far as it can be traced in the head, is most readily -to be traced in the occipital region and becomes lost in the region -of the face. For if, as we have seen, the segmentation consequent on<span class="pagenum" id="Page_223">[223]</span> -mechanical actions and reactions must progress from without inwards, -affecting last of all the axis; and if, as we have seen, the region -of the head is so circumstanced that the causes of segmentation act -but feebly even on its periphery; then that terminal portion of the -primitive notochord which is included in the head, having to undergo no -lateral bendings, may ossify without division into segments.</p> - -<p>Of other incidental evidences supplied by comparative morphology, let -me next refer to the supernumerary bones, which the theory of Goethe -and Oken as elaborated by Prof. Owen, has to get rid of by gratuitous -suppositions. In many fishes, for example, there are what have been -called interneural spines and interhæmal spines. These cannot by any -ingenuity be affiliated upon the archetypal vertebra, and they are -therefore arbitrarily rejected as bones belonging to the exo-skeleton; -though in shape and texture they are similar to the spines between -which they are placed. On the hypothesis of evolution, however, these -additional bones are accounted for as arising under actions like those -that gave origin to the bones adjacent to them. And similarly with such -bones as those called sesamoid; together with others too numerous to -name.</p> - - -<p class="p2">§ 259. Of course the foregoing synthesis is to be taken simply as an -adumbration of the process by which the vertebrate structure may have -arisen through the continued actions of known agencies. The motive -for attempting it has been two-fold. Having, as before said, given -reasons for concluding that the segments of a vertebrate animal are not -homologous in the same sense as are those of an annulose animal, it -seemed needful to do something towards showing how they are otherwise -to be accounted for; and having here, for our general subject, the -likenesses and differences among the parts of organisms, as determined -by incident forces, it seemed out of the question to pass by the -problem presented by the vertebrate skeleton.</p> - -<p><span class="pagenum" id="Page_224">[224]</span></p> - -<p>Leaving out all that is hypothetical, the general argument may be -briefly presented thus:—The evolution from the simplest known -vertebrate animal of a powerful and active vertebrate animal, implies -the development of a stronger internal fulcrum. The internal fulcrum -cannot be made stronger without becoming more dense. And it cannot -become more dense while retaining its lateral flexibility, without -becoming divided into segments. Further, in conformity with the general -principles thus far traced, these segments must be alike in proportion -as the forces to which they are exposed are alike, and unlike in -proportion as these forces are unlike; and so there necessarily results -that unity in variety by which the vertebral column is from the -beginning characterized. Once more, we see that the explanation extends -to those innumerable and more marked divergences from homogeneity, -which vertebræ undergo in the various higher animals. Thus, the -production of vertebræ, the production of likenesses among vertebræ, -the production of unlikenesses among vertebræ, and the production of -unlikenesses among vertebral columns, are interpretable as parts of one -general process, and as harmonizing with one general principle.</p> - -<p>Whether sufficient or insufficient, the explanation here given assigns -causes of known kinds producing effects such as they are known to -produce. It does not, as a solution of one mystery, offer another -mystery of which no solution is to be asked. It does not allege a -Platonic ἰδέα, or fictitious entity, which explains the vertebrate -skeleton by absorbing into itself all the inexplicability. On the -contrary, it assumes nothing beyond agencies by which structures in -general are moulded—agencies by which these particular structures -are, indeed, notoriously modifiable. An ascertained cause of certain -traits in vertebræ and other bones, it extends to all other traits of -vertebræ; and at the same time assimilates the morphological phenomena -they present to much wider classes of morphological phenomena.</p> - -<p><span class="pagenum" id="Page_225">[225]</span></p> - -<hr class="tb" /> - -<p>[<span class="smcap">Note.</span>—The theory set forth in the foregoing chapter, -is an elaboration of one suggested at the close of a criticism -of Prof. Owen’s <i>Archetype and Homologies of the Vertebrate -Skeleton</i>, already referred to in <a href="#sect210">§ 210</a> as having been published -in the <i>Medico-Chirurgical Review</i> for October, 1858. It is -now reproduced in Appendix B. Since the issue of this elaborated -exposition, in No. 15 of my serial in December, 1865, verifications of -it have from time to time been published. In his work <i>The Primary -Factors of Organic Evolution</i>, Prof. Cope of Philadelphia writes:—</p> - -<p>“Mr. Herbert Spencer has endeavoured to account for the origin of the -segmentation of muscles into myotomes, and the division of the sheath -of the notochord into vertebræ, by supposing it to be due to the -lateral swimming movements of the fishes, which first exhibit these -structures. With this view various later authors have agreed, and I -have offered some additional evidence of the soundness of this position -with respect to the vertebral axis of Batrachia, and the origin of -limb articulations. It is true that the origin of segmentation in the -vertebral column of the true fishes and the Batrachia turns out to have -been less simple in its process than was suggested by Mr. Spencer, but -his general principle holds good, now that paleontology has cleared up -the subject” (pp. 367–8).</p> - -<p>An allusion in the foregoing extract is made by Prof. Cope to certain -observations set forth in his work entitled <i>The Origin of the -Fittest</i>. On pp. 305–6 of it will be found the following sentences:—</p> - -<p>“Now, all the Permian land-animals, reptiles and batrachians, retain -this notochord with the elements of osseous vertebræ, in a greater or -less degree of completeness. There are some in South Africa, I believe, -in which the ossification has come clear through the notochord; but -they are few.... There is something to be said as to the condition -of the column from a mechanical standpoint, and it is this: that the -chorda exists, with its osseous elements disposed<span class="pagenum" id="Page_226">[226]</span> about it; and in the -Permian batrachians, equally related to salamanders and frogs, these -osseous elements are arranged in the sheath or skin of the chorda; -and they are in the form of regular concave segments, very much like -such segments as you can take from the skin of an orange—but parts -of a cylinder, and having greater or less dimensions according to the -group or species. Now, the point of divergence of these segments is -on the side of the column. The contacts are placed on the side of the -column where the segments separate—the upper segments rising and the -lower segments coming downward. To the upper segments are attached the -arches and their articulations, and the lower segments are like the -segments of a cylinder. If you take a flexible cylinder, and cover it -with a more or less inflexible skin or sheath, and bend that cylinder -sidewise, you of course will find that the wrinkles or fractures of -that part of the surface will take place along the line of the shortest -curve, which is on the side; and, as a matter of fact, you have breaks -of very much the character of the segments of the Permian Batrachia.... -In the cylinder bending both ways, of course the shortest line of -curve is right at the centre of the side of that cylinder, and the -longest curve is of course at the summit and base, and the shortest -curve will be the point of fracture. And that is exactly what I presume -has happened in the case of the construction of the segments of the -sheath of the vertebral column, by the lateral motion of the animal in -swimming, and which has been the actual cause of the disposition of the -osseous material in its form.... That is the state of the vertebral -column of many of the Vertebrata of the Permian period.”</p> - -<p>In his essay on “The Mechanical Causes of the Development of the -Hard Parts of the Mammalia,” published in the American <i>Journal of -Morphology</i> (Vol. III), Prof. Cope has carried the interpretation -further, by showing that in kindred ways the genesis of articulations -and limb-bones may be explained.<span class="pagenum" id="Page_227">[227]</span> On p. 163 he enunciates the general -principle of his interpretation as follows:—</p> - -<p>“It cannot have been otherwise than that, since the motions of animals -continued during the evolution of their hard parts, these hard parts -grew in exact adaptation to these movements. Thus at the points of -greatest flexure joints would be formed, and between these joints the -deposit would be continuous.”</p> - -<p>Evidently if osseous structures are produced by deposits of calcareous -matters in pre-existing cartilaginous structures, or other structures -of flexible materials, the deposits must be so carried on that while -dense resistant masses are produced these must admit of such free -movements as the creature’s life necessitates, and must so form adapted -joints.</p> - -<p>Let it be understood, however, that the hypothesis set forth in -the foregoing chapter and extended by Prof. Cope, which serves to -interpret a large part of the phenomena of osseous structures in -the <i>Vertebrata</i>, does not serve to interpret them all. While -the formation of hard parts has been in large measure initiated and -regulated by tensions and pressures, there are hard parts the formation -of which cannot be thus explained. The bones of the skull are the -most obvious instances. These are apparently referable to no other -cause than the survival of the fittest—the survival of individual -animals in which greater density of the brain-covering yielded better -protection against external injuries. Without enumerating other -instances which might be given, it will suffice to recognize the truth -that natural selection of favourable variations and the inheritance of -functionally-produced changes have all along co-operated: each of them -in some cases acting alone, but in other cases both acting together.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_228">[228]</span></p> - -<h3>CHAPTER XVI.<br /> -<span class="subhed1">THE SHAPES OF ANIMAL CELLS.</span></h3></div> - - -<p>§ 260. Among animals as among plants, the laws of morphological -differentiation must be conformed to by the morphological units, as -well as by the larger parts and by the wholes formed of them. It -remains here to point out that the conformity is traceable where the -conditions are simple.</p> - - <div class="figcenter" id="i_228"> - <img - class="p2" - src="images/i_228.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 294.</p> - </div> - -<p class="p2">In the shapes assumed by those rapidly-multiplying cells out of which -each animal is developed, there is a conspicuous subordination to -the surrounding actions. Fig. <a href="#i_228">294</a> represents the cellular embryonic -mass that arises by repeated spontaneous fissions. In it we see how -the cells, originally spherical, are changed by pressure against one -another and against the limiting membrane; and how their likenesses -and unlikenesses are determined by the likenesses and unlikenesses -of the forces to which they are exposed. This fact may be thought -scarcely worth pointing out. But it is worth pointing out, because what -is here so obvious a consequence of mechanical actions, is in other -cases a consequence of actions composite in their kinds and involved -in their distribution. Just as the equalities and inequalities of -dimensions among aggregated cells, are here caused by the equalities -and inequalities among their mutual pressures in different directions; -so, though less manifestly, the equalities<span class="pagenum" id="Page_229">[229]</span> and inequalities of -dimensions among other aggregated cells, are caused by the equalities -and inequalities of the osmotic, chemical, thermal, and other forces -besides the mechanical, to which their different positions subject them.</p> - - -<p class="p2">§ 261. This we shall readily see on observing the ordinary structures -of limiting membranes, internal and external. In Fig. <a href="#i_229a">295</a>, is shown -a much-magnified section of a papilla from the gum. The cells of -which it is composed originate in its deeper part; and are at first -approximately spherical. Those of them which, as they develop, are -thrust outwards by the new cells that continually take their places, -have their shapes gradually changed. As they grow and successively -advance to replace the superficial cells, when these exfoliate, they -become exposed to forces which are more and more different in the -direction of the surface from what they are in lateral directions; and -their dimensions gradually assume corresponding differences.</p> - - <div class="figcenter" id="i_229a"> - <img - class="p2" - src="images/i_229a.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 295.</p> - </div> - - <div class="figcenter" id="i_229b"> - <img - class="p2" - src="images/i_229b.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 296.</p> - </div> - -<p class="p2">Another species of limiting membrane, called cylinder-epithelium, -is represented in Fig. <a href="#i_229b">296</a>. Though its mode of development is -such as to render the shapes of its cells quite unlike those of -pavement-epithelium, as the above-described kind is sometimes called, -its cells equally exemplify the same general truth. For the chief -contrast which each of them presents, is the contrast between its -dimension at right angles to the surface of the membrane, and its -dimension parallel to that surface.</p> - -<p>It is needless for our present purpose to examine further<span class="pagenum" id="Page_230">[230]</span> the evidence -furnished by Histology; nor, indeed, would further examination of this -evidence be likely to yield definite results. In the cases given above -we have marked differences among the incident forces; and therefore -have a chance of finding, as we do find, relations between these and -differences of form. But the cells composing masses of tissue are -severally subject to forces which are indeterminate; and therefore -the interpretation of their shapes is impracticable. It must suffice -to observe that so far as the facts go they are congruous with the -hypothesis.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_231">[231]</span></p> - -<h3>CHAPTER XVII.<br /> -<span class="subhed1">SUMMARY OF MORPHOLOGICAL DEVELOPMENT.</span></h3></div> - - -<p class="p2">§ 262. That any formula should be capable of expressing a common -character in the shapes of things so unlike as a tree and a cow, a -flower and a centipede, is a remarkable fact; and is a fact which -affords strong <i>primâ facie</i> evidence of truth. For in proportion -to the diversity and multiplicity of the cases to which any statement -applies, is the probability that it sets forth the essential relations. -Those connexions which remain constant under all varieties of -manifestation, are most likely to be the causal connexions.</p> - -<p>Still higher will appear the likelihood of an alleged law of organic -form possessing so great a comprehensiveness, when we remember that on -the hypothesis of Evolution, there must exist between all organisms -and their environments, certain congruities expressible in terms of -their actions and reactions. The forces being, on this hypothesis, the -causes of the forms, it is inferable, <i>à priori</i>, that the forms -must admit of generalization in terms of the forces; and hence, such -a generalization arrived at <i>à posteriori</i>, gains the further -probability due to fulfilment of anticipation.</p> - -<p>Nearer yet to certainty seems the conclusion thus reached, on finding -that it does but assert in their special manifestations, the laws of -Evolution in general—the laws of that universal re-distribution of -matter and motion which hold<span class="pagenum" id="Page_232">[232]</span> throughout the totality of things, as -well as in each of its parts.</p> - -<p>It will be useful to glance back over the various minor inferences -arrived at, and contemplate them in their <i>ensemble</i> from these -higher points of view.</p> - - -<p class="p2">§ 263. That process of integration which every plant displays during -its life, we found reason to think has gone on during the life of the -vegetal kingdom as a whole. Protoplasm into cells, cells into folia, -folia into axes, axes into branched combinations—such, in brief, are -the stages passed through by every shrub; and such appear to have been -the stages through which plants of successively-higher kinds have been -evolved from lower kinds. Even among certain groups of plants now -existing, we find aggregates of the first order passing through various -gradations into aggregates of the second order—here forming small, -incoherent, indefinite assemblages, and there forming large, definite, -coherent fronds. Similar transitions are traceable through which these -integrated aggregates of the second order pass into aggregates of -the third order: in one species the unions of parent-fronds with the -fronds that bud out from them, being temporary, and in another species -such unions being longer continued; until, in species still higher, -by a gemmation which is habitual and regular, there is produced a -definitely-integrated aggregate of the third order—an axis bearing -fronds or leaves. And even between this type and a type further -compounded, a link occurs in the plants which cast off, in the shape of -bulbils, some of the young axes they produce. As among plants, so among -animals. A like spontaneous fission of cells ends here in separation, -there in partial aggregation, while elsewhere, by closer combination -of the multiplying units, there arises a coherent and tolerably -definite individual of the second order. By the budding of individuals -of the second order, there are in some cases produced other separate -individuals like them; in some<span class="pagenum" id="Page_233">[233]</span> cases temporary aggregates of such like -individuals; and in other cases permanent aggregates of them: certain -of which become so definitely integrated that the individualities of -their component members are almost lost in a tertiary individuality.</p> - -<p>Along with this progressive integration there has gone on a progressive -differentiation. Vegetal units of whatever order, originally -homogeneous, have become heterogeneous while they have become united. -Spherical cells aggregating into threads, into laminæ, into masses, and -into special tissues, lose their sphericity; and instead of remaining -all alike assume innumerable unlikenesses—from uniformity pass -into multiformity. Fronds combining to form axes, severally acquire -definite differences between their attached ends and their free ends; -while they also diverge from one another in their shapes at different -parts of the axes they compose. And axes, uniting into aggregates of -a still higher order, become contrasted in their sizes, curvatures, -and the arrangements of their appendages. Similarly among animals. -Those components of them which, with a certain license, we class as -morphological units, while losing their minor individualities in the -major individualities formed of them, grow definitely unlike as they -grow definitely combined. And where the aggregates so produced become, -by coalescence, segments of aggregates of a still higher order, they, -too, diverge from one another in their shapes.</p> - -<p>The morphological differentiation which thus goes hand in hand with -morphological integration, is clearly what the perpetually-complicating -conditions would lead us to anticipate. Every addition of a new unit -to an aggregate of such units, must affect the circumstances of the -other units in all varieties of ways and degrees, according to their -relative positions—must alter the distribution of mechanical strains -throughout the mass, must modify the process of nutrition, must affect -the relations of neighbouring parts to surrounding diffused actions; -that is, must initiate a changed incidence<span class="pagenum" id="Page_234">[234]</span> of forces tending ever to -produce changed structural arrangements.</p> - - -<p class="p2">§ 264. This broad statement of the correspondence between the general -facts of Morphological Development and the principles of Evolution -at large, may be reduced to statements of a much more specific kind. -The phenomena of symmetry and unsymmetry and asymmetry, which we have -traced out among organic forms, are demonstrably in harmony with those -laws of the re-distribution of matter and motion to which Evolution -conforms. Besides the myriad-fold illustrations of the instability of -the homogeneous, afforded by these aggregates of units of each order, -which, at first alike, lapse gradually into unlikeness; and besides -the myriad-fold illustrations of the multiplication of effects, which -these ever-complicating differentiations exhibit to us; we have also -myriad-fold illustrations of the definite equalities and inequalities -of structures, produced by definite equalities and inequalities of -forces.</p> - -<p>The proposition arrived at when dealing with the causes of Evolution, -“that in the actions and reactions of force and matter, an unlikeness -in either of the factors necessitates an unlikeness in the effects; and -that in the absence of unlikeness in either of the factors the effects -must be alike” (<i>First Principles</i>, § 169), is a proposition which -implies all these particular likenesses and unlikenesses of parts -which we have been tracing. For have we not everywhere seen that the -strongest contrasts are between the parts that are most contrasted in -their conditions; while the most similar parts are those most similarly -conditioned? In every plant the leading difference is between the -attached end and the free end; in every branch it is the same; in every -leaf it is the same. And in every plant the leading likenesses are -those between the two sides of the branch, the two sides of the leaf, -and the two sides of the flower, where these parts are two-sided in -their conditions; or between all sides of the<span class="pagenum" id="Page_235">[235]</span> branch, all sides of -the leaf, and all sides of the flower, where these parts are similarly -conditioned on all sides. So, too, is it with animals which move about. -The most marked contrasts they present are those between the part in -advance and the part behind, and between the upper part and the under -part; while there is complete correspondence between the two sides. -Externally the likenesses and differences among limbs, and internally -the likenesses and differences among vertebræ, are expressible in terms -of this same law.</p> - -<p>And here, indeed, we may see clearly that these truths are corollaries -from that ultimate truth to which all phenomena of Evolution are -referable. It is an inevitable deduction from the persistence of force, -that organic forms which have been progressively evolved, must present -just those fundamental traits of form which we find them present. It -cannot but be that during the intercourse between an organism and its -environment, equal forces acting under equal conditions must produce -equal effects; for to say otherwise is, by implication, to say that -some force can produce more or less than its equivalent effect, which -is to deny the persistence of force. Hence those parts of an organism -which are, by its habits of life, exposed to like amounts and like -combinations of actions and reactions, must develop alike; while -unlikenesses of development must as unavoidably follow unlikenesses -among these agencies. And this being so, all the specialities of -symmetry and unsymmetry and asymmetry which we have traced, are -necessary consequences.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_237">[237]</span></p> - -<h2>PART V.<br /> -<span class="subhed">PHYSIOLOGICAL DEVELOPMENT.</span></h2></div> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_239">[239]</span></p> - -<h3>CHAPTER I.<br /> -<span class="subhed1">THE PROBLEMS OF PHYSIOLOGY.</span></h3></div> - - -<p>§ 265. The questions to be treated under the above title are widely -different from those which it ordinarily expresses. We have no -alternative, however, but to use Physiology in a sense co-extensive -with that in which we have used Morphology. We must here consider -the facts of function in a manner parallel to that in which we -have, in the foregoing Part, considered the facts of structure. -As, hitherto, we have concerned ourselves with those most general -phenomena of organic form which, holding irrespective of class and -order and sub-kingdom, illustrate the processes of integration and -differentiation characterizing Evolution at large; so, now, we have -to concern ourselves with the evidences of those differentiations and -integrations of organic functions which have simultaneously arisen, -and which similarly transcend the limits of zoological and botanical -divisions. How heterogeneities of action have progressed along with -heterogeneities of structure—that is the inquiry before us; and -obviously, in pursuing it, all the specialities with which Physiology -usually deals can serve us only as materials.</p> - -<p>Before entering on the study of Morphological Development, it -was pointed out that while facts of structure may be empirically -generalized apart from facts of function, they cannot be rationally -interpreted apart; and throughout the<span class="pagenum" id="Page_240">[240]</span> foregoing pages this truth has -been made abundantly manifest. Here we are obliged to recognize the -interdependence still more distinctly; for the phenomena of function -cannot even be conceived without direct and perpetual consciousness of -the phenomena of structure. Though the subject-matter of Physiology -is as broadly distinguished from the subject-matter of Morphology as -motion is from matter; yet, just as the laws of motion cannot be known -apart from some matter moved, so there can be no knowledge of function -without a knowledge of some structure as performing function.</p> - -<p>Much more than this is obvious. The study of functions, considered from -our present point of view as arising by Evolution, must be carried on -<i>mainly</i> by the study of the correlative structures. Doubtless, -by experimenting on the organisms which are growing and moving around -us, we may ascertain the connexions existing among certain of their -actions, while we have little or no knowledge of the special parts -concerned in those actions. In a living animal that can be conveniently -kept under observation, we may learn the way in which conspicuous -functions vary together—how the rate of a man’s pulse increases with -the amount of muscular exertion he is undergoing; or how a horse’s -rapidity of breathing is in part dependent on his speed. But though -observations of this order are indispensable—though by accumulation -and comparison of such observations we learn which parts perform which -functions—though such observations, prosecuted so as to disclose -the actions of all parts under all circumstances, constitute, when -properly generalized and co-ordinated, what is commonly understood as -Physiology; yet such observations help us but a little way towards -learning how functions came to be established and specialized. -We have next to no power of tracing up the genesis of a function -considered purely as a function—no opportunity of observing the -progressively-increasing quantities of a given action that have arisen -in any order of organisms. In nearly all cases we are able only to -show<span class="pagenum" id="Page_241">[241]</span> the greater growth of the part which we have found performs the -action, and to infer that greater action of the part has accompanied -greater growth of it. The tracing out of Physiological Development, -then, becomes substantially a tracing out of the development of -the organs by which the functions are known to be discharged—the -differentiation and integration of the functions being presumed to have -progressed hand in hand with the differentiation and integration of the -organs. Between the inquiry pursued in Part IV, and the inquiry to be -pursued in this Part, the contrast is that, in the first place, facts -of structure are now to be used to interpret facts of function, instead -of conversely; and, in the second place, the facts of structure to be -so used are not those of conspicuous shape so much as those of minute -texture and chemical composition.</p> - - -<p class="p2">§ 266. The problems of Physiology, in the wide sense above -described, are, like the problems of Morphology, to be considered -as problems to which answers must be given in terms of incident -forces. On the hypothesis of Evolution these specializations of -tissues and accompanying concentrations of functions, must, like the -specializations of shape in an organism and its component divisions, -be due to the actions and reactions which its intercourse with the -environment involves; and the task before us is to explain how they are -wrought—how they are to be comprehended as results of such actions and -reactions.</p> - -<p>Or, to define these problems still more specifically:—Those extremely -unstable substances composing the protoplasm of which organisms are -mainly built, have to be traced through the various modifications in -their properties and powers, that are entailed on them by changes of -relation to agencies of all kinds. Those organic colloids which pass -from liquid to solid and from soluble to insoluble on the slightest -molecular disturbance—those albuminoid matters which, as we see in -clotted blood or the coagulable lymph poured<span class="pagenum" id="Page_242">[242]</span> out on abraded surfaces -and causing adhesion between inflamed membranes, assume new forms -with the greatest readiness—are to have their metamorphoses studied -in connexion with the influences at work. Those compounds which, as -we see in the quickly-acquired brownness of a bitten apple or in the -dark stains produced by the milky juice of a Dandelion, immediately -begin to alter when the surrounding actions alter, are to be everywhere -considered as undergoing modifications by modified conditions. Organic -bodies, consisting of substances that, as I here purposely remind the -reader, are prone beyond all others to change when the incident forces -are changed, we must contemplate as in all their parts differently -changed in response to the different changes of the incident forces. -And then we have to regard the concomitant differentiations of their -reactions as being concomitant differentiations of their functions.</p> - -<p>Here, as before, we must take into account two classes of factors. -We have to bear in mind the inherited results of actions to which -antecedent organisms were exposed, and to join with these the results -of present actions. Each organism is to be considered as presenting -a moving equilibrium of functions, and a correlative arrangement -of structures, produced by the aggregate of actions and reactions -that have taken place between all ancestral organisms and their -environments. The tendency in each organism to repeat this adjusted -arrangement of functions and structures, must be regarded as from time -to time interfered with by actions to which its inherited equilibrium -is not adjusted—actions to which, therefore, its equilibrium has to be -re-adjusted. And in studying physiological development we have in all -cases to contemplate the progressing compromise between the old and the -new, ending in a restored balance or adaptation.</p> - -<p>Manifestly our data are so scanty that nothing more than very general -and approximate interpretations of this kind are possible. If the -hypothesis of Evolution furnishes us with a rude conception of the -way in which the<span class="pagenum" id="Page_243">[243]</span> more conspicuous and important differentiations of -functions have arisen, it is as much as can be expected.</p> - - -<p class="p2">§ 267. It will be best, for brevity and clearness, to deal with these -physiological problems as we dealt with the morphological ones—to -carry on the inductive statement and the deductive interpretation -hand in hand: so disposing of each general truth before passing -to the next. Treating separately vegetal organisms and animal -organisms, we will in each kingdom consider:—first, the physiological -differentiations and accompanying changes of structure which arise -between outer tissues and inner tissues; next, those which arise -between different parts of the outer tissues; and, finally, those which -arise between different parts of the inner tissues. What little has -to be said concerning physiological integration must come last. For -though, in tracing up Morphological Evolution, we have to study those -processes of integration by which organic aggregates are formed, before -studying the differentiations that arise among their parts; we must, -contrariwise, in tracing up Physiological Evolution, study the genesis -of the different functions before we study the interdependence that -eventually arises among them and constitutes physiological unity.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_244">[244]</span></p> - -<h3>CHAPTER II.<br /> -<span class="subhed1">DIFFERENTIATIONS BETWEEN THE OUTER AND INNER TISSUES OF PLANTS.</span></h3></div> - - -<p>§ 268. The simplest plant presents a contrast between its peripheral -substance and its central substance. In each protophyte, be it a -spherical cell or a branched tube, or such a more-specialized form as a -Desmid, a marked unlikeness exists between the limiting layer and that -which it limits. These vegetal aggregates of the first order may differ -widely from one another in the natures of their outer coats and in the -natures of their contents. As in the Palmella-form of one of the lower -<i>Algæ</i>, there may exist a clothing of jelly; or, as in Diatom, the -walls may take the form of silicious valves variously sculptured. The -contained matter may be partly or wholly here green, there red, and in -other cases brown. But amid all these diversities there is this one -uniformity—a strong distinction between the parts in contact with the -environment and the parts not in contact with the environment.</p> - -<p>When we remember that this trait is one which these simple living -bodies have in common with bodies that are not living—when we -remember that each inorganic mass eventually has its outer part more -or less differentiated from its inner part, here by oxidation, there -by drying, and elsewhere by the actions of light, of moisture, of -frost; we can scarcely resist the conclusion that, in the one case -as in the other, the contrast is due to the unlike actions to which -the<span class="pagenum" id="Page_245">[245]</span> parts are subject. Given an originally-homogeneous portion of -protoplasm, and it follows from the general laws of Evolution (First -Principles, §§ 149–155), first, that it must lose its homogeneity, and, -second, that the leading dissimilarities must arise between the parts -most-dissimilarly conditioned—that is, between the outside and the -inside. The exterior must bear amounts and kinds of force unlike the -amounts and kinds which the interior bears; and from the persistence -of force it follows inevitably that unlike effects must be wrought on -them—they must be differentiated.</p> - -<p>What is the limit towards which the differentiation tends? We have seen -that the re-distribution of matter and motion whence, under certain -conditions, evolution results, can never cease until equilibrium is -reached—proximately a moving equilibrium, and finally a complete -equilibrium (<i>First Principles</i>, §§ 170–175). Hence, the -differentiation must go on until it establishes such differences in the -parts as shall balance the differences in the forces acting on them. -When dealing with equilibration in general, we saw that this process -is what is called adaptation (<i>First Principles</i>, § 173); and, in -this work, we saw that by it the totality of functions of an organism -is brought into correspondence with the totality of actions affecting -it (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect159">§§ 159–163</a>). Manifestly in this case, as in all others, either -death or adjustment must eventually result. A force falling on one of -these minute aggregates of protoplasm, must expend itself in working -its equivalent of change. If this force is such that in expending -itself it disturbs beyond rectification the balance of the organic -processes, then the aggregate is disintegrated or decomposed. But if it -does not overthrow that moving equilibrium constituting the life of the -aggregate, then the aggregate continues in that modified form produced -by the expenditure of the force. Thus, by direct equilibration, -continually furthered by indirect equilibration, there must arise this -distinction between the outer part adapted to meet outer forces, and -the inner part adapted to meet inner forces. And<span class="pagenum" id="Page_246">[246]</span> their respective -actions, as thus meeting outer and inner forces, must be what we call -their respective functions.</p> - - -<p class="p2">§ 269. Aggregates of the second order exhibit parallel traits, -admitting of parallel interpretations. Integrated masses of cells or -units homologous with protophytes, habitually show us contrasts between -the characters of the superficial tissues and the central tissues. Such -among these aggregates of the second order as have their component -units arranged into threads or laminæ, single or double, cannot, of -course, furnish contrasts of this kind; for all their units are as much -external as internal. We must turn to the more or less massive forms.</p> - -<p>Of these, among <i>Fungi</i>, the common Puff-ball is a good -example—good because it presents this fundamental differentiation -but little complicated by others. In it we have a cortical layer -of interwoven hyphæ obviously unlike the mass of spores which it -incloses. So far as the unlikeness between external and internal -parts is concerned, we see here a relation analogous to that existing -in the simple cell; and we see in it a similar meaning: there is a -physiological differentiation corresponding to the difference in the -incidence of forces.</p> - -<p>Under various forms the <i>Algæ</i> show just the same relation. -Where, as in <i>Codium Bursa</i>, we have the ramified tubular -branches of the thallus aggregated into a hollow globular mass, the -outer and inner surfaces are contrasted both in colour and structure, -though the tubules composing the two surfaces are continuous with one -another. In <i>Rivularia</i>, again, we see the like, both in the -radial arrangement of the imbedded threads and in the difference of -colour between the exterior of the imbedding jelly and its interior. -The more-developed <i>Algæ</i> of all kinds repeat the antithesis. -In branched stems, when they consist of more than single rows of -cells, the outer cells become unlike the inner, as shown in Fig. <a href="#i_029">35</a>. -Such types as <i>Chrysymenia rosea</i> show us this<span class="pagenum" id="Page_247">[247]</span> unlikeness very -conspicuously. And it holds even with ribbon-shaped fronds. Wherever -one of these is composed of three, four, or more layers, as in -<i>Laminaria</i> and <i>Punctaria</i>, the cells of the external layers -are strongly distinguished from those of the internal layers, both by -their comparative smallness and by their deep colour.</p> - - -<p class="p2">§ 270. The higher plants variously display the like fundamental -distinction between outer and inner tissues. Each leaf, thin as it is, -exemplifies this differentiation of the parts immediately in contact -with the environment from the parts not in immediate contact with -the environment. Its epidermal cells, forming a protecting envelope, -diverge physically and chemically from the mesophyll cells, which carry -on the more active functions. And the contrast may be observed to -establish itself in the course of development. At first the component -cells of the leaf are all alike; and this unlikeness between the cells -of the outer and inner layers, arises simultaneously with the rise of -differences in their conditions—differences that have acted on all -ancestral leaves as they act on the individual leaf.</p> - -<p>An unlikeness more marked in kind but similar in meaning, exists -between the bark of every branch and the tissues it clothes. The -phænogamic axis, especially when it undergoes what is known as -secondary thickening, is commonly characterized by an outer zone of -cells (the cork layer) differing from the inner layers in character and -function, as it differs from them in position. Subject as this outer -layer is to the unmitigated actions of forces around—to abrasions, to -extremes of heat and cold, to evaporation and soaking with water—its -units have to be brought into equilibrium with these more violent -actions, and have acquired molecular constitutions more stable -than those of the interior cells. That is to say, the forces which -differentiate the cortical part from the rest are the forces which it -has to resist, and from which it passively protects the parts within. -How<span class="pagenum" id="Page_248">[248]</span> clearly this heterogeneity of structure and function is consequent -upon intercourse with the environment, every tree and shrub shows. The -young shoots, alike of annuals and perennials, are quite green and soft -at their extremities. Among plants of short lives, there is usually -but a slight development of bark or none at all: such traces of it as -the surface of the axis acquires being seen only at its lowermost or -oldest portion. In long-lived plants, however, this formation of a -tough opaque coating takes place more rapidly; and shows us distinctly -the connexion between the degree of differentiation and the length of -exposure. For, in a growing twig, we see that the bark, invisible at -the bud, thickens by insensible gradations as we go downwards to the -junction of the twig with the branch; and we come to still thicker -parts of it as we descend along the branch towards the main stem. -Moreover, on examining main stems we find that while in some trees the -bark, cracked by expansion of the wood, drops off in flakes, leaving -exposed patches of the inner tissue which presently become green and -finally develop new bark; in other trees the exfoliated flakes continue -adherent, and in the course of years form a rugged fissured coat: so -producing a still more marked contrast between outside and inside. Of -course the establishment of this heterogeneity is furthered by natural -selection, which, where a protective covering is needed, gives an -advantage to those individuals in which it has become strongest. But -that this divergence of structure commences as a direct adaptation, is -clearly shown by other facts than the foregoing. There is the fact that -many of the plants which in our gardens develop bark with considerable -rapidity, do not develop it with the same rapidity in a greenhouse. And -there is the fact that plants which, in some climates, have their stems -covered only by thin semi-transparent layers, acquire thick opaque -layers when taken to other climates.</p> - -<p>Just noting, for the sake of completeness, that in the roots of the -higher plants there arises a contrast between<span class="pagenum" id="Page_249">[249]</span> outer and inner parts, -parallel to the one we have traced in their branches, let me draw -attention to another differentiation of the same ultimate nature, which -the higher plants exhibit to us—a differentiation which, familiar -though it is, gains a new meaning by association with those named -above, and makes their meaning still more manifest. Each great plant -shows it. When, by the budding of axes out of axes, there is produced -one of those highly-compounded Phænogams which we call a tree, the -central part of the aggregate becomes functionally and structurally -unlike the peripheral part. On looking into a large tree, or even -a small one which has thick foliage, like the Laurel, we see that -the internal branches are almost or quite bare of leaves, while the -leaf-clad branches form an external stratum; and all our experience -unites in proving that this contrast arises by degrees, as fast as -the growth of the tree entails a contrast between the conditions -to which inner and outer branches are exposed. Now when, in these -most-composite aggregates, we see a differentiation between peripheral -and central parts demonstrably caused by a difference in the relations -of these parts to environing forces, we get support for the conclusion -otherwise reached, that there is a parallel cause for the parallel -differentiations exhibited by all aggregates of lower orders—branches, -leaves, cells.</p> - - -<p class="p2">§ 271. Before leaving this most general physiological differentiation, -it may be well to say something respecting certain secondary -unlikenesses which usually arise between interior and exterior. For the -contrast is not, as might be supposed from the foregoing descriptions, -a simple contrast: it is a compound contrast. The outer structure -itself is usually divisible into concentric structures. This is equally -true of a protophyte and of a phænogamic axis. Between the centre of -an independent vegetal cell and its surface, there are at least two -layers; and the bark coating the substance of a shoot, besides being -itself compound, includes<span class="pagenum" id="Page_250">[250]</span> another tissue lying between it and the -wood. What is the physical interpretation of these facts?</p> - -<p>When a mass of something we distinguish as inert matter is exposed -to external agencies capable of working changes in it—when it is -chemically acted upon, or when, being dry, it is allowed to soak, or -when, being wet, it is allowed to dry—the changes set up progress in -an equable way from the surface towards the centre. At any time during -the process (supposing no other action supervenes) the modification -wrought, first completed at the outside, either gradually diminishes -as we approach the centre, or ceases suddenly at a certain distance -from the centre. But now suppose that the mass, instead of being -inert, is the seat of active changes—suppose that it is a portion of -complex colloidal substance, permeable by light and by fluids capable -of affecting its unstable molecules—suppose that its interior is -a source of forces continually liberated and diffusing themselves -outwards. Is it not likely that while at the centre the action of the -internally-liberated forces will dominate, and while at the surface -the action of the environing forces will dominate, there will be -between the two a certain place at which their actions balance? May -we not expect that this will be the place where the most unstable -matter exists—the place outside of which the matter becomes relatively -stable in the face of external forces, and inside of which the matter -becomes relatively stable in the face of internal forces? And must we -not conclude that though part of the adjustment is due to indirect -equilibration, the initiation of it is due to direct equilibration?</p> - -<p>But we are here chiefly concerned with the more general interpretation, -which is independent of any such speculation as the foregoing. These -contrasted tissues and the contrasted functions they severally perform -are, beyond question, subordinated to the relations of outside and -inside. And the evidence makes it tolerably clear that the unlike -actions or forces involved by the relations of outside and inside, -determine these contrasts—partly directly and partly indirectly.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_251">[251]</span></p> - -<h3>CHAPTER III.<br /> -<span class="subhed1">DIFFERENTIATIONS AMONG THE OUTER TISSUES OF PLANTS.</span></h3></div> - - -<p>§ 272. The motionless protococcoid forms of lower <i>Algæ</i>, which -do not permanently expose any parts of their surfaces to actions -unlike those which other parts are exposed to, have no parts of their -surfaces unlike the rest in function and composition. This is what -the hypothesis prepares us for. If physiological differentiations -are determined by differences in the incidence of forces, then there -will be no such differentiations where there are no such differences. -Contrariwise, it is to be expected that the most conspicuous -unlikeness of function and minute structure will arise between the -most-dissimilarly circumstanced parts of the surface. We find that -they do. The upper end and the lower end, or, more strictly speaking, -the free end and the attached end, habitually present the strongest -physiological contrasts.</p> - -<p>Even aggregates of the first order illustrate this truth. Such -so-called unicellular plants as those delineated in Figs. <a href="#i_022b">4, 5, and 6</a>, -show us, on comparing the contents of their fixed ends and their loose -ends, that different processes are going on in them, and that different -functions are being performed by their limiting membranes. <i>Caulerpa -prolifera</i>, which “consists of a little creeping stem with roots -below and leaves above,” originating “in the growth of a body which may -be regarded as an individual cell,” supplies a still-better example. -Among aggregates<span class="pagenum" id="Page_252">[252]</span> of the second order a like connexion is displayed in -more various modes but with equal consistency. As before, the Puff-ball -served to exemplify the primary physiological differentiation of outer -parts from inner parts; so, here, it supplies a simple illustration of -the way in which the differentiated outer part is re-differentiated, -in correspondence with the chief contrast in its relations to the -environment. The only marked unlikeness which the cortical layer of the -Puff-ball presents, is that between the portion next the ground and -the opposite portion. The better-developed <i>Fungi</i> exhibit a more -decided heterogeneity of parallel kind. Such incrusting <i>Algæ</i> -as <i>Ralfsia verrucosa</i> furnish a kindred contrast; and in the -higher <i>Algæ</i> it is uniformly repeated. Phænogams display this -physiological differentiation very conspicuously. That earth and air -are unlike portions of the environment, subjecting roots and leaves -to unlike physical forces, which entail on them unlike reactions, and -that the unlike functions and structures of their respective surfaces -are fitted to these unlike physical forces, are familiar facts which it -would be needless here to name, were it not that they must be counted -as coming within a wider group of facts.</p> - -<p>Is this unlikeness between the outer tissues of the attached ends -and those of the free ends in plants, determined by their converse -with the unlike parts of the environment? That they result from an -equilibration partly arising in the individual and partly arising by -the survival of individuals in which it has been carried furthest, is -inferable <i>à priori</i>; and this <i>à priori</i> argument may be -adequately enforced by arguments of the inductive order. A few typical -ones must here suffice. The gemmules of the <i>Marchantia</i> are -little disc-shaped masses of cells composed of two or more layers. -Their sides being alike, there is nothing to determine which side falls -lowermost when one of them is detached. Whichever side falls lowermost, -however, presently begins to send out rootlets, while<span class="pagenum" id="Page_253">[253]</span> the uppermost -side begins to assume those characters which distinguish the face of -the frond. When this differentiation has commenced, the tendency to its -complete establishment becomes more and more decided; as is proved by -the fact that if the positions of the surfaces be altered, the gemmule -bends itself so as to re-adjust them: the change towards equilibrium -with environing forces having been once set up, there is acquired, -as it were, an increasing momentum which resists any counter-change. -But the evidence shows that at the outset, the relations to earth -and air alone determine the differentiation of the under surface -from the upper. The experiences of the gardener, multiplying his -plants by cuttings and layers, constitute another class of evidences -not to be omitted: they are commonplace but instructive examples of -physiological differentiation. While circumstanced as it usually is, -the meristematic tissue of each branch in a Phænogam continues to -perform its ordinary function—regularly producing on its outer side -the cortical substances, and on its inner side the vascular and woody -tissues. But change the conditions to those which the underground part -of the plant is exposed to, and there begins another differentiation -resulting in underground structures. Contact with water often suffices -alone to produce this result, as in the branches of some trees when -they droop into a pool, or as occasionally with a cutting placed in a -bottle of water; and when the light is excluded by imbedding the end -of the cutting, or the middle of the still-attached branch, in the -earth, this production of tissues adapted to the function of absorbing -moisture and mineral constituents proceeds still more readily. -With such cases may be grouped those in which this development of -underground organs by an above-ground tissue, is not exceptional but -habitual. Creeping plants furnish good illustrations. From the shoots -of the Ground-Ivy, rootlets are put out into the soil in a manner -differing but little from that in which they are put out by an imbedded -layer; save<span class="pagenum" id="Page_254">[254]</span> that the process follows naturally-induced conditions -instead of following artificially-induced conditions. But in the common -Ivy which, instead of running along the surface of the earth, runs -up inclined or vertical surfaces, we see the process interestingly -modified without being essentially changed. The rootlets, here -differentiated by their conditions into organs of attachment much more -than organs of absorption, still develop on that side of the shoot next -the supporting surface, and do not develop where the shoot, growing -away from the tree or wall, is surrounded equally on all sides by light -and air: thus showing, undeniably, that the production of the rootlets -is determined by the differential incidence of forces. Though survival -of the fittest doubtless furthered this transition yet it clearly -did not initiate it. That greenness which may be observed in these -Ivy-branch rootlets while they are quite young, soft, and unshaded, -introduces us to facts which are the converse of the foregoing facts; -and proves that the parts ordinarily imbedded in the soil and adapted -to its actions, acquire, often in very marked degrees, the superficial -structures of the aërial parts, when they are exposed to light and air. -This may be witnessed in Maize, which, when luxuriant, sends out from -its nodes near the ground, clusters of roots that are thick, succulent, -and of the same colour as the leaves. Examples more familiar to us -in England occur in every field of turnips. On noting how green is -the uncovered part of a turnip-root, and how manifestly the area over -which the greenness extends varies with the area exposed to light, as -well as with the degree of the exposure, it will be seen that beyond -question, root-tissue assumes to a considerable extent the appearances -and function of leaf tissue, when subject to the same agencies. Let -us not forget, too, that where exposed roots do not approach in -superficial character towards leaves, they approach in superficial -character towards stems: becoming clothed with a thick, fissured bark, -like that of the trunk and<span class="pagenum" id="Page_255">[255]</span> branches. But the most conclusive evidence -is furnished by the actual substitutions of surface-structures and -functions, that occur in aërial organs which have taken to growing -permanently under ground, and in underground organs which have taken to -growing permanently in the air. On the one hand, there is the rhizome -exemplified by Ginger—a stem which, instead of shooting up vertically, -runs horizontally below the surface of the soil, and assumes the -character of a root, alike in colour, texture, and production of -rootlets; and there is that kind of swollen underground axis, bearing -axillary buds, which the Potato exemplifies—a structure which, though -homologically an axis, simulates a tuberous root in surface-character, -and when exposed to the air, manifests no greater readiness to develop -chlorophyll than a tuberous root does. On the other hand, there are the -aërial roots of certain Orchids which, habitually green at their tips, -continue green throughout their whole lengths when kept moist; which -have become leaf-like not only by this development of chlorophyll, but -also by the acquirement of stomata; and which do not bury themselves in -the soil when they have the opportunity.<a id="FNanchor_46" href="#Footnote_46" class="fnanchor">[46]</a> Thus we have aërial organs -so completely changed to fit underground actions, that they will not -resume aërial functions; and underground organs so completely changed -to fit aërial actions, that they will not resume underground functions.</p> - -<p>That the physiological differentiation between the part of a plant’s -surface which is exposed to light and air and the part which is exposed -to darkness and moisture and solid<span class="pagenum" id="Page_256">[256]</span> matter, is primarily due to the -unlike actions of these unlike parts of the environment, is, then, -clearly implied by observed facts—more clearly, indeed, than was to -be expected. Considering how strong must be the inherited tendency -of a plant to assume those special characters, physiological as well -as morphological, which have resulted from an enormous accumulation -of antecedent actions, it may be even thought surprising that this -tendency can be counteracted to so great an extent by changed -conditions. Such a degree of modifiability becomes comprehensible only -when we remember how little a plant’s functions are integrated, and how -much, therefore, the functions going on in each part may be altered -without having to overcome the momentum of the functions throughout -the whole plant. But this modifiability being as great as it is, we -can have no difficulty in understanding how, by the cumulative aid -of natural selection, this primary differentiation of the surface in -plants has become what we see it.</p> - - -<p class="p2">§ 273. We will leave now these contrasts between the free surfaces -of plants and their attached or imbedded surfaces, and turn our -attention to the secondary contrasts existing between different -parts of their free surfaces. Were a full statement of the evidence -practicable, it would be proper here to dwell on that which is -furnished by the inferior classes. It might be pointed out in detail -that where, as among the <i>Algæ</i>, the free surfaces are not -dissimilarly conditioned, there is no systematic differentiation -of them—that the frond of an <i>Ulva</i>, the ribbon-shaped -divisions of a <i>Laminaria</i>, and the dichotomous expansions -of the <i>Fuci</i> which clothe the rocks between tide-marks, are -alike on both sides; because, swayed about in all directions as -they are by the waves and tides, their sides are equally affected. -Conversely, from the <i>Fungi</i> might be drawn abundant proof -that even among Thallophytes, unlikenesses arise between different -parts of the free surfaces when their circumstances are unlike.<span class="pagenum" id="Page_257">[257]</span> In -such laterally-growing kinds as are shown in Fig. <a href="#i_138">196<i>b</i></a>, the -honey-combed under surface and the smooth leathery upper surface, -have their contrasts related to contrasted conditions; and in the -adjacently-figured Agarics, and other stalked genera, the pileus -exhibits a parallel difference, explicable in a parallel way. But -passing over Cryptogams it must suffice if we examine more at length -these traits as they are displayed by Phænogams. Let us first note the -dissimilarities between the outer tissues of stems and leaves.</p> - -<p>That these dissimilarities arose by degrees, as fast as the units -of which the phænogamic axis is composed became integrated, is a -conclusion in harmony with the truth that in every shoot of every -plant, they are at first slight and become gradually marked. Already, -in briefly tracing the contrasts between the outer and inner tissues -of plants, some facts have been named showing, by implication, how -the cessation of the leaf-function in axes is due to that change of -conditions entailed by the discharge of other functions. Here we have -to consider more closely facts of this class, together with others -immediately to the point. On pulling off from a stem of grass the -successive sheaths of its leaves, the more-inclosed parts of which are -of a fainter green than the outer parts, it will be found that the -tubular axis eventually reached is of a still fainter green; but when -the axis eventually shoots up into a flowering stem, its exposed part -acquires as bright a green as the leaves. In other Monocotyledons, the -leaf-sheaths of which are successively burst and exfoliated by the -swelling axis, it may be observed that where the dead sheaths do not -much obstruct the light and air, the surface of the axis underneath is -full of chlorophyll. <i>Dendrobium</i> is an example. But when the dead -sheaths accumulate into an opaque envelope, the chlorophyll is absent, -and also, we may infer, the function which its presence habitually -implies. Carrying with us this evidence, we shall recognize a like -relation in Dicotyledons. While its outer layer remains tolerably -transparent, an exogenous stem or<span class="pagenum" id="Page_258">[258]</span> branch continues to show, by the -formation of chlorophyll, that it shares in the duties of the leaves; -but in proportion as a bark which the light cannot penetrate is -produced by the adherent flakes of dead skin, or by the actual deposit -of a protective substance, the differentiation of duties becomes more -decided. Cactuses and Euphorbias supply us with converse facts having -the same implication. The succulent axes so strangely combined in -these plants, maintain for a long time the translucency of their outer -layers and their greenness; and they so efficiently perform the offices -of leaves that leaves are not produced. In some cases, axes that are -not succulent participate largely in the leaf-function, or entirely -usurp it—still, however, by fulfilling the same essential conditions. -Occasionally, as in <i>Statice brassicæfolia</i>, stems become fringed; -and the fringes they bear assume, along with the thinness of leaves, -their darker green and general aspect. In the genus <i>Ruscus</i>, -the flattened axis simulates so closely the leaf-structure, that -were it not for the flower borne on its mid-rib, or edge, its axial -nature would hardly be suspected. And let us not omit to note that -where axes usurp the characters of leaves, in their attitudes as -well as in their shapes and thicknesses, there are contrasts between -their under and upper surfaces, answering to the contrasts between -the relations of these surfaces to the light. Of this <i>Ruscus -androgynus</i> furnishes a striking example. In it the difference -which the unaided eye perceives is much less conspicuous than that -disclosed by the microscope; for I find that while the face of the -pseudo-leaf has no stomata, the back is abundantly supplied with them. -One more illustration must be added. Equally for the morphological -and physiological truths which it enforces, the <i>Mühlenbeckia -platyclada</i> is one of the most instructive of plants. In it the -simulation of forms and usurpation of functions, are carried out in -a much more marvellous way than among the <i>Cactaceæ</i>. Imagine a -growth resembling in outline a very long willow-leaf, but without a -mid-rib, and having its two surfaces alike.<span class="pagenum" id="Page_259">[259]</span> Imagine that across this -thin, green, semi-transparent structure, there are from ten to thirty -divisions, which prove to be the successive nodes of an axis. Imagine -that along the edges of this leaf-shaped aggregate of internodes, there -arise axillary buds, some of which unfold into flowers, and others of -which shoot up vertically into growths like the one which bears them. -Imagine a whole plant thus seemingly composed of jointed willow-leaves -growing from one another’s edges, and some conception will be formed of -the <i>Mühlenbeckia</i>. The two facts which have meaning for us here -are—first, that the performance of leaf-functions by these axes goes -along with the assumption of a leaf-like translucency; and, second, -that these flattened axes, retaining their upright attitudes, and -therefore keeping their two faces similarly conditioned, have these two -faces alike in colour and texture.</p> - -<p>That physiological differentiation of the surface which arises in -Phænogams between axial organs and foliar organs, is thus traceable -with tolerable clearness to those differences between their conditions -which integration has entailed—partly in the way above described and -partly in other ways still to be named. By its relative position, as -being shaded by the leaves, the axis is less-favourably circumstanced -for performing those assimilative actions effected by the aid of light. -Further, that relatively-small ratio of surface to mass in the axis, -which is necessitated by its functions as a support and a channel -for circulation, prevents it from taking in, with the same facility -as the leaves, those surrounding gases from which matter is to be -assimilated. Both these special causes, however, in common with that -previously assigned, fall within the general cause. And in the fact -that where the differential conditions do not exist, the physiological -differentiation does not arise, or is obliterated, we have clear proof -that it is determined by unlikenesses in the relations of the parts to -the environment.</p> - - -<p class="p2">§ 274. From this most general contrast between aërial<span class="pagenum" id="Page_260">[260]</span> -surface-tissues—those of axes and those of folia—we pass now to the -more special contrasts of like kind existing in folia themselves. -Leaves present us with superficial differentiations of structure and -function; and we have to consider the relations between these and the -environing forces.</p> - -<p>Over the whole surface of every phænogamic leaf, as over the fronds of -the <i>Pteridophyta</i>, there extends a simple or compound epidermal -layer, formed of cells that are closely united at their edges and -devoid (in the Flowering Plants) of that granular colouring matter -(chlorophyll) contained in the layers of cells they inclose: the result -being that the membrane formed of them is comparatively transparent. On -the submerged leaves of aquatic Phænogams, this outer layer is thin, -delicate, and permeable by water; but on leaves exposed to the air, and -especially on their upper surfaces, is comparatively strong, dense, -often smooth and impermeable by water: being thus fitted to prevent the -rapid escape of the contained juices by evaporation. Similarly, while -the leaves of terrestrial plants which live in temperate climates, -usually have comparatively thin coats thus composed, in climates that -are both hot and dry, leaves are commonly clothed with a very thick -cuticle. Nor is this all. The outside of an aërial leaf differs from -that of a submerged leaf by containing a deposit of waxy substance. -Whether this be exuded by the exposed surfaces of the cells, as some -contend, or whether it is deposited within the cells, as thought by -others, matters not in so far as the general result is concerned. In -either case a waterproof coating is formed at the outermost sides of -these outermost cells; and in many cases produces that polish by which -the upper surface of the leaf is more or less distinguished from the -under surface. This external pellicle presents us with another contrast -of allied meaning. On the upper surfaces of leaves subject to the -direct action of the sun’s rays, there are either few or none of those -minute openings, or stomata, through which gases can enter or escape; -but on the under surfaces these stomata<span class="pagenum" id="Page_261">[261]</span> are abundant: a distribution -which, while permitting free absorption of the needful carbonic acid, -puts a check on the exit of watery vapour. Two general exceptions to -this arrangement may be noted. Leaves that float on the water have all -their stomata on their upper sides, and leaves that are submerged have -no stomata—modifications obviously appropriate to the conditions. -What is to be said respecting the genesis of these differentiations? -For the last there seems no direct cause: its cause must be indirect. -The unlike actions to which the upper and under surfaces of leaves are -subject, have no apparent tendency to produce unlikeness in the number -of their breathing holes. Here the natural selection of spontaneous -variations furnishes the only feasible explanation. For the first, -however, there is a possible cause in the immediate actions of incident -forces, which survival of the fittest continually furthers.</p> - -<p>The fluid exhaling through the walls of the cells next the air, will be -likely to leave behind suspended substances on their outer surfaces. -On remembering the pellicle which is apt to form on thick solutions or -emulsions as they dry, and how this pellicle as it grows retards the -further drying, it will be perceived that the deposit of waxy matter -next to the outer surfaces of the cuticular cells in leaves, is not -improbably initiated by the evaporation which it eventually checks. -Should it be so, there results a very simple case of equilibration. -Where the loss of water is too great, this waxy pellicle left behind by -the escaping water will protect most those individuals of the species -in which it is thickest or densest; and by inheritance and continual -survival of the fittest, there will be established in the species that -thickness of the layer which brings the evaporation to a balance with -the supply of water.</p> - -<p>Another superficial differentiation, still more familiar, has to be -noted. Every child soon learns to distinguish by its colour the upper -side of a leaf from its under side, if the leaf is one that has grown -in such way as to establish the relations of upper and under. The upper -surfaces of leaves are<span class="pagenum" id="Page_262">[262]</span> habitually of a deeper green than the under. -Microscopic examination shows that this deeper green results from the -closer clustering of those parenchyma-cells full of chlorophyll that -are in some way concerned with the assimilative actions; while beneath -them are more numerous intercellular passages communicating with those -openings or stomata through which is absorbed the needful air. Now when -it is remembered that the formation of chlorophyll is clearly traceable -to the action of light—when it is remembered that leaves are pale -where they are much shaded and colourless when developed in the dark, -as in the heart of a Cabbage—when it is remembered that succulent axes -and petioles, like those of Sea-kale and Celery, remain white while -the light is kept from them and become green when exposed; it cannot -be questioned that this greater production of chlorophyll next to the -upper surface of a leaf, is directly consequent on the greater amount -of light received. Here, as in so many other cases, we must regard -the differentiation as in part due to direct equilibration and in -part to indirect equilibration. Familiar facts compel us to conclude -that from the beginning, each individual foliar organ has undergone -a certain immediate adaptation of its surfaces to the incidence of -light; that when there arose a mode of growth which exposed the leaves -of successive generations in similar ways, this immediately-produced -adaptation, ever tending to be transmitted, was furthered by the -survival of individuals inheriting it in the greatest degree; and that -so there was gradually established that difference between the two -surfaces which each leaf displays before it unfolds to the light, but -which becomes more marked when it has unfolded.<a id="FNanchor_47" href="#Footnote_47" class="fnanchor">[47]</a></p> - -<p><span class="pagenum" id="Page_263">[263]</span></p> - -<p>From the ordinary cases let us now pass to the exceptional cases. We -will look first at those in which the two faces of the leaves differ -but little, or not at all—their circumstances being similar or equal. -Leaves that grow in approximately-upright attitudes, and attitudes -which do not maintain the relative positions of the two surfaces with -constancy, may be expected to display an unusual likeness between the -two surfaces; and among them we see it. The Grasses may be named as a -group exemplifying this relation; and if, instead of comparing them -as a group with other groups, we compare those dwarf kinds of them -which spread out their leaves horizontally, with the large aspiring -kinds, such as <i>Arundo</i>, we trace a like antithesis: in the one -the contrast of upper and under is very obvious, while in the other -it is scarcely to be detected. Leaves of various other Monocotyledons -that grow in a similar way, similarly show us a near approach to -uniformity of the two surfaces; as instance the genus <i>Clivia</i> -and the thinner-leaved kinds of <i>Yucca</i>. Where the contrast of -upper and under is greatly diminished by the assumption of a rounded or -cylindrical form, instead of a flattened form, the same thing happens. -The genus <i>Kleinia</i> furnishes illustrations. It may be remarked, -too, that even within the limits of this genus there are instructive -variations; for while in <i>Kleinia ficoides</i> the leaves, shaped -like pea-pods, are broadest in a vertical direction, and have their -lateral surfaces alike in conditions and structure, in other species -the leaves, broader horizontally than vertically, exhibit unlikeness -between the upper and under sides. Equally to the point is the evidence -furnished by vertically-growing leaves that are cylindrical, as those -of <i>Sanseviera cylindrica</i>, or as those of the Rush-tribe: the -similarly-placed surface has all around a similar character. Of kindred -meaning,<span class="pagenum" id="Page_264">[264]</span> and still more conclusive, are the cases in which the under -side of the leaf, being more exposed to light than the upper side, -usurps the character and function of the upper side. If a common Flag -be pulled to pieces, it will be seen that what answers to the face -in other leaves, forms merely the inside of the sheath including the -younger leaves, and is obliterated higher up. The two surfaces of the -blade answer to the two under halves of a leaf that has been, as it -were, folded together lengthways, with the two halves of its upper -surface in contact. And here, in default of an upper surface, the under -surface acquires its character and discharges its function. A like -substitution occurs in <i>Aristea corymbosa</i>; and there are some of -the Orchids, as <i>Lockhartia</i>, which display it in a very obvious -way.</p> - -<p>When joined with the foregoing evidence, the evidence which another -kind of substitution supplies is of great weight. I refer to that which -occurs in the Australian Acacias, already instanced as throwing light -on morphological changes. In these plants the leaves properly so-called -are undeveloped, and the foot-stalks, flattened out into foliaceous -shapes, acquire veins and mid-ribs, and so far simulate leaves as -ordinarily to be taken for them: a fact in itself of much physiological -significance. But that which it concerns us especially to note, is -the absence of distinction between the two faces of these phyllodes, -as they are named, and the cause of its absence. These transformed -petioles do not flatten themselves out horizontally, so as to acquire -under and upper sides, as most true leaves do; but they flatten -themselves out vertically: the result being that their two sides are -similarly circumstanced with respect to light and other agencies; and -there is consequently nothing to cause their differentiation. And then -we find an analogous case where differential conditions arise, and -where some differentiation results. In <i>Oxalis bupleurifolia</i>, -Fig. <a href="#i_041">66</a>, there is a similar flattening out of the petiole into a -pseudo-leaf; but in it the flattening takes place in the same plane as -the leaf,<span class="pagenum" id="Page_265">[265]</span> so as to produce an under and an upper surface; and here the -two surfaces of the pseudo-leaf are slightly unlike—in contour if in -nothing else.</p> - - -<p class="p2">§ 275. We now come to such physiological differentiations among the -outer tissues of plants, as are displayed in the contrasts between -foliar organs on the same axis, or on different axes—contrasts between -the seed-leaves and the leaves subsequently formed, between submerged -and aërial leaves in certain aquatic plants, between leaves and bracts, -and between bracts and sepals. To deal even briefly with these implies -information which even a professed botanist would have to increase by -special inquiries, before attempting interpretations. Here it must -suffice to say something respecting those marked unlikenesses existing -between the tissues of the more characteristic parts of flowers, and -the tissues of the homologous foliar organs.</p> - -<p>It was pointed out in <a href="#sect196">§ 196</a>, that the terminal folia of a phænogamic -axis have sundry characters in common with such fronds as those -out of which we concluded that the phænogamic axis has arisen by -integration—common characters of a kind to be expected. In their -simple cellular composition, comparative want of chlorophyll, and -deficiency of vascular structures, the undeveloped ends of leaf-shoots -and the developed ends of flower-shoots, approach to the fronds of the -simpler Archegoniates. We also noted between them another resemblance. -It is said of the <i>Jungermanniaceæ</i>, that “though under certain -circumstances of a pure green, they are inclined to be shaded with -red, purple, chocolate, or other tints;” and answering to this we -have the facts that such colours commonly occur in the terminal folia -of a phænogamic axis, when arrest of its development leads to the -formation of a flower, and that very frequently they are visible at -the ends of leaf-axes. In the unfolding parts of shoots, more or less -of red, or copper-colour, or chocolate-colour, may generally be seen: -often, indeed, it characterizes<span class="pagenum" id="Page_266">[266]</span> the leaves for some time after they -are unfolded. Occasionally the traces of it are permanent; and, as in -the scarlet terminal leaves of <i>Poinsettia pulcherrima</i>, we see -that it may become, and continue, extremely conspicuous. The question, -then, now to be asked is—has this colouring by which the immature -part of the phænogamic axis is characterized, anything to do with the -colouring of flowers? Has this difference between undeveloped folia and -folia that are further developed, been increased by natural selection -where an advantage accrued from it, until it has ended in the strong -contrast we now see? I think we may not irrationally infer that this -has happened.</p> - -<p>Facts, very numerous and varied, united to warrant us in concluding -that gamogenesis commences where the forces which conduce to growth are -nearly equilibrated by the forces which resist growth (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect78">§ 78</a>); and the -induction that in plants, fertilized germs are produced at places where -there is an approach towards this balance, we found to be in harmony -with the deduction that an advantage to the species must be gained by -sending off migrating progeny from points where nutrition is failing. -Other things equal, failure of nutrition may be expected in parts which -have the most remote or most indirect access to the materials furnished -by the roots—materials which have to be carried great distances by -a very imperfect apparatus. The ends of lateral axes are therefore -the probable points of fructification, in aggregates of the third -order that have taken to growing vertically. But if these points at -which nutrition is failing, are also the points at which the colours -inherited from lower types are likely to recur in more marked degrees -than elsewhere; then we may infer that the organs of fructification -will not unfrequently co-exist with such colours at the ends of such -axes. How may the resulting contrast between the older fronds and the -fronds next the germ-producing organs be increased? If uninterfered -with it would be likely to diminish. These traits inherited from remote -ancestry might be expected<span class="pagenum" id="Page_267">[267]</span> slowly to fade away. How, then, is the -intensification of them to be explained?</p> - -<p>If a contrast of the kind described favours the propagation of a race -in which it exists, it will be maintained and increased; and if we -take into account an agency of which Mr. Darwin has shown the great -importance—the agency of insects—we shall have little difficulty -in understanding how such a contrast may facilitate propagation. We -cannot, of course, here assume the agency of insects so specialized -in their habits as Bees and Butterflies; for their specialized habits -imply the pre-existence of the contrast to be explained. But there is -an insect-agency of a more general kind which may be fairly counted -upon as coming into action. Various small Flies and Beetles wander -over the surfaces of plants in search of food. It is a legitimate -assumption that they will frequent most those parts in which they find -most food, or food most to their liking—especially if at the same time -they gain the advantage of concealment. Now the ends of axes, formed -of young, soft, and closely-packed folia, are the parts which more -than any others offer these several advantages. They afford shelter -from enemies; they frequently contain exuded juices; and when they do -not, their tissues are so tender as to be easily pierced in search -of the sap. If, then, from the first, as at present, these ends of -axes have been favourite haunts of small insects; and if, where the -closely-clustered folia contained the generative organs, the insects -frequenting them occasionally carried adherent fructifying cells from -one plant to another, and so aided fertilization; it would follow -that anything which made such terminal clusters more attractive to -such insects, or more conspicuous to them, or both, would further the -multiplication of the race, and would so be continually increased by -the extra multiplication of individuals in which it was greatest. -Here we find the clue. This contrast of colour between the folia next -to the fructifying parts and all other folia, must constantly have -facilitated insect-agency; supposing<span class="pagenum" id="Page_268">[268]</span> the insects to have had the power -of distinguishing between colours. That Bees and Butterflies have this -power is manifest. They may be watched flying from flower to flower, -disregarding all other parts of the plants. And if the less-specialized -insects possessed some degree of such discrimination, then the initial -contrasts of colour above described would be maintained and increased. -Let such a connexion be once established, and it must tend to become -more decided. Insects most able to discern the parts of plants which -afford what they seek, will be those most likely to survive and leave -offspring. Plants presenting most of the desired food, and showing most -clearly where it lies, will have their fertilization and multiplication -furthered in the greatest degree. And so the mutual adaptation will -become ever closer; while it is rendered at the same time more varied -by the special requirements of the insects and of the plants in each -locality, under each change of conditions. Of course, the genesis -of the sweet secretions and the odours of flowers, has a parallel -interpretation. The simultaneous production of honey, or some kindred -substance, is implied above; since, unless a bait co-existed with -the colour, the colour would not attract insects, and would not be -maintained and intensified by natural selection. Gums, and resins, and -balsams, are familiar products of plants; apparently, in many cases, -excreted as useless matters from various parts of their surfaces. These -substances, admitting of wide variations in quality, as they do, afford -opportunities for the action of natural selection wherever any of -them, attractive to insects, happen to be produced near the organs of -fructification. And this action of natural selection once set up, may -lead to the establishment of a local excretion, to the production of an -excretion more and more attractive, and to the disposal of the organ -containing it in such a way as most to facilitate the carrying away of -pollen. Similarly and simultaneously with odours. Odours, like colours, -draw insects to flowers. After<span class="pagenum" id="Page_269">[269]</span> observing how Bees come swarming into a -house where honey is largely exposed, or how Wasps find their way into -a shop containing much ripe fruit, it cannot be questioned that insects -are to a considerable extent guided by scent. Being thus sensitive -to the aromatic substances which flowers exhale, they may, when the -flowers are in large masses, be attracted by them from distances -at which the flowers themselves are invisible. And manifestly, the -flowers which so attract them from the greatest distances, increasing -thereby their chances of efficient fertilization, will be most likely -to perpetuate themselves. That is to say, survival of the fittest -must tend to produce perfumes that are both more powerful and more -attractive.</p> - -<p>These physiological differentiations, then, which mark off the -foliar organs constituting flowers from other foliar organs, are -the consequences of indirect equilibration. They are not due to the -immediate actions of unlike incident forces on the parts of the -individual plant; but they are due to the actions of such unlike -incident forces on the aggregate of individuals, generation after -generation.<a id="FNanchor_48" href="#Footnote_48" class="fnanchor">[48]</a></p> - - -<p class="p2">§ 276. The unity of interpretation which we here find for phenomena -of such various orders, could hardly be found<span class="pagenum" id="Page_270">[270]</span> were the phenomena -otherwise caused. That the stronger and the feebler contrasts among the -different parts of the outer tissues in plants, should so constantly -occur along with stronger and feebler contrasts among the incident -forces, is in itself weighty evidence that unlike outer actions have -caused unlike inner actions, and correspondingly-unlike structures; -either by changing the functional equilibrium in the individual, or by -changing it in the race, or by both.</p> - -<p>Even in the absence of more direct proof, there would be great -significance in the marked differences that habitually exist between -the exposed and imbedded parts of plants, between the stems and the -leaves, and between the upper and under surfaces of the leaves. The -significance of these differences is increased when we discover that -they vary in degree as the differences in the conditions vary in -degree. Still greater becomes the force of the evidence on finding -that these strongly-contrasted parts may, when placed in one another’s -conditions, and kept in them from generation to generation, permanently -assume one another’s functions, and, in a great degree, one another’s -structures. Even more conclusive yet is the argument rendered, by the -discovery that, where these substitutions of function and structure -take place, the superinduced modifications differ in different -circumstances; just as the original modifications do. The fact that -a flattened stem simulating a vertically-growing leaf has its two -surfaces alike, while when it simulates a horizontally-growing leaf its -upper and under surfaces differ, is a fact which, standing alone, might -prove little, but proves much when joined with all the other evidence. -And its profound meaning becomes the more obvious on discovering that -the same thing happens with petioles when they usurp leaf-functions.</p> - -<p>Finally, when we remember how rapidly analogous modifications of -function and structure arise in the superficial tissues of individual -plants, the general inference can scarcely be resisted. When we -meet with so striking a case as that<span class="pagenum" id="Page_271">[271]</span> of the <i>Begonia</i>-leaf, a -fragment of which stuck in the ground produces roots from its under -surface and leaves from its upper surface—when we see that though, -in this case, the typical structure of the plant presently begins to -control the organizing process, yet the initial differentiations are -set up by the differential actions of the environment; the presumption -becomes extremely strong that the heterogeneities of surface which -we have considered, result, as alleged, directly or indirectly from -heterogeneities in the incident forces.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_272">[272]</span></p> - -<h3>CHAPTER IV.<br /> -<span class="subhed1">DIFFERENTIATIONS AMONG THE INNER TISSUES OF PLANTS.<a id="FNanchor_49" href="#Footnote_49" class="fnanchor">[49]</a></span></h3></div> - - -<p>§ 277. In passing from plants formed of threads or thin laminæ, to -plants having some massiveness, we find that after the external and -internal parts have become distinguished from one another, there arise -distinctions among the internal parts themselves, as well as among the -external parts themselves: the primarily-differentiated parts are both -re-differentiated.</p> - -<p>From types of very low organisation illustrations of this may be -drawn. In the thinner kinds of <i>Laminaria</i> there exists but the -single contrast between the outer layer of cells and an inner layer; -but in larger species of the same genus, as <i>L. digitata</i>, there -are three unlike layers on each side of a central layer differing -from them—augmentation of bulk is accompanied by multiplication of -concentric internal structures, having their unlikenesses obviously -related to unlikenesses in their conditions. In <i>Furcellaria</i> and -various <i>Algæ</i> of similarly swollen forms, the like relation may -be traced.</p> - -<p>Just indicating the generality of this contrast, but not<span class="pagenum" id="Page_273">[273]</span> attempting to -seek in these lower types for any more specific interpretation of it, -let us pass to the higher types. The argument will be amply enforced by -the evidence obtained from them. We will look first at the conditions -which they have to fulfil; and then at the ways in which the functions -and structures adapting them to these conditions arise.</p> - - -<p class="p2">§ 278. A terrestrial plant that grows vertically needs no marked -modification of its internal tissues, so long as the height it reaches -is very small. As we before saw, the spiral or cylindrical rolling -up of a simple cellular frond, or the more bulky growth of a simple -cellular axis, may give the requisite strength; and the requisite -circulation may be carried on through the unchanged cellular tissue. -But in proportion as the height to be attained and the mass to be -supported increase, the supporting part must acquire greater bulk or -greater density, or both; and some modification that shall facilitate -the transfer of nutritive liquids must take place. Hence, in the -inner tissues of plants we may expect to find that structural changes -answering to these requirements become marked, as the growth of the -aërial part becomes great. Facts correspond with these expectations.</p> - -<p>Among the humbler Cormophytes, which creep over or raise themselves -but little above, the surfaces they flourish upon, there is scarcely -any internal differentiation: the vascular and woody structures, if -not in all cases absolutely unrepresented, are rarely and very feebly -indicated. But among the higher types—the Ferns and Lycopodiums—which -raise their fronds to considerable heights, there are vascular bundles -and hard tissues like wood; and by the Tree-Ferns massive axes are -developed. That the relation which thus shows itself among Cryptogams -is habitual among Phænogams, scarcely needs saying.</p> - -<p>Phænogams, however, are not universally thus characterized in a decided -way. Besides the comparative want of woody tissue in flowering plants -of humble growth, and<span class="pagenum" id="Page_274">[274]</span> besides the paucity of vessels in ordinary -water-plants, there are cases of much more marked divergence from -this typical internal structure. These exceptional cases occur under -exceptional conditions, and are highly instructive. They are of two -kinds. One group of them is furnished by certain plants which are -parasitic on the exposed roots of trees—parasitic not partially, -as the Mistletoe, but to the extent of subsisting wholly on the sap -they absorb. Fungus-like in colour and texture, and having scales -for leaves, these <i>Balanophoræ</i> and <i>Rafflesiaceæ</i> are -recognizable as Phænogams by scarcely any other traits than their -fructifications. Along with their aborted leaves and absence of -chlorophyll, there is a great degradation of those internal tissues -by which Phænogams are commonly distinguished. Though Dr. [now Sir -J.] Hooker has shown that they are not, as some botanists thought, -devoid of spiral vessels; yet, as shown by the mistake previously -made in classifying them, their appliances for circulation are -rudimentary. And this trait goes along with a greatly-simplified -distribution of nutriment. In the absence of leaves there can be but -little down-current of sap, such as leaves usually supply to roots: -there cannot be much beyond an upward current of the absorbed juices. -The other cases occur where circulation is arrested or checked in a -different way; namely, in plants that are wholly submerged. These -are the <i>Podostemaceæ</i>. Clothing as they do the submerged -rocks, their roots play the part of rhizomes, being attached to the -substratum by hairs and other processes, and having the leaf-bearing -and flower-bearing shoots on their surfaces. The latter spread out -more or less horizontally and are also fixed to the substratum in the -same manner as the roots. Observe then the connexion of facts. One -of these <i>Podostemaceæ</i> needs no internal stiffening substance, -for it exists in a medium of its own specific gravity; and being in a -position to absorb water over its entire surface, it has no need for a -circulation of crude sap—nor, indeed, in the absence of evaporation -from any part of its surface, could<span class="pagenum" id="Page_275">[275]</span> any active circulation take -place. Here, accordingly, the tracheal and mechanical elements are -undeveloped. Though spiral vessels are not entirely absent, yet they -are so rare as to do no more than verify the inference of phænogamic -relationship drawn from the flowers.</p> - -<p>The method of agreement, the method of difference, and the method of -concomitant variations, thus unite in proving a direct relation between -the demand for support and circulation, and the existence of these -vascular woody bundles which the higher plants habitually possess. -The question which we have to consider is—Under what influences are -these structures, answering to these requirements, developed? How are -these internal differentiations caused? The inquiry may be conveniently -divided. Though the supporting tissues and the tissues concerned in the -circulation of liquids are closely connected, and indeed entangled, -with one another, we may fitly deal with them apart. Let us take first -the supporting tissue.</p> - - -<p class="p2">§ 279. Many commonplace facts indicate that the mechanical strains to -which upright-growing plants are exposed, themselves cause increase -of the dense deposits by which such plants are enabled to resist -such strains. There is the fact that the massiveness of a tree-trunk -varies according to the stress habitually put upon it. If the contrast -between the slender stem of a tree growing in a wood and the bulky stem -of a kindred tree growing in the fields, be ascribed to difference -of nutrition rather than difference of exposure to winds; there is -still the fact that a tree trained against a wall has a less bulky -stem than a tree of the same kind growing unsupported; and that -between the long weak branches of the one and the stiff ones of the -other there are decided contrasts. If it be objected that a tree so -trained and branches so borne have relatively less foliage, and that -therefore these unlikenesses also are due to unlikenesses of general -nutrition, which may in part be true; there are still such cases as -those of<span class="pagenum" id="Page_276">[276]</span> garden plants, which when held up by tying them to sticks -have weaker stems than when they are unpropped, and sink down if their -props are taken away. Again, there is the evidence supplied by roots. -Though the contrast between the feeble roots of a sheltered tree -and the strong roots of an exposed tree, may, like the contrast of -their stems, be mainly due to difference of nutrition, and therefore -supplies but doubtful evidence, we get tolerably clear evidence where -trees growing on inclined rocky surfaces, send into crevices that -afford little moisture or nutriment, roots which nevertheless become -thick where they are so directed as to bear great strains. Suspicion -thus raised is strengthened into conviction by special evidences -occurring in the places where they are to be expected. The Cactuses, -with their succulent growths that pass into woody growths slowly -and irregularly, give us the opportunity of tracing the conditions -under which the wood is formed. Good examples occur in the genus -<i>Cereus</i>, and especially in forms like <i>C. crenulatus</i>. Here, -from a massive vertically-growing rod of fleshy tissue, two inches -or more in diameter, there grow at intervals lateral rods similarly -bulky, which, quickly curving themselves, take vertical directions. -One of these heavy branches puts great strains on its own substance -and that of the stem at their point of junction; and here both of them -become brown and hard, while they continue green and succulent all -around. Such differentiations may be traced internally before they -are visible on the surface. If a joint of an <i>Opuntia</i> be sliced -through longitudinally, the greater resistance to the knife all around -the narrow neck, indicates there a larger deposit of lignin than -elsewhere; and a section of the tissue placed under the microscope, -exhibits at the narrowest part a concentration of the woody and -vascular bundles. Clear evidence of another kind has been noted by -Mr. Darwin, in the organs of attachment of climbing plants. Speaking -of <i>Solanum jasminoides</i> he says:—“When the flexible petiole -of a half-or a quarter-grown leaf has clasped any object, in three<span class="pagenum" id="Page_277">[277]</span> -or four days it increases much in thickness, and after several weeks -becomes wonderfully hard and rigid; so that I could hardly remove one -from its support. On comparing a thin transverse slice of this petiole -with one from the next or older leaf beneath, which had not clasped -anything, its diameter was found to be fully doubled, and its structure -greatly changed.... This clasped petiole had actually become thicker -than the stem close beneath; and this was chiefly due to the greater -thickness of the ring of wood, which presented, both in transverse -and longitudinal sections, a closely similar structure in the petiole -and axis. The assumption by a petiole of this structure is a singular -morphological fact; but it is a still more singular physiological fact -that so great a change should have been induced by the mere act of -clasping a support.”</p> - -<p>If there is a direct relation between mechanical stress and the -formation of wood, it ought to explain for us the internal distribution -of the wood. Let us see whether it does this.</p> - -<p>When seeking in mechanical actions and reactions the cause of that -indurated structure which forms the vertebrate axis (<a href="#sect254">§§ 254–7</a>), it -was pointed out that in a transversely-strained mass, the greatest -pressures and tensions are thrown on the molecules of the concave and -convex surfaces. Hence, supposing the transversely-strained mass to -be a cylinder, bent backwards and forwards not in one plane but now -in this plane and now in that, its peripheral layers will be those on -which the greatest stress falls. An ordinary dicotyledonous axis is -such a cylinder so strained. The maintenance of its attitude either as -a lateral shoot or a vertical shoot, implies subjection to the bendings -caused by its own weight and by the ever-varying wind. These bendings -imply tensions and pressures falling most severely first on one side of -its outer layers and then on another. And if the dense substance able -to resist these tensions and pressures is deposited most where they are -greatest, we ought to find it taking the shape of a cylindrical casing. -This is just what<span class="pagenum" id="Page_278">[278]</span> we do find. On cutting across a shoot in course of -formation, we see its central space either unoccupied or occupied only -by soft tissue. That the layer of hard tissue surrounding this is not -the outermost layer, is true: there lies beyond it the cambium layer, -from which it is formed, the phloëm, and the cortex. But outside of the -soft phloëm there is frequently another layer of dense tissue now known -as the pericyclic fibres, having frequently a tenacity greater even -than that of the wood—a layer which, while it protects the cambium -and offers additional resistance to the transverse strain, admits of -being fissured as fast as the cylinder of wood thickens. That is to -say, the deposit of resisting substance is as completely peripheral as -the exogenous mode of growth permits. So, too, in general arrangement -is it with the ordinary monocotyledonous stem. Different as is here -the internal structure, there yet holds the same general distribution -of tissues, answering to the same mechanical conditions. The vascular -woody bundles, more abundant towards the outside of the stem than -near the centre, produce a harder casing surrounding a softer core. -In the supporting structures of leaves we find significant deviations -from this arrangement. While axes are on the average exposed to equal -strains on all sides, most leaves, spreading out their surfaces -horizontally, have their petioles subject to strains that are not alike -in all directions; and in them the hard tissue is differently arranged. -Its transverse section is not ring-shaped but crescent-shaped: the two -horns being directed towards the upper surface of the petiole. That -this arrangement is one which answers to the mechanical conditions, -is not easy to demonstrate: we must satisfy ourselves by noting that -here, where the distribution of forces is different, the distribution -of resisting tissue is different. And then, showing conclusively the -connexion between these differences, we have the fact that in petioles -growing vertically and supporting peltate leaves—petioles which are -therefore<span class="pagenum" id="Page_279">[279]</span> subject to equal transverse strains on all sides—the -vascular bundles are arranged cylindrically, as in axes.</p> - -<p>Such, then, are some of the reasons for concluding that the development -of the supporting tissue in plants, is caused by the incident forces -which this tissue has to resist. The individuals in which this direct -balancing of inner and outer actions progresses most favourably, are -those which, other things equal, are most likely to prosper; and, by -habitual survival of the fittest, there is established a systematic and -constant distribution of a deposit adapted to the circumstances of each -type.</p> - - -<p class="p2">§ 280. The function of circulation may now be dealt with. We have to -consider here by what structures this is discharged; and what connexion -exists between the demand for them and the genesis of them.</p> - -<p>The contrast between the rates at which a dye passes through simple -cellular tissue and cellular tissue of which the units have been -elongated, indicates one of the structural changes required to -facilitate circulation. If placed with its cut surface in a coloured -liquid, the parenchyma of a potato or the medullary mass of a -cabbage-stalk, will absorb the liquid with extreme slowness; but if -the stalk of a fungus be similarly placed, the liquid runs up it, and -especially up its loose central substance, very quickly. On comparing -the tissues which thus behave so differently, we find that whereas in -the one case the component cells, packed close together, have deviated -from their primitive sphericity only as much as mutual pressure -necessitates, in the other case they are drawn out into long tubules -with narrow spaces among them—the greatest dimensions of the tubules -and the spaces being in the direction which the dye takes so rapidly. -That which we should infer, then, from the laws of capillary action, -is experimentally shown: liquid moving through tissues follows the -lines in which the elements of the tissues are most<span class="pagenum" id="Page_280">[280]</span> elongated. It does -this for two reasons. That narrowing of the cells and intercellular -spaces which accompanies their elongation, facilitates capillarity; -and at the same time fewer of the septa formed by the joined ends of -the cells have to be passed through in a given distance. Hence the -general fact that the establishment of a rudimentary vascular system, -is the formation of bundles of cells lengthened in the direction -which the liquid is to take. This we see very obviously among the -lower Cormophytes. In one of the lichen-like Liverworts, the veins -which, branching through its frond, serve as communications with its -scattered rootlets, are formed of cells longer than those composing the -general tissue of the frond: the lengths of these cells corresponding -in their directions with the lengths of the veins. So, too, is it -with the mid-ribs of such fronds as assume more definite shapes; and -so, too, is it with the creeping stems which unite many such fronds. -That is to say, the current which sets towards the growing part from -the part which supplies certain materials for growth, sets through -a portion of the tissues composed of units that are longer in the -line of the current than at right angles to that line. The like is -true of Phænogams. Omitting all other characteristics of those parts -of them through which chiefly the currents of sap flow, we find the -uniform fact to be that they consist of cells and intercellular spaces -distinguished from others by their lengths. It is thus with veins, -and mid-ribs, and petioles; and if we wish proof that it is thus with -stems, we have but to observe the course taken by a coloured solution -into which a stem is inserted.</p> - -<p>What is the original cause of this differentiation? Is it possible -that this modification of cell-structure which favours the transfer of -liquid towards each place of demand, is itself caused by the current -which the demand sets up? Does the stream make its own channel? There -are various reasons for thinking that it does. In the first place, -the simplest and earliest channels, such as we see in the Liverworts, -do not<span class="pagenum" id="Page_281">[281]</span> develop in any systematic way, but branch out irregularly, -following everywhere the irregular lobes of the fronds as these spread; -and on examining under a magnifier the places at which the veins are -lost in the cellular tissue, it will be seen that the cells are there -slightly longer than those around: suggesting that the lengthening of -them which produces an extension of the veins, takes place as fast -as the growth of the tissue beyond causes a current to pass through -them. In the second place, a disappearance of the granular contents of -these cells accompanies their union into a vein—a result which the -transmission of a current may not improbably bring about. But be the -special causes of this differentiation what they may, the evidence -favours very much the conclusion that the general cause is the setting -up of a current towards a place where the sap is being consumed. In the -histological development of the higher plants we find confirmation. -The more finished distributing canals in Phænogams are formed of cells -previously lengthened. At parts of which the typical structure is -fixed, and the development direct, this fact is not easy to trace; -the cells rapidly take their elongated structures in anticipation of -their predetermined functions. But in places where new vessels are -required in adaptation to a modifying growth, we may clearly trace -this succession. The swelling root of a turnip, continually having its -vascular system further developed, and the component vessels lengthened -as well as multiplied, gives us an opportunity of watching the process. -In it we see that the reticulated cells which unite to form ducts, -arise in the midst of bundles of cells that have previously become -elongated, and that they arise by transformation of such elongated -cells; and we also see that these bundles of elongated cells have an -arrangement suggestive of their formation by passing currents.</p> - -<p>Are there grounds for thinking that these further transformations by -which strings of elongated cells pass into vessels lined with spiral, -annular, reticulated, or other<span class="pagenum" id="Page_282">[282]</span> frameworks, are also in any way -determined by the currents of sap carried? There are some such grounds.</p> - -<p>As just indicated, the only places where we may look for evidence -with any rational hope of finding it, are places where some local -requirement for vessels has arisen in consequence of some local -development which the type does not involve. In these cases we find -such evidence. Good illustrations occur in those genera of the -<i>Cactaceæ</i>, which simulate leaves, like <i>Epiphyllum</i> and -<i>Phyllocactus</i>. A branch of one of these is outlined in Fig. <a href="#i_178">256</a>. -As before explained this is a flattened axis; and the notches along -its edges are the seats of the axillary buds. Most of these axillary -buds are arrested; but occasionally one of them grows. Now if, taking -an <i>Epiphyllum</i>-shoot which bears a lateral shoot, we compare the -parts of it that are near the aborted axillary buds with the part that -is near the developed axillary bud, we find a conspicuous difference. -In the neighbourhood of an aborted axillary bud there is no external -sign of any internal differentiation; and on holding up the branch -against the light, the uniform translucency shows that there is no -greater amount of dense tissue near it than in other parts of the -succulent mass. But where an axillary bud has developed, a prominent -rounded ridge joins the mid-rib of the lateral branch with the mid-rib -of the parent branch. In the midst of this rounded ridge an opaque core -may be seen. And on cutting through it, this opaque core proves to be -full of vascular bundles imbedded in woody deposits. Clearly, these -clusters of vessels imply transformations of the tissues, caused by -the passage of increased currents of sap. The vessels were not there -when the axillary bud was formed; they would not have developed had -the axillary bud proved abortive; but they arise as fast as growth -of the axillary bud draws the sap along the lines in which they lie. -Verification is obtained by examining the internal structures. If -longitudinal sections be made through a growing bud of <i>Opuntia</i> -or<span class="pagenum" id="Page_283">[283]</span> <i>Cereus</i>, it will be found that the vessels in course of -formation converge towards the point of growth, as they would do if the -sap-currents determined their formation; that they are most developed -near their place of convergence, which they would be if so produced; -and that their terminations in the tissue of the parent shoot are -partially-formed lines of irregular elongated cells, like those out of -which the vessels of a leaf or bud are developed.</p> - -<p>Concluding, then, that sap-vessels arise along the lines of least -resistance, through which currents are drawn or forced, the question -to be asked is—What physical process produces them? Their component -cells, united end to end more or less irregularly in ways determined -by their original positions, form a channel much more permeable, both -longitudinally and laterally, than the tissue around. How is this -greater permeability caused? The idea, first propounded I believe by -Wolff, that the adjoined ends of the cells are perforated or destroyed -by the passing current, is one for which much is to be said. Whether -these septa are dissolved by the liquids they transmit, or whether they -are burst by those sudden gushes which, as we shall hereafter see, must -frequently take place along these canals, need not be discussed: it is -sufficient for us that the septa do, in many cases, disappear, leaving -internal ridges showing their positions; and, in other cases, become -extremely porous. Though it is manifest that this is not the process -of vascular development in tissues that unfold after pr-determined -types, since, in these, the dehiscences or perforations of septa occur -before such direct actions can have come into play; yet it is still -possible that the disappearances of septa which now arise by repetition -of the type were established in the type by such direct actions. Be -this as it may, however, a simultaneous change undergone by these -longitudinally-united cells must be otherwise caused. Frame-works are -formed in them—frameworks which, closely fitting their inner surfaces, -may consist either of successive rings, or continuous<span class="pagenum" id="Page_284">[284]</span> spiral threads, -or networks, or structures between spirals and networks, or networks -with openings so far diminished that the cells containing them are -distinguished as fenestrated. Their differences omitted, however, these -structures have the common character that, while supporting the coats -of the vessels, they also give special facilities for the passage of -liquids, both through the sides of the transformed cells and through -their united ends, where these are not destroyed.</p> - -<p>To attempt any physical interpretation of this change is scarcely -safe: the conditions are so complex. There are reasons for suspecting, -however, that it arises from a vacuolation of the substance deposited -on the cell-wall. If rapidly deposited, as it is likely to be along -lines where sap is freely supplied, this may, in passing from the -state of a soluble colloid to that of an insoluble colloid, so -contract as to leave uncovered spaces on the cell-membrane; and this -change, originally consequent on a physico-chemical action, may be -so maintained and utilized by natural selection, as to result in -structures of definite kinds, regularly formed in growing parts in -anticipation of functions to be afterwards discharged. But, without -alleging any special cause for this metamorphosis, we may reasonably -conclude that it is in some way consequent upon the carrying of sap. -If we examine tissues such as that in the interior of a growing -turnip that has not yet become stringy, we may, in the first place, -find bundles of elongated cells not having yet developed in them -those fenestrated or reticulated structures by which the ducts are -eventually characterized. Along the centres of adjacent bundles we may -find incomplete lines of such cells—some that are partially or wholly -transformed, with some between them that are not transformed. In other -bundles, completed chains of such transformed cells are visible. And -then, in still older bundles, there are several complete chains running -side by side. All which facts imply a metamorphosis of the<span class="pagenum" id="Page_285">[285]</span> elongated -cells, indirectly caused by the continued action of the currents -carried.</p> - - -<p class="p2" id="sect281">§ 281. Here, however, presents itself a further problem. Taking -it as manifest that there is a typical distribution of supporting -tissue adapted to meet the mechanical strains a plant is exposed to -by its typical mode of growth, and also that there goes on special -adaptation of the supporting tissue to the special strains the -individual plant has to bear; and taking it as tolerably evident that -the sap-channels are originally determined by the passage of currents -along lines of least resistance; there still remains the ultimate -question—Through what physical actions are established these general -and special adjustments of supporting tissue to the strains borne, -and these distributions of nutritive liquid required to make possible -such adjustments? Clearly, if the external actions produce internal -reactions; and if this play of actions and reactions results in a -balancing of the strains by the resistances; we may rationally suspect -that the incident forces are directly conducive to the structural -changes by which they are met. Let us consider how they must work.</p> - -<p>When any part of a plant is bent by the wind, the tissues on its convex -surface are subject to longitudinal tension, and these extended outer -layers compress the layers beneath them. Such of the vessels or canals -in these subjacent layers as contain sap, must have some of this sap -expelled. Part of it will be squeezed through the more or less porous -walls of the canals into the surrounding tissue, thus supplying it with -assimilable materials; while part of it, and probably the larger part, -will be thrust along the canals longitudinally upwards and downwards. -When the branch or twig or leaf-stalk recoils, these vessels, relieved -from pressure, expand to their original diameters. As they expand, the -sap rushes back into them from above and below. In whichever of these -directions least has been expelled by the compression,<span class="pagenum" id="Page_286">[286]</span> from that -direction most must return during the dilation; seeing that the force -which more efficiently resisted the thrusting back of the sap is the -same force which urges it into the expanded vessels again, when they -are relieved from pressure. At the next bend of the part a further -portion of sap will be squeezed out, and a further portion thrust -forwards along the vessels. This rude pumping process thus serves for -propelling the sap to heights which it could not reach by capillary -action, at the same time that it incidentally serves to feed the parts -in which it takes place. It strengthens them, too, just in proportion -to the stress to be borne; since the more severe and the more repeated -the strains, the greater must be the exudation of sap from the vessels -or ducts into the surrounding tissue, and the greater the thickening -of this tissue by secondary deposits. By this same action the movement -of the sap is determined either upwards or downwards, according to the -conditions. While the leaves are active and evaporation is going on -from them, these oscillations of the branches and petioles urge forward -the sap into them; because so long as the vessels of the leaves are -being emptied, the sap in the compressed vessels of the oscillating -parts will meet with less resistance in the direction of the leaves -than in the opposite direction. But when evaporation ceases at night, -this will no longer be the case. The sap drawn to the oscillating -parts, to supply the place of the exuded sap, must come from the -directions of least resistance. A slight breeze will bring it back from -the leaves into the gently-swaying twigs, a stronger breeze into the -bending branches, a gale into the strained stem and roots—roots in -which longitudinal tension produces, in another way, the same effects -that transverse tension does in the branches.</p> - -<p>Two possible misinterpretations must be guarded against. It is not to -be supposed that this force-pump action causes movement of the sap -towards one point rather than another: it is simply an aid to its -movement. From the stock of sap<span class="pagenum" id="Page_287">[287]</span> distributed through the plant, more -or less is everywhere being abstracted—here by evaporation, here by -the unfolding of the parts into their typical shapes, here by both. The -result is a tension on the contained liquid columns, which is greatest -now in this direction and now in that. This tension it is which must be -regarded as the force that determines the current upwards or downwards; -and all which the mechanical actions do is to facilitate the transfer -to the places of greatest demand. Hence it happens that in a plant -prevented from oscillating, but having a typical tendency to assume -a certain height and bulk, the demands set up by its unfolding parts -will still cause currents; and there will still be alternate ascents -and descents, according as the varying conditions change the direction -of greatest demand—the only difference being that, in the absence of -oscillations, the growth will be less vigorous. Similarly, it must not -be supposed that mechanical actions are here alleged to be the sole -causes of wood formation in the individual plant. The tendency of the -individual plant to form wood at places where wood has been habitually -formed by ancestral plants, is manifestly a cause, and, indeed, the -chief cause. In this, as in all other cases, inherited structures -repeat themselves irrespective of the circumstances of the individual: -absence of the appropriate conditions resulting simply in imperfect -repetition of the structures. Hence the fact that in trained trees and -hothouse shrubs, dense substance is still largely deposited; though -not so largely as where the normal mechanical strains have acted. -Hence, too, the fact, that in such plants as the Elephant’s-foot or the -<i>Welwitschia mirabilis</i>, which for untold generations can have -undergone no oscillations, there is an extensive formation of wood -(though not to any considerable height above the ground), in repetition -of an ancestral type: natural selection having here maintained the -habit as securing some other advantage than that of support.</p> - -<p>Still, it must be borne in mind that though intermittent<span class="pagenum" id="Page_288">[288]</span> mechanical -strains cannot be assigned as the direct causes of these internal -differentiations in plants that are artificially sheltered or -supported, they are assignable as the indirect causes; since the -inherited structures, repeated apart from such strains, are themselves -interpretable as accumulated results of such strains acting on -successive generations of ancestral plants. This will become clear on -combining the several threads of the argument and bringing it to a -close, which we may now do.</p> - - -<p class="p2">§ 282. To put the co-operative actions in their actual order, -would require us to consider them as working on individuals small -modifications that become conspicuous and definite only by inheritance -and gradual increase; but it will aid our comprehension without leading -us into error, if we suppose the whole process resumed in a single -continuously-existing plant.</p> - -<p>As the plant erects the integrated series of fronds whose united -parts form its rudimentary axis, the increasing area of frond surface -exposed to the sun’s rays entails an increasing draught upon the -liquids contained in the rudimentary axis. The currents of sap so -produced, once established along certain lines of cells that offer -least resistance, render them by their continuous passage more and -more permeable. This establishment of channels is aided by the wind. -Each bend produced by it while yet the tissue is undifferentiated, -squeezes towards the place of growth and evaporation the liquids -that are passing by osmosis from cell to cell; and when the lines of -movement become defined, each bend helps, by forcing the liquid along -these lines, to remove obstructions and make continuous canals. As fast -as this transfer of sap is facilitated, so fast is the plant enabled -further to raise itself, and add to its assimilating surfaces; and so -fast do the transverse strains, becoming greater, give more efficient -aid. The canals thus formed can be neither in the centre of the -rudimentary axis nor at its surface: for at neither of these<span class="pagenum" id="Page_289">[289]</span> places -can the transverse strains produce any considerable compressions. -They must arise along a tract between the outside of the axis and its -core—a tract along which there occur the severest squeezes between the -stretched outer layers and the internal mass. Just that distribution -which we find, is the distribution which these mechanical actions tend -to establish.</p> - -<p>As the plant gains in height, and as the mass of its foliage -accumulates, the strains thrown upon its axis, and especially the -lower part of its axis, rapidly increase. Supposing the forms to -remain similar, the strains must increase in the ratio of the cubes of -the dimensions; or even in a somewhat higher ratio. One consequence -must be that the compressions to which the vessels at the lower -part of the incipient stem are subject, become greater as fast as -the height to which the sap has to be raised becomes greater; and -another consequence must be that the local exudation of sap produced -by the pressure is proportionately augmented. Hence the materials for -interstitial nutrition being there supplied more abundantly, we may -expect thickening of the surrounding tissues to show itself there -first: in other words, wood will be formed round the vessels of the -lower part of the incipient stem. The resulting greater ability of this -lower part of the stem to bear strains, renders possible an increase of -height; and while after an increase of height the lowest part becomes -still further strained, and still further thickens, the part above it, -exposed to like actions, undergoes a like thickening. This induration, -while it spreads upwards, also spreads outwards. As fast as the rude -cylinder of dense matter formed in this way, begins to inclose the -original vessels, it begins to play the part of a resistant mass, which -more and more prevents the contained vessels from being squeezed; -while between it and the outer layers the greatest compression occurs -at each bend. Thus at the same time that the original vessels become -useless, the peripheral cells of the developing wood become those which -have their liquid<span class="pagenum" id="Page_290">[290]</span> contents squeezed out longitudinally and laterally -with increasing force; and, consequently, amid them are formed new -sap-channels, from which there is the most active local exudation, -producing the greatest deposit of dense matter.</p> - -<p>Thus fusing together, as it were, the individualities of successive -generations of plants, and recognizing as all-important that -facilitation of the process which natural selection has all along -given, we are enabled to interpret the chief internal differentiations -of plants as consequent on an equilibration between inner and outer -forces. Here, indeed, we see illustrated in a way more than usually -easy to follow, the eventual balancing of outer actions by inner -reactions. The relation between the demand for liquid and the formation -of channels that supply liquid, as well as that between the incidence -of strains and the deposit of substance which resists strains, are -among the clearest special examples of the general truth that the -moving equilibrium of an organism, if not overthrown by an incident -force, must eventually be adjusted to it.</p> - -<p>The processes here traced out are, of course, not to be taken as the -only differentiating processes to which the inner tissues of plants -have been subject. Besides the chief changes we have considered, -various less conspicuous changes have taken place. These must be -passed over as arising in ways too involved to admit of specific -interpretations; even supposing them to have been produced by causes of -the kind assigned. But the probability, or rather indeed the certainty, -is that some of them have not been so produced. Here, as in nearly -all other cases, indirect equilibration has worked in aid of direct -equilibration; and in many cases indirect equilibration has been the -sole agency. Besides ascribing to natural selection the rise of various -internal modifications of other classes than those above treated, we -must ascribe some even of these to natural selection. It is so with the -dense deposits which form thorns and the shells of nuts: these cannot -have resulted from any inner reactions immediately<span class="pagenum" id="Page_291">[291]</span> called forth by -outer actions; but must have resulted immediately through the effects -of such outer actions on the species. Let it be understood, therefore, -that the differentiations to which the foregoing interpretation -applies, are only those most conspicuous ones which are directly -related to the most conspicuous incident forces. They must be taken as -instances on the strength of which we may conclude that other internal -differentiations have had a natural genesis, though in ways that we -cannot trace.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_292">[292]</span></p> - -<h3>CHAPTER V.<br /> -<span class="subhed1">PHYSIOLOGICAL INTEGRATION IN PLANTS.</span></h3></div> - - -<p>§ 283. A good deal has been implied on this topic in the preceding -chapters. Here, however, we must for a brief space turn our attention -immediately to it.</p> - -<p>Plants do not display integration in such distinct and multiplied -ways as do animals. But its advance may be traced both directly and -indirectly—directly in the increasing co-ordination of actions, and -indirectly in the effect of this upon the powers and habits.</p> - -<p>Let us group the facts under these heads: ascending in both cases from -the lower to the higher types.</p> - - -<p class="p2">§ 284. The inferior <i>Algæ</i>, along with little unlikeness of -parts, show us little mutual dependence of parts. Having surfaces -similarly circumstanced everywhere, much physiological division of -labour cannot arise; and therefore there cannot be much physiological -unity. Among the superior <i>Algæ</i>, however, the differentiation -between the attached part and the free part is accompanied by some -integration. There is evidently a certain transfer of materials, which -is doubtless facilitated by the elongated forms of the cells in the -stem, and probably leads to the formation of dense tissue at the places -of greatest strain, in a way akin to that recently explained in other -cases. And where there is this co-ordination of actions, the parts are -so far mutually dependent that<span class="pagenum" id="Page_293">[293]</span> each dies if detached from the other. -That though the organization is so low neither part can reproduce the -other and survive by so doing, is probably due to the circumstance -that neither part contains any considerable stock of untransformed -protoplasm, out of which new tissues may be produced.</p> - -<p>Fungi and Lichens present no very significant advances of integration. -We will therefore pass at once to the Archegoniates. In those of them -which, either as single fronds or strings of fronds, spread over -surfaces, and which, rooting themselves as they spread, do not need -that each part should receive aid from remote parts, there is no -developed vascular system serving to facilitate transfer of nutriment: -the parts being little differentiated there is but little integration. -But along with assumption of the upright attitude and the accompanying -specializations, producing vessels for distributing sap and hard tissue -for giving mechanical support, there arises a decided physiological -division of labour; rendering the aërial part dependent on the embedded -part and the embedded part dependent on the aërial part. Here, indeed, -as elsewhere, these concomitant changes are but two aspects of the -same change. Always the gain of power to discharge a special function -involves a loss of power to perform other functions; and always, -therefore, increased mutual dependence constituting physiological -integration, must keep pace with that increased fitting of particular -parts to particular duties which constitutes physiological -differentiation.</p> - -<p>Making a great advance among the Archegoniates, this physiological -integration reaches its climax among Phænogams. In them we see -interdependence throughout masses that are immense. Along with -specialized appliances for support and transfer, we find an exchange of -aid at great distances. We see roots giving the vast aërial growth a -hold tenacious enough to withstand violent winds, and supplying water -enough even during periods of drought; we see a stem and branches of -corresponding strength for upholding<span class="pagenum" id="Page_294">[294]</span> the assimilating organs under -ordinary and extraordinary strains; and in these assimilating organs -we see elaborate appliances for yielding to the stem and roots the -materials enabling them to fulfil their offices. As a consequence of -which greater integration accompanying the greater differentiation, -there is ability to maintain life over an immense period under marked -vicissitudes.</p> - -<p>Even more conspicuously exemplified in Phænogams, is that physiological -integration which holds together the functions not of the individual -only but of the species as a whole. The organs of reproduction, both in -their relations to other parts of the individual bearing them and in -their relations to corresponding parts of other individuals, show us a -kind of integration conducing to the better preservation of the race; -as those already specified conduce to the better preservation of the -individual. In the first place, this greater co-ordination of functions -just described, itself enables Phænogams to bequeath to the germs they -cast off, stores of nutriment, protective envelopes, and more or less -of organization: so giving them greater chances of rooting themselves. -In the second place, certain differentiations among the parts of -fructification, the meaning of which Mr. Darwin has so admirably -explained, give to the individuals of the species a kind of integration -that makes possible a mutual aid in the production of vigorous -offspring. And it is interesting to observe how, in that dimorphism -by which in some cases this mutual aid is made more efficient, the -greater degree of integration is dependent on the greater degree of -differentiation—not simply differentiation of the fructifying organs -from other parts of the plant bearing them, but differentiation of -these fructifying organs from the homologous organs of neighbouring -individuals of the same race. Another form of this co-ordination of -functions which conduces to the maintenance of the species, may be -here named—partly for its intrinsic interest. I refer to the strange -processes of multiplication occurring in the genus <i>Bryophyllum</i>. -It is well known that<span class="pagenum" id="Page_295">[295]</span> the succulent leaves of <i>B. calycinum</i>, -borne on foot-stalks so brittle that they are easily snapped by the -wind, send forth from their edges when they fall to the ground, -buds which root themselves and grow into independent plants. The -correlation here obviously furthering the preservation of the race, -is more definitely established in another species of the genus—<i>B. -proliferum</i>. This plant, shooting up to a considerable height, and -having a stem containing but little woody fibre, habitually breaks -near the bottom while still in flower; and is thus generally prevented -from ripening its seeds. The multiplication is, however, secured in -another way. Before the stem is broken young plants have budded out -from the pedicels of the flowers, and have grown to considerable -lengths; and on the fall of the parent they forthwith commence their -separate lives. Here natural selection has established a remarkable -kind of co-ordination between a special habit of growth and decay, and -a special habit of proliferation.</p> - - -<p class="p2">§ 285. The advance of physiological integration among plants as we -ascend to the higher types, is implied by their greater constancy of -structure, as well as by the stricter limitations of their habitats and -modes of life. “Complexity of structure is generally accompanied with a -greater tendency to permanence in form,” says Dr. [now Sir J.] Hooker; -or, conversely, “the least complex are also the most variable.” This is -the second aspect under which we have to contemplate the facts.</p> - -<p>The differences between the simpler <i>Algæ</i> and <i>Fungi</i> -are so feebly marked that botanists have had great difficulty in -framing definitions of these classes. This structural indefiniteness -is accompanied by functional indefiniteness. <i>Algæ</i>, which are -mostly aquatic, include many small forms that frequent the damp places -preferred by <i>Fungi</i>. Among <i>Fungi</i>, there are kinds which -lead submerged lives like the <i>Algæ</i>. Besides this indistinctness -of the classes, there is great variability in the shapes and modes -of life of their species—a variability<span class="pagenum" id="Page_296">[296]</span> so great that what were at -first taken to be different species, or different genera, or even -different orders, have proved to be merely varieties of one species. -So inconstant in structure are the <i>Algæ</i> that Schleiden quotes -with approval the opinion of Kutzing, that “there are no species but -merely forms of <i>Algæ</i>:” an opinion which though now rejected -sufficiently implies extreme indefiniteness. In all which facts we see -that these lowest types of plants, little differentiated, are also but -little integrated.</p> - -<p>Archegoniates present a like relation between the small specialization -of functions which constitutes physiological differentiation, and -the small combination of functions which constitutes physiological -integration. “Mosses,” says Mr. Berkeley, “are no less variable than -other cryptogams, and are therefore frequently very difficult to -distinguish. Not only will the same species exhibit great diversity -in the size, mode of branching, form and nervation of the leaves, but -the characters of even the peristome itself are not constant.” And -concerning the classification of the remaining group, <i>Filicales</i>, -he says:—“Not only is there great difficulty in arranging ferns -satisfactorily, but it is even more difficult to determine the limits -of species.”</p> - -<p>After this vagueness of separation as well as inconstancy of structure -and habit among the lower plants, the stability of structure and -habit and divisibility of groups among the higher plants, appear -relatively marked. Though Phænogams are much more variable than most -botanists have until lately allowed, yet the definitions of species and -genera may be made with far greater precision, and the forms are far -less capable of change, than among Cryptogams. And this comparative -fixity of type, implying, as it does, a closer combination of the -component functions, we see to be the accompaniment of the greater -differentiation of those functions and of the structures performing -them. That these characters are correlatives is further shown by the -fact that the higher plants are more restricted in their habitats -than<span class="pagenum" id="Page_297">[297]</span> the lower plants, both in space and time. “The much narrower -delimitation in area of animals than plants,” says Sir J. Hooker, “and -greater restriction of Faunas than Floras, should lead us to anticipate -that plant-types are, geologically speaking, more ancient and permanent -than the higher animal types are, and so I believe them to be, and I -would extend the doctrine even to plants of highly complex structure.” -“Those classes and orders which are the least complex in organization -are the most widely distributed.”</p> - - -<p class="p2" id="sect286">§ 286. Thus that which the general doctrine of evolution leads us -to anticipate, we find implied by the facts. The physiological -division of labour among parts, can go on only in proportion to the -mutual dependence of parts; and the mutual dependence of parts can -progress only as fast as there arise structures by which the parts are -efficiently combined, and the mutual utilization of their actions made -easy.</p> - -<p>To say definitely by what process is brought about this co-ordination -of functions which accompanies their specialization, is hardly -practicable. Direct and indirect equilibration doubtless co-operate -in establishing it. We may see, for example, that every increase of -fitness for function produced in the aërial part of a plant by light, -as well as every increase of fitness for function produced in its -imbedded part by the direct action of the moist earth, must conduce -to an increased current of the liquid evaporated from the one and -supplied by the other—must serve, therefore, to aid the formation -of sap-channels in the ways already described; that is—must serve -to develop the structures through which mutual aid of the parts is -given: the additional differentiation tends immediately to bring -about the additional integration. Contrariwise, it is obvious that -an interdependence such as we see between the secretion of honey and -the fertilization of germs, or between the deposit of albumen in the -cotyledons of an embryo-plant and its subsequent striking root, is -a kind of integration in the actions of the individual or of the<span class="pagenum" id="Page_298">[298]</span> -species, which no differentiation has a direct tendency to initiate. -Hence we must regard the total results as due to a plexus of influences -acting simultaneously on the individual and on the species: some -chiefly affecting the one and some chiefly affecting the other.</p> - -<hr class="tb" /> - -<p>[<span class="smcap">Note.</span>—In <i>Nature</i> for June 11, 1896, Dr. Maxwell -Masters, in an essay on “Plant Breeding,” names an instructive fact -concerning the production of varieties by selection of slightly -divergent forms. He says:—</p> - -<p>“To the untrained eye, the primordial differences noted are often very -slight; even the botanist, unless his attention be specially directed -to the matter, fails to see minute differences which are perceptible -enough to the raiser or his workmen. Nor must it be thought that these -variations, difficult as they are to recognise in the beginning, are -unimportant. On the contrary, they are interesting, physiologically, -as the potential origin of new species, and very often they are -commercially valuable also. These apparently trifling morphological -differences are often associated with physiological variations which -render some varieties, say of wheat, much better enabled to resist -mildew and disease generally than others. Some, again, prove to be -better adapted for certain soils or for some climates than others; some -are less liable to injury from predatory birds than others, and so on.”</p> - -<p>Thus we are shown that, to a much greater degree than might be -supposed, minute changes of forms and functions in one part of a plant -are correlated with changes of forms and functions throughout it. The -interdependence—that is to say, the physiological integration—is very -close at the same time that it is very complex.</p> - -<p>Here while naming these facts in illustration of physiological -integration in plants I name them because they illustrate an important -truth bearing upon the general question of heredity which I have dealt -with in Appendix G, and to which I now especially draw attention.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_299">[299]</span></p> - -<h3>CHAPTER VI.<br /> -<span class="subhed1">DIFFERENTIATIONS BETWEEN THE OUTER AND INNER TISSUES OF ANIMALS.</span></h3></div> - - -<p>§ 287. What was said respecting the primary physiological -differentiation in plants, applies with little beyond change of terms -to animals. Among <i>Protozoa</i>, as among <i>Protophyta</i>, the -first definite contrast of parts is that between outside and inside. -The speck of jelly or sarcode which appears to constitute the simplest -animal, proves, on closer examination, to be a mass of substance -containing a nucleus—a periplast in the midst of which there is a -minute endoplast, consisting of a spherical membrane and its contents.</p> - -<p>This parallel, only just traceable among these Rhizopods, which are -perpetually changing the distribution of their outer substance, becomes -at once marked in those higher <i>Protozoa</i> which have fixed shapes, -and maintain constant relations between their surfaces and their -environments. Indeed the Rhizopods themselves, on passing into a state -of quiescence in which the relations of outer and inner parts are -fixed, become encysted: there is formed a hardened outer coat different -from the matter which it contains. And what is here a temporary -character answering to a temporary definiteness of conditions, is -in the <i>Infusoria</i> a constant character, answering to definite -conditions that are constant. Each of these minute creatures, though -not coated by a distinct membrane, has an outer layer of excreted -substance forming a delicate cuticle.</p> - - -<p class="p2" id="sect288">§ 288. The early establishment of this primary contrast of<span class="pagenum" id="Page_300">[300]</span> tissues -answering to this primary contrast of conditions, is no less -conspicuous in aggregates of the second order. The feebly-integrated -units of a Sponge, with individualities so little merged in that of -the whole they form that most of them still retain their separate -activities, nevertheless show us, in the unlikeness that arises between -the outermost layer and the contained mass, the effect of converse with -unlike conditions. This outermost layer is composed of units somewhat -flattened and united into a continuous membrane—a kind of rudimentary -skin.</p> - -<p>Secondary aggregates in which the lives of the units are more -subordinate to the life of the whole, carry this distinction further. -The leading physiological trait of every cœlenterate animal is the -divisibility of its substance into endoderm and ectoderm—the part -next the food and the part next the environment. Fig. <a href="#i_090">147</a> (<a href="#sect201">§ 201</a>), -representing a portion of the body-wall of a <i>Hydra</i> seen -in section, gives some idea of this fundamental differentiation. -The creature consists of a simple sac, the cavity of which is in -communication with the surrounding water; and hence the unlikeness -between the outer and inner layers has not become great. The essential -contrast is that between the differentiated parts of what was -originally the same part—a uniform membrane composed of juxtaposed -cells.</p> - -<p>For here, indeed, we are shown unmistakably how the primary contrast -of structures follows upon the primary contrast of conditions. The -ordinary form from which low types of the <i>Metazoa</i> set out, is a -hollow sphere formed of cells packed side by side—a blastula, as it -is called: all these cells being similarly exposed to the environment. -The blastula presently changes into what is called a gastrula—a form -resulting from the introversion of one of the sides of the blastula. -If there be taken a small ball of vulcanized india-rubber, say an -inch or more in diameter, and having a hole in it through which the -air may escape, and if one side of it be thrust inwards so as to -produce a cup, and if the<span class="pagenum" id="Page_301">[301]</span> wide opening of the cup be supposed to -contract, thus becoming a narrow opening, there will result something -like the gastrula form. Manifestly that part of the original layer -which has become internal is differently conditioned from the rest -which remains external: the one continuing to hold converse with the -forces of the environment, while the other begins to hold converse -with the nutritive matters taken into the sac-formed chamber—the -archenteron or primitive stomach. Interesting evidence of the primitive -externality of the digestive cavity is yielded by the fact that whereas -the blastula consisted of ciliated cells, and whereas the ciliation -persists throughout life on the outer layer, or parts of it, in sundry -low types—even in some Chætopods—it persists also on the alimentary -tract of sundry low types: not only in the <i>Hydra</i> but commonly in -Nemertines, in some <i>Platyhelminthes</i>, and even in some leeches.</p> - -<p>Besides being enabled thus to understand how an aggregate of -<i>Amœba</i>-form units, originally consisting of a single layer, -may pass into an aggregate consisting of a double layer; we may also -understand under what influences the transition takes place. If the -habit which some of the primary aggregates have, of wrapping themselves -round masses of nutriment, is followed by a secondary aggregate, -there will naturally arise just that re-differentiation which the -<i>Hydra</i> shows us.</p> - - -<p class="p2" id="sect289">§ 289. This account of the primary differentiation carries us only -half-way towards a true conception of the distinction between outer -and inner tissues. Though, using words in their current senses, this -introverted part of the primitive layer has become internal in contrast -with the remainder, which continues external, yet this introverted -part has not become internal in the strict physiological sense. For -it remains subject to the actions of those environing matters which -are taken in as food: such environing matters, when they happen to be -moving prey, acting upon it much as they<span class="pagenum" id="Page_302">[302]</span> might act upon the exterior. -So that this introverted part has a quasi-externality. It has not -the same absolute internality as have those parts which never come -in contact with products of the outer world. Here we must briefly -recognize the distinction between these parts and the parts thus far -considered.</p> - -<p>Reverting to our symbol, the india-rubber ball, it will be seen that -the introversion may be so complete that the cavity is obliterated, -with the result that the internal surfaces of the outer and inner -layers come in contact. This is the state reached in the simplest -cœlenterate animal, the <i>Hydra</i>: there being in it nothing more -than a thin structureless lamella between the ectoderm and endoderm, -as shown in Fig. <a href="#i_090">147</a>. This lamella represents all that there is of -strictly internal tissues. But the introversion, instead of bringing -the inner surfaces of the ball into contact, may be so far incomplete -as to leave a space, and in various creatures and embryos of others, -symbolized by this arrangement, this space becomes occupied by a tissue -formed from one or other or both of the two primary tissues—the -mesoblast or mesoderm. This intermediate layer, sometimes, as in the -<i>Medusa</i>, growing into a mass of jelly serving as a fulcrum for -the creature’s contractions, or, as in the Sponge, giving a passive -basis to the active tissues, becomes in higher animals the layer out -of which the structures that support the body and move it about, as -well as those that distribute prepared nutriment, are developed. From -it arise the bones, the muscles, and the vascular system—the masses -of differentiated tissue which are truly internal and occupy what is -called the body-cavity or peri-visceral space.</p> - -<p>In the higher types of animals this space comes to be partially -occupied by a structure that may be described as a cavity within -a cavity—the cœlom. Most zoologists regard this as arising by a -re-introversion of the <i>archenteron</i> or primary alimentary sac. It -is easily to be perceived that after the introversion which produces -this digestive cavity, the<span class="pagenum" id="Page_303">[303]</span> wall of the cavity may be again introverted -in such way as to intrude into the peri-visceral space. The cœlom thus -formed is subsequently shut off. Becoming included among the more -truly internal structures, and in part giving origin to certain lining -membranes, it has for its chief function the formation of organs for -the excretion and emission of nitrogenous waste and of the generative -products: some portions of it retaining, as a consequence, indirect -connexions with the environment and characters usually accompanying -such connexions.</p> - -<p>Here we are not concerned with further details: the aim being simply to -indicate the way in which out of the original layer, wholly external, -there arise, by primary and secondary introversions, and the formation -of intermediate membranes and spaces, the chief contrasts between -outer and inner tissues, and how there simultaneously go on the -differentiations accompanying different conditions.</p> - - -<p class="p2">§ 289<i>a</i>. Another all-important differentiation between outer -tissues and inner tissues has now to be set forth—that by which the -nervous system becomes established and distinguished. Strangely enough, -like the one above described, it is sequent upon an introversion: -the nervous system is primarily a skin-structure and develops by the -infolding of this skin-structure.</p> - -<p>In creatures possessing the earliest rudiments of nerves these exist -in certain superficial cells. Each has a small tubular orifice from -which projects a minute hair, and each has on its under side processes -running into the tissue below, and serving, as it seems, to conduct -impressions from the projecting hair when it is disturbed by contacts -with foreign bodies. A plexus of fibres bringing the inner processes -of such cells into communication arises, and forms something like -a nervous layer capable of propagating impulses in all directions. -At a subsequent stage some of the superficial cells, ceasing to be -themselves the recipients of external stimuli, sink inwards and become -ganglion-cells connected<span class="pagenum" id="Page_304">[304]</span> with the nervous plexus—agents, as we must -suppose, for the reception, multiplication, and diffusion of the -impulses received from the outer cells.</p> - -<p>As thus far developed, the nervous structure is one fitted only -for a vague stimulation of dispersed contractile fibres, causing -movements of an undirected kind. A concentration of these superficial -nervous structures is a probable preliminary to the next change—an -all-important change. For a part of the surface begins to sink inwards, -forming, in the <i>Vertebrata</i>, a groove; and from the lining cells -of this groove, which presently closes over, the central parts of -the nervous system arise: definite nerves having meantime, as we may -suppose, been developed out of the indefinite nervous plexus.</p> - -<p>Neglecting what there is in this of a speculative nature, it is -sufficient for the present purpose to recognize the undoubted fact that -the nervous system is developed from the ectoderm, and that, originally -external, it is made internal by a process of sinking in or by a -process of definite introversion.</p> - - -<p class="p2">§ 290. Whether direct equilibration or indirect equilibration has had -the greater share in producing these fundamental contrasts between -the inner and outer tissues of animals, must be left undecided. The -two causes have all along co-operated—modification of the individual -accumulated by inheritance predominating in some cases, and in other -cases modification of the race by survival of the incidentally fittest. -On the other hand, the action of the medium on the organism cannot fail -to change its surface more than its centre, and so differentiate the -two; while, on the other hand, the surfaces of organisms inhabiting -the same medium display extreme unlikenesses which cannot be due to -the immediate actions of their medium. Let us dwell a moment on the -antithesis.</p> - -<p>We have abundant evidence that animal protoplasm is rapidly modified by -light, heat, air, water, and the salts contained in water—coagulated, -turned from soluble into insoluble, partially changed into isomeric -compounds, or otherwise<span class="pagenum" id="Page_305">[305]</span> chemically altered. Immediate metamorphoses -of this kind are often obviously produced in ova by changes of their -media. At the outset, therefore, before yet there existed any such -differentiation as that which now usually arises by inheritance, -these environing agencies must have tended to originate a protective -envelope. For a modification produced by them on the superficial part -of the protoplasm, must either have been a decomposition or else the -formation of a compound which remained stable under their subsequent -action. There would be generated an outer layer of substance that was -so molecularly immobile as to be incapable of further metamorphoses, -while it would shield the contained protoplasm from that too-great -action of external forces which, by rapidly changing the unstable -equilibrium of its molecules into a relatively stable equilibrium, -would arrest development. Evidently organic evolution, whether -individual or general, must always and everywhere have been subordinate -to these physical necessities. Though natural selection, beginning with -minute portions of protoplasm, must all along have tended to establish -a molecular composition apt to undergo this differentiation of surface -from centre to the most favourable extent, yet it must all along have -done so while controlled by this process of direct equilibration.</p> - -<p>Contrariwise, the many and great unlikenesses among the dermal -structures of creatures inhabiting the same element, cannot be ascribed -to any such cause. The contrasts between naked and shelled Gastropods, -between marine Worms and Crustaceans, between soft-skinned Fishes and -Fishes in armour like the <i>Pterichthys</i>, must have been produced -entirely by natural selection. Environing forces are, as before, the -ultimate causes; but the forces are now not so much those exercised by -the medium as those exercised by the other inhabitants of the medium; -and they do not act by modifying the surface of the individual, but -by killing off individuals whose surfaces are least fitted to the -requirements: thus slowly affecting the species. Still the dermal -skeleton bristling<span class="pagenum" id="Page_306">[306]</span> with spines, which protects the <i>Diodon</i> or -the <i>Cyclichthys</i> from enemies it could not escape, comes within -the general formula of an outer tissue differentiated from inner -tissues by the outer actions to which the creature is exposed: the -differentiation having gone on until there is equilibrium between the -destructive forces to be met and the protective forces which meet them.</p> - -<p>If we venture to apportion the respective shares which mediate and -immediate actions have had in differentiating outer from inner tissues, -we shall probably not be far wrong in ascribing that part of the result -which is alike in all animals, mainly to the direct actions of their -media, while we ascribe the multitudinous unlikenesses of the results -in various animals, partly to the indirect actions of the media, and -partly to the indirect actions of other animals by which the media are -inhabited. That is to say, while assigning the specialities of the -differentiations to the specialities of converse with the agencies in -the environment, most of them organic, we may assign to the constant -and universal converse with its inorganic agencies, the universal -characteristic of tegumentary structures—their growth outwards from a -layer lying below the surface which continually produces new substance -to replace the substance worn away or cast off.</p> - -<p>Here let me add a piece of evidence which strengthens the general -argument, at the same time that it justifies this apportionment. When -ulceration has gone deep enough to destroy the tegumentary structures, -these are never reproduced. The puckered surface formed where an ulcer -heals, or where a serious burn has destroyed the skin, consists of -modified connective tissue, which, as the healing goes on, spreads -inwards from the edges of the ulcer: some of it, perhaps, growing from -the portions of connective tissue that dip down between the muscular -bundles. This connective tissue is normally covered by the epidermis -and thus sheltered from environing actions. What has happened to it? -It has now become the outermost layer. And how does it comport<span class="pagenum" id="Page_307">[307]</span> itself -under its new conditions? It produces a superficial substance which -plays the part of the epidermis and grows outwardly. For since the -surface, subject to friction and exfoliation, has to be continually -renewed, there must be a continual reproduction of an outermost layer -from a layer beneath. That is to say, the contact of this deep-seated -tissue with outer agencies, produces in it some approach towards -that character which we find universally characterizes outer tissue. -But while we see under this exposure to the conditions common to -all integument, a tendency to assume the structure common to all -integument, we see no tendency to assume any of the specialities of -tegumentary structure: no rudiments of glands or hair sacs make their -appearance.</p> - -<p>Analogous conclusions may be drawn respecting the processes of -differentiation by which from the outer layer nervous tissue and -finally a nervous system are evolved. Here, also, both direct and -indirect equilibration appear to have operated. Two reasons may be -assigned for the belief that the transformation of certain superficial -cells into sensitive cells was initiated by exposure to external -stimuli. The first is that, extremely unstable as protoplasm is, -disturbances received by the outer side of a specially-exposed cell -could scarcely fail to cause changes passing through it towards the -interior mass of the body, and that perpetual repetition of such -changes would tend to generate channels of easy transmission through -the protoplasm. The second reason is that, if we do not assume this -process of initiation but assume that survival of the fittest was -the sole agency, then no reason can be assigned why the nervous -system should not have been at the outset formed internally instead -of being initiated externally and then transferred to the interior: -the roundabout process would be inexplicable. At the same time the -production of a central nervous system by introversion of superficial -sensitive cells cannot be ascribed to the differentiating effects -of external stimuli, but must be ascribed to natural selection. No -perpetual repetition of<span class="pagenum" id="Page_308">[308]</span> outer disturbances would cause the sinking -inwards, and covering up, of the specially-sensitive area and -the plexus below it. But it is manifest that since these nervous -structures, at once all-important and easily injured, would be safer -if removed from the surface, survival of the fittest, continually -preserving those in which they were more deeply seated, would tend to -produce an arrangement in which all parts but the actual receivers of -external stimuli became internal.</p> - -<p>Hence, contemplating generally these two fundamental differentiations -of inner from outer tissues, we may conclude that though their first -stages resulted from direct equilibration, their subsequent and higher -stages resulted from indirect equilibration.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_309">[309]</span></p> - -<h3>CHAPTER VII.<br /> -<span class="subhed1">DIFFERENTIATIONS AMONG THE OUTER TISSUES OF ANIMALS.</span></h3></div> - - -<p>§ 291. The outer tissues of animals, originally homogeneous over their -whole surfaces, pass into a heterogeneity which fits their respective -parts to their respective conditions. So numerous and varied are the -implied differentiations, that it is impracticable here to deal with -them all even in outline. To trace them up through classes of animals -of increasing degrees of aggregation, would carry us into undue detail.</p> - -<p>Did space permit, it would be possible to point out among the -<i>Protozoa</i>, various cases analogous to that of the <i>Arcella</i>; -which may be described as like a microscopic Limpet, having a -sarcode body of which the upper surface has become horny, while -the lower surface with its protruding pseudopodia, retains the -primitive jelly-like character. That differentiations of this -kind have been gradually established among these minute creatures -through the unlike relations of their parts to the environment, is -an inference supported by a form which, while the rest of the body -has a scarcely distinguishable coating, “agrees with <i>Arcella</i> -and <i>Difflugia</i> in having the pseudopodia protrusible from one -extremity only of the body.”</p> - -<p>Many parallel specializations of surface among aggregates of the -second order might be instanced from the <i>Cœlenterata</i>. In -the <i>Hydra</i>, the ectoderm presents over its whole area no -conspicuous unlikenesses; but there usually exist in the hydroid -polypes of superior types, decided contrasts between<span class="pagenum" id="Page_310">[310]</span> the higher and -lower parts. While the higher parts retain their original characters, -the lower parts excrete hard outer layers yielding support and -protection. Various stages of the differentiation might be followed. -“In <i>Hydractinia</i>,” says Prof. Green, this horny layer “becomes -elevated at intervals to form numerous rough processes or spines, -while over the general surface of the ectoderm its presence is almost -imperceptible.” In other types, as in <i>Cordylophora</i>, it spreads -part way up the animal’s sides, ending indefinitely. In <i>Bimeria</i> -it “extends itself so as to enclose the entire body of each polypite, -leaving bare only the mouth and tips of the tentacles.” While in -<i>Campanularia</i> it has become a partially-detached outer cell, into -which the creature can retract its exposed parts.</p> - -<p>But it is as needless as it would be wearisome to trace through the -several sub-kingdoms the rise of these multiform contrasts, with the -view of seeking interpretations of them. It will suffice if we take a -few groups of the illustrations furnished by the higher animals.</p> - - -<p class="p2">§ 292. We may begin with those modifications of surface which subserve -respiration. Though we ordinarily think of respiration as the quite -special function of a quite special organ, yet originally it is not -so. Little-developed animals part with their carbonic acid and absorb -oxygen, through the general surface of the body. Even in the lower -types of the higher classes, the general surface of the body aids -largely in aërating the blood; and the parts which discharge the -greater part of this function are substantially nothing more than -slightly altered and extended portions of the skin.</p> - -<p>Such differentiations, marked in various degrees, are to be seen among -<i>Mollusca</i>. In the <i>Pteropoda</i> the only modification which -appears to facilitate respiration, is the minute vascularity of one -part of the skin. Higher types possess special skin-developments. -The <i>Doris</i> has appendages developed into elaborately-branched -forms—small trees of blood-vessels<span class="pagenum" id="Page_311">[311]</span> covered by slightly-changed dermal -tissues. And these arborescent branchiæ are gathered together into a -single cluster. Thus there is evidence that large external respiratory -organs have arisen by degrees from simple skin: as, indeed, they do -arise during the development of each individual having them. Just as -gradually as in the embryo a simple bud on the integument, with its -contained vascular loop, passes by secondary buddings into a tree-like -growth penetrated everywhere by dividing and subdividing blood-vessels; -so gradually has there probably proceeded the differentiation which has -turned part of the outer surface into an organ for excreting carbonic -acid and absorbing oxygen.</p> - -<p>Certain inferior vertebrate animals present us with a like -metamorphosis of tissues. These are the <i>Amphibia</i>. The branchiæ -here developed from the skin, are covered with cellular epidermis, not -much thinner than that covering the rest of the body. Like it they -have their surfaces speckled with pigment-cells; and are not even -conspicuous by their extra vascularity—where they are temporary at -least. They facilitate the exchange of gases in scarcely any other -way than by affording a larger area of contact with the water, and -interposing a rather thinner layer of tissue between the water and the -blood-vessels. Those very simple branchiæ of the larval <i>Amphibia</i> -that have them but for a short time, graduate into the more complex -ones of those that have them for a long time or permanently; showing, -as before, the small stages by which this heterogeneity of surface -accompanying heterogeneity of function may arise.</p> - -<p>In what way are such differentiations established? Mainly, no doubt, by -natural selection; but also to some degree, I think, by the inheritance -of direct adaptations. That a portion of the integument at which -aëration is favoured by local conditions, should thereby be led to grow -into a larger surface of aëration, appears improbable. Survival of -those individuals which happen to have this portion of the integument<span class="pagenum" id="Page_312">[312]</span> -somewhat more-developed, seems here the only likely cause.</p> - - -<p class="p2">§ 293. Among the conspicuous modifications by which the -originally-uniform outer layer is rendered multiform, are the -protective structures. Let us look first at the few cases in which the -formation of these is ascribable mainly to direct equilibration.</p> - -<p>Already reference has been more than once made to those thickenings -that occur where the skin is exposed to unusual pressure and friction. -Are these adaptations inheritable? and may they, by accumulation -through many generations, produce permanent dermal structures fitted -to permanent or frequently-recurring stress? Take, for instance, the -callosities on the knuckles of the <i>Gorilla</i>, which are adapted -to its habit of partially supporting itself on its closed hands -when moving along the ground. Shall we suppose that these defensive -thickenings are produced afresh in each individual by the direct -actions; or that they are inherited modifications caused by such direct -actions; or that they are wholly due to the natural selection of -spontaneous variations? The last supposition does not seem a probable -one. Such thickenings, if spontaneous, would be no more likely to occur -on the knuckles than on any other of the hundred equal areas forming -the skin-surface at large; and the chances against their simultaneous -occurrence on all eight knuckles would be incalculable. Moreover, the -implication would be that those slight extra thicknesses of skin on the -knuckles, with which we must suppose the selection to have commenced, -were so advantageous as to cause survivals of the individuals -having them, in presence of other superiorities possessed by other -individuals. Then that survivals so caused, if they ever occurred at -all, should have occurred with the frequency requisite to establish and -increase the variation, is hardly supposable. And if we reject, as also -unlikely, the reproduction of these callosities <i>de novo</i> in each -individual (for<span class="pagenum" id="Page_313">[313]</span> this would imply that after a thousand generations -each young gorilla began with knuckles having skin no thicker than -elsewhere), there remains only the inference that they have arisen by -the transmission and accumulation of functional adaptations. Another -case which seems interpretable only in an analogous way, is that of -the spurs that are developed on the wings of certain birds—on those -of the Chaja screamer for example. These are weapons of offence and -defence. It is a familiar fact that some birds strike with their -wings, often giving severe blows; and in the birds named, the blows -are made more formidable by the horny, dagger-shaped growths standing -out from those points on the wings which deliver them. Are these spurs -directly or indirectly adaptive? To conclude that natural selection of -spontaneous variations has caused them, is to conclude that, without -any local stimulus, thickenings of the skin occurred symmetrically -on the two wings at the places required; that such thickenings, so -localized, happened to arise in birds given to using their wings in -fight; and that on their first appearance the thickenings were decided -enough to give appreciable advantages to the individuals distinguished -by them—advantages in bearing the reactions of the blows if not in -inflicting the blows. But to conclude this is, I think, to conclude -against probability. Contrariwise, if we assume that the thickening -of the epidermis produced by habitual rough usage is inheritable, the -development of these structures presents no difficulty. The points of -impact would become indurated in wings used for striking with unusual -frequency. The callosities of surface thus generated, rendering the -parts less sensitive, would enable the bird in which they arose to -give, without injury to itself, more violent blows and a greater number -of them: so, in some cases, helping it to conquer and multiply. Among -its descendants, inheriting the modification and the accompanying -habit, the thickening would be further increased in the same way: -survival of the fittest tending ever to accelerate the process.<span class="pagenum" id="Page_314">[314]</span> -Presently the horny nodes so formed, hitherto defensive only in their -effects, would, by their prominence, become offensive—would make -the blows given more hurtful. And now natural selection, aiding more -actively, would mould the nodes into spurs: the individuals in which -the nodes were most pointed would be apt to survive and propagate; and -the pointedness generation after generation thus increased, would end -in the well-adapted shape we see.</p> - -<p>But if in these cases the differentiations which fit particular parts -of the outer tissues to bear rough usage are caused mainly by the -direct balancing of external actions by internal reactions, then we -may suspect that the like is true of other modifications that occur -where special strains and abrasions have to be met. Possibly it is -true of sundry parts that are formed of hardened epidermis, such as -the nails, claws, hoofs, and hollow horns of Mammals; “all of which,” -says Prof. Huxley, “are constructed on essentially the same plan, being -diverticula of the whole integument, the outer layer of whose ecderon -has undergone horny metamorphosis.” Leaving open, however, the question -what tegumentary structures are due to direct equilibration, furthered -and controlled by indirect equilibration, it is tolerably clear that -direct equilibration has been one of the factors.</p> - - -<p class="p2" id="sect294">§ 294. Dermal structures of another class are developed mainly, if not -wholly, by the actions of external causes on species rather than on -individuals. These are the various kinds of clothing—hairs, feathers, -quills, scales, scutes. Though it is no longer thought as at one time -that all these various tegumentary structures are homologous with one -another, yet it is unquestionable that sundry of the more conspicuous -ones are. Those which are extremely unlike may be seen linked together -by a long series of graduated forms. A retrograde metamorphosis from -feathers to appendages that are almost scale-like, is well seen in -the coat of the Penguin. There is manifest a transition from the<span class="pagenum" id="Page_315">[315]</span> -bird-like covering to the fish-like covering—a transition so gradual -that no place can be found where an appreciable break occurs; and if -the scale-like appendages are not truly scales yet they exemplify -an extreme metamorphosis. Less striking, perhaps, but scarcely less -significant, are the modifications through which we pass from feathers -to hairs, on the surfaces of the Ostrich and the Cassowary. The skin -of the Porcupine shows us hairs and quills united by a series of -intermediate structures, differing from one another inappreciably. Even -more remarkable are certain other alliances of dermal structures. “It -may be taken as certain, I think,” says Prof. Huxley, “that the scales, -plates, and spines of all fishes are homologous organs; nor as less so -that the tegumentary spines of the Plagiostomes are homologous with -their teeth, and thence with the teeth of all vertebrata.”</p> - -<p>Further details concerning these tegumentary structures are not needful -for present purposes, and are indeed but indirectly relevant to the -subject of physiological development. Here they are of interest to us -only by involving the general question—What physical influences have -brought them into existence? Still with a view to definite presentation -of the problem, it will be well to contemplate the mode of development -common to the most familiar of them.</p> - -<p>Suppose a small pit to be formed on the previously flat skin; and -suppose that the growth and casting off of horny cells which goes on -over the skin in general, continues to go on at the usual rate over the -depressed surface of this pit. Clearly the quantity of horny matter -produced within this hollow, will be greater than that produced on a -level portion of the skin subtending an equal area of the animal’s -outside. Suppose such a pit to be deepened until it becomes a small -sac. If the exfoliation goes on as before, the result will be that the -horny matter, expelled, as it must be, through the mouth of the sac, -which now bears a small proportion to the internal surface of the sac, -will be<span class="pagenum" id="Page_316">[316]</span> large in quantity compared with that exfoliated from a portion -of the skin equal in area to the mouth of the sac: there will be a -conspicuous thrusting forth of horny matter. Suppose once more that -the sac, instead of remaining simple, has its bottom pushed up into -its interior, like the bottom of a wine-bottle—the introversion being -carried so far that the introverted part reaches nearly to the external -opening, and leaves scarcely any space between the introverted part and -the walls of the sac. It is easy to see that the exfoliation continuing -from the surface of the introverted part, as well as from the inside -of the sac generally, the horny matter cast off will form a double -layer; and will come out of the sac in the shape of a tube having -within its lower end the introverted part, as the core on which it is -moulded, and from the apex of which is cast off the substance filling, -less densely, its interior. The structure resulting will be what we -know as a hair. Manifestly by progressive enlargement of the sac, and -further complication of that introverted part on which the excreted -substance is moulded, the protruding growth may be rendered larger and -more involved, as we see it in quills and feathers. So that insensible -steps, thus indicated in principle, carry us from the exfoliation of -epidermis by a flat surface, to the exfoliation of it by a hollow -simple sac, an introverted sac, and a sac further complicated; each of -which produces its modified kind of tegumentary appendage.</p> - -<p>But now, after contemplating this typical illustration, we return to -the general question. What are the agencies which have been operative -in developing these skin-structures? Indirect equilibration must have -worked almost alone in producing them. No direct incidence of forces -can have developed the enamelled armour of the <i>Lepidosteus</i> or -the tesselated plates of the <i>Glyptodon</i> and its modern allies. -Survival of the fittest must here and in multitudinous other cases be -regarded as the sole cause.</p> - - -<p class="p2">§ 295. Among many other differentiations of the outer<span class="pagenum" id="Page_317">[317]</span> tissues, the -most worthy to be noticed in the space that remains, are those by which -organs of sense are formed. We will begin with the simplest and most -closely-allied to the foregoing.</p> - -<p>Every hair that is not too long or flexible to convey to its rooted end -a strain put upon its free end, is a rudimentary tactual organ; as may -be readily proved by touching one of those growing on the back of the -hand. If, then, a creature has certain hairs so placed that they are -habitually touched by the objects with which it deals, or amid which -it moves, an advantage is likely to accrue if these hairs are modified -in a way that enables them the better to transmit the impressions -derived. Such modified hairs we have in the <i>vibrissæ</i>, or, as -they are commonly called, the “whiskers” possessed by Cats and feline -animals generally, as well as by Seals and many Rodents. These hairs -are long enough to reach objects at considerable distances; they are so -stiff that forces applied to their free ends, cause movements of their -imbedded ends; and the sacs containing their imbedded ends being well -covered with nerve-fibres, these developed hairs serve as instruments -of exploration. By constant use of them the animal learns to judge of -the relative positions of objects past which, or towards which, it -is moving. When stealthily approaching prey or stealthily escaping -enemies, such aids to perception are obviously important: indeed their -importance has been proved by the diminished power of self-guidance in -the dark, that results from cutting them off. These, then, are dermal -appendages originally serving the purpose of clothing, but afterwards -differentiated into sense-organs.</p> - -<p>That eyes are essentially dermal structures seems scarcely conceivable. -Yet an examination of their rudimentary types, and of their genesis -in creatures that have them well developed, shows us that they really -arise by successive modifications of the double layer composing the -integument. They make their first appearance among the simpler animals -as specks of pigment, covered by portions of epidermis slightly<span class="pagenum" id="Page_318">[318]</span> -convex and a little more transparent than that around it. Here their -fundamental community of structure with the skin is easy to trace; and -the formation of them by differentiation of it presents no difficulty. -Not so far in advance of these as much to obscure the relationship, -are the eyes which the Crustaceans possess. In every fishmonger’s shop -we may see that the eyes of a Lobster are carried on pedicles; and -when the Lobster casts its shell, the outer coat of each eye, being -continuous with the epidermis of its pedicle, is thrown off along with -the rest of the exo-skeleton. Beneath the transparent epidermic layer, -there exists a group of eyes of the kind which we see in an insect; -and these, according to a high authority, are inclosed in the dermal -system. Describing the arrangement of the parts, M. Milne Edwards -writes:—“But the most remarkable circumstance is, that the large -cavity within which the whole of these parallel columns, every one of -which is itself a perfect eye, are contained, is closed posteriorly by -a membrane, which appears to be neither more nor less than the middle -tegumentary membrane, pierced for the passage of the optic nerve; so -that the ocular chamber at large results from the separation at a point -of the two external layers of the general envelope.” Thus too is it, in -the main, even with the highly developed eyes of the <i>Vertebrata</i>. -“The three pairs of sensory organs appertaining to the higher senses,” -says Prof. Huxley—“the nasal sacs, the eyes, and the ears—arise as -simple cœcal involutions of the external integument of the head of -the embryo. That such is the case, so far as the olfactory sacs are -concerned, is obvious, and it is not difficult to observe that the -lens and the anterior chamber of the eye are produced in a perfectly -similar manner. It is not so easy to see that the labyrinth of the ear -arises in this way, as the sac resulting from the involution of the -integument is small, and remains open but a very short time. But I have -so frequently verified Huschke’s and Remak’s statement that it does so -arise, that<span class="pagenum" id="Page_319">[319]</span> I entertain no doubt whatever of the fact. The outer ends -of the olfactory sacs remain open, but those of the ocular and auditory -sacs rapidly close up, and shut off their contents from all direct -communication with the exterior.” That is to say, the eye considered as -an optical apparatus is produced by metamorphoses of the skin: the only -parts of it not thus produced, being the membranes lying between the -sclerotic and the vitreous humour, including those retinal structures -formed in them. All is tegumentary save that which has to appreciate -the impressions which the modified integument concentrates upon it.</p> - -<p>Thus, as Prof. Huxley has somewhere pointed out, there is a -substantial parallelism between all the sensory organs in their modes -of development; as there is, too, between their modes of action. -A <i>vibrissa</i> may be taken as their common type. Increased -impressibility by an external stimulus, requires an increased -peripheral expansion of the nervous system on which the stimulus may -fall; and this is secured by an introversion of the integument, forming -a sac on the walls of which a nerve may ramify. That the more extended -sensory area thus constituted may be acted upon, there requires some -apparatus conveying to it from without the appropriate stimulus; and -in the case of the <i>vibrissa</i>, this apparatus is the epidermic -growth which, under the form of a hair, protrudes from the sac. And -that the greatest sensitiveness may be obtained, the external action -must be exaggerated or multiplied by the apparatus which conveys it -to the recipient nerve; as, in the case of the <i>vibrissa</i>, it is -by the development of a hair into an elastic lever, that transforms -the slight force acting through considerable space on its exposed end, -into a greater force acting through a smaller space at its rooted end. -Similarly with the organs of the higher senses. In a rudimentary eye, -the slightly modified sense cell has but a rudimentary nerve to take -cognizance of the impression; and to concentrate the impression upon -it, there is nothing beyond a thickening of the epidermis into a<span class="pagenum" id="Page_320">[320]</span> -lens-shape. But the developed eye shows us a termination of the nerve -greatly expanded and divided to receive the external stimulus. It shows -us an introverted portion of the integument containing the apparatus -by which the external stimulus is conveyed to the recipient nerve. The -structure developed in this sac not only conveys the stimulus, but -also, like its homologue, concentrates it; and in the one case as in -the other, the structure which does this is an epidermic growth from -the bottom of the sac. Even with the ear it is the same. Again we have -an introverted portion of the integument, on the walls of which the -nerve is distributed in the primitive ear. The otolithes contained -in the sac thus formed, are bodies which are set in motion by the -vibrations of the surrounding water, and convey these vibrations in an -exaggerated form to the nerves. And though it is not alleged that these -otolithes are developed from the epidermic lining of the chamber, yet -as, if not so developed, they are concretions from the contents of an -epidermic sac, they must still be regarded as epidermic products.</p> - -<p>Whether these differentiations are due wholly to indirect -equilibration, or whether direct equilibration has had a share in -working them, are questions that must be left open. Possibly a short -hair so placed on a mammal’s face as to be very often touched, may, -by conveying excitations to the nerves and vessels at its root, cause -extra growth of the bulb and its appendages, and so the development of -a <i>vibrissa</i> may be furthered. Possibly, too, the light itself, to -which the tissues of some inferior animals are everywhere sensitive, -may aid in setting up certain of the modifications by which the nervous -parts of visual organs are formed: producing, as it must, the most -powerful effects at those points on the surface which the movements of -the animal expose to the greatest and most frequent contrasts of light -and shade; and propagating from those points currents of molecular -change through the organism. But it seems clear that the complexities<span class="pagenum" id="Page_321">[321]</span> -of the sensory organs are not thus explicable. They must have arisen by -the natural selection of favourable variations.</p> - - -<p class="p2">§ 296. A group of facts, serving to elucidate those put together in -the several foregoing sections, has to be added. I have reserved -this group to the last, partly because it is transitional—links the -differentiations of the literally outer tissues with those of the truly -inner tissues. Though physically internal, the mucous coat of the -alimentary canal has a <i>quasi</i>-externality from a physiological -point of view. As was pointed out in the last chapter, the skin and -the assimilating surface have this in common, that they come in direct -contact with matters not belonging to the organism; and we saw that -along with this community of relation to alien substances, there is a -certain community of structure and development. The like holds with the -linings of all internal cavities and canals that have external openings.</p> - -<p>The transition from the literally outer tissues to those tissues -which are intermediate between them and the truly inner tissues, -is visible at all the orifices of the body; where skin and mucous -membrane are continuous, and the one passes insensibly into the -other. This visible continuity is associated not simply with a great -degree of morphological continuity, but also with a great degree of -physiological continuity. That is to say, these literally outer and -<i>quasi</i>-outer layers are capable of rapidly assuming one another’s -structures and functions when subject to one another’s conditions. -Mucous surfaces, normally kept covered, become skin-like if exposed -to the air; but resume more or less fully their normal characters -when restored to their normal positions. These are truths familiar to -pathologists. They continually meet with proofs that permanent eversion -of the mucous membrane, even where it is by prolapse of a part deeply -seated within the body, is followed by an adaptation eventually almost -complete: originally moist, tender to the touch, and irritated by the -air, the surface gradually becomes covered<span class="pagenum" id="Page_322">[322]</span> with a thick, dry cuticle; -and is then scarcely more sensitive than ordinary integument.</p> - -<p>Whether this equilibration between new outer forces and reactive inner -forces, which is thus directly produced in individuals, is similarly -produced in races, must remain as a question not to be answered in a -positive way. On the one hand, we have the fact that among the higher -animals there are cases of <i>quasi</i>-outer tissues which are in -one species habitually ensheathed, while in another species they are -not ensheathed; and that these two tissues, though unquestionably -homologous, differ as much as skin and mucous membrane differ. On the -other hand, there are certain analogous changes of surface, as on the -abdomen of the Hermit-Crab, which give warrant to the supposition -that survival of the fittest is the chief agent in establishing such -differentiations; since the abdomen of a Hermit-Crab, bathed by water -within the shell it occupies, is not exposed to physical conditions -that directly tend to differentiate its surface from the surface of -the thorax. But though in cases like this last, we must assign the -result to the natural selection of variations arising incidentally; we -may, I think, legitimately assign the result to the immediate action -of changed conditions where, as in cases like the first, we see these -producing in the individual, effects of the kinds observed in the race.</p> - -<p>However this may be, the force of the general argument remains the -same. In these exchanges of structure and function between the outer -and <i>quasi</i>-outer tissues, we get undeniable proof that they are -easily differentiable. And seeing this, we are enabled the more clearly -to see how there have, in course of time, arisen those extreme and -multitudinous differentiations of the outer tissues which have been -glanced at.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_323">[323]</span></p> - -<h3>CHAPTER VIII.<br /> -<span class="subhed1">DIFFERENTIATIONS AMONG THE INNER TISSUES OF ANIMALS.</span></h3></div> - - -<p>§ 297. The change from the outside of the lips to their inside, -introduces us to a new series of interesting and instructive facts, -joining on to those with which the last chapter closed. They concern -the differentiations of those coats of the alimentary canal which, as -we have seen, are physiologically outer, though physically inner.</p> - -<p>These coats are greatly modified at different parts; and their -modifications vary greatly in different animals. In the lower types, -where they compose a simple tube running from end to end of the body, -they are almost uniform in their histological characters; but on -ascending from these types, we find them presenting an increasing -variety of minute structures between their two ends. The argument -will be adequately enforced if we limit ourselves to the leading -modifications they display in some of the higher animals.</p> - -<p>The successive parts of the alimentary canal are so placed with respect -to its contents, that the physical and chemical changes undergone by -its contents while passing from one end to the other, inevitably tend -to transform its originally homogeneous surface into a heterogeneous -surface. Clearly, the effect produced on the food at any part of -the canal by trituration, by adding a secretion, or by absorbing -its nutritive matters, implies the delivery of the food into the -next part of the canal in a state more or less unlike its previous<span class="pagenum" id="Page_324">[324]</span> -states—implies that the surface with which it now comes in contact -is differently affected by it from the preceding surfaces—implies, -that is, a differentiating action. To use concrete language;—food -that is broken down in the mouth acts on the œsophagus and stomach -in a way unlike that which it would have done had it been swallowed -whole; the masticated food, to which certain solvents or ferments -are added, becomes to the intestine a different substance from that -which it must have otherwise been; and the altered food, resolved -by these additions into its proximate principles, cannot have those -proximate principles absorbed in the next part of the intestine, -without the remoter parts being affected as they would not have been -in the absence of absorption. It is true that in developed alimentary -canals, such as the reasoning here tacitly assumes, these marked -successive differentiations of the food are themselves the results -of pre-established differentiations in the successive parts of the -canal. But it is also true that actions and reactions like those -here so definitely marked, must go on indefinitely in an undeveloped -alimentary canal. If the food is changed at all in the course of its -transit, which it must be if the creature is to live by it, then it -cannot but act dissimilarly on the successive tracts of the alimentary -canal, and cannot but be dissimilarly reacted on by them. Inevitably, -therefore, the uniformity of the surface must lapse into greater or -less multiformity: the differentiation of each part tending ever to -initiate differentiations of other parts.</p> - -<p>Not, indeed, that the implied process of direct equilibration can -be regarded as the sole process. Indirect equilibration aids; and, -doubtless, there are some of the modifications which only indirect -equilibration can accomplish. But we have here one unquestionable -cause—a cause that is known to work in individuals, changes of the -kind alleged. Where, for instance, cancerous disease of the œsophagus -so narrows the passage into the stomach as to prevent easy descent of -the food, the œsophagus above the obstruction becomes<span class="pagenum" id="Page_325">[325]</span> enlarged into a -kind of pouch; and the inner surface of this pouch begins to secrete -juices that produce in the food a kind of rude digestion. Again, -stricture of the intestine, when it arises gradually, is followed by -hypertrophy of the muscular coat of the intestine above the constricted -part: the ordinary peristaltic movements being insufficient to force -the food forwards, and the lodged food serving as a constant stimulus -to contraction, the muscular fibres, habitually more exercised, -become more bulky. The deduction from general principles being thus -inductively enforced, we cannot, I think, resist the conclusion that -the direct actions and reactions between the food and the alimentary -canal have been largely instrumental in establishing the contrasts -among its parts. And we shall hold this view with the more confidence -on observing how satisfactorily, in pursuance of it, we are enabled to -explain one of the most striking of these differentiations, which we -will take as a type of the class.</p> - -<p>The gizzard of a bird is an expanded portion of the alimentary canal, -specially fitted to give the food that trituration which the toothless -mouth of a bird cannot give. Besides having a greatly-developed -muscular coat, this grinding-chamber is lined with a thick, hard -cuticle, capable of bearing the friction of the pebbles swallowed to -serve as grindstones. This differentiation of the mucous coat into a -ridged and tubercled layer of horny matter—a differentiation which, -in the analogous organs of certain <i>Mollusca</i>, is carried to the -extent of producing from this membrane cartilaginous plates, and even -teeth—varies in birds of different kinds, according to their food. -It is moderate in birds that feed on flesh and fish, and extreme in -granivorous birds and others that live on hard substances. How does -this immense modification of the alimentary canal originate? In the -stomach of a mammal, the macerating and solvent actions are united -with that triturating action which finishes what the teeth have mainly -done; but in the bird, unable to masticate, these internal functions -are specialized, and while the crop is the<span class="pagenum" id="Page_326">[326]</span> macerating chamber, the -gizzard becomes a chamber adapted to triturate more effectually. This -adaptation requires simply an exaggeration of certain structures -and actions which characterize stomachs in general, and, in a less -degree, alimentary canals throughout their whole lengths. The massive -muscles of the gizzard are simply extreme developments of the muscular -tunic, which is already considerably developed over the stomach, and -incloses also the œsophagus and the intestine. The indurated lining of -the gizzard, thickened into horny buttons at the places of severest -pressure, is nothing more than a greatly strengthened and modified -epithelium. And the grinding action of the gizzard is but a specialized -form of that rhythmical contraction by which an ordinary stomach kneads -the contained food, and which in the œsophagus effects the act of -swallowing, while in the intestine it becomes the peristaltic motion. -Allied as the gizzard thus clearly is in structure and action to the -stomach and alimentary canal in general; and capable of being gradually -differentiated from a stomach where a growing habit of swallowing -food unmasticated entails more trituration to be performed before -the food passes the pylorus; the question is—Does this change of -structure arise by direct adaptation? There is warrant for the belief -that it does. Besides such collateral evidence as that mucous membrane -becomes horny on the toothless gums of old people, when subject to -continual rough usage, and that the muscular coat of the intestine -thickens where unusual activity is demanded of it, we have the direct -evidence of experiment. Hunter habituated a sea-gull to feed on grain, -and found that the lining of its gizzard became hardened, while the -gizzard-muscles doubled in thickness. A like change in the diet of a -kite was followed by like results. Clearly, if differentiations so -produced in the individuals of a race under changed habits, are in any -degree inheritable, a structure like a gizzard will originate through -the direct actions and reactions between the food and the alimentary -canal.</p> - -<p><span class="pagenum" id="Page_327">[327]</span></p> - -<p>Another case—a very interesting one, somewhat allied to this—is -presented by the ruminating animals. Here several dilatations of -the alimentary canal precede the true stomach; and in them large -quantities of unmasticated food are stored, to be afterwards returned -to the mouth and masticated at leisure. What conditions have made -this specialization advantageous? and by what process has it been -established? To both these questions the facts indicate answers -which are not unsatisfactory. [Creatures that obtain their food very -irregularly—now having more than they can consume, and now being for -long periods without any—must, in the first place, be apt, when very -hungry, to eat to the extreme limits of their capacities; and must, -in the second place, profit by peculiarities which enable them to -compensate themselves for long fasts, past and future. A perch which, -when its stomach is full of young frogs, goes on filling its œsophagus -also; or a trout which, rising to the fisherman’s fly, proves when -taken off the hook to be full of worms and insect-larvæ up to the very -mouth, gains by its ability to take in such unusual supplies of food -when it meets with them—obviously thrives better than it would do -could it never eat more than a stomachful. That this ability to feed -greatly in excess of immediate requirement, is one that varies in -individuals of the same race, we see in the marked contrast between -our own powers in this respect, and the powers of uncivilized men; -whose fasting and gorging are to us so astonishing. Carrying with us -these considerations, we shall not be surprised at finding dilatations -of the œsophagus in vultures and eagles, which get their prey at long -intervals in large masses; and we may naturally look for them, too, in -birds like pigeons, which, coming in flocks upon occasional supplies -of grain, individually profit by devouring the greatest quantity in -a given time. Now where the trituration of the food is, as in these -cases, carried on in a lower part of the alimentary canal, nothing -further is required than the storing-chamber; but for a mammal, -having its grinding<span class="pagenum" id="Page_328">[328]</span> apparatus in its mouth, to gain by the habit of -hurriedly swallowing unmasticated food, it must also have the habit of -regurgitating the food for subsequent mastication. This correlation of -habits with their answering structures, may, as we shall see, arise in -a very simple way. The starting point of the explanation is a familiar -fact—the fact that indigestion, often resulting from excess of food, -is apt to cause that reversed peristaltic action known as vomiting. -From this we pass to the fact, also within the experience of most -persons, that during slight indigestion the stomach sometimes quietly -regurgitates a small part of its contents as far as the back of the -mouth—giving an unpleasant acquaintance with the taste of the gastric -juices. Exceptional facts of the same class help the argument a step -further. “There are certain individuals who are capable of returning, -at will, a greater or smaller portion of the contents of the digesting -stomach into the cavity of the mouth.... In some of these cases, the -expulsion of the food has required a violent effort. In the majority -it has been easily evoked or suppressed. While in others, it has been -almost uncontrollable; or its non-occurrence at the habitual time -has been followed by a painful feeling of fulness, or by the act of -vomiting.” Here we have a certain physiological action, occasionally -happening in most persons and in some developed into a habit more or -less pronounced: indigestion being the habitual antecedent. Suppose, -then, that gregarious animals, living on innutritive food such as -grass, are subject to a like physiological action, and are capable of -like variations in the degree of it. What will naturally happen? They -wander in herds, now over places where food is scarce and now coming -to places where it is abundant. Some masticate their food completely -before swallowing it, while some masticate it incompletely. If an -oasis, presently bared by their grazing, has not supplied to the whole -herd a full meal, then the individuals which masticate completely -will have had less than those which masticate incompletely—will -not<span class="pagenum" id="Page_329">[329]</span> have had enough. Those which masticate incompletely and distend -their stomachs with food difficult to digest, will be liable to these -regurgitations; but if they re-masticate what is thus returned to -the mouth (and we know that animals often eat again what they have -vomited), then the extra quantity of food taken, eventually made -digestible, will yield them more nourishment than is obtained by those -which masticate completely at first. The habit initiated in this -natural way, and aiding survival when food is scarce, will be apt to -cause modifications of the alimentary canal. We know that dilatations -of canals readily arise under habitual distensions. We know that canals -habitually distended become gradually more tolerant of the contained -masses that at first irritated them. And we know that there commonly -take place adaptive modifications of their surfaces. Hence if a habit -of this kind and the structural changes resulting from it, are in -any degree inheritable, it is clear that, increasing in successive -generations, both immediately by the cumulative effect of repetitions -and mediately by survival of the individuals in which they are most -decided, they may go on until they end in the peculiarities which -Ruminants display.</p> - - -<p class="p2">§ 298. There are structures belonging to the same group which cannot, -however, be accounted for in this way. They are the organs that -secrete special products facilitating digestion—the liver, pancreas, -and various smaller glands. All these appendages of the alimentary -canal, large and independent as some of them seem, really arise by -differentiations from its coats. The primordial liver consists of -nothing more than bile-cells scattered along a tract of the intestinal -surface. Accumulation of these bile-cells is accompanied by increased -growth of the surface which bears them—a growth which at first takes -the form of a <i>cul-de-sac</i>, having an outside that projects from -the intestine into the peri-visceral cavity. As the mass of bile-cells -becomes greater, there arise secondary<span class="pagenum" id="Page_330">[330]</span> lateral cavities opening into -the primary one, and through it into the intestine; until, eventually, -these cavities with their coatings of bile-cells, become ramifying -ducts distributed through the solid mass we know as a liver. How is -this differentiation caused?</p> - -<p>Before attempting any answer to this question, it is requisite to -inquire the nature of bile. Is that which the liver throws into -the intestines a waste product of the organic actions? or is it a -secretion aiding digestion? or is it a mixture of these? Modern -investigations imply that it is most likely the last. The liver -is found to have a compound function. Bernard has proved to the -satisfaction of physiologists, that there goes on in it a formation of -glycogen—a substance which is transformed into sugar before it leaves -the liver and is afterwards carried away by the blood to eventually -disappear in the active organs, chiefly the muscles. It is also shown, -experimentally, that there are generated in the liver certain biliary -acids; and by the aid either of these or of some other compounds, it is -clear that bile renders certain materials more absorbable. Its effect -on fat is demonstrable out of the body; and the greatly diminished -absorption of fat from the food when the discharge of bile into the -intestine is prevented, is probably one of the causes of that pining -away which results. But while recognizing the fact that the bile -consists in part of a solvent, or solvents, aiding digestion, there -is abundant evidence that one element of it is an effete product; -and probably this is the primary element. The yellow-green substance -called biliverdine in herbivora and bilirubin in man and carnivora, -which gives its colour to bile, is a product the greater part of which -is normally cast out from the system continually, as is shown by the -contrast between the normal and abnormal colours of fæcal matters, and -as is still more strikingly shown by the effects on the system when -there is a stoppage of the excretion, and an attack of jaundice. Hence -we are warranted in classing biliverdine as a waste product, and we<span class="pagenum" id="Page_331">[331]</span> -may fairly infer that the excretion of it is the original function of -the liver.</p> - -<p>One further preliminary is requisite. We must for a moment return to -those physico-chemical data set down in the first chapter of this work -(<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect7">§§ 7–8</a>). We there saw that the complex and large-atomed colloids which -mainly compose living organic matter, have extremely little molecular -mobility; and, consequently, extremely little power of diffusing -themselves. Whereas we saw not only that those absorbed matters, -gaseous and liquid, which further the decomposition of living organic -matter, have very high diffusibilities, but also that the products -of the decomposition are much more diffusible than the components of -living organic matter. And we saw that, as a consequence of this, the -tissues give ready entrance to the substances which decompose them, -and ready exit to the substances into which they are decomposed. Hence -it follows that, under its initial form, uncomplicated by nervous and -other agencies, the escape of effete matters from the organism, is a -physical action parallel to that which goes on among mixed colloids -and crystalloids that are dead or even inorganic. Excretion is a -specialized form of this spontaneous action; and we have to inquire how -the specialization arises.</p> - -<p>Two causes conspire to establish it. The first is that these products -of decomposition are diffusible in widely different degrees. While -the carbonic acid and water permeate the tissues with ease in all -directions, and escape more or less from the exposed surfaces, urea, -and other waste substances incapable of being vaporized, cannot escape -thus readily. The second is that the different parts of the body, being -subject to different physical conditions, are from the outset sure -severally to favour the exit of these various products of decomposition -in various degrees. How these causes must have co-operated in -localizing the excretions, we shall see on remembering how they now -co-operate in localizing the separation of morbid materials. The -characteristic substances of<span class="pagenum" id="Page_332">[332]</span> gout and rheumatism have their habitual -places of deposit. Tuberculous matter, though it may be present in -various organs, gravitates towards some much more than towards others. -Certain products of disease are habitually got rid of by the skin, -instead of collecting internally. Mostly, these have special parts of -the skin which they affect rather than the rest; and there are those -which, by breaking out symmetrically on the two sides of the body, -show how definitely the places of their excretion are determined by -certain favouring conditions, which corresponding parts may be presumed -to furnish in equal degrees. Further, it is to be observed of these -morbid substances circulating in the blood, that having once commenced -segregating at particular places, they tend to continue segregating -at those places. Assuming, then, as we may fairly do, that this -localization of excretion, which we see continually commencing afresh -with morbid matters, has always gone on with the matters produced by -the waste of the tissues, let us take a further step, and ask how -localizations become fixed. Other things equal, that which from its -physical conditions is a place of least resistance to the exit of -an effete product, will tend to become established as the place of -excretion; since the rapid exit of an effete product will profit the -organism. Other things equal, a place at which the excreted matter -produces least detrimental effect will become the established place. If -at any point the excreted matter produces a beneficial effect, then, -other things equal, survival of the fittest will determine it to this -point. And if facility of escape anywhere goes along with utilization -of the escaping substance, then, other things equal, the excretion will -be there localized still more decisively by survival of the fittest.</p> - -<p>Such being the conditions of the problem, let us ask what will happen -with the lining membrane of the alimentary canal. This, physiologically -considered, is an external surface; and matters thrown off from it -make their way out of the body. It is also a surface along which is -moving the food<span class="pagenum" id="Page_333">[333]</span> to be digested. Now, among the various waste products -continually escaping from the living tissues, some of the more complex -ones, not very stable in composition, are likely, if added to the food, -to set up changes in it. Such changes may either aid or hinder the -preparation of the food for absorption. If an effete matter, making its -exit through the wall of the intestine, hinders the digestive process, -the enfeeblement and disappearance of individuals in which this -happens, will prevent the intestine from becoming the established place -for its exit. While if it aids the digestive process, the intestine -will, for converse reasons, become more and more the place to which -its exit is limited. Equally manifest is it that if there is one part -of this alimentary canal at which, more than at any other part, the -favourable effect results, this will become the place of excretion.</p> - -<p>Thus, then, reverting to the case in question, we may understand how a -product to be cast out, such as biliverdine, if it either directly or -indirectly serves a useful purpose, when poured into a particular part -of the intestine, may lead to the formation of a patch of excreting -cells on its wall; and once this place of excretion having been -established, the development of a liver is simply a question of time -and natural selection.</p> - - -<p class="p2">§ 299. A differentiation of another order occurring in the alimentary -canal, is that by which a part of it is developed into a lateral -chamber or chambers, through which carbonic acid exhales and oxygen is -absorbed. Comparative anatomy and embryology unite in showing that a -lung is formed, just as a liver or other appendage of the alimentary -canal is formed, by the growth of a hollow bud into the peri-visceral -cavity, or space between the alimentary canal and the wall of the -body. The interior of this bud is simply a <i>cul-de-sac</i> of the -alimentary canal, with the mucous lining of which its own mucous lining -is continuous. And the development of this <i>cul-de-sac</i> into an -air-chamber, simple or compound, is<span class="pagenum" id="Page_334">[334]</span> merely a great extension of area -in the internal surface of the <i>cul-de-sac</i>, along with that -specialization which fits it for excreting and absorbing substances -different from those which other parts of the mucous surface excrete -and absorb. These lateral air-chambers, universal among the higher -<i>Vertebrata</i> and very general among the lower, and everywhere -attached to the alimentary canal between the mouth and the stomach, -have not in all cases the respiratory function. In most fishes that -have them they are what we know as swim-bladders. In some fishes the -cavities of these swim-bladders are completely shut off from the -alimentary canal: nevertheless showing, by the communications which -they have with it during the embryonic stages, that they are originally -<i>diverticula</i> from it. In other fishes there is a permanent -<i>ductus pneumaticus</i>, uniting the cavity of the swim-bladder with -that of the gullet: the function, however, being still not respiratory -in an appreciable degree, if at all. But in certain still extant -representatives of the sauroid fishes, as the <i>Lepidosteus</i>, -the air-bladder is “divided into two sacs that possess a cellular -structure,” and “the trachea which proceeds from it opens high up in -the throat, and is surrounded with a glottis.” In the <i>Amphibia</i> -the corresponding organs are chambers over the surfaces of which there -are saccular depressions, indicating a transition towards the air-cells -characterizing lungs; and accompanying this advance we see, as in the -common <i>Triton</i>, the habit of coming up to the surface and taking -down a fresh supply of air in place of that discharged.</p> - -<p>How are the internal air-chambers, respiratory or nonrespiratory, -developed? Upwards from the amphibian stage, in which they are -partially refilled at long intervals, there is no difficulty in -understanding how, by infinitesimal steps, they pass into complex -and ever-moving lungs. But how is the differentiation that produces -them initiated? How comes a portion of the internal surface to be -specialized for converse with a medium to which it is not naturally<span class="pagenum" id="Page_335">[335]</span> -exposed? The problem appears a difficult one; but there is a not -unsatisfactory solution of it.</p> - -<p>When many gold-fish are kept in a small aquarium, as with thoughtless -cruelty they frequently are, they swim close to the surface, so as to -breathe that water which is from instant to instant absorbing fresh -oxygen. In doing this they often put their mouths partly above the -surface, so that in closing them they take in bubbles of air; and -sometimes they may be seen to continue doing this—the relief due to -the slight extra aëration of blood so secured, being the stimulus -to continue. Air thus taken in may be detained. If a fish that has -taken in a bubble turns its head downwards, the bubble will ascend -to the back of its mouth, and there lodge; and coming within reach -of the contractions of the œsophagus, it may be swallowed. If, then, -among fish thus naturally led upon occasion to take in air-bubbles, -there are any having slight differences in the alimentary canal that -facilitate lodgment of the air, or slight nervous differences such as -in human beings cause an accidental action to become “a trick,” it -must happen that if an advantage accrues from the habitual detention -of air-bubbles, those individuals most apt to detain them will, -other things equal, be more likely than the rest to survive; and by -the survival of descendants inheriting their peculiarities in the -greatest degrees, and increasing them, an established structure and an -established habit may arise. And that they do in some way arise we have -proof. The common Loach swallows air, which it afterwards discharges -loaded with carbonic acid.</p> - -<p>From air thus swallowed the advantages that may be derived are of two -kinds. In the first place, the fish is made specifically lighter, and -the muscular effort needed to keep it from sinking is diminished—or, -indeed, if the bubble is of the right size, is altogether saved. -The contrast between the movements of a Goby, which, after swimming -up towards the surface, falls rapidly to the bottom on ceasing its -exertions, and the movements of a Trout, which remains suspended just<span class="pagenum" id="Page_336">[336]</span> -balancing itself by slight undulations of its fins, shows how great -an economy results from an internal float, to fishes which seek their -food in mid-water or at the surface. Hence the habit of swallowing -air having been initiated in the way described, we see why natural -selection will, in certain fishes, aid modifications of the alimentary -canal favouring its lodgment—modifications constituting air-sacs. -In the second place, while from air thus lodged in air-sacs thus -developed, the advantage will be that of flotation only if the air -is infrequently changed or never changed, the advantage will be that -of supplementary respiration if the air-sacs are from time to time -partially emptied and refilled. The requirements of the animal will -determine which of the two functions predominates. Let us glance at the -different sets of conditions under which these divergent modifications -may be expected to arise.</p> - -<p>The respiratory development is not likely to take place in fishes -that inhabit seas or rivers in which the supply of aërated water -never fails: there is no obvious reason why the established branchial -respiration should be replaced by a pulmonic respiration. Indeed, if -a fish’s branchial respiration is adequate to its needs, a loss would -result from the effort of coming to the surface for air; especially -during those first stages of pulmonic development when the extra -aëration achieved was but small. Hence in fishes so circumstanced, -the air-chambers arising in the way described would naturally become -specialized mainly or wholly into floats. Their contained air being -infrequently changed, no advantage would arise from the development -of vascular plexuses over their surfaces; nothing would be gained -by keeping open the communication between them and the alimentary -canal; and there might thus eventually result closed chambers the -gaseous contents of which, instead of being obtained from without, -were secreted from their walls, as gases often are from mucous -membranes. Contrariwise, aquatic vertebrates in which the swallowing of -air-bubbles, becoming<span class="pagenum" id="Page_337">[337]</span> habitual, had led to the formation of sacs that -lodged the bubbles; and which continued to inhabit waters not always -supplying them with sufficient oxygen, might be expected to have the -sacs further developed, and the practice of changing the contained -air made regular, if either of two advantages resulted—either the -advantage of being able to live in old habitats that had become -untenable without this modification, or the advantage of being able to -occupy new habitats. Now it is just where these advantages are gained -that we see the pulmonic respiration coming in aid of the branchial -respiration, and in various degrees replacing it. Shallow waters are -liable to three changes which conspire to make this supplementary -respiration beneficial. The summer’s sun heats them, and raising the -temperatures of the animals they contain, accelerates the circulation -in these animals, exalts their functional activities, increases the -production of carbonic acid, and thus makes aëration of the blood more -needful than usual. Meanwhile the heated water, instead of yielding -to the highly carbonized blood brought to the branchiæ the usual -quantity of oxygen, yields less than usual; for as the heat of the -water increases, the quantity of air it contains diminishes. And this -greater demand for oxygen joined with smaller supply, pushed to an -extreme where the water is nearly all evaporated, is at last still -more intensely felt in consequence of the excess of carbonic acid -discharged by the numerous creatures congregated in the muddy puddles -that remain. Here, then, it is, that the habit of taking in air-bubbles -is likely to become established, and the organs for utilizing them -developed; and here it is, accordingly, that we find all stages of the -transition to aërial respiration. The Loach before-mentioned, which -swallows air, frequents small waters liable to be considerably warmed. -The <i>Amphipnous Cuchia</i>, an anomalous eel-shaped fish, which has -vascular air-sacs opening out at the back of the mouth, “is generally -found lurking in holes and crevices, on the muddy banks of marshes or -slow-moving rivers”; and<span class="pagenum" id="Page_338">[338]</span> though its air-sacs are not morphological -equivalents of those above described, yet they equally well illustrate -the relation between such organs and the environing condition. Still -more significant is the fact that the <i>Lepidosiren</i>, or “mudfish” -as it is called from its habits, though it is a true fish nevertheless -has lungs. But it is among the <i>Amphibia</i> that we see most -conspicuously this relation between the development of air-breathing -organs, and the peculiarities of the habitats. Pools, more or less -dissipated annually, and so rendered uninhabitable by most fishes, are -very generally peopled by these transitional types. Just as we see, -too, that in various climates and in various kinds of shallow waters, -the supplementary aërial respiration is needful in different degrees; -so do we find among the <i>Amphibia</i> many stages in the substitution -of the one respiration for the other. The facts, then, are such as give -to the hypothesis a <i>vraisemblance</i> greater than could have been -expected.</p> - -<p>The relative effects of direct and indirect equilibration in -establishing this further heterogeneity, must, as in many other -cases, remain undecided. The habit of taking in bubbles is scarcely -interpretable as a result of spontaneous variation: we must regard it -as arising accidentally during the effort to obtain the most aërated -water; as being persevered in because of the relief obtained; and as -growing by repetition into a tendency bequeathed to offspring, and -by them, or some of them, increased and transmitted. The formation -of the first slight modifications of the alimentary canal favouring -the lodgment of bubbles, is not to be thus explained. Some favourable -variation in the shape of the passage must here have been the initial -step. But the gradual increase of this structural modification by the -survival of individuals in which it is carried furthest, will, I think, -be all along aided by immediate adaptation. The part of the alimentary -canal previously kept from the air, but now habitually in contact with -the air, must be in some degree modified by the action of the air; -and the directly-produced modification, increasing<span class="pagenum" id="Page_339">[339]</span> in the individual -and in successive individuals, cannot cease until there is a complete -balance between the actions of the changed agency and the changed -tissue.</p> - - -<p class="p2">§ 300. We come now to differentiations among the truly inner -tissues—the tissues which have direct converse neither with the -environment nor with the foreign substances taken into the organism -from the environment. These, speaking broadly, are the tissues -which lie between the double layer forming the integument with its -appendages, and the double layer forming the alimentary canal with -its <i>diverticula</i>. We will take first the differentiation which -produces the vascular system.</p> - -<p>Certain forces producing and aiding distribution of liquids in animals, -come into play before any vascular system exists; and continue to -further circulation after the development of a vascular system. The -first of these is osmotic exchange, acting locally and having an -indirect general action; the second is local variation of pressure, -which movement of the body throws on the tissues and their contained -liquids. A few words are needed in elucidation of each. If in any -creature, however simple, different changes are going on in parts -that are differently conditioned—if, as in a <i>Hydra</i>, one -surface is exposed to the surrounding medium while the other surface -is exposed to dissolved food; then between the unlike liquids which -the dissimilarly-placed parts contain, osmotic currents must arise; -and a movement of liquid through the intermediate tissue must go on -as long as an unlikeness between the liquids is kept up. This primary -cause of re-distribution remains one of the causes of re-distribution -in every more-developed organism: the passage of matters into and -out of the capillaries is everywhere thus set up. And obviously in -producing these local currents, osmose must also indirectly produce -general currents, or aid them if otherwise produced. In the absence -of a pumping organ, this force is probably an important aid to that<span class="pagenum" id="Page_340">[340]</span> -movement of the nutritive liquids which the functions set up. How -the second cause—the changes of internal pressure which an animal’s -movements produce—furthers circulation, will be sufficiently manifest. -That parts which are bent or strained necessarily have their contained -vessels squeezed, has been shown (<a href="#sect281">§ 281</a>); and whether the bend or -strain is caused, as in a plant, by an external force, or, as usually -in an animal, by an internal force, there must be a thrusting of -liquids towards places of least resistance—commonly places of greatest -consumption. This which in animals without hearts is a main agent of -circulation, continues to further it very considerably even among the -highest animals. In these the effect becomes as it were systematized. -The valves in the veins necessitate perpetual propulsions towards the -heart.</p> - -<p>Even in such simple types as the <i>Hydrozoa</i>, cavities in the -tissues faintly indicate a structure which facilitates the transfer of -nutritive matters. These cavities become reservoirs filled with the -plasma that slowly oozes through the substance of the body; and every -movement of the animal, accompanied as it must be by changed pressures -and tensions on these reservoirs, tends here to fill them and there to -squeeze out their contents in that or the other direction—possibly -aiding to produce, by union of several cavities, those lacunæ or -irregular canals which the body in some cases presents.</p> - -<p>Irregular canals of this kind, not lined with any membranes but -being simply cavities running through the flesh, mainly constitute -the vascular system in <i>Polyzoa</i> and <i>Brachiopoda</i> and -some <i>Mollusca</i>. Though the central parts of a vascular system -are rudely developed, yet its peripheral parts consist of sinuses -permeating the tissues. The higher orders of <i>Mollusca</i> have -a more-developed system of vessels or arteries, which run into the -substance of the body and end in lacunæ or simple fissures. This ending -in lacunæ takes place at various distances from the vascular centre. In -some genera the arterial structure is carried to the periphery of the -blood-system, while in others it stops short midway.<span class="pagenum" id="Page_341">[341]</span> Throughout most -orders of the <i>Mollusca</i> the back current of blood continues to -be carried by channels of the original kind: there are no true veins, -but the blood having been delivered into the tissues, finds its way -back to the peri-visceral cavity through inosculating sinuses. Among -the Cephalopods, however, the afferent blood-canals, as well as the -efferent ones, acquire distinct walls. On putting together these facts, -we may conceive pretty clearly the stages of vascular development. -From the original reservoir of nutritive liquid between the alimentary -canal and the wall of the body, a portion partially shut off becomes a -contractile vessel; and by its actions there is produced a more rapid -transfer of the nutritive liquid than was originally produced by the -motions of the animal. Clearly, the extension of this contractile tube -and the development from it of branches running hither and thither -into the tissues, must, by defining the channels of blood throughout a -part of its course, render its distribution more regular and active. -As fast as this centrifugal growth advances, so fast are the efferent -currents of blood, prevented from escaping laterally, obliged to move -from the centre towards the circumference; and so fast also does -the less developed set of channels become, of necessity, occupied -by afferent currents. When, by a parallel increase of definiteness, -the lacunæ and irregular sinuses through which the afferent currents -pass, become transformed into veins, the accompanying disappearance of -all stagnant or slow-moving collections of blood, implies a further -improvement in the circulation.</p> - -<p>By what agency is effected this differentiation of a definite vascular -system? No sufficient reply is obvious. The genesis of the primordial -heart is not comprehensible as a result of direct equilibration, and we -cannot readily see our way to it as a result of indirect equilibration; -for it is difficult to imagine what favourable variation natural -selection could have seized hold of to produce such a structure. A -contractile tube that aided the distribution of nutritive<span class="pagenum" id="Page_342">[342]</span> liquid, -having been once established, survival of the fittest would suffice -for its gradual extension and its successive modifications. But what -were the early stages of the contractile tube, while it was yet not -sufficiently formed to help circulation, and while it must nevertheless -have had some advantage without which no selective process could go -on? The question seems insoluble. To another part of the question, -however, an answer may be ventured. If we ask the origin of these -ramifying channels which, first appearing as simple lacunæ, eventually -become vessels having definite walls, a reply admitting of considerable -justification, is, that the currents of nutritive liquid forced and -drawn hither and thither through the tissues, themselves initiate these -channels. We know that streams running over and through solid and -quasi-solid inorganic matter, tend to excavate definite courses. We saw -reason for concluding that the development of sap-channels in plants -conforms to this general principle. May we not then suspect that the -nutritive liquid contained in the tissue of a simple animal, made to -ooze now in this direction and now in that by the changes of pressure -which the animal’s movements cause, comes to have certain lines along -which it is thrust backwards and forwards more than along other lines; -and must by repeated passings make these more and more permeable until -they become lacunæ? Such actions will inevitably go on; and such -actions appear competent to produce some, at least, of the observed -effects. The leading facts which indicate that this is a part-cause of -vascular development are these.</p> - -<p>Growths normally recurring in certain places at certain intervals, -are accompanied by local formations of blood-vessels. The periodic -maturation of ova among the <i>Mammalia</i> supplies an instance. -Through the stroma of an ovarium are distributed innumerable minute -vesicles, which, in their early stages, are microscopic. Of these, -severally contained in their minute ovi-sacs, any one may develop: the -determining<span class="pagenum" id="Page_343">[343]</span> cause being probably some slight excess of nutrition. When -the development is becoming rapid, the capillaries of the neighbouring -stroma increase and form a plexus on the walls of the ovi-sac. Now -since there is no typical distribution of the developing ova; and since -the increase of an ovum to a certain size precedes the increase of -vascularity round it; we can scarcely help concluding that the setting -up of currents towards the point of growth determines the formation of -the blood-vessels. It may be that having once commenced, this local -vascular structure completes itself in a typical manner; but it seems -clear that this greater development of blood-vessels around the growing -ovum is initiated by the draught towards it. Abnormal growths show -still better this relation of cause and effect. The false membranes -sometimes found in the bronchial tubes in inflammatory diseases, may -perhaps fairly be held abnormal in but a partial sense: it may be said -that their vascular systems are formed after the type of the membranes -to which they are akin. But this can scarcely be said of the morbid -growths classed as malignant. The blood-vessels in an encephaloid -cancer, are led to enlarge and ramify, often to an immense extent, by -the unfolding of the morbid mass to which they carry blood. Alien as -is the structure as a whole to the type of the organism; and alien in -great measure as is its tissue to the tissue on which it is seated; -it nevertheless happens that the growth of the alien tissue and -accompanying abstraction of materials from the blood-vessels, determine -a corresponding growth of these blood-vessels. Unless, then, we say -that there is a providentially-created type of vascular structure for -each kind of morbid growth (and even this would not much help us, since -the vascular structure has no constancy within the limits of each -kind), we are compelled to admit that in some way or other the currents -of blood are here directly instrumental in forming their own channels. -One more piece of evidence, before cited as exemplifying adaptation (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect67">§ 67</a>), -may be called to mind.<span class="pagenum" id="Page_344">[344]</span> When any main channel for blood, leading -to or from a certain part of the body, has been rendered impervious, -others among the channels leading to or from this same part, enlarge to -the extent requisite for fulfilling the extra function that falls upon -them: the enlargement being caused, as we must infer, by the increase -of the currents carried.</p> - -<p>Here, then, are facts warranting inductively the deduction above drawn. -It is true that we are left in the dark respecting the complexities -of the process. How the channels for blood come to have limiting -membranes, and many of them muscular coats, the hypothesis does not -help us to say. But the evidence assigned goes far to warrant the -belief that vascular development is initiated by direct equilibration; -though indirect equilibration may have had the larger share in -establishing the structures which distinguish finished vascular systems.</p> - - -<p class="p2">§ 301. Of the inner tissues which remain let us next take bone. In what -manner is differentiated this dense substance serving in most cases for -internal support?</p> - -<p>When considering the vertebrate skeleton under its morphological aspect -(<a href="#sect256">§ 256</a>), it was pointed out that the formation of dense tissues, -internal as well as external, is, in some cases at least, brought -about by the mechanical forces to be resisted. Through what process -it is brought about we could not then stay to inquire: this question -being not morphological but physiological. Answers to some kindred -questions have since been attempted. Certain actions to which the -internal dense tissues of plants may be ascribed, have been indicated; -and more recently, analogous actions have been assigned as causes of -some external dense tissues of animals. We have now to ask whether -actions of the same nature have produced these internal dense tissues -of animals.</p> - -<p>The problem is an involved one. Bones have more than one stage. They -are membranous or cartilaginous before they become osseous; and their -successive component substances<span class="pagenum" id="Page_345">[345]</span> so far differ that the effects -of mechanical actions upon them differ. And having to deal with -transitional states in which bone is formed of mixed tissues, having -unlike physical properties and unlike minute structures, the effects of -strains become too complicated to follow with precision. Anything in -the way of interpretation must therefore be regarded as tentative. If -analysis and comparison show that the phenomena are not inconsistent -with the hypothesis of mechanical genesis, it is as much as can be -expected. Let us first observe more nearly the mechanical conditions to -which bones are subject.</p> - -<p>The endo-skeleton of a mammal with the muscles and ligaments holding -it together, may be rudely compared to a structure built up of struts -and ties; of which, speaking generally, the struts bear the pressures -and the ties bear the tensions. The framework of an ordinary iron -roof will give an idea of the functions of these two elements, and of -the mechanical characters required by them. Such a framework consists -partly of pieces which have each to bear a thrust in the direction of -its length, and partly of pieces which have each to bear a pull in the -direction of its length; and these struts and ties are differently -formed to adapt them to these different strains. Further, it should -be remarked that though the rigidity of the framework depends on the -ties which are flexible, as much as on the struts which are stiff, yet -the ties help to give the rigidity simply by so holding the struts -in position that they cannot escape from the thrusts which fall on -them. Now the like relation holds with a difference among the bones -and muscles: the difference being that here the ties admit of being -lengthened or shortened and the struts of being moved about upon their -joints. The mechanical relations are not altered by this, however. -The actions are of essentially the same kind in an animal that is -standing, or keeping itself in a strained attitude, as in one that is -changing its attitude—the same in so far that we have in each a set -of flexible parts that are pulling and a set of<span class="pagenum" id="Page_346">[346]</span> rigid parts that are -resisting. It needs but to remember the sudden collapse and fall which -take place when the muscles are paralyzed, or to remember the inability -of a bare skeleton to support itself, to see that the struts without -the ties cannot suffice. And we have but to think of the formless mass -into which a man would sink when deprived of his bones, to see that -the ties without the struts cannot suffice. To trace the way in which -a particular bone has its particular thrust thrown upon it, may not -always be practicable. Though it is easy to perceive how a flexor or -extensor of the arm causes by its tension a reactive pressure along the -line of the humerus, and is enabled to produce its effect only by the -rigidity of the humerus; yet it is not so easy to perceive how such -bones as those of a horse’s pelvis are similarly acted upon. Still, as -the weight of the hind quarters has to be transferred from the back to -the feet, and must be so transferred through the bones, it is manifest -that though these bones form a very crooked line, the weight must -produce a pressure along the axis of each: the muscles and ligaments -concerned serving here, as in other cases, so to hold the bones that -they bear the pressure instead of being displaced by it. Not forgetting -that many processes of the bones have to bear tensions, we may then -say that generally, though by no means universally, bones are internal -dense masses that have to bear pressures—pressures which in the -cylindrical bones become longitudinal thrusts. Leaving out exceptional -cases, let us consider bones as masses thus circumstanced.</p> - -<p>When giving reasons for the belief that the vertebrate skeleton is -mechanically originated, one of the facts put in evidence was, that -in the vertebrate series the transition from the cartilaginous to the -osseous spine begins peripherally (<a href="#sect257">§ 257</a>): each vertebra being at first -a ring of bone surrounding a mass of cartilage. And it was pointed -out that this peripheral ossification is ossification at the region -of greatest pressures. Now it is not vertebræ only that follow this -course of development. In a cylindrical bone, though<span class="pagenum" id="Page_347">[347]</span> it is differently -circumstanced, the places of commencing ossification are still the -places on which the severest stress falls. Let us consider how such a -bone that has to bear a longitudinal pressure is mechanically affected. -If the end of a walking-cane be thrust with force against the ground, -the cane bends; and partially resuming its straightness when relieved, -again bends, usually towards the same side, when the thrust is renewed. -A bend so caused acts on the fibres of the cane in nearly the same -way as does a bend caused by supporting the cane horizontally at its -two ends and suspending a weight from its middle. In either case the -fibres on the convex side are extended and the fibres on the concave -side compressed. Kindred actions occur in a rod that is so thick -as not to yield visibly under the force applied. In the absence of -complete homogeneity of its substance, complete symmetry in its form, -and an application of a force exactly along its axis, there must be -some lateral deflection; and therefore some distribution of tensions -and pressures of the kind indicated. And then, as the fact which here -specially concerns us, we have to note that the strongest tensions -and pressures are borne by the outer layers of fibres. Now the shaft -of a long bone, subject to mechanical actions of this kind, similarly -has its outer layer most strained. In this layer, therefore, on the -mechanical hypothesis, ossification should commence, and here it does -commence—commences, too, midway between the ends, where the bends -produce on the superficial parts their most intense effects. But we -have not in this place simply to observe that ossification commences at -the places of greatest stress, but to ask what causes it to do this. -Can we trace the physical actions which set up this deposit of dense -tissue? It is, I think, possible to indicate a “true cause” that is at -work; though whether it is a sufficient cause may be questioned. We -concluded that in certain other cases, the formation of dense tissue -indirectly results from the alternate squeezing and relaxation of the -vessels running through the part; and the inquiry now to be made is, -whether, in developing bone,<span class="pagenum" id="Page_348">[348]</span> the same actions go on in such ways as to -produce the observed effects. At the outset we are met by what seems a -fatal difficulty—cartilage is a non-vascular tissue: this substance -of which unossified bones consist is not permeated by minute canals -carrying nutritive liquid, and cannot, therefore, be a seat of actions -such as those assigned. This apparent difficulty, however, furnishes a -confirmation. For cartilage that is wholly without permeating canals -does not ossify: ossification takes place only at those parts of it -into which the canals penetrate. Hence, we get additional reason for -suspecting that bone-formation is due to the alleged cause; since it -occurs where mechanical strains can produce the actions described, but -does not occur where mechanical strains cannot produce them. Let us -consider more closely what the several factors are. It will suffice -for the argument if we commence with the external vascular layer as -already existing, and consider what will take place in it. Cartilage -is elastic—is somewhat extensible, and spreads out laterally under -pressure, but resumes its form when relieved. How, then, will the -minute channels traversing it in all directions be affected at the -places where it is strained by a bend? Those on the convex side will -be laterally squeezed, in the same way that we saw the sap-vessels on -the convex side of a bent branch are squeezed; and as exudation of the -sap into the adjacent prosenchyma will be caused in the one case, so, -in the other, there will be caused exudation of serum into the adjacent -cartilage: extra nutrition and increase of strength resulting in both -cases. The parallel ceases here, however. In the shoot of a plant, bent -in various directions by the wind, the side which was lately compressed -is now extended; and hence that squeezing of the sap-vessels which -results from extension, suffices to feed and harden the tissue on all -sides of the shoot. But it is not so with a bone. Having yielded on -one side under longitudinal pressure, and resumed as nearly as may be -its previous shape when the pressure is<span class="pagenum" id="Page_349">[349]</span> taken off, the bone yields -again towards the same side when again longitudinally pressed. Hence -the substance of its concave side, never rendered convex by a bend -in the opposite direction, would not receive any extra nutrition did -no other action come into play. But if we consider how intermittent -pressures must act on cartilage, we shall see that there will result -extra nutrition of the concave side also. Squeeze between two pieces of -glass a thin bit of caoutchouc which has a hole through it. While the -caoutchouc spreads out away from the centre, it also spreads inwards, -so as partially to close the hole. Everywhere its molecules move away -in directions of least resistance; and for those near the hole, the -direction of least resistance is towards the hole. Let this hole stand -for the transverse section of one of the minute canals or channels -passing through cartilage, and it will be manifest that on the side of -the unossified bone made concave in the way described, the compressed -cartilage will squeeze the canals traversing it; and, in the absence -of perfect homogeneity in the cartilage, the squeeze will cause extra -exudation from the canals into the cartilage. Thus every additional -strain will give to the cartilage it falls upon, an additional supply -of the materials for growth. So that presently the side which, by -yielding more than any other, proves itself to be the weakest, will -cease to be the weakest. What further will happen? Some other side -will yield a little—the bends will take place in some other plane; -and the portions of cartilage on which repeated tensions and pressures -now fall will be strengthened. Thus the rate of nutrition, greatest at -the place where the bending is greatest, and changing as the incidence -of forces changes, will bring about at every point a balance between -the resistances and the strains. Thus, too, there will be determined -that peripheral induration which we see in bones so circumstanced. -As in a shoot we saw that the woody deposit takes place towards the -outside of the cylinder, where, according to the hypothesis, it ought -to take place; so, here, we see that the<span class="pagenum" id="Page_350">[350]</span> excess of exudation and -hardening, occurring where the strains are most intense, will form a -cylinder having a dense outside and a porous or hollow inside. These -processes will be essentially the same in bones subject to more complex -mechanical actions, such as sundry of the flat bones and others that -serve as internal fulcra. Be the strains transverse or longitudinal, -be they torsion strains or mixed strains, the outer parts of the -bone will be more affected by them than its inner parts. They will -therefore tend everywhere to produce resisting masses having outer -parts more dense than their inner parts. And by causing most growth -where they are most intense, they will call out reactive forces -adequate to balance them. There are doubtless obstacles in the way -of this interpretation. It may be said that the forces acting on the -outer layers in the manner described, would compress the canals too -little to produce the alleged effects; and if evenly distributed along -the whole lengths of the layers, they would probably do so. But it -needs only to bend a flexible mass and observe the tendency to form -creases on the concave surface, to feel assured that along the surface -of an ossifying bone, the yielding of the tissue when bent will not -be uniform. In the absence of complete homogeneity, the interstitial -yielding will take place at some points more than others, and at one -point above all others. When, at the weakest point—the centre of -commencing ossification—an extra amount of deposit has been caused, -it will cease to be the weakest; and adjacent points, now the weakest, -will become the places of yielding and induration. It may be further -objected that the hypothesis is incompatible with the persistence -of cartilage for so long a time between the epiphysis of bones and -the bony masses which they terminate. But there is the reply that -the places occupied by this cartilage being places at which the bone -lengthens, the non-ossification is in part apparent only—it is rather -that new cartilage is formed as fast as the pre-existing cartilage -ossifies; and there is the further reply<span class="pagenum" id="Page_351">[351]</span> that the slowness of the -ultimate ossification of this part, is due to its non-vascularity, and -to mechanical conditions which are unfavourable to its acquirement of -vascularity. Once more, there is the demurrer that in the epiphyses -ossification does not begin at the surface but within the mass of -the cartilage. Explanation of this implies ability to follow out the -mechanical actions in a resilient substance which, like india-rubber, -admits of being distorted in all ways by pressure and recovering its -form, and it seems impossible to say how the more superficial and more -deep-seated canals traversing it will be respectively affected.</p> - -<p>Of course it is not meant that this osseous development by direct -equilibration takes place in the individual. Though it is a corollary -from the argument that in each individual the process must be furthered -and modified by the particular actions to which the particular bones -are exposed; yet the leading traits of structure assumed by the bones -are assumed in conformity with the inherited type. This, however, is -no difficulty. The type itself is to be regarded as the accumulated -result of such modifications, transmitted and increased from generation -to generation. The actions above described as taking place in the -bone of an individual, must be understood as producing their total -effect little by little in the corresponding bones of a long series of -individuals. Even if but a small modification can be so wrought in the -individual, yet if such modification, or a part of it, is inheritable, -we may readily understand how, in the course of geologic epochs, the -observed structures may arise in the assigned way.</p> - -<p>Here may fitly be added a strong confirmation. If we find cases -where individual bones, subject in exceptional degrees to the -actions described, present in exceptional amounts the modifications -attributed to them, we are greatly helped in understanding how there -may be produced in the race that aggregate of modifications which -the hypothesis implies. Such cases occur in ricketty children. I -am indebted to Mr. Busk for pointing out these abnormal formations -of dense tissue, that are not apparently explicable as results of<span class="pagenum" id="Page_352">[352]</span> -mechanical actions and reactions. It was only on tracing out the -processes here at work, that there suggested itself the specific -interpretation of the normal process, as above set forth. When, from -constitutional defect, bones do not ossify with due rapidity, and are -meanwhile subject to the ordinary strains, they become distorted. -Remembering how a mass which has been made to yield in any direction -by a force it cannot withstand, is some little time before it recovers -completely its previous form, and usually, indeed, undergoes what -is called a “permanent set;” it is inferable that when a bone is -repeatedly bent at the same time that the liquid contained in its -canals is poor in the materials for forming dense tissue, there -will not take place a proportionate strengthening of the parts most -strained; and these parts will give way. This happens in rickets. But -this having happened, there goes on what, in teleological language, -we call a remedial process. Supposing the bone to be one commonly -affected—a femur; and supposing a permanent bend to have been caused -in it by the weight of the body; the subsequent result is an unusual -deposition of cartilaginous and osseous matter on the concave side of -the bone. If the bone is represented by a strung bow, then the deposit -occurs at the part represented by the space between the bow and the -string. And thus occurring where its resistance is most effective, -it increases until the approximately-straight piece of bone formed -within the arc, has become strong enough to bear the pressure without -appreciably yielding. Now this direct adaptation, seeming so like a -special provision, and furnishing so remarkable an instance of what, -in medical but unscientific language, is called the <i>vis medicatrix -naturæ</i>, is simply a result of the above-described mechanical -actions and reactions, going on under the exceptional conditions. Each -time such a bent bone is subject to a force which again bends it, the -severest compression falls on the substance of its concave side. Each -time, then, the canals running through this part of its substance are -violently squeezed—far<span class="pagenum" id="Page_353">[353]</span> more squeezed than they or any other of the -canals would have been, had the bone remained straight. Hence, on every -repetition of the strain, these canals near the concave surface have -their contents forced out in more than normal abundance. The materials -for the formation of tissue are supplied in quantity greater than can -be assimilated by the tissue already formed; and from the excess of -exuded plasma, new tissue arises.<a id="FNanchor_50" href="#Footnote_50" class="fnanchor">[50]</a> A layer of organizable material -accumulates between the concave surface and the periosteum; in this, -according to the ordinary course of tissue-growth, new vessels appear; -and the added layer presently assumes the histological character of the -layer from which it has grown. What next happens? This added layer, -further from the neutral axis than that which has thrown it out, is now -the most severely compressed, and its vessels are the most severely -squeezed. The place of greatest exudation and most rapid deposit -of matter, is therefore transferred to this new layer; and at the -same time that active nutrition increases its density, the excess of -organizable material forms another layer external to it: the successive -layers so added, encroaching on the space between the concave surface -of the bone and the chord of its arc. What limits the encroachment on -this space?—what stops the process of filling it up? The answer to -this question will be manifest when observing that there comes into -play a cause which gradually diminishes the forces falling on each new -layer. For the transverse sectional area is step by step increased; and -an increase of the area over which the weight borne is distributed, -implies a relatively smaller pressure upon each part of it. Further, as -the transverse dimensions of the bone increase, the materials composing -its convex and concave layers, becoming further from the neutral axis, -become better<span class="pagenum" id="Page_354">[354]</span> placed for resisting the strains to be borne. So that -both by the increased quantity of dense matter and by its mechanically -more-advantageous position, the bendings of the bone are progressively -decreased. But as they are decreased, each new layer formed on the -concave surface has its substance and its vessels less compressed; and -the resulting growth and induration are rendered less rapid. Evidently, -then, the additions, slowly diminishing, will eventually cease; and -this will happen when the bone no longer bends. That is to say, the -thickening of the bone will reach its limit when there is equilibrium -between the incident forces and the forces which resist them. Here, -indeed, we may trace with great clearness the process of direct -equilibration—may see how an unusual force, falling on the moving -equilibrium of an organism and not overthrowing it, goes on working -modifications until the reaction balances the action.</p> - -<p>That, however, which now chiefly concerns us, is to note how this -marked adaptation supports the general argument. Unquestionably bone -is in this case formed under the influence of mechanical stress, and -formed just where it most effectually meets the stress. This result, -not otherwise explained, is explained by the hypothesis above set -forth. And when we see that this special deposit of bone is accounted -for by actions like those to which bone-formation in general is -ascribed, the probability that these are the actions at work becomes -very great.<a id="FNanchor_51" href="#Footnote_51" class="fnanchor">[51]</a></p> - -<p><span class="pagenum" id="Page_355">[355]</span></p> - -<p>Of course it is not alleged that osseous structures arise in this -way alone. The bones of the skull and various dermal bones cannot be -thus interpreted. Here the natural selection of favourable variations -appears the only assignable cause—the equilibration is indirect. We -know that ossific deposits now and then occur in tissues where they -are not usually found; and such deposits, originally abnormal, if they -occurred in places where advantages arose from them, might readily be -established and increased by survival of the fittest. Especially might -we expect this to happen when a constitutional tendency to form bone -had been established by actions of the kind described; for it is a -familiar fact that differentiated types of tissue, having once become -elements of an organism, are apt occasionally to arise in unusual -places, and there to repeat all their peculiar histological characters. -And this may possibly be the reason why the bones of the skull, though -not exposed to forces such as those which produce, in other bones, -dense outer layers including less dense interiors, nevertheless repeat -this general trait of bony structure. While, however, it is beyond -doubt that some bones are not due to the direct influence of mechanical -stress, we may, I think, conclude that mechanical stress initiates -bone-formation.</p> - - -<p class="p2">§ 302. What is the origin of nerve? In what way do its properties stand -related to the properties of that protoplasm whence the tissues in -general arise? and in what way is it differentiated from protoplasm -simultaneously with the other tissues? These are profoundly interesting -questions; but questions to which positive answers cannot be expected. -All that can be done is to indicate answers which seem feasible.</p> - -<p>That the property specially displayed by nerve, is a property<span class="pagenum" id="Page_356">[356]</span> which -protoplasm possesses in a lower degree, is manifest. The sarcode -of a Rhizopod and the substance of an unimpregnated ovum, exhibit -movements that imply a propagation of stimulus from one part of -the mass to another. We have not far to seek for a probable origin -of this phenomenon. There is good reason for ascribing it to the -extreme instability of the organic colloids of which protoplasm -consists. These, in common with colloids in general, assume -different isomeric forms with great facility; and they display not -simply isomerism but polymerism. Further, this readiness to undergo -molecular re-arrangement, habitually shows itself in colloids by -the rapid propagation of the re-arrangement from part to part. As -Prof. Graham has shown, matter in this state often “pectizes” almost -instantaneously—a touch will transform an entire mass. That is to say, -the change of molecular state once set up at one end, spreads to the -other end—there is a progress of a stimulus to change; and this is -what we see in a nerve. So much being understood, let us re-state the -case more completely.</p> - -<p>Molecular change, implying as it does motion of molecules, communicates -motion to adjacent molecules; be they of the same kind or of a -different kind. If the adjacent molecules, either of the same kind or -of a different kind, be stable in composition, a temporary increase -of oscillation in them as wholes, or in their parts, may be the only -result; but if they are unstable there are apt to arise changes of -arrangement among them, or among their parts, of more or less permanent -kinds. Especially is this so with the complex molecules which form -colloidal matter, and with the organic colloids above all. Hence it is -to be inferred that a molecular disturbance in any part of a living -animal, set up by either an external or internal agency, will almost -certainly disturb and change some of the surrounding colloids not -originally implicated—will diffuse a wave of change towards other -parts of the organism: a wave which will, in the absence of perfect -homogeneity, travel further in some directions than in<span class="pagenum" id="Page_357">[357]</span> others. Let us -ask next what will determine the differences of distance travelled in -different directions. Obviously any molecular agitation spreading from -a centre, will go furthest along routes that offer least resistance. -What routes will these be? Those along which there lie most molecules -that are easily changed by the diffused molecular motion, and which -yet do not take up much molecular motion in assuming their new states. -Molecules which are tolerably stable will not readily propagate the -agitation; for they will absorb it in the increase of their own -oscillations, instead of passing it on. Molecules which are unstable -but which, in assuming isomeric forms, absorb motion, will not readily -propagate it; since it will disappear in working the changes in them. -But unstable molecules which, in being isomerically transformed, do not -absorb motion, and still more those which, in being so transformed, -give out motion, will readily propagate any molecular agitation; since -they will pass on the impulse either undiminished, or increased, to -adjacent molecules. If then we assume, as we are not only warranted -in doing but are obliged to do, that protoplasm contains two or more -colloids, either mingled or feebly combined (since it cannot consist of -simple albumen or fibrin or casein, or any allied proximate principle); -it may be concluded that any molecular agitation set up by what we call -a stimulus, will diffuse itself further along some lines than along -others, if the components of the protoplasm are not quite homogeneously -dispersed, and if some of them are isomerically transformed more -easily, or with less expenditure of motion, than others; and it will -especially travel along spaces occupied chiefly by those molecules -which give out molecular motion during their metamorphoses, if there -should be any such. But now let us ask what structural effects -will be wrought along a tract traversed by this wave of molecular -disturbance. As is shown by those transformations which so rapidly -propagate themselves through colloids, molecules that have undergone a -certain change of form,<span class="pagenum" id="Page_358">[358]</span> are apt to communicate a like change of form -to adjacent molecules of the same kind—the impact of each overthrow -is passed on and produces another overthrow. Probably the proneness -towards isochronism of molecular movements necessitates this. If any -molecule has had its components re-arranged, and their oscillations -consequently altered, there result movements not concordant with the -movements in adjacent untransformed molecules, but which, impressing -themselves on the parts of such untransformed molecules, tend to -generate in them concordant movements—tend, that is, to produce -the re-arrangements involved by these concordant movements. Is this -action limited to strictly isomeric substances? or may it extend to -substances that are closely-allied? If along with the molecules of -a compound colloid there are mingled those of some kindred colloid; -or if with the molecules of this compound colloid there are mingled -the components out of which other such molecules may be formed; then -there arises the question—does the same influence which tends to -propagate the isomeric transformations, tend also to form new molecules -of the same kind out of the adjacent components? There is reason to -suspect that it does. Already when treating of the nutrition of parts -(<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect64">§ 64</a>), it was pointed out that we are obliged to recognize a power -possessed by each tissue to build up, out of the materials brought -to it, molecules of the same type as those of which it is formed. -This building up of like molecules seems explicable as caused by the -tendency of the new components which the blood supplies, to acquire -movements isochronous with those of the like components in the tissue; -which they can do only by uniting into like compound molecules. -Necessarily they must gravitate towards a state of equilibrium; such -state of equilibrium—moving equilibrium of course—must be one in -which they oscillate in the same times with neighbouring molecules; -and so to oscillate they must fall into groups identical with the -groups around them. If this be a general principle of<span class="pagenum" id="Page_359">[359]</span> tissue-growth -and repair, we may conclude that it will apply in the case before -us. A wave of molecular disturbance passing along a tract of mingled -colloids closely-allied in composition, and isomerically transforming -the molecules of one of them, will be apt at the same time to form -some new molecules of the same type, at any place where there exist -the proximate components, either uncombined or feebly combined in some -not very different way. And this will be most likely to occur where -the molecules of the colloid that are undergoing the isomeric change, -predominate, but have scattered through them the other molecules out of -which they may be formed, either by composition or modification. That -is to say, a wave of molecular disturbance diffused from a centre, and -travelling furthest along a line where lie most molecules that can be -isomerically transformed with facility, will be likely at the same time -to further differentiate this line, and make it more characterized than -before by the easy-transformability of its molecules. One additional -step, and the interpretation is reached. Analogy shows it to be not -improbable that these organic colloids, isomerically transformed by -slight molecular impact or increase of molecular motion, will some of -them resume their previous molecular structures after the disturbance -has passed. We know that what are stable molecular arrangements under -one degree of molecular agitation, are not stable under another degree; -and there is evidence that re-arrangements of an inconspicuous kind -are occasionally brought about by very slight changes of molecular -agitation. Water supplies a clear case. Prof. Graham infers that water -undergoes a molecular re-arrangement at about 32°—that ice has a -colloid form as well as a crystalloid form, dependent on temperature. -Send through it an extra wave of the molecular agitation we call heat, -and its molecules aggregate in one way. Let the wave die away, and its -molecules resume their previous mode of aggregation. And obviously -such transformations may be repeated backwards and forwards within -narrow limits of temperature.<span class="pagenum" id="Page_360">[360]</span> Now among the extremely unstable organic -colloids, such a phenomenon is far more likely to happen. Suppose, -then, that the nerve-colloid is one of which the molecules are changed -in form by a passing wave of extra agitation, but resume their previous -form when the wave has passed: the previous form being the most stable -under the conditions which then recur. What follows? It follows that -these molecules will be ready again to undergo isomeric transformation -when there again occurs the stimulus; will, as before, propagate the -transformation most along the tract where such molecules are most -abundant; will, as before, tend to form new molecules of their own -type; will, as before, make the line along which they lie one of easier -transfer for the molecular agitation. Every repetition will help to -increase, to integrate, to define more completely, the course of the -escaping molecular motion—extending its remoter part while it makes -its nearer part more permeable—will help, that is, to form a line of -discharge, a line for conducting impressions, a nerve.</p> - -<p>Such seems to me a not unfair series of deductions from the known -habitudes of colloids in general and the organic colloids in -particular. And I think that the implied nature and properties of nerve -correspond better with the observed phenomena than do the nature and -properties implied by other hypotheses. Of course the speculation as -it here stands is but tentative, and leaves much unexplained. It gives -no obvious reply to the questions—what causes the formation of nerves -in directions adapted to the needs? what determines their appropriate -connexions?—questions, however, to which, when we come to deal with -physiological integration, we may find not unsatisfactory answers. -Moreover it says nothing about the genesis of ganglia. A ganglion, -it is clear, must consist of a colloidal matter equally unstable, or -still more unstable, which, when disturbed, falls into some different -molecular arrangement, perhaps chemically simpler, and gives out in -so doing a large amount of molecular motion—serves as a reservoir of -molecular motion which may be suddenly<span class="pagenum" id="Page_361">[361]</span> discharged along an efferent -nerve or nerves, when excitement of an afferent nerve has disengaged -it. How such a structure as this results, the hypothesis does not show. -But admitting these shortcomings it may still be held that we are, in -the way pointed out, enabled to form some idea of the actions by which -nervous tissue is differentiated.</p> - - -<p class="p2">§ 303. A speculation akin to, and continuous with, the last, -is suggested by an inquiry into the origin of muscular tissue. -Contractility as well as irritability is a property of protoplasm -or sarcode; and, as before suggested (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect22">§ 22</a>), is not improbably -due to isomeric change in one or more of its component colloids. -It is a feasible supposition that of the several isomeric changes -simultaneously set up among these component colloids, some may be -accompanied by change of bulk and some not. Clearly the isomeric -change undergone by the colloid which we suppose to form nerve, must -be one not accompanied by appreciable change of bulk; since change of -bulk implies “internal work,” as physicists term it, and therefore -expenditure of force. Conversely, the colloid out of which muscle -originates, may be one that readily passes into an isomeric state -in which it occupies less space: the molecular disturbance causing -this contraction being communicated to it from adjacent portions of -nerve-substance that are molecularly disturbed; or being otherwise -communicated to it by direct mechanical or chemical stimuli: as happens -where nerves do not exist, or where their influence has been cut off. -This interpretation seems, indeed, to be directly at variance with -the fact that muscle does not diminish in bulk during contraction -but merely changes its shape. That which we see take place with the -muscle as a whole, is said also to take place with each fibre—while -it shortens it also broadens. There is, however, a possible solution -of this difficulty. A contracting colloid yields up its water; and -the contracted colloid <i>plus</i> the free water, may have the same -bulk as before though the colloid has less. If it be replied that in -this<span class="pagenum" id="Page_362">[362]</span> case the water should become visible between the substance of -the fibre and its sarcolemma or sheath, it may be rejoined that this -is not necessary—it may be deposited interstitially. Possibly the -striated structure is one that facilitates its exudation and subsequent -re-absorption; and to this may be due the superiority of striated -muscle in rapidity of contraction. Granting the speculative character -of this interpretation, let us see how far it agrees with the facts. -If the actions are as here supposed, the contracted or more integrated -state of the muscular colloid will be that which it tends continually -to assume—that into which it has an increasing aptitude to pass when -artificial paralysis has been produced, as shown by Dr. Norris—that -into which it lapses completely in <i>rigor mortis</i>. The sensible -motion generated by the contraction can arise only from the -transformation of insensible motion. This insensible motion suddenly -yielded up by a contracting mass, implies the fall of its component -molecules into more stable arrangements. And there can be no such fall -unless the previous arrangement is unstable. From this point of view, -too, it is possible to see how the hydro-carbons and carbo-hydrates -consumed in muscular action, may produce their effects. For these -non-nitrogenous elements of food, when consumed in the tissues, give -out large amounts of molecular motion. They do this in presence of -the muscular colloids which have lost molecular motion during their -fall in the stable or contracted state. From the molecular motion they -give out, may be restored the molecular motion lost by the contracted -colloids; and these contracted colloids may thus have their molecules -raised to that unstable state from which, again falling, they can again -generate mechanical motion.</p> - -<p>This conception of the nature and mode of action of muscle, while it -is suggested by known properties of colloidal matter and conforms to -the recent conclusions of organic chemistry and molecular physics, -establishes a comprehensible relation between the vital actions of -the lower and the higher<span class="pagenum" id="Page_363">[363]</span> animals. If we contemplate the movements -of cilia, of a Rhizopod’s pseudopodia, of a Polype’s body, or of -the long pendant tentacles of a <i>Medusa</i>, we shall see great -congruity between them and this hypothesis. Bearing in mind that the -contractile substance of developed muscle is affected not by nervous -influence only, but, where nervous influence is destroyed, is made to -contract by mechanical disturbance and chemical action, we may infer -that it does not differ intrinsically from the primordial contractile -substance which, in the lowest animals, changes its bulk under other -stimuli than the nervous. We shall see significance in the fact -ascertained by Dr. Ransom, that various agents which excite and arrest -nervo-muscular movements in developed animals, excite and arrest the -protoplasmic movements in ova. We shall understand how tissues not yet -differentiated into muscle and nerve, have this joint irritability and -contractility; how muscle and nerve may arise by the segregation of -their mingled colloids, the one of which, not appreciably altering its -bulk during isomeric change, readily propagates molecular disturbance, -while the other, contracting when isomerically changed, less readily -passes on the molecular disturbance; and how, by this differentiation -and integration of the conducting and the contracting colloids, the one -ramifying through the other, it becomes possible for a whole mass to -contract suddenly, instead of contracting gradually, as it does when -undifferentiated.</p> - -<p>The question remaining to be asked is—What causes the specialization -of contractile substance?—What causes the growth of colloid masses -which monopolize this contractility, and leave kindred colloids to -monopolize other properties? Has natural selection gradually localized -and increased the primordial muscular substance? or has the frequent -recurrence of irritations and consequent contractions at particular -parts done it? We have, I think, reason to conclude that direct -equilibration rather than indirect equilibration has been chiefly -operative. The reasoning that was used in the case<span class="pagenum" id="Page_364">[364]</span> of nerve applies -equally in the case of muscle. A portion of undifferentiated tissue -containing a predominance of the colloid that contracts in changing, -will, during each change, tend to form new molecules of its own type -from the other colloids diffused through it: the tendency of these -entangled colloids to fall into unity with those around them, will -be aided by every shock of isomeric transformation. Hence, repeated -contractions will further the growth of the contracting mass, and -advance its differentiation and integration. If, too, we remember that -the muscular colloid is made to contract by mechanical disturbance, and -that among mechanical disturbances one which will most readily affect -it simultaneously throughout its mass is caused by stretching, we -shall be considerably helped towards understanding how the contractile -tissues are developed. If extension of a muscular colloid previously -at rest, produces in it that molecular disturbance which leads to -isomeric change and decrease of bulk, then there is no difficulty in -explaining the movements of cilia; the formation of a contractile -layer in the vascular system becomes comprehensible; each dilatation -of a blood-vessel caused by a gush of blood, will be followed by a -constriction; the heart will pulsate violently in proportion as it is -violently distended; arteries will develop in power as the stress upon -them becomes greater; and we shall similarly have an explanation of the -increased muscularity of the alimentary canal which is brought about by -increased distension of it.</p> - -<p>That the production of contractile tissue in certain localities, -is due to the more frequent excitement in those localities of the -contractility possessed by undifferentiated tissue in general, is a -view harmonizing with traits which the differentiated contractile -tissue exhibits. These are the relations between muscular exercise, -muscular power, and muscular structure; and it is the more needful -for us here to notice them because of certain anomalies they present, -which, at first sight, seem inconsistent with the belief that<span class="pagenum" id="Page_365">[365]</span> the -functionally-determined modifications of muscle are inheritable.</p> - -<p>Muscles disagree greatly in their tints: all gradations between white -and deep red being observable. Contrasts are visible between the -muscles of different animals, between the muscles of the same animal -at different ages, and between different muscles of the same animal -at the same age. We will glance at the facts under these heads: -noting under each of them the connexion which here chiefly concerns -us—that between the activity of muscle and its depth of colour. The -cold-blooded <i>Vertebrata</i> are, taken as a group, distinguished -from the warmblooded by the whiteness of their flesh; and they are -also distinguished by their comparative inertness. Though a fish -or a reptile can exert considerable force for a short time, it is -not capable of prolonged exertion. Birds and mammals show greater -endurance along with the darker-coloured muscles. If among birds -themselves or mammals themselves we make comparisons, we meet with -kindred contrasts—especially between wild and domestic creatures of -allied kinds. Barn-door fowls are lighter-fleshed than most untamed -gallinaceous birds; and among these last the pheasant, moving about but -little, is lighter-fleshed than the partridge and the grouse which are -more nomadic. The muscles of the sheep are not on the average so dark -as those of the deer; and it is said that the flesh of the wild-boar is -darker than that of the pig. Perhaps, however, the contrast between the -hare and the rabbit affords, among familiar animals, the best example -of the alleged relation: the dark-fleshed hare having no retreat and -making wide excursions, while the white-fleshed rabbit, passing a -great part of its time in its burrow, rarely wanders far from home. -The parallel contrast between young and old animals has a parallel -meaning. Veal is much whiter than beef, and lamb is of lighter colour -than mutton. Though at first sight these facts may not seem to furnish -confirmatory evidence, since lambs in their play appear to<span class="pagenum" id="Page_366">[366]</span> expend -more muscular force than their sedate dams; yet the meaning of the -contrast is really as alleged. For in consequence of the law that the -strains which animals have to overcome, increase as the cubes of the -dimensions, while their powers of overcoming them increase only as -the squares (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect46">§ 46</a>), the movements of an adult animal cost much more -in muscular effort than do those of a young animal: the result being -that the sheep and the cow exercise their muscles more vigorously in -their quiet movements, than the lamb and the calf in their lively -movements. It may be added as significant, that the domestic animal -in which no very marked darkening of the flesh takes place along with -increasing age, namely the pig, is one which, ordinarily kept in a sty, -leads so quiescent a life that the assigned cause of darkening does -not come into action. But perhaps the most conclusive evidences are -the contrasts which exist between the active and inactive muscles of -the same animal. Between the leg-muscles of fowls and their pectoral -muscles, the difference of colour is familiar; and we know that fowls -exercise their leg-muscles much more than the muscles which move their -wings. Similarly in the turkey, in the guinea fowl, in the pheasant. -And then, adding much to the force of this evidence, we see that in -partridges and grouse, which belong to the same order as our domestic -fowls but use their wings as constantly as their legs, little or -no difference is visible between the colour of these two groups of -muscles. Special contrasts like these do not, however, exhaust the -proofs; for there is a still more significant general contrast. The -muscle of the heart, which is the most active of all muscles, is the -darkest of all muscles.</p> - -<p>The connexion of phenomena thus shown in so many ways, implies that -the bulk of a muscle is by no means the sole measure of the quantity -of force it can evolve. It would seem that, other things equal, the -depth of colour varies with the constancy of action; while, other -things equal, the bulk varies with the amount of force that has to be -put forth upon occasion.<span class="pagenum" id="Page_367">[367]</span> These of course are approximate relations. -More correctly we may say that the actions of pale muscles are either -relatively feeble though frequent (as in the massive flanks of a fish), -or relatively infrequent though strong (as in the pectoral muscles of -a common fowl); while the actions of dark muscles are both frequent -and strong. Some such differentiation may be anticipated by inference -from the respective physiological requirements. A muscle which has -upon occasion to evolve considerable force, but which has thereafter a -long period of rest during which repair may restore it to efficiency, -requires neither a large reserve of the contractile substance that is -in some way deteriorated by action, nor highly developed appliances for -bringing it nutritive materials and removing effete products. Where, -contrariwise, an exerted muscle which has undergone much molecular -change in evolving much mechanical force, has soon again to evolve -much mechanical force, and so on continually; it is clear that either -the quantity of contractile substance present must be great, or the -apparatus for nutrition and depuration must be very efficient, or both. -Hence we may look for marked unlikenesses of minute structure between -muscles which are markedly contrasted in activity. And we may suspect -that these conspicuous contrasts of colour between active and inactive -muscles, are due to these implied differences of minute structure: -partly differences between the numbers of blood-vessels and partly -differences between the quantities or qualities of sarcous matter.</p> - -<p>Here, then, we have a key to the apparent anomaly above hinted at—the -maintenance of bulk by certain muscles which have been rendered -comparatively inactive by changed habits of life. That the pectoral -muscles of those domestic birds which fly but little, have not dwindled -to any great extent, has been thought a fact at variance with the -conclusion that functionally-produced adaptations are inheritable. -It has been argued that if parts which are exercised increase, not -only in the individual but in the race, while parts which<span class="pagenum" id="Page_368">[368]</span> become -less active decrease; then a notable difference of size should exist -between the muscles used for flight in birds that fly much, and those -in birds of an allied kind that fly little. But, as we here see, this -is not the true implication. The change in such cases must be chiefly -in vascularity and abundance of contractile substance; and cannot be, -to any great extent, in bulk. For a bird to fly at all, its pectoral -muscles, bones of attachment, and all accompanying appliances, must be -kept up to a certain level of power. If the parts dwindle much, the -creature will be unable to lift itself from the ground. Bearing in mind -that the force which a bird expends to sustain itself in the air during -each successive instant of a short flight is, other things equal, -the same as it expends in each successive instant of a long flight, -we shall see that the muscles employed in the two cases must have -something like equal intensities of contractile power; and that the -structural differences between them must have relation mainly to the -lengths of time during which they can continue to repeat contractions -of like intensity. That is to say, while the power of flight is -retained at all, the muscles and bones cannot greatly dwindle; but the -dwindling, in birds whose flights are short or infrequent or both, -will be in the reserve stock of the substance that is incapacitated by -action, or in the appliances that keep the apparatus in repair, or in -both. Only where, as in the struthious birds, the habit of flight is -lost, can we expect atrophy of all the parts concerned in flight; and -here we find it.</p> - -<p>Are such differentiations among the muscles functionally-produced? or -are they produced by the natural selection of variations distinguished -as spontaneous? We have, I think, good grounds for concluding that -they are functionally-produced. We know that in individual men and -animals, the power of sustained action in muscles is rapidly adaptable -to the amount of sustained action required. We know that being “out of -condition,” is usually less shown by the inability to put out a violent -effort than by the inability to continue<span class="pagenum" id="Page_369">[369]</span> making violent efforts; and -we know that the result of training for prize-fights and races, is more -shown in the prolongation of energy than in the intensification of -energy. At the same time, experience has taught us that the structural -change which accompanies this functional change, is not so much a -change in the bulk of the muscles as a change in their internal state: -instead of being soft and flabby they become hard. We have inductive -proof, then, that exercise of a muscle causes some interstitial -growth along with the power of more sustained action; and there can -be no doubt that the one is a condition to the other. What is this -interstitial growth? There is reason to suspect that it is in part an -increased deposit of the sarcous substance and in part a development of -blood-vessels. Microscopic observation tends to confirm the conclusions -before drawn, that repetition of contractions furthers the formation -of the matter which contracts, and that greater draughts of blood -determine greater vascularity. And if the contrasts of molecular -structure and the contrasts of vascularity, directly caused in muscles -by contrasts in their activities, are to any degree inheritable; -there results an explanation of those constitutional differences in -the colours and textures of muscles, which accompany constitutional -differences in their degrees of activity.</p> - -<p>It may be added that if we are warranted in so ascribing the -differentiations of muscles from one another to direct equilibration, -then we have the more reason for thinking that the differentiation -of muscles in general from other structures is also due to direct -equilibration. That unlikenesses between parts of the contractile -tissues having unlike functions, are caused by the unlikenesses of -their functions, renders it the more probable that the unlikenesses -between contractile tissue and other tissues, have been caused by -analogous unlikenesses.</p> - - -<p class="p2">§ 304. These interpretations, which have already occupied too -large a space, must here be closed. Of course out of<span class="pagenum" id="Page_370">[370]</span> phenomena so -multitudinous and varied, it has been impracticable to deal with any -but the most important; and it has been practicable to deal with these -only in a general way. Much, however, as remains to be explained, I -think the possibility of tracing, in so many cases, the actions to -which these internal differentiations may rationally be ascribed, -makes it likely that the remaining internal differentiations are -due to kindred actions. We find evidence that, in more cases than -seemed probable, these actions produce their effects directly on the -individual; and that the unlikenesses are produced by accumulation -of such effects from generation to generation. While for all the -other unlikenesses, we have, as an adequate cause, the indirect -effects wrought by the survival, generation after generation, of the -individuals in which favourable variations have occurred—variations -such as those of which human anatomy furnishes endless instances. -Thus accounting for so much, we may not unreasonably presume that -these co-operative processes of direct and indirect equilibration will -account for what remains.</p> - -<hr class="tb" /> - -<p>[<span class="smcap">Note.</span>—After having dismissed this revised chapter as done -with, and sent it to the printer, further thought concerning those -differentiations which produce bone, has reminded me of a fact of -extreme and varied significance named in the first volume. I refer -to the formation of adaptive structures round the ends of dislocated -bones, and to the formation of “false joints.”</p> - -<p>These are ontogenetic changes of which phylogeny yields no explanation. -They do not repeat the traits of ancestral organisms, and they cannot -be ascribed to either of the recognized evolutionary factors. If a -humerus be broken across and, failing to set, presently comes to have -its two loose ends so modified as in a measure to simulate the parts of -a normal joint—the ends becoming smooth, covered with periosteum and -supplied with fibrous tissue, and attached by ligaments in such ways -as to allow of restrained movements—it<span class="pagenum" id="Page_371">[371]</span> is impossible to think that -natural selection has had anything to do with the power of adjustment -thus shown. No survival of individuals in which adaptations of this -kind, now in one place and now in another, were better and better -effected, could account for acquirement of the ability. Nor can it be -supposed that the ability might result from a functionally-produced -habit; since it is scarcely conceivable that the number of cases in -which individuals profited by it (at first a little and gradually more) -could be such (even did they survive) as to affect the constitution of -the species. Both of the alleged causes of structural modifications -are out of court. It is manifest, too, that the foregoing hypothesis -respecting bone-formation yields us not the slightest help.</p> - -<p>But on carefully considering the facts, certain phenomena of profound -meaning may strike us. Here, in a part of the body where no such -tissues ordinarily exist and to which no such structures are ordinarily -appropriate, there arise tissues and structures adapted to the physical -circumstances imposed on that part. Out of what do these abnormal -but appropriate tissues arise? The substances around—osseous, -cartilaginous, membranous—consist of differentiated elements too -far specialized to allow of transformation. These new tissues, then, -must originate from the undifferentiated protoplasm pervading the -part. The units of this protoplasm, subject to the actions proper -to an articulation, begin to assume the appropriate histological -traits—are determined by local stimuli to form tissues ordinarily -associated with such stimuli. What is the inevitable implication? These -units—physiological or constitutional, as we may call them—must -have possessed latent potentialities of falling into these special -arrangements under stress of such conditions. At one point there arises -periosteum and at another ligamentous tissue, while for the shaping of -the ends of the bones—here into a rude hinged form and there into a -rude ball-and-socket form, according to the habitual movements—there -goes on some appropriate deposit<span class="pagenum" id="Page_372">[372]</span> of bone. Hence we must conclude that -in the units of protoplasm which have not yet been organized into -special tissues, there resides the ability to take on one or other type -of histological structure according to circumstances; and, further, -that there resides in each of them the still more marvellous ability -to co-operate with kindred units dispersed around in developing that -arrangement of the parts required to constitute a “false joint.” So -that while these units have a general proclivity towards the structure -of the organism as a whole, they have also proclivities towards -structures proper to the local conditions into which they fall. -There is latent in each unit the constitution of the entire organism -and by implication the constitution of every organ; and each unit -while co-operating with the aggregate is ready to take part in that -particular arrangement proper to the position it has fallen into. If -the reader will refer back to <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect97">§§ 97<i>d</i>, 97<i>e</i></a>, in which it -is shown that each member of a human society possesses a combination -of potentialities like these, he will be the better enabled to believe -that this thing <i>may be</i> so while he is unable to conceive how it -<i>is</i> so.</p> - -<p>And here, indeed, let it be pointed out how completely irrelevant is -the test of conceivableness as applied to these ultimate physiological -actions. For as here, from the un-united ends of the broken bone, there -presently arises a rude joint with fit membranes, ligaments, and even -synovial fluid, though we are absolutely unable to imagine the process -by which the adjacent tissues produce this structure; so there may -be from an organ enlarged by function, such reactive effect upon the -system at large as eventually to influence the reproductive cells, -though we may be absolutely unable to imagine how this can be done.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_373">[373]</span></p> - -<h3>CHAPTER IX.<br /> -<span class="subhed1">PHYSIOLOGICAL INTEGRATION IN ANIMALS.</span></h3></div> - - -<p>§ 305. Physiological differentiation and physiological integration, -are correlatives that vary together. We have but to recollect the -familiar parallel between the division of labour in a society and the -physiological division of labour, to see that as fast as the kinds -of work performed by the component parts of an organism become more -numerous, and as fast as each part becomes more restricted to its -own work, so fast must the parts have their actions combined in such -ways that no one can go on without the rest and the rest cannot go on -without each one.</p> - -<p>Here our inquiry must be, how the relationship of these two -processes is established—what causes the integration to advance -<i>pari passu</i> with the differentiation. Though it is manifest, -<i>à priori</i>, that the mutual dependence of functions must be -proportionate to the specialization of functions; yet it remains to -find the mode in which the increasing co-ordination is determined.</p> - -<p>Already, among the Inductions of Biology, this relation between -differentiation and integration has been specified and illustrated -(<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect59">§ 59</a>). Before dealing with it deductively, a few further examples, -grouped so as to exhibit its several aspects, will be advantageous.</p> - - -<p class="p2">§ 306. If the lowly-organized <i>Planaria</i> has its body broken -up and its gullet detached, this will, for a while, continue<span class="pagenum" id="Page_374">[374]</span> to -perform its function when called upon, just as though it were in its -place: a fragment of the creature’s own body placed in the gullet, -will be propelled through it, or swallowed by it. But, as the seeming -strangeness of this fact implies, we find no such independent actions -of analogous parts in the higher animals. Again, a piece cut out of -the disc of a <i>Medusa</i> continues with great persistence repeating -those rhythmical contractions which we see in the disc as a whole; -and thus proves to us that the contractile function in each portion -of the disc, is in great measure independent. But it is not so with -the locomotive organs of more differentiated types. When separated -from the rest these lose their powers of movement. The only member of -a vertebrate animal which continues to act after detachment, is the -heart; and the heart has motor powers complete within itself.</p> - -<p>Where there is this small dependence of each part upon the whole, -there is but small dependence of the whole upon each part. The longer -time which it takes for the arrest of a function to produce death in -a less-differentiated animal than in a more-differentiated animal, -may be illustrated by the case of respiration. Suffocation in a man -speedily causes resistance to the passage of the blood through the -capillaries, followed by congestion and stoppage of the heart: great -disturbance throughout the system results in a few seconds, and in -a minute or two all the functions cease. But in a frog, with its -undeveloped respiratory organ, and a skin through which a considerable -aëration of the blood is carried on, breathing may be suspended for -a long time without injury. Doubtless this difference is proximately -due to the greater functional activity in the one case than in the -other, and the more pressing need for discharging the produced carbon -dioxide; but the greater functional activity being itself made possible -by the higher specialization of functions, this remains the primary -cause of the greater dependence of the other functions on respiration, -where the respiratory apparatus has become highly specialized. Here<span class="pagenum" id="Page_375">[375]</span> -indeed, we see the relation under another aspect. This more rapid -rhythm of the functions which increased heterogeneity of structure -makes possible, is itself a means of integrating the functions. Watch, -when it is running down, a complicated machine of which the parts are -not accurately adjusted, or are so worn as to be somewhat loose. There -will be observed certain irregularities of movement just before it -comes to rest—certain of the parts which stop first, are again made to -move a little by the continued movement of the rest, and then become -themselves, in turn, the causes of renewed motion in other parts which -have ceased to move. That is to say, while the connected rhythmical -changes of the machine are quick, their actions and reactions on one -another are regular—all the motions are well integrated; but as the -velocity diminishes irregularities arise—the motions become somewhat -disintegrated. Similarly with organic functions: increase of their -rapidity involves increase of a joint momentum which controls each -and co-ordinates all. Thus if we compare a snake with a mammal, we -see that its functions are not tied together so closely. The mammal, -and especially the superior mammal, requires food with considerable -regularity; keeps up a respiration which varies within but moderate -limits; and has periods of activity and rest that alternate evenly and -frequently. But the snake, taking food at long intervals, may have -these intervals greatly extended without fatal results; its dormant and -its active states recur less uniformly; and its rate of respiration -varies within much wider limits—now being scarcely perceptible and -now, as you may prove by exciting it, becoming conspicuous. So that -here, where the rhythms are very slow, they are individually less -regular, and are united into a less regular compound rhythm—are less -integrated.</p> - -<p>Perhaps the clearest general idea of the co-ordination of functions -that accompanies their specialization, is obtained by observing the -slowness with which a little-differentiated animal responds to a -stimulus applied to one of its parts,<span class="pagenum" id="Page_376">[376]</span> and the rapidity with which -such a local stimulus is responded to by a more-differentiated animal. -A sea-anemone and a fly will serve for the comparison. A tentacle of -a sea-anemone, when touched, slowly contracts; and if the touch has -been rude, the contraction presently extends to the other tentacles -and eventually to the entire body: the stimulus to movement is -gradually diffused throughout the organism. But if you touch a fly, -or rather if you come near enough to threaten a touch, the entire -apparatus of flight is instantly brought into combined action. Whence -arises this contrast? The one creature has but faintly specialized -contractile organs, and fibres for conveying impressions. The other -has definite muscles and nerves and a co-ordinating centre. The parts -of the little-differentiated sea-anemone have their functions so -feebly co-ordinated, that one may be strongly affected for some time -before any effect is felt by another at a distance from it; but in the -much-differentiated fly, various remote parts instantly have changes -propagated to them from the affected part, and by their united actions -thus set up, the whole organism adjusts itself so as to avoid the -danger.</p> - -<p>These few added illustrations will make the nature of this general -relation sufficiently clear. Let us now pass to the interpretation of -it.</p> - - -<p class="p2">§ 307. If a <i>Hydra</i> is cut in two, the nutritive liquids -diffused through its substance cannot escape rapidly, since there -are no open channels for them; and hence the conditions of the parts -at a distance from the cut is but little affected. But where, as in -the more-differentiated animals, the nutritive liquid is contained -in vessels which have continuous communications, cutting the body -in two, or cutting off any considerable portion of it, is followed -by escape of the liquid from these vessels to a large extent; and -this affects the nutrition and efficiency of organs remote from the -place of injury. Then where, as in further-developed creatures, -there exists an apparatus for propelling the blood<span class="pagenum" id="Page_377">[377]</span> through these -ramifying channels, injury of a single one will cause a loss of blood -that quickly prostrates the entire organism. Hence the rise of a -completely-differentiated vascular system, is the rise of a system -which integrates all members of the body, by making each dependent on -the integrity of the vascular system, and therefore on the integrity -of each member through which it ramifies. In another mode, too, the -establishment of a distributing apparatus produces a physiological -union that is great in proportion as this distributing apparatus is -efficient. As fast as it assumes a function unlike the rest, each part -of an animal modifies the blood in a way more or less unlike the rest, -both by the materials it abstracts and by the products it adds; and -hence the more differentiated the vascular system becomes, the more -does it integrate all parts by making each of them feel the qualitative -modification of the blood which every other has produced. This is -simply and conspicuously exemplified by the lungs. In the absence of a -vascular system, or in the absence of one that is well marked off from -the imbedding tissues, the nutritive plasma or the crude blood, gets -what small aëration it can, only by coming near the creature’s outer -surface, or those inner surfaces which are bathed by water. But where -there have been formed definite channels branching throughout the body, -and particularly where there exist specialized organs for pumping the -blood through these channels, it manifestly becomes possible for the -aëration to be carried on in one part peculiarly modified to further -it, while all other parts have the aërated blood brought to them. And -how greatly the differentiation of the vascular system thus becomes a -means of integrating the various organs, is shown by the fatal result -that follows when the current of aërated blood is interrupted.</p> - -<p>Here, indeed, it becomes obvious both that certain physiological -differentiations make possible certain physiological integrations; -and that, conversely, these integrations make possible other -differentiations. Besides the waste products<span class="pagenum" id="Page_378">[378]</span> which escape through the -lungs, there are waste products which escape through the skin, the -kidneys, the liver. The blood has separated from it in each of these -structures, the particular product which this structure has become -adapted to separate; leaving the other products to be separated by -the other adapted structures. How have these special adaptations been -made possible? By union of the organs as recipients of one circulating -mass of blood. While there is no efficient apparatus for transfer of -materials through the body, the waste products of each part have to -make their escape locally; and the local channels of escape must be -competent to take off indifferently all the waste products. But it -becomes practicable and advantageous for the differently-localized -excreting structures to become fitted to separate different waste -products, as soon as the common circulation through them grows so -efficient that the product left unexcreted by one is quickly carried to -another better fitted to excrete it. So that the integration of them -through a common vascular system, is the condition under which only -they can become differentiated. Perhaps the clearest idea of the way in -which differentiation leads to integration, and how, again, increased -integration makes possible still further differentiation, will be -obtained by contemplating the analogous dependence in the social -organism. While it has no roads, a country cannot have its industries -much specialized: each locality must produce, as best it can, the -various commodities it consumes, so long as it has no facilities for -barter with other localities. But the localities being unlike in their -natural fitnesses for the various industries, there tends ever to -arise some exchange of the commodities they can respectively produce -with least labour. This exchange leads to the formation of channels -of communication. The currents of commodities once set up, make -their foot-paths and horse-tracks more permeable; and as fast as the -resistance to exchange becomes less, the currents of commodities become -greater. Each locality takes more of the products<span class="pagenum" id="Page_379">[379]</span> of adjacent ones, -and each locality devotes itself more to the particular industry for -which it is naturally best fitted: the functional integration makes -possible a further functional differentiation. This further functional -differentiation reacts. The greater demand for the special product of -each locality, excites improvements in production—leads to the use of -methods which both cheapen and perfect the commodity. Hence results a -still more active exchange; a still clearer opening of the channels of -communication; a still closer mutual dependence. Yet another influence -comes into play. As fast as the intercourse, at first only between -neighbouring localities, makes for itself better roads—as fast as -rivers are bridged and marshes made easily passable, the resistance to -distribution becomes so far diminished, that the things grown or made -in each district can be profitably carried to a greater distance; and -as the economical integration is thus extended over a wider area, the -economical differentiation is again increased; since each district, -having a larger market for its commodity, is led to devote itself more -exclusively to producing this commodity. These actions and reactions -continue until the various localities, becoming greatly developed -and highly specialized in their industries, are at the same time -functionally integrated by a network of roads, and finally railways, -along which rapidly circulate the currents severally sent out and -received by the localities. And it will be manifest that in individual -organisms a like correlative progress must have been caused in an -analogous way.</p> - - -<p class="p2">§ 308. Another and higher form of physiological integration in animals, -is that which the nervous system effects. Each part as it becomes -specialized, begins to act upon the rest not only indirectly through -the matters it takes from and adds to the blood, but also directly -through the molecular disturbances it sets up and diffuses. Whether -nerves themselves are differentiated by the molecular disturbances -thus propagated in certain directions, or whether they are otherwise<span class="pagenum" id="Page_380">[380]</span> -differentiated, it must equally happen that as fast as they become -channels along which molecular disturbances travel, the parts they -connect become physiologically integrated, in so far that a change -in one initiates a change in the other. We may dimly perceive that -if portions of what was originally a uniform mass having a common -function, undertake subdivisions of the function, the molecular changes -going on in them will be in some way complementary to one another: -that peculiar form of molecular motion which the one has lost in -becoming specialized, the other has gained in becoming specialized. -And if the molecular motion that was common to the two portions while -they were undifferentiated, becomes divided into two complementary -kinds of molecular motion; then between these portions there will be -a contrast of molecular motions such that whatever is <i>plus</i> in -the one will be <i>minus</i> in the other; and hence there will be a -special tendency towards a restoration of the molecular equilibrium -between the two: the molecular motion continually propagated away from -either will have its line of least resistance in the direction of the -other. If, as argued in the last chapter, repeated restorations of -molecular equilibrium, always following the line of least resistance, -tend ever to make it a line of diminished resistance; then, in -proportion as any parts become more physiologically integrated by -the establishment of this channel for the easy transmission of -molecular motion between them, they may become more physiologically -differentiated. The contrast between their molecular motions leads to -the line of discharge; the line of discharge, once formed, permits a -greater contrast of their molecular motions to arise; thereupon the -quantities of molecular motion transferred to restore equilibrium, -being increased, the channel of transfer is made more permeable; and -its further permeability, so caused, renders possible a still more -marked unlikeness of action between the parts. Thus the differentiation -and the integration progress hand in hand as before. How the same -principle holds throughout<span class="pagenum" id="Page_381">[381]</span> the higher stages of nervous development, -can be seen only still more vaguely. Nevertheless, it is comprehensible -that as functions become further divided, there will arise the -need for sub-connexions along which there may take place secondary -equilibrations subordinate to the main ones. It is manifest, too, that -whereas the differentiation of functions proceeds, not necessarily by -division into two, but often by division into several, and usually in -such ways as not to leave any two functions that are just complementary -to one another, the restorations of equilibrium cannot be so simple -as above supposed. And especially when we bear in mind that many -differentiated functions, as those of the senses, cannot be held -complementary to any other functions in particular; it becomes manifest -that the equilibrations that have to be made in an organism of much -heterogeneity, are extremely complex, and do not take place between -each organ and some other, but between each organ and all the others. -The peculiarity of the molecular motion propagated from each organ, -has to be neutralized by some counter-peculiarity in the average of -the molecular motions with which it is brought into relation. All the -variously-modified molecular motions from the various parts, must have -their pluses and minuses mutually cancelled: if not locally, then at -some centre to which each unbalanced motion travels until it meets with -some opposite unbalanced motion to destroy it. Still, involved as these -actions must become, it is possible to see how the general principle -illustrated by the simple case above supposed, will continue to hold. -For always the molecular motion proceeding from any one differentiated -part, will travel most readily towards that place where a molecular -motion most complementary to it in kind exists—no matter whether this -complementary molecular motion be that proceeding from any one other -organ, or the <i>resultant</i> of the molecular motions proceeding from -many other organs. So that the tendency will be for each channel of -communication or nerve, to unite itself with some centre or ganglion, -where it<span class="pagenum" id="Page_382">[382]</span> comes into relation with other nerves. And if there be any -parts of its peculiar molecular motion uncancelled by the molecular -motions it meets at this centre; or if, as will probably happen, the -average molecular motion which it there unites to produce, differs from -the average molecular motion elsewhere; then, as before, there will -arise a discharge along another channel or nerve to another centre -or ganglion, where the residuary difference may be cancelled by the -differences it meets; or whence it may be still further propagated till -it is so cancelled. Thus there will be a tendency to a general nervous -integration keeping pace with the differentiation.</p> - -<p>Of course this must be taken as nothing more than the indication of -initial tendencies—not as an hypothesis sufficient to account for all -the facts. It leaves out of sight the origin and functions of ganglia, -considered as something more than nerve-junctions. Were there only -these lines of easy transmission of molecular disturbance, a change -set up in one organ could never do more than produce its equivalent of -change in some other or others; and there could be none of that large -amount of motion initiated by a small sensation, which we habitually -see. The facts show, unmistakably, that the slight disturbance -communicated to a ganglion, causes an overthrow of that highly-unstable -nervous matter contained in it, and a discharge from it of the -greatly-increased quantity of molecular motion so generated. This, -however, is beyond our immediate topic. All we have here to note is the -interdependence and unification of functions that naturally follow the -differentiation of them.</p> - - -<p class="p2">§ 309. Something might be added concerning the further class of -integrations by which organisms are constituted mechanically-coherent -wholes. Carrying further certain of the arguments contained in the -last chapter, it might be not unreasonably inferred that the binding -together of parts by bones, muscles, and ligaments, is a secondary -result of<span class="pagenum" id="Page_383">[383]</span> those same actions by which bones, muscles, and ligaments -are specialized. But adequate treatment of this division of the subject -is at present scarcely possible.</p> - -<p>What little of fact and inference has been above set down, will, -however, serve to make comprehensible the general truths respecting -which, in their main outlines, there can be no question. Beginning with -the feebly-differentiated sponge, of which the integration is also so -feeble that cutting off a piece interferes in no appreciable degree -with the activity and growth of the rest, it is undeniable that the -advance is through stages in which the multiplication of unlike parts -having unlike actions, is accompanied by an increasing interdependence -of the parts and their actions; until we come to structures like our -own, in which a slight change initiated in one part will instantly and -powerfully affect all other parts—will convulse an immense number of -muscles, send a wave of contraction through all the blood-vessels, -awaken a crowd of ideas with an accompanying gush of emotions, affect -the action of the lungs, of the stomach, and of all the secreting -organs. And while it is a manifest necessity that along with this -subdivision of functions which the higher organisms show us, there -must be this close co-ordination of them, the foregoing paragraphs -suggest how this necessary correlation is brought about. For a great -part of the physiological union that accompanies the physiological -specialization, there appears to be a sufficient cause in the process -of direct equilibration; and indirect equilibration may be fairly -presumed a sufficient cause for that which remains.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_384">[384]</span></p> - -<h3>CHAPTER X.<br /> -<span class="subhed1">SUMMARY OF PHYSIOLOGICAL DEVELOPMENT.</span></h3></div> - - -<p>§ 310. Intercourse between each part and the particular conditions -to which it is exposed, either habitually in the individual -or occasionally in the race, thus appears to be the origin of -physiological development; as we found it to be the origin of -morphological development. The unlikenesses of form that arise among -members of an aggregate that were originally alike, we traced to -unlikenesses in the incident forces. And in the foregoing chapters we -have traced to unlikenesses in the incident forces, those unlikenesses -of minute structure and chemical composition that simultaneously arise -among the parts.</p> - -<p>In summing up the special truths illustrative of this general truth, -it will be proper here to contemplate more especially their dependence -on first principles. Dealing with biological phenomena as phenomena of -evolution, we have to interpret not only the increasing morphological -heterogeneity of organisms, but also their increasing physiological -heterogeneity, in terms of the re-distribution of matter and motion. -While we make our rapid re-survey of the facts, let us then more -particularly observe how they are subordinate to the universal course -of this re-distribution.</p> - - -<p class="p2">§ 311. The instability of the homogeneous, or, strictly speaking, the -inevitable lapse of the more homogeneous into the less homogeneous, -which we before saw endlessly exemplified<span class="pagenum" id="Page_385">[385]</span> by the morphological -differentiations of the parts of organisms, we have here seen -afresh exemplified in ways also countless, by the physiological -differentiations of their parts. And in the one case as in the other, -this change from uniformity to multiformity in organic aggregates, is -caused, as it is in all inorganic aggregates, by the necessary exposure -of their component parts to actions unlike in kind or quantity or -both. General proof of this is furnished by the order in which the -differences appear. If parts are rendered physiologically heterogeneous -by the heterogeneity of the incident forces, then the earliest -contrasts should be between parts that are the most strongly contrasted -in their relations to incident forces; the next earliest contrasts -should occur where there are the next strongest contrasts in these -relations; and so on. It turns out that they do so.</p> - -<p>Everywhere the differentiation of outside from inside comes first. -In the simplest plants the unlikeness of the cell-wall to the -cell-contents is the conspicuous trait of structure. The contrasts seen -in the simplest animals are of the same kind: the film that covers -a Rhizopod and the more indurated coat of an Infusorian, are more -unlike the contained sarcode than the other parts of this are from -one another; and the tendency during the life of the animal is for -the unlikeness to become greater. What is true of <i>Protophyta</i> -and <i>Protozoa</i>, is true of the germs of all organisms up to the -highest: the differentiation of outer from inner is the first step. -When the protoplasm of an <i>Alga</i>-cell has broken up into the -clusters of granules which are eventually to become spores, each of -these quickly acquires a membranous coating, constituting an unlikeness -between surface and centre. Similarly with the ovule of every higher -plant: the mass of cells forming it, early exhibits an outside layer -of cells distinguished from the cells within. With animal-germs it is -the same. Be it in a ciliated gemmule, be it in the unfertilized ova -of <i>Aphides</i> and of the <i>Cecidomyia</i>, or be it in true ova, -the primary differentiation conforms to the relations<span class="pagenum" id="Page_386">[386]</span> of exterior and -interior. If we turn to adult organisms, vegetal or animal, we see -that whether they do or do not display other contrasts of parts, they -always display this contrast. Though otherwise almost homogeneous, such -<i>Fungi</i> as the puff-ball, or, among <i>Algæ</i>, all which have -a thallus of any thickness, present marked differences between those -of their cells which are in immediate contact with the environment -and those which are not. Such differences they present in common with -every higher plant; which, here in the shape of bark and there in the -shape of cuticle, has an envelope inclosing it even up to its petals -and stamens. In like manner among animals, there is always either a -true skin or an outer coat analogous to one. Wherever aggregates of -the first order have united into aggregates of the second and third -orders—wherever they have become the morphological units of such -higher aggregates—the outermost of them have grown unlike those lying -within. Even the Sponge is not without a layer that may by analogy be -called dermal.</p> - -<p>This lapse of the relatively homogeneous into the relatively -heterogeneous, first showing itself, as on the hypothesis of evolution -it must do, by the rise of an unlikeness between outside and inside, -goes on next to show itself, as we infer that it must do, by the -establishment of secondary contrasts among the outer parts answering -to secondary contrasts among the forces falling on them. So long -as the whole surface of a plant remains similarly related to the -environment, as in a <i>Protococcus</i>, it remains uniform; but -when there come to be an attached surface and a free surface, these, -being subject to unlike actions, are rendered unlike. This is visible -even in a unicellular <i>Alga</i> when it becomes fixed; it is shown -in the distinction between the under and upper parts of ordinary -<i>Fungi</i>; and we see it in the universal difference between the -imbedded ends and the exposed ends of the higher plants. And then among -the less marked contrasts of surface answering to the less marked -contrasts in the incident<span class="pagenum" id="Page_387">[387]</span> forces, come those between the upper and -under sides of leaves; which, as we have seen, vary in degree as the -contrasts of forces vary in degree, and disappear where these contrasts -disappear. Equally clear proof is furnished by animals, that the -original uniformity of surface lapses into multiformity, in proportion -as the actions of the environment upon the surface become multiform. -In a Worm, burrowing through damp soil which acts equally on all its -sides, or in a <i>Tænia</i>, uniformly bathed by the contents of the -intestine it inhabits, the parts of the integument do not appreciably -differ from one another; but in creatures not surrounded by the -same agencies, as those that crawl and those that have their bodies -partially inclosed, there are unlikenesses of integument corresponding -to unlikenesses of the conditions. A snail’s foot has an under surface -not uniform with the exposed surface of its body, and this again is -not uniform with the protected surface. Among articulate animals there -is usually a distinction between the ventral and the dorsal aspects; -and in those of the <i>Arthropoda</i> which subject their anterior and -posterior ends to different environing agencies, as do the ant-lion -and the hermit-crab, these become superficially differentiated. -Analogous general contrasts occur among the <i>Vertebrata</i>. -Fishes, though their outsides are uniformly bathed by water, have -their backs more exposed to light than their bellies, and the two -are commonly distinct in colour. When it is not the back and belly -which are thus dissimilarly conditioned, but the sides, as in the -<i>Pleuronectidæ</i>, then it is the sides which become contrasted; and -there may be significance in the fact that those abnormal individuals -of this order which revert to the ancestral undistorted type, and -swim vertically, have the two sides alike. In such higher vertebrates -as reptiles, we see repeated this differentiation of the upper and -under surfaces: especially in those of them which, like snakes, expose -these surfaces to the most diverse actions. Even in birds and mammals -which usually, by raising the under surface considerably above the -ground,<span class="pagenum" id="Page_388">[388]</span> greatly diminish the contrast between its conditions and the -conditions to which the upper surface is subject, there still remains -some unlikeness of clothing answering to the remaining unlikeness -between the conditions. Thus, without by any means saying that all such -differentiations are directly caused by differences in the actions of -incident forces, which, as before shown (<a href="#sect294">§ 294</a>), they cannot be, it is -clear that many of them are so caused. It is clear that parts of the -surface exposed to very unlike environing agencies, become very unlike; -and this is all that needs to be shown.</p> - -<p>Complex as are the transformations of the inner parts of organisms -from the relatively homogeneous into the relatively heterogeneous, we -still see among them a conformity to the same general order. In both -plants and animals the earlier internal differentiations answer to the -stronger contrasts of conditions. Plants, absorbing all their nutriment -through their outer surfaces, are internally modified mainly by the -transfer of materials and by mechanical stress. Such of them as do not -raise their fronds above the surface, have their inner tissues subject -to no marked contrasts save those caused by currents of sap; and the -lines of lengthened and otherwise changed cells which are formed where -these currents run, and are most conspicuous where these currents must -obviously be the strongest, are the only decided differentiations of -the interior. But where, as in the higher Cryptogams and in Phænogams, -the leaves are upheld, and the supporting stem is transversely bent by -the wind, the inner tissues, subject to different amounts of mechanical -strain, differentiate accordingly: the deposit of dense substance -commences in that region where the sap-containing cells and canals -suffer the greatest intermittent compressions. Animals, or at least -such of them as take food into their interiors, are subject to forces -of another class tending to destroy their original homogeneity. Food -is a foreign substance which acts on the interior as an environing -object which touches it acts on the exterior—is<span class="pagenum" id="Page_389">[389]</span> literally a portion -of the environment which, when swallowed, becomes a cause of internal -differentiations as the rest of the environment continues a cause -of external differentiations. How essentially parallel are the two -sets of actions and reactions, we have seen implied by the primordial -identity of the endoderm and ectoderm in simple animals, and of the -skin and mucous membrane in complex animals (<a href="#sect288">§§ 288</a>, <a href="#sect289">289</a>). Here we have -further to observe that as food is the original source of internal -differentiations, these may be expected to show themselves first -where the influence of the food is greatest; and to appear later in -proportion as the parts are more removed from the influence of the -food. They do this. In animals of low type, the coats of the alimentary -cavity or canal are more differentiated than the tissue which lies -between the alimentary canal and the wall of the body. This tissue -in the higher <i>Cœlenterata</i>, is a feebly-organized parenchyma -traversed by canals lined with simple ciliated cells; and in the lower -<i>Mollusca</i> the structures bounding the peri-visceral cavity -and its ramifying sinuses, are similarly imperfect. Further, it is -observable that the differentiation of this peri-visceral sac and its -sinuses into a vascular system, proceeds centrifugally from the region -where the absorbed nutriment enters the mass of circulating liquid, and -where this liquid is qualitatively more unlike the tissues than it is -at the remoter parts of the body.</p> - -<p>Physiological development, then, is initiated by that instability -of the homogeneous which we have seen to be everywhere a cause of -evolution (<i>First Principles</i>, §§ 149–155). That the passage -from comparative uniformity of composition and minute structure to -comparative multiformity, is set up in organic aggregates, as in all -other aggregates, by the necessary unlikenesses of the actions to which -the parts are subject, is shown by the universal rise of the primary -differentiation into the parts that are universally most contrasted in -their circumstances, and by the rise of secondary differentiations<span class="pagenum" id="Page_390">[390]</span> -obviously related in their order to secondary contrasts of conditions.</p> - - -<p class="p2">§ 312. How physiological development has all along been aided by the -multiplication of effects—how each differentiation has ever tended to -become the parent of new differentiations, we have had, incidentally, -various illustrations. Let us here review the working of this cause.</p> - -<p>Among plants we see it in the production of progressively-multiplying -heterogeneities of tissue by progressive increase of bulk. The -integration of fronds into axes and of axes into groups of axes, -sets up unlikenesses of action among the integrated units, followed -by unlikenesses of minute structure. Each gust transversely strains -the various parts of the stem in various degrees, and longitudinally -strains in various degrees the roots; and while there is inequality of -stress at every place in stem and branch, so, at every place in stem -and branch, the outer layers and the successively inner layers are -severally extended and compressed to unequal amounts, and have unequal -modifications wrought in them. Let the tree add to its periphery -another generation of the units composing it, and immediately the -mechanical strains on the supporting parts are all changed in different -degrees, initiating new differences internally. Externally, too, new -differences are initiated. Shaded by the leaf-bearing outer stratum -of shoots, the inner structures cease to bear leaves, or to put out -shoots which bear leaves; and instead of that green covering which -they originally had, become covered with bark of increasing thickness. -Manifestly, then, the larger integration of units that are originally -simple and uniform, entails physiological changes of various orders, -varying in their degrees at all parts of the aggregate. Each branch -which, favourably circumstanced, flourishes more than its neighbours, -becomes a cause of physiological differentiations, not only in its -neighbours from which it abstracts sap and presently<span class="pagenum" id="Page_391">[391]</span> turns from -leaf-bearers into fruit-bearers, but also in the remoter parts.</p> - -<p>That among animals physiological development is furthered by the -multiplication of effects, we have lately seen proved by the many -changes in other organs, which the growth or modification of each -excreting and secreting organ initiates. By the abstracted as well as -by the added materials, it alters the quality of the blood passing -through all members of the body; or by the liquid it pours into the -alimentary canal, it acts on the food, and through it on the blood, -and through it on the system as a whole: an additional differentiation -in one part thus setting up additional differentiations in many other -parts; from each of which, again, secondary differentiating forces -reverberate through the organism. Or, to take an influence of another -order, we have seen how the modified mechanical action of any member -not only modifies that member, but becomes, by its reactions, a cause -of secondary modifications—how, for example, the burrowing habits -of the common mole, leading to an almost exclusive use of the fore -limbs, have entailed a dwindling of the hind limbs, and a concomitant -dwindling of the pelvis, which, becoming too small for the passage of -the young, has initiated still more anomalous modifications.</p> - -<p>So that throughout physiological development, as in evolution at large, -the multiplication of effects has been a factor constantly at work, and -working more actively as the development has advanced. The secondary -changes wrought by each primary change, have necessarily become more -numerous in proportion as organisms have become more complex. And -every increased multiplication of effects, further differentiating the -organism and, by consequence, further integrating it, has prepared the -way for still higher differentiations and integrations similarly caused.</p> - - -<p class="p2">§ 313. The general truth next to be resumed, is that these processes -have for their limit a state of equilibrium—proximately<span class="pagenum" id="Page_392">[392]</span> a moving -equilibrium and ultimately a complete equilibrium. The changes we have -contemplated are but the concomitants of a progressing equilibration. -In every aggregate which we call living, as well as in all other -aggregates, the instability of the homogeneous is but another name -for the absence of balance between the incident forces and the forces -which the aggregate opposes to them; and the passage into heterogeneity -is the passage towards a state of balance. And to say that in every -aggregate, organic or other, there goes on a multiplication of effects, -is but to say that one part which has a fresh force impressed on it, -must go on changing and communicating secondary changes, until the -whole of the impressed force has been used up in generating equivalent -reactive forces.</p> - -<p>The principle that whatever new action an organism is subject to, must -either overthrow the moving equilibrium of its functions and cause the -sudden equilibration called death, or else must progressively alter the -organic rhythms until, by the establishment of a new reaction balancing -the new action a new moving equilibrium is produced, applies as much -to each member of an organism as to the organism in its totality. Any -force falling on any part not adapted to bear it, must either cause -local destruction of tissue, or must, without destroying the tissue, -continue to change it until it can change it no further; that is—until -the modified reaction of the part has become equal to the modified -action. Whatever the nature of the force this must happen. If it is a -mechanical force, then the immediate effect is some distortion of the -part—a distortion having for its limit that attitude in which the -resistance of the structures to further change of position, balances -the force tending to produce the further change; and the ultimate -effect, supposing the force to be continuous or recurrent, is such a -permanent alteration of form, or alteration of structure, or both, as -establishes a permanent balance. If the force is physico-chemical, or -chemical, the general result is still the same: the component molecules -of<span class="pagenum" id="Page_393">[393]</span> the tissue must have their molecular arrangements changed, and the -change in their molecular arrangements must go on until their molecular -motions are so re-adjusted as to equilibrate the molecular motions of -the new physico-chemical or chemical agent. In other words, the organic -matter composing the part, if it continues to be organic matter at all, -must assume that molecular composition which enables it to bear, or as -we say adapts it to, the incident forces.</p> - -<p>Nor is it less certain that throughout the organism as a whole, -equilibration is alike the proximate limit of the changes wrought by -each action, as well as the ultimate limit of the changes wrought by -any recurrent actions or continuous action. The movements every instant -going on, are movements towards a new state of equilibrium. Raising -a limb causes a simultaneous shifting of the centre of gravity, and -such altered tensions and pressures throughout the body as re-adjust -the disturbed balance. Passage of liquid into or out of a tissue, -implies some excess of force in one direction there at work; and ceases -only when the force so diminishes or the counter-forces so increase -that the excess disappears. A nervous discharge is reflected and -re-reflected from part to part, until it has all been used up in the -re-arrangements produced—equilibrated by the reactions called out. And -what is thus obviously true of every normal change, is equally true of -every abnormal change—every disturbance of the established rhythm of -the functions. If such disturbance is a single one, the perturbations -set up by it, reverberating throughout the system, leave its moving -equilibrium slightly altered. If the disturbance is repeated or -persistent, its successive effects accumulate until they have produced -a new moving equilibrium adjusted to the new force.</p> - -<p>Each re-balancing of actions, having for its necessary concomitant a -modification of tissues, it is an obvious corollary that organisms -subjected to successive changes of conditions, must undergo successive -differentiations and re-differentiations. Direct equilibration in -organisms, with all its accompanying<span class="pagenum" id="Page_394">[394]</span> structural alterations, is as -certain as is that universal progress towards equilibrium of which -it forms part. And just as certain is that indirect equilibration -in organisms to which the remaining large class of differentiations -is due. The development of favourable variations by the killing of -individuals in which they do not occur or are least marked, is, as -before, a balancing between certain local structures and the forces -they are exposed to; and is no less inevitable than the other.</p> - - -<p class="p2">§ 314. In all which universal laws, we find ourselves again brought -down to the persistence of force, as the deepest knowable cause of -those modifications which constitute physiological development; as -it is the deepest knowable cause of all other evolution. Here, as -elsewhere, the perpetual lapse from less to greater heterogeneity, -the perpetual begetting of secondary modifications by each primary -modification, and the perpetual approach to a temporary balance on the -way towards a final balance, are necessary implications of the ultimate -fact that force cannot disappear but can only change its form.</p> - -<p>It is an unquestionable deduction from the persistence of force, that -in every individual organism each new incident force must work its -equivalent of change; and that where it is a constant or recurrent -force, the limit of the change it works must be an adaptation of -structure such as opposes to the new outer force an equal inner force. -The only thing open to question is, whether such re-adjustment is -inheritable; and further consideration will, I think, show, that to say -it is not inheritable is indirectly to say that force does not persist. -If all parts of an organism have their functions co-ordinated into a -moving equilibrium, such that every part perpetually influences all -other parts, and cannot be changed without initiating changes in all -other parts—if the limit of change is the establishment of a complete -harmony among the movements, molecular and other, of all parts; then<span class="pagenum" id="Page_395">[395]</span> -among other parts that are modified, molecularly or otherwise, must -be those which cast off the germs of new organisms. The molecules of -their produced germs must tend ever to conform the motions of their -components, and therefore the arrangements of their components, to the -molecular forces of the organism as a whole; and if this aggregate of -molecular forces be modified in its distribution by a local change -of structure, the molecules of the germs must be gradually changed -in the motions and arrangements of their components, until they are -re-adjusted to the aggregate of molecular forces.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_396">[396]</span></p> - -<h3>CHAPTER X<sup>A</sup>.<br /> -<span class="subhed1">THE INTEGRATION OF THE ORGANIC WORLD.</span></h3></div> - - -<p>§ 314<i>a</i>. That from the beginning of life there has been an -ever-increasing heterogeneity in the Earth’s Flora and Fauna, is -a truth recognized by all biologists who accept the doctrine of -evolution. In discussing the origin of species Mr. Darwin and others -have been mainly occupied in explaining the genesis of now this and -now that form of organism, considered as a member of one or other -series, and regarded as becoming differentiated from its allies. But by -implication, if not avowedly, there has been simultaneously accepted -the belief that the forms continually produced by divergences and -re-divergences, have constituted an assemblage increasingly multiform -in its included kinds. And this, which we are shown by the process of -organic evolution as followed out in its details, is a corollary from -the doctrine of evolution at large, as was pointed out in § 159 of -<i>First Principles</i>.</p> - -<p>Meanwhile there has been little if any recognition of an accompanying -change, no less fundamental. In the general transformation which -constitutes Evolution, differentiation and integration advance hand -in hand; so that along with the production of unlike parts there -progresses the union of these unlike parts into a whole. Examples of -various kinds before given will recur to the reader, and an addition -to them has just been set forth in the chapter on “Physiological -Integration.” One more example, world-wide in its reach, has still to -be named.</p> - -<p><span class="pagenum" id="Page_397">[397]</span></p> - -<p>For here it remains to point out that along with the increasing -multiplication of types of organisms covering the Earth’s surface, -there has been ever going on an increasing mutual dependence of -them—an increasing integration of the entire aggregate of living -things.</p> - -<p>Many facts which are obvious and many which are quite familiar will -be named as evidence. But I must be excused for reminding the reader -of things that he knows and things that he may easily observe, since, -unless the evidence, trite as it may be, is gathered together and -properly marshalled, the generalization enunciated will not be thought -valid.</p> - - -<p class="p2">§ 314<i>b</i>. Respecting the physiological characters of the earliest -forms there is an assumption from which no escape seems possible—the -assumption that they united animal and vegetal characters. Even among -existing microscopic types of the lowest classes, there is such -community of plant-traits and animal-traits that doubts respecting -their proper places in one or the other kingdom are continually -raised—doubts, too, whether, if regarded as vegetal, they are to be -grouped as algoid or fungoid.</p> - -<p>Here, however, without entering on moot questions, we may draw the -<i>à priori</i> conclusion that these earliest living things were -double-natured, in so far that they must have had the ability to -assimilate from the inorganic world all the materials of which -protoplasm consists—must therefore, along with the power of -appropriating carbon from its gaseous compound, also have had the power -of appropriating nitrogen, either from one of its combined oxides -or directly from the air with which water is more or less charged. -For before organic substances existed there could have been none but -inorganic sources from which nitrogen could be obtained.</p> - -<p>This conclusion concerns us only because it implies homogeneity of -nature in these primordial forms of life. There could not at first -have existed among these minutest of <i>Protozoa</i> even such vague -distinctions as are now presented<span class="pagenum" id="Page_398">[398]</span> in a shadowy way by their modern -representatives. And the implication is that during the period -throughout which these smallest, lowest, and simplest living things -alone existed, there could have been, in the absence of kinds, no -mutual dependence.</p> - -<p>Since, among various of the lowest types now known to us, the same -individual exhibits a life which is now predominantly vegetal and now -predominantly animal, we cannot err in assuming that there eventually -took place differentiations of this original plant-animal type into -types permanently unlike: some in which the traits were more markedly -vegetal and others in which they were more markedly animal. As fast as -this differentiation arose, there came the beginnings of co-operation -between the predominantly vegetal types which by the aid of light -formed organic matter from the inorganic world, and the predominantly -animal types which, in chief measure, utilized the matter so formed. -Evidently with the rise of such a differentiation came an incipient -mutual dependence. If to the implied algoid type and the animal type -there be added the fungoid type, somewhat intermediate in character, -which in a large proportion of cases lives on the decaying remnants of -the other two, we are furnished with a rude conception of the primary -differentiations and the accompanying vague mutual dependences.</p> - -<p>Speculation aside, it suffices to say that early in the history of -life there must have arisen the distinction between <i>Protozoa</i> -and <i>Protophyta</i>, and that this distinction foreshadowed that -widest contrast which the higher organic world presents—the contrast -between plants and animals. It is needless to do more than name the -mutual dependence between these two great divisions. That, as being -respectively decomposers of carbon dioxide and exhalers of carbon -dioxide, they act reciprocally, as also in some measure by interchange -of nitrogenous matters; and that the implied general co-operation -serves in an indirect way to unite their lives, and in that<span class="pagenum" id="Page_399">[399]</span> sense to -integrate the two kingdoms; needs not to be insisted upon. Further -complications of the mutual dependence will be mentioned by and by. For -the present it suffices to recognize this division of organic functions -as the first which arose and as continuing to be that fundamental one -which more than all others binds organisms at large together.</p> - - -<p class="p2">§ 314<i>c</i>. It will be thought by many readers that in speaking of -the contrasted vital activities of plants and animals as constituting -a “division of organic functions,” I am straining words beyond their -meanings; since the conception of organic functions postulates an -organized whole in which they exist, and plants and animals constitute -no such organized whole. But there is at hand an unexpected defence for -this conception—a defence not forthcoming a generation ago, but which -now all biologists will recognize as relevant. I refer to the phenomena -of symbiosis. These present various cases in which the plant-function -and the animal-function are carried on in the same body,—cases in -which the co-operation is not between separate vegetal organisms which -accumulate nutritive matters and separate animal organisms which -consume them, but is a co-operation between vegetal elements and animal -elements forming parts of the same organism.</p> - -<p>As introductory to examples of these must first, however, be named an -example of such co-operation between the two great classes of vegetal -organisms—the fungoid and the algoid. Incredible as the statement once -seemed, it is a statement now accepted, that what we know as lichens, -and used to consider as plants forming a certain low class, are now -found to be not plants in the ordinary sense at all, but compound -growths formed of minute algæ and minute fungi, carrying on their lives -together: the algæ furnishing to the fungi certain constituents they -need but cannot directly obtain, and the fungi profiting by certain -materials they obtain from the algæ, either while living or while -individually decaying. Whence it would seem that after the microscopic -vegetal<span class="pagenum" id="Page_400">[400]</span> type had become in a large degree differentiated into two main -types, in adaptation to different conditions of life, and had acquired -appropriate specialities of nature, there grew up this communistic -arrangement between certain of them, enabling each to benefit by the -powers which the other had acquired: evidently an exchange of services, -a physiological division of labour, a mutual dependence of functions -analogous to that which exists between functions in an ordinary plant -or animal.</p> - -<p>Not differing in principle but only in application, is that symbiosis -above referred to as existing between <i>Protophyta</i> and many -<i>Protozoa</i>, as well as between such <i>Protophyta</i> and the -lowest kinds of <i>Metazoa</i>. A recent statement that certain amœbæ, -made green by contained chlorophyll, continue to grow and multiply -after they have consumed what nutritive matter may be at hand, is in -harmony with various facts alleged of other <i>Protozoa</i>—various -other kinds of <i>Rhizopods</i>, various <i>Heliozoa</i>, numerous -ciliated and flagellated <i>Infusoria</i>. Among <i>Metazoa</i> -the like association occurs in one of the sponges, in the <i>Hydra -viridis</i>, in various turbellarians, in a rotifer, and even in two -molluscs. In these cases the partnership between the vegetal cells and -the animal cells (existing either as units or as an organized group -such as a polype), is a partnership which, as before, profits each of -the partners—an inference supported by the fact that <i>Metazoa</i> -containing these algoid cells usually place themselves where the light -falls upon them, and can therefore further the production of the -carbo-hydrates which eventually become useful to the animal cells, -while these in some way reciprocate the benefit.</p> - -<p>Here, then, we have exchange of services between associated -plant-elements and animal-elements—a performance by them of different -organic functions for the benefit of the aggregate which they unite -to form. Hence, when these vegetal elements and animal elements -are separately embodied in plants and animals, which profit by -one another,<span class="pagenum" id="Page_401">[401]</span> we may still properly regard their respective lives -as mutually-dependent organic functions, as said in the preceding -section. We are enabled the better to see how the Earth’s Flora and -Fauna, which are respectively accumulators of motion and expenders of -motion, form mutually-dependent parts of a whole, and are in that sense -integrated. And we shall be prepared to see how all other relations -between organisms which make them subservient one to another, similarly -constitute elements in a general integration of the organic world.</p> - - -<p class="p2">§ 314<i>d</i>. Another form of mutual dependence and consequently of -integration is conspicuous—that which accompanied the progressive -increase of size in organisms of the higher classes. We have but to -contemplate the possibilities to see that life must necessarily have -commenced with minute forms, and that the progress to larger ones must -have been by small steps.</p> - -<p>For had creatures of appreciable sizes been the first to exist they -would inevitably have disappeared from lack of food. Having no resource -but to devour one another, they would quickly have brought life to an -end. There must have been smaller types serving as prey for larger -ones before these could continue to exist and to multiply: microbes -affording food to infusoria, infusoria affording food to such sized -creatures as the <i>Entomostraca</i>, these again supplying food to -small fishes, such as loch-trout, and these last yielding to larger -fishes masses sufficiently great for their needs: each higher grade -requiring lower grades of appropriate bulk. It needs but to ask what -would become of tigers if there were no mammals larger than mice, -to see that the animal world is a linked assemblage, of which the -connected members stand within certain ratios of mass; and that during -the evolution of higher and larger types the linking of grades has -become closer.</p> - -<p>That among plants considered as an aggregate relations of like kind, -though far less distinct ones, have all along<span class="pagenum" id="Page_402">[402]</span> been growing may be -reasonably concluded. In a world peopled only by microscopic types -there could not have existed the conditions needful for large trees. -Gradual disintegration of rock-surfaces, partly effected by physical -agencies and partly by low forms of plants, had to prepare the way for -superior plants. The production of sufficient soil by mineralogical -decay as well as by the decay of organisms, plant and animal, may be -regarded as having been a preliminary to larger plant-growth; and -though at present the dependence is far less close than that among -animals, yet the benefits yielded to metaphytes by the decomposing -actions carried on by protophytes, as well as those carried on by -microbes permeating the soil, imply a continued general interdependence -throughout the aggregate of plant-forms, apart from more special -interdependences. And then along with this indebtedness of the greater -plants to the smaller during the process of evolution, there must be -named that indebtedness of plant-life to animal-life which Mr. Darwin -has shown in his book on the agency of worms as producers of mould.</p> - - -<p class="p2">§ 314<i>e</i>. Services of one to another, and consequent unions, of -more special kinds are infinitely varied, alike within each kingdom -and between the two kingdoms. I refer to those seen in parasitism, -commensalism, and other forms of association. While they do not -conduce to unions of the kind thus far considered, these nevertheless -constitute innumerable links whereby the lives of organisms, plant and -animal, are tied together; sometimes for the advantage of both but in -most cases for the benefit of one to the injury of the other.</p> - -<p>Among plants the degrees of dependence are various. Unable to raise -themselves into the air and light, some climb, like the ivy, by -modified rootlets, or spirally coil themselves, or hang by tendrils. -Others there are which gradually strangle the trees they embrace, or -which, like lichens in damp climates, festooning the smaller trees, -by and by cause<span class="pagenum" id="Page_403">[403]</span> their decay. Of higher types of epiphytes which -use trees only to gain elevation, the orchids may be instanced. -And then we have plants which, like the mistletoe, fix themselves -on the bark of their hosts, utilizing them partly for purposes of -elevation and partly by appropriation of their juices. After these -may be named those extreme cases in which the parasitic plants, -ceasing to have any chlorophyll-bearing leaves, live wholly on the -juices of the invaded plants. At home the common dodder, and in the -tropics the <i>Rafflesiaceæ</i>, belong to this group. There must be -added the numerous forms of minute fungi which in like manner thrive -at the expense of the plants they infest. In all these cases the -interdependence is one-sided, though, as we shall presently see, while -detrimental to one of the two concerned, it is not always detrimental -to the organic world as a whole.</p> - -<p>That utilization of one by another among animals which causes immediate -death, is familiar enough in the relations between carnivores and -herbivores. Almost as familiar are those seen in parasitism. Less -familiar are those seen in commensalism; and the least familiar are -those which show us exchange of services. Among these last—the -mutually-beneficial relations—that between the crocodile and the -bird which picks parasites out of its teeth is a striking one; and no -less so is that of the pique-gouffe, an African bird which pierces -the tumour on a buffalo’s back that incloses a parasite. Then of -another kind we have the connexion between aphides and ants: the -one profiting by being carried to better pastures and the other by -increased saccharine excretion. Next comes the class of messmates, -the connexions between some of which are relatively innocent, as -witness the Sea-anemone which settles itself on the shell occupied -by a Hermit-crab, or as witness the <i>Remora</i> fixed on a shark’s -skin. Less innocent is the relation under which one of the two seizes -a share of the food obtained by the other, like the annelid which -insinuates itself between the Hermit-crab and the whelk-shell it -inhabits, or like the small fishes<span class="pagenum" id="Page_404">[404]</span> inhabiting certain <i>Medusæ</i>, -or those which nestle in the branchial sac of the <i>Lophius</i>. After -these may be named the less injurious forms of parasites proper—those -which, distinguished as <i>Epizoa</i>, fix themselves on the skins of -their hosts, permanently or temporarily, such as, of the one kind, the -<i>Lernæa</i> on fishes, and of the other kind the Tick on mammals -and birds. Then there come the other class of parasites, most of them -highly injurious, distinguished as <i>Entozoa</i>, living within the -bodies of their hosts, now in parts of their alimentary canals, now on -other of their mucous surfaces, and now in various of their organs: -these last two groups being so numerous in their kinds that there are -commonly more species than one proper to each larger animal. One stage -further in the complication meets us in the parasites upon parasites.</p> - -<p>But now the general fact, to which these brief indications are -introductory, is that the use made of one organism by another has been -ever widening and becoming more involved. Among plants utilization of -the larger by the smaller—of trees by epiphytes and parasites—must -have arisen since the times when the larger came into existence—times -relatively late in the course of organic evolution. Moreover most -of the plants which utilize others, either by climbing up them or -settling themselves high up on their stems or sucking their juices, -are phænogams, and the plants they utilize are also phænogams; so -that these innumerable interdependences must have been established -since the phænogamic type has become so predominant in respect of -both size and kind. Similarly among animals. Though there are many -parasites belonging, like the Trematodes, to very low classes, there -are many which belong to the <i>Arthropoda</i>, and, being degraded -forms of that class, must have come into existence after Arthropods -of considerable structure had been evolved. Again, a large part -of the animals infested by <i>Epizoa</i> and <i>Entozoa</i> are -vertebrates—many of the highest types; and as these are relatively -modern all this parasitism must be of<span class="pagenum" id="Page_405">[405]</span> late date. So, too, of -much commensalism and many mutually-beneficial associations. The -reciprocal services of ants and aphides must have originated since the -<i>Hymenoptera</i> and <i>Hemiptera</i> became established types, and -since the days when certain insects of the ant-type had become social, -and since the days when aphides had become degraded members of their -order: both dates being relatively recent. And still more recent must -have been the commensalism between the ants and the many species of -other insects which inhabit their nests.</p> - -<p>Leaving out relations of the kinds just named, it seems that down from -those between carnivores and their prey to those between lice and their -hosts, such relations profit one of the two species concerned and -injure the other, and that there the matter ends. But it does not end -there; for that multiplication of effects to which people are usually -blind, brings about changes which, as hinted above, though injurious -to the individual are beneficial to the species, and which, when not -beneficial to the species, are often beneficial to the aggregate of -species.</p> - -<p>Even where animals of one class live by devouring animals of another -class, we see, on looking beyond the immediate results, certain remote -results that are advantageous. In the first place the process is -one by which inferior individuals—the least agile, swift, strong, -or sagacious—are picked out and prevented from leaving posterity -and lowering the average quality of their kind. At the same time -individuals made feeble by injury or old age, are among those to be -killed and saved from suffering prolonged pains: the evils of death by -disease and starvation being thus limited to the predatory animals, -relatively small in their numbers. Meanwhile a check is put on undue -multiplication. Where a tract of country has been overrun by rabbits, -weasels, thriving on the abundant supply of food, presently become -numerous enough to bring the population of rabbits within moderate -limits; and by doing this benefit not only all those kinds of<span class="pagenum" id="Page_406">[406]</span> plants -which are being eaten down, and all those other animals which live on -such plants, but also the rabbits themselves; since, increasing beyond -the means of subsistence, a large part of them would, if not killed, -die of hunger. Between aphides and lady-birds we see a connexion -of like nature: great increase of the first yielding abundant food -to larvæ of the second, ending after a season or so in swarms of -lady-birds, and consequently of their larvæ, whereby the aphides, -immensely diminished, cease so greatly to injure various plants and -the animals dependent on them. Even minute parasites, by the evils -they inflict on one species, profit others: instance the enormous -destruction of flies which a microscopic fungus caused a few years -ago—a destruction which relieved not only man but all the animals -which flies irritate: often so much as to hinder them from feeding. -Such instances remind us how numerous are the bonds by which the lives -of organisms are tied together.</p> - - -<p class="p2">§ 314<i>f</i>. I have reserved to the last the clearest and most -striking illustration of this progressing integration throughout the -organic world. I refer to the mutually-beneficial relations established -between plants and animals through the agency of flowers and insects.</p> - -<p>Everyone nowadays has been made familiar with the process of -plant-fertilization, and knows that (leaving out of consideration -plants fertilized by wind-borne pollen) the ability to bear seed -depends largely on the aid given by bees, butterflies, and moths. The -exchange of services has been growing ever more various and complicated -during long past periods. We have the acquirement by flowers of bright -colours serving to guide these insects to places where honey is to be -found; and we have their perfumes, also serving for guidance. Then we -have the many different arrangements, often complicated, by which the -visiting insects are obliged to carry away pollen and dust with it the -stigmas of flowers on which they subsequently settle: thus effecting -crossfertilization.<span class="pagenum" id="Page_407">[407]</span> <i>Pari passu</i> have gone on insect-developments -made possible by these arrangements and furthering them. Especially -must be named the modification of certain <i>Hymenoptera</i> into -honey-storing bees: the implication being that the entire economy -established by these social insects has been sequent on the growth -of this system of reciprocal benefits. And then, just instancing the -dependence between a particular flower having a long tubular corolla, -and a particular moth having an appropriately long proboscis, it -suffices to say that innumerable specialities of this general relation -everywhere multiply the links by which the vegetal world and the animal -world are here connected. That the effects of the connections tell -largely on the prosperity of both, is suggested by some instances Mr. -Darwin gives, and by a statement recently made in the United States, -by Dr. L. O. Howard, that the greater fostering of bees would much -increase certain of the crops.</p> - -<p>But now observe the broad fact to which these few details concerning -plant-fertilization are introductory. All these general and special -relations between plants and animals have arisen since the phænogamic -type came into existence—have, indeed, arisen since the higher members -of that type, the Angiosperms, have appeared; for the Gymnosperms do -not play any part in this intercommunion. But so far as we can judge -of present results of geologic explorations, there were no Angiosperms -during the Eozoic and Paleozoic periods. So that this class of -connexions between animals and vegetals must have been established -since carboniferous times—a period long, indeed, but far shorter than -that which organic evolution at large has occupied.</p> - - -<p class="p2">§ 314<i>g</i>. I have but just touched on some salient parts of a -subject, immense in extent and extremely involved, which it would take -a volume to set forth adequately. Enough has been said, however, to -indicate the truth which it is the purpose of the chapter to bring into -view and emphasize—<span class="pagenum" id="Page_408">[408]</span> the truth that both of the two great laws of -evolution are exemplified in the organic world as a whole, as they are -exemplified in every organism, and in all other things.</p> - -<p>The reader has long since become familiar with the generalization that -while Evolution is a change from the homogeneous to the heterogeneous, -it is also a change from the incoherent to the coherent; and this -change from the incoherent to the coherent has been above exhibited -as going on even throughout that vast assemblage of organisms, plant -and animal, which cover the Earth’s surface. In what we are obliged -to conceive as the earliest stage, when the most minute types of life -alone existed, the aggregate of living things was at once homogeneous -and incoherent. In the course of epochs immeasurable in duration, this -uniform aggregate of beings has been becoming more multiform. And now -we see that instead of forms of life everywhere without the slightest -union caused by mutual dependence, there have slowly arisen forms of -life among which mutual dependences have entailed vital connexions -correspondingly marked. Along with progressing differentiation there -has ever been progressing integration. So that we may recognize -something like a growing life of the entire aggregate of organisms in -addition to the lives of individual organisms—an exchange of services -among parts enhancing the life of the whole.</p> - -<p>In this final generalization the law of Evolution is manifested under -its most transcendental form.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_409">[409]</span></p> - -<h2>PART VI.<br /> -<span class="subhed">LAWS OF MULTIPLICATION.</span></h2></div> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_411">[411]</span></p> - -<h3>CHAPTER I.<br /> -<span class="subhed1">THE FACTORS.<a id="FNanchor_52" href="#Footnote_52" class="fnanchor">[52]</a></span></h3></div> - - -<p>§ 315. If organisms have been evolved, their respective powers of -multiplication must have been determined by natural causes. Grant that -the countless specialities of structure and function in plants and -animals, have arisen from the actions and reactions between them and -their environments, continued from generation to generation; and it -follows that from these actions and reactions have also arisen those -countless degrees of fertility which we see among them. As in all other -respects an adaptation of each species to its conditions of existence -is directly or indirectly brought about; so must there be directly or -indirectly brought about an adaptation of its reproductive activity to -its conditions of existence.</p> - -<p>We may expect to find, too, that permanent and temporary<span class="pagenum" id="Page_412">[412]</span> differences -of fertility have the same general interpretation. If the small -variations of structure and function that arise within the limits -of each species, are due to actions like those which, by their -long-accumulating effects, have produced the immense contrasts between -the various types; we may conclude that, similarly, the actions to -which changes in the rate of multiplication of each species are due, -also produce, in great periods of time, the enormous differences -between the rates of multiplication of different species.</p> - -<p>Before inquiring in what ways the rapidities of increase are adjusted -to the requirements, both temporary and permanent, it will be needful -to look at the factors. Let us set down first those which belong to the -environment, and then those which belong to the organism.</p> - - -<p class="p2">§ 316. Every living aggregate being one of which the inner actions are -adjusted to balance outer actions, it follows that the maintenance of -its moving equilibrium depends on its exposure to the right amounts of -these actions. Its moving equilibrium may be overturned if one of these -actions is either too great or too small in amount; and it may be so -overturned either by excess or defect of some inorganic agency in its -environment, or by excess or defect of some organic agency.</p> - -<p>Thus a plant, constitutionally fitted to a certain warmth and -humidity, is killed by extremes of temperature, as well as by extremes -of drought and moisture. It may dwindle away from want of soil, or -die from the presence of too great or too small a quantity of some -mineral substance which the soil supplies to it. In like manner, every -animal can maintain the balance of its functions so long only as the -environment adds to or deducts from its heat at rates not exceeding -definite limits. Water, too, must be accessible in amount sufficient to -compensate loss. If the parched air is rapidly abstracting its liquid -which there is no pool or river to restore, its functions cease; and -if it is an aquatic creature,<span class="pagenum" id="Page_413">[413]</span> drought may kill it either by drying up -its medium or by giving it a medium inadequately aërated. Thus each -organism, adjusted to a certain average in the actions of its inorganic -environment, or rather, we should say, adjusted to certain moderate -deviations from this average, is destroyed by extreme deviations. So, -too, is it with the environing organic agencies. Among plants, only -the parasitic kinds and those united by symbiosis (as well as a few -innocent “lodgers”) depend for their individual preservation on the -presence of certain other organisms (though the presence of certain -other organisms is needful to most plants for the preservation of the -race by aiding fertilization). Here, for the continuance of individual -life, particular organisms must be absent or not very numerous—beasts -that browse, caterpillars that devour leaves, aphides that suck juices. -Among animals, however, the maintenance of the functional balance is -both positively and negatively dependent on the amounts of surrounding -organic agents. There must be an accessible sufficiency of the plants -or animals serving for food; and of organisms that are predatory or -parasitic or otherwise detrimental, the number must not pass a certain -limit.</p> - -<p>This dependence of the moving equilibrium in every individual organism -on an adjustment of its forces to the forces of the environment, and -the overthrow of this equilibrium by failure of the adjustment, is -comprehensive of all cases. At first sight it does not seem to include -what we call natural death; but only death by violence, or starvation, -or cold, or drought. But in reality natural death, no less than every -other kind of death, is caused by the failure to meet some outer action -by a proportionate inner action. The apparent difference is due to -the fact that in old age, when the quantity of force evolved in the -organism gradually diminishes, the momentum of the functions becomes -step by step less, and the variations of the external forces relatively -greater; until there finally comes an occasion when some quite moderate -deviation from that average to which the<span class="pagenum" id="Page_414">[414]</span> feeble moving equilibrium is -adjusted, produces in it a fatal perturbation.</p> - - -<p class="p2">§ 317. The individuals of every species being thus dependent on certain -environing actions; and severally having their moving equilibria sooner -or later overthrown by one or other of these environing actions; we -have next to consider in what ways the environing actions are so met -as to prevent extinction of the species. There are two essentially -different ways. There may be in each individual a small or great -ability to adjust itself to variations of the agencies around it and to -a small or great number of such varying agencies—there may be little -or much power of preserving the balance of the functions. And there may -be much or little power of producing new individuals to replace those -whose moving equilibria have been overthrown. A few facts must be set -down to enforce these abstract statements.</p> - -<p>There are both active and passive adaptations by which organisms -are enabled to survive adverse influences. Plants show us but few -active adaptations: that of the Pitcher-plant and those of the -reproductive parts of some flowers (which do not, however, conduce to -self-preservation) are exceptional instances. But plants have various -passive adaptations; as thorns, stinging hairs, poisonous and acrid -juices, repugnant odours, and the woolliness or toughness that makes -their leaves uneatable. Animals exhibit far more numerous adjustments, -both passive and active. In some cases they survive desiccation, they -hybernate, they acquire thicker clothing, and so are fitted to bear -unfavourable inorganic actions; and they are in many cases fitted -passively to meet the adverse actions of other organisms, by bearing -spines or armour or shells, by simulating neighbouring objects in -colour or form or both, by emitting disagreeable odours, or by having -disgusting tastes. In still more numerous ways they actively contend -with unfavourable conditions. Against the seasons they guard by storing -up food, by secreting themselves in<span class="pagenum" id="Page_415">[415]</span> crevices, or by forming burrows -and nests. They save themselves from enemies by developed powers of -locomotion, taking the shape of swiftness or agility or aptitude for -changing their media; by their strength either alone or aided by -weapons; lastly by their intelligence, without which, indeed, their -other superiorities would avail them little. And then these various -active powers serving for defence, become, in other cases, the powers -that enable animals to aggress, and to preserve their lives by the -success of their aggressions.</p> - -<p>The second process by which extinction is prevented—the formation of -new individuals to replace the individuals destroyed—is carried on, -as described in the chapter on “Genesis,” by two methods, the sexual -and the asexual. Plants multiply by spontaneous fission, by gemmation, -by proliferation, and by the evolution of young ones from detached -cells and scales and leaves; and they also multiply by the casting -off of spores and sporangia and seeds. In like manner among animals, -there are varied kinds of agamogenesis, from spontaneous fission up to -parthenogenesis, all of them conducing to rapid increase of numbers; -and we have the more familiar process of gamogenesis, also carried -on in a great variety of ways. This formation of new individuals to -replace the old, is, however, inadequately conceived if we contemplate -only the number born or detached on each occasion. There are four -factors, all variable, on which the rate of multiplication depends. -The first is the age at which reproduction commences; the second is -the frequency with which broods are produced; the third is the number -contained in each brood; and the fourth is the length of time during -which the bringing forth of broods continues. There must be taken into -account a further element—the amount of aid given by the parent to -each germ in the shape of stored-up nutriment, continuous feeding, -warmth, protection, &c.: on which amount of aid, varying between -immensely wide limits, depends the number of<span class="pagenum" id="Page_416">[416]</span> the new individuals -that survive long enough to replace the old, and perform the same -reproductive process.</p> - -<p>Thus, regarding every living organism as having a moving equilibrium -dependent on environing forces, but ever liable to be overthrown by -irregularities in those forces, and always so overthrown sooner or -later; we see that each species of organism can be maintained only -by the generation of new individuals with a certain rapidity, and by -helping them more or less fully to establish their moving equilibria.</p> - - -<p class="p2">§ 318. Such are the factors with which we are here concerned. I have -presented them in abstract shapes for the purpose of showing how they -are expressible in general terms of force—how they stand related to -the ultimate laws of re-distribution of matter and motion.</p> - -<p>For the purposes of the argument now to follow, we may, however, -conveniently deal with these factors under a more familiar guise. -Ignoring their other aspects, we may class the factors which affect -each race of organisms as forming two conflicting sets. On the one -hand, by what we call natural death, by enemies, by lack of food, by -atmospheric changes, &c., the race is constantly being destroyed. On -the other hand, partly by the endurance, the strength, the swiftness, -and the sagacity of its members, and partly by their fertility, it -is constantly being maintained. These conflicting sets of factors -may be generalized as—the forces destructive of race and the forces -preservative of race. So generalizing them, let us ask what are the -necessary implications.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_417">[417]</span></p> - -<h3>CHAPTER II.<br /> -<span class="subhed1"><i>À PRIORI</i> PRINCIPLE.</span></h3></div> - - -<p>§ 319. The number of a species must at any time be either decreasing -or stationary or increasing. If, generation after generation, its -members die faster than others are born, the species must dwindle -and finally disappear. If its rate of multiplication is equal to its -rate of mortality, there can be no numerical change in it. And if the -deductions by death are fewer than the additions by birth, the species -must become more abundant. These we may safely set down as necessities. -The forces destructive of race must be either greater than the forces -preservative of race, or equal to them, or less than them; and there -cannot but result these effects on number.</p> - -<p>We are here concerned only with races that continue to exist; and may -therefore leave out of consideration those in which the destructive -forces, remaining permanently in excess of the preservative forces, -cause extinction. Practically, too, we may exclude the stationary -condition; for the chances are infinity to one against the maintenance -of a permanent equality between the births and the deaths. Hence, our -inquiry resolves itself into this:—In races that continue to exist, -what laws of numerical variation result from these variable conflicting -forces, which are respectively destructive of race and preservative of -race?</p> - - -<p class="p2">§ 320. Clearly if the forces destructive of race, when once<span class="pagenum" id="Page_418">[418]</span> in excess, -had nothing to prevent them from remaining in excess, the race would -disappear; and clearly if the forces preservative of race, when once in -excess, had nothing to prevent them from remaining in excess, the race -would go on increasing to infinity. In the absence of any compensating -actions, the only possible avoidance of these opposite extremes would -be an unstable equilibrium between the conflicting forces, resulting -in a perfectly constant number of the species: a state which we know -does not exist, and against the existence of which the probabilities -are, as already said, infinite. It follows, then, that as in every -continuously-existing species, neither of the two conflicting sets -of forces remains permanently in excess; there must be some way of -stopping that excess of the one or the other which is ever occurring.</p> - -<p>How is this done? Should any one allege, in conformity with the old -method of interpretation, that there is in each case a providential -interposition to rectify the disturbed balance, he commits himself to -the supposition that of the millions of species inhabiting the Earth, -each one is yearly regulated in its degree of fertility by a miracle; -since in no two years do the forces which foster, or the forces which -check, each species, remain the same; and therefore, in no two years -is there required the same fertility to balance the mortality. Few if -any will say that God continually alters the reproductive activity -of every parasitic fungus and every Tape-worm or <i>Trichina</i>, -so as to prevent its extinction or undue multiplication; which they -must say if they adopt the hypothesis of supernatural adjustment. And -in the absence of this hypothesis there remains only one other. The -alternative possibility is, that the balance of the preservative and -destructive forces is self-sustaining—is of the kind distinguished as -a stable equilibrium: an equilibrium such that any excess of one of -the forces at work, itself generates, by the deviation it produces, -certain counter-forces which eventually out-balance it, and initiate an -opposite deviation.<span class="pagenum" id="Page_419">[419]</span> Let us consider how, in the case before us, such a -stable equilibrium must be constituted.</p> - - -<p class="p2">§ 321. When a season favourable to it, or a diminution of creatures -detrimental to it, causes any species to become more numerous than -usual, an immediate increase of certain destructive influences takes -place. If it be a plant, the supposed greater abundance itself implies -fuller occupation of the places available for growth—an occupation -which, leaving fewer such places as the multiplication goes on, -becomes a check on further multiplication—itself causes a greater -mortality of seeds that fail to root themselves. And afterwards, in -addition to this passive resistance to continued increase, there comes -an active resistance: the creatures which thrive at the expense of -the species—the larvae, the birds, the herbivores—increase too. If -it be an animal that has grown more numerous, then, unless by some -exceptional coincidence a simultaneous and proportionate addition to -the animals or plants serving for food has occurred, there must result -a relative scarcity of food. Enemies, too, be they beasts of prey or -be they parasites, must quickly begin to multiply. Hence, each kind -of organism, previously existing in something like its normal number, -cannot have its number raised without a rise of the destructive forces, -negative and positive, quickly commencing. Both negative and positive -destructive forces must augment until this increase of the species is -arrested. The competition for places on which to grow, if the species -be vegetal, or for food if it be animal, must become more intense as -the over-peopling of the habitat progresses; until there is reached -the limit at which the mortality equals the reproduction. And as, at -the same time, enemies will multiply with a rapidity which soon brings -them abreast of the augmented supply of prey, the positive restraint -they exert will help to bring about an earlier arrest of the expansion -than pressure of population alone would cause. One more inference may -be<span class="pagenum" id="Page_420">[420]</span> drawn. Had the species to meet no repressing influence save that -negative one of relatively-diminished space or relatively-diminished -food-supply, the cause leading to its increase might carry it up -to the limit set by this, and there leave it: its enlarged number -might be permanent. But the positive repressing influence that has -been called into existence, will prevent this. For the increase of -enemies, commencing, as it must, after the increase of the species, -and advancing in geometrical progression until it is itself checked -in like manner, will end in an excess of enemies. Whereupon must -result a mortality of the species greater than its multiplication—a -decrease which will continue until its habitat is under-peopled, its -unduly-numerous enemies decimated by starvation, and the destroying -agencies reduced to a minimum. Whence will follow another increase.</p> - -<p>Thus, as before indicated (<i>First Prin.</i> §§ 85, 173), there is -here, as wherever antagonistic forces are in action, an alternate -predominance of each, causing a rhythmical movement—a rhythmical -movement which constitutes a moving equilibrium in those cases where -the forces are not dissipated with appreciable rapidity, or are -re-supplied as fast as they are dissipated. While, therefore, on the -one hand, we see that the continued existence of a species necessarily -implies some action by which the destructive and preservative forces -are self-adjusted; we see, on the other hand, that such an action is an -inevitable consequence of the universal process of equilibration.</p> - - -<p class="p2">§322. Is this the sole equilibration which must exist? Clearly not. -The temporary compensating adjustments of multiplication to mortality -in each species, are but introductory to the permanent compensating -adjustments of multiplication to mortality among species in general. -The above reasoning would hold just as it now does, were all species -equally prolific and all equally short-lived. It yields no<span class="pagenum" id="Page_421">[421]</span> answer -to the inquiries—why do their fertilities differ so enormously, -or why do their mortalities differ so enormously? and how is the -general fertility adapted to the general mortality in each? The -balancing process we have contemplated can go on only within moderate -limits—must fail entirely in the absence of a due proportion -between the ordinary birth-rate and the ordinary death-rate. If the -reproduction of mice proceeded as slowly as the reproduction of men, -mice would be extinct before a new generation could arise: even did -their natural lives extend to fifteen or sixteen years, it would still -be extremely improbable that any would for so long survive all the -dangers they are exposed to. Conversely, did oxen propagate as fast -as infusoria, the race would die of starvation in a week. Hence, the -minor adjustment of varying multiplication to varying mortality in each -species, implies some major adjustment of average multiplication to -average mortality. What must this adjustment be?</p> - -<p>We have already seen that the forces preservative of race are -two—ability in each member of the race to preserve itself, and ability -to produce other members—power to maintain individual life, and power -to generate the species. These must vary inversely. When, from lowness -of organization, the ability to contend with external dangers is -small, there must be great fertility to compensate for the consequent -mortality; otherwise the race must die out. When, on the contrary, high -endowments give much capacity of self-preservation, a correspondingly -low degree of fertility is requisite. Given the dangers to be met as a -constant quantity; then as the ability to meet them must be a constant -quantity too; and as this is made up of the two factors, power to -maintain individual life and power to multiply, these cannot do other -than vary inversely: one must decrease as the other increases.</p> - -<p>It needs but to conceive the results of nonconformity to this law, -to see that every species must either conform to it or cease to -exist. Suppose, first, a species whose individuals,<span class="pagenum" id="Page_422">[422]</span> having but small -self-preservative powers, are rapidly destroyed, to be at the same -time without reproductive powers proportionately great. The defect -of fertility, if extreme, will result in the death of one generation -before another has grown up. If less extreme, it will entail a -scarcity such that in the next generation sexual congress will be too -infrequent to maintain even the small number which remains; and the -race will dwindle with increasing rapidity. If still less extreme, the -consequent degree of sparseness, while not so great as to prevent an -adequate number of procreative unions, will be so great as to render -special food abundant and special enemies few—will thus diminish -the destructive forces so much that the self-preservative forces -will become <i>relatively</i> great: so great, relatively, that when -combined with the small ability to propagate the species, they will -suffice to balance the small destructive forces. Suppose, next, a -species whose individuals have high powers of self-preservation, while -they have powers of multiplication much beyond what is needful. The -excess of fertility, if extreme, will cause sudden extinction of the -species by starvation. If less extreme, it must produce a permanent -increase in the number of the species; and this, followed by intenser -competition for food and augmented number of enemies, will involve -such an increase of the dangers to individual life, that the great -self-preserving powers of the individuals will not be more than -sufficient to cope with them. That is to say, if the fertility is -relatively too great, then the ability to maintain individual life -inevitably becomes smaller, <i>relatively</i> to the requirements; and -the inverse proportion is thus established.</p> - -<p>So that when, from comparing the different states of the same species, -we go on to compare the states of different species, we see that there -is an analogous adjustment—analogous in the sense that great mortality -is associated with great multiplication, and small mortality with small -multiplication. And we see that the unlikeness of the cases consists<span class="pagenum" id="Page_423">[423]</span> -merely in this, that what is a temporary relation in the one is a -permanent relation in the other.</p> - - -<p class="p2">§ 323. For the moment it does not concern us to inquire what is the -origin of this permanent relation. That which we have now to note, is -simply that in some way or other there must be established an inverse -proportion between the power to sustain individual life and the power -to produce new individuals. Whether or not this permanent relation is -self-adjusting in long periods of time, as the temporary relation is -self-adjusting in short periods of time, is a separate question. The -purpose of this chapter is fulfilled by showing that such a permanent -relation must exist.</p> - -<p>But having recognized the <i>à priori</i> principle that in races -which continuously survive, the forces destructive of race must be -equilibrated by the forces preservative of race; and that, supposing -these are constant, there must be an inverse proportion between -self-preservation and race-preservation; we may go on to inquire how -this relation, necessary in theory, arises in fact. Leaving out the -untenable hypothesis of a supernatural pre-adjustment, we have to ask -in what way an adjustment comes about as a result of Evolution. Is it -due to the survival of varieties in which the proportion of fertility -to mortality happens to be the best? Or is the fertility adapted to the -mortality in a more direct way? To these questions let us now address -ourselves.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_424">[424]</span></p> - -<h3>CHAPTER III.<br /> -<span class="subhed1">OBVERSE <i>À PRIORI</i> PRINCIPLE.</span></h3></div> - - -<p>§ 324. When dealing with its phenomena inductively, we saw that however -it may be carried on, Genesis “is a process of negative or positive -disintegration; and is thus essentially opposed to that process of -integration which is the primary process in individual evolution.” -(<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect76">§ 76</a>.) Each new individual, whether separated as a germ or in some -more-developed form, is a deduction from the mass of a pre-existing -individual or of two pre-existing individuals. Whatever nutritive -matter is stored-up along with the germ, if it be deposited in the -shape of an egg, is so much nutritive matter lost to the parent. -No drop of blood can be absorbed by the fœtus, nor any draught of -milk sucked by the young when born, without taking from the mother -tissue-forming and force-evolving materials to an equivalent amount. -And all subsequent supplies given to progeny, if they are nurtured, -involve, to a parent or parents, so much waste in exertion which does -not bring its return in assimilated food.</p> - -<p>Conversely, the continued aggregation of materials into one organism, -renders impossible the formation of other organisms out of those -materials. As much assimilated food as is united into a single whole, -is so much assimilated food withheld from a plurality of wholes which -might else have been produced. Given the absorbed nutriment as a -constant quantity, and the longer the building of it up into a concrete -shape goes on, the longer must be postponed any building<span class="pagenum" id="Page_425">[425]</span> of it up into -discrete shapes. And, similarly, the larger the proportion of matter -consumed in the functional actions of parents, the smaller must be the -proportion of matter which can remain to establish and support the -functional actions of offspring.</p> - -<p>Though the necessity of these universal relations is tolerably obvious -as thus stated generally, it will be useful to dwell for a brief space -on their leading aspects.</p> - - -<p class="p2">§ 325. That disintegration which constitutes genesis, may be such as -to disperse entirely the aggregate which integration has previously -produced—the parent may dissolve wholly into progeny. This dissolution -of each aggregate into two or many aggregates, may occur at very short -intervals, in which case the bulk attained can be but extremely small; -or it may occur at longer intervals, in which case a larger bulk may be -attained.</p> - -<p>Instead of quickly losing its own individuality in the individualities -of its offspring, each member of the race may, after growing for a -time, have portions of its substance begin to develop into the parental -shape and presently detach themselves; and the parent, maintaining its -own identity, may continue indefinitely so to produce young ones. But -clearly, the earlier it commences doing this, and the more rapidly it -does it, the sooner must the increase of its own bulk be stopped.</p> - -<p>Or again, growth and development continuing for a long period without -any deduction of materials, an individual of considerable size and -organization may result; and then the abstraction of substance for -the formation of new individuals, or rather the eggs of them, may -be so great that as soon as the eggs are laid the parent dies of -exhaustion—dies, that is, from an excessive loss of the nutritive -matters needed for its own activities.<a id="FNanchor_53" href="#Footnote_53" class="fnanchor">[53]</a></p> - -<p><span class="pagenum" id="Page_426">[426]</span></p> - -<p>Once more, the deduction of materials for the propagation of the -species may be postponed long enough to allow of great bulk and complex -structure being attained. The procreative subtraction then setting -in, while it checks and presently stops growth, may be so moderate -as to leave vital capital sufficient to carry on the activities of -the parent; may go on as long as parental vigour suffices to furnish, -without fatal result, the materials needed to produce young ones; and -may cease when such a surplus cannot be supplied, leaving the parental -life to continue.</p> - - -<p class="p2">§ 326. The opposite side of this antagonism has also several aspects. -Progress of organic evolution may be shown in increased bulk, in -increased structure, in increased amount or variety of action, or -in combinations of these; and under any of its forms this carrying -higher of each individuality, implies a correlative retardation in the -establishment of new individualities.</p> - -<p>Other things equal, every normal addition to the bulk of an organism -is an augmentation of its life.<a id="FNanchor_54" href="#Footnote_54" class="fnanchor">[54]</a> Besides being an advance in -integration, it implies a greater total of activities gone through in -the assimilation of materials; and it implies, thereafter, a greater -total of the vital changes taking place from moment to moment in all -parts of the enlarged mass. Moreover, while increased size is thus, -in so far, the expression of increased life, it is also, where the -organism is active, the expression of increased ability to maintain -life—increased strength. Aggregation of substance is almost the only -mode in which self-preserving power is shown among the lowest types; -and even among the highest, sustaining the body in its integrity -is that in which self-preservation fundamentally consists—is the -end which the widest intelligence is indirectly<span class="pagenum" id="Page_427">[427]</span> made to subserve. -While, on the one hand, the increase of tissue constituting growth is -conservative both in essence and in result; on the other hand, decrease -of tissue, either from injury, disease, or old age, is in both essence -and result the reverse. And if so, every addition to individual life -thus implied, necessarily delays or diminishes the casting off of -matter to form new individuals.</p> - -<p>Other things equal, too, a greater degree of organization involves -a smaller degree of that disorganization shown by the separation -of reproductive gemmæ and germs. Detachment of a living portion or -portions from what was previously a living whole, is a ceasing of -co-ordination; and is therefore essentially at variance with that -establishment of greater co-ordination which is achieved by structural -development. In the extreme cases where a living mass is continually -dividing and subdividing, it is manifest that there cannot arise -much physiological division of labour; since progress towards mutual -dependence of parts is prevented by the parts becoming independent. -Contrariwise, it is equally clear that in proportion as the -physiological division of labour is carried far, the separative process -must be localized in some comparatively small portion of the organism, -where it may go on without affecting the general structure—must -become relatively subordinate. The advance that is shown by greater -heterogeneity, must be a hindrance to multiplication in another way. -For organization entails cost. That transfer and transformation -of materials implied by differentiation, can be effected only by -expenditure of force; and this supposes consumption of digested and -absorbed food, which might otherwise have gone to make new organisms, -or the germs of them. Hence, that individual evolution which consists -in progressive differentiation, as well as that which consists in -progressive integration, necessarily diminishes that species of -dissolution, general or local, which propagation of the race exhibits.</p> - -<p>In active organisms we have yet a further opposition<span class="pagenum" id="Page_428">[428]</span> between -self-maintenance and maintenance of the race. All motion, sensible and -insensible, generated by an animal for the preservation of its life, -is motion liberated from decomposed nutriment—nutriment which, if -not thus decomposed, would have been available for reproduction; or -rather—might have been replaced by nutriment fitted for reproductive -purposes, absorbed from other kinds of food. Hence, in proportion as -the activities increase—in proportion as, by its more varied, complex, -rapid, and vigorous actions, an animal gains power to support itself -and to cope with surrounding dangers, it must lose power to propagate.</p> - - -<p class="p2" id="sect327">§ 327. How may this antagonism be best expressed in a brief way? If -self-preservation displayed itself in the highest organisms, as it -does in the lowest, in little else but continuous growth; and if -race-preservation consisted always, as it does often, of nothing beyond -detachment of portions from the parental mass; then the antagonism -would be, throughout, the obviously-necessary one of integration and -disintegration. Maintenance of the individual and propagation of the -species, being respectively aggregative and separative, it would be -as self-evident that they vary inversely, as it is self-evident that -addition and subtraction undo one another. But though the simplest -types show us the opposition of self-maintenance and race-maintenance -almost wholly under this form; and though higher types, up to the most -complex, exhibit it to a great extent under this form; yet, as we have -just seen, this is not its only form. The total material monopolized -by the individual and withheld from the race, must be stated as the -quantity united to form its fabric, <i>plus</i> the quantity expended -in differentiating its fabric, <i>plus</i> the quantity expended in its -self-conserving actions. Similarly, the total material devoted to the -race at the expense of the individual, includes that which is directly -subtracted from the parent in the shape of egg or fœtus, <i>plus</i> -that which is directly subtracted in the shape of milk, <i>plus</i><span class="pagenum" id="Page_429">[429]</span> -that which is indirectly subtracted in the shape of matter consumed -in exertions for fostering the young. Hence this inverse variation -is not expressible in simple terms of aggregation and separation. As -we advance to more highly-evolved organisms, the total cost of an -individual becomes very much greater than is implied by the amount of -tissue composing it. So, too, the total cost of producing each new -individual becomes very much greater than that of its mere substance. -And it is between these two total costs that the antagonism exists.</p> - -<p>We may, indeed, reduce the antagonism to a form comprehensive of all -cases, if we consider it as existing between the sums of the forces, -latent and active, used for the two purposes. The molecules which make -up a plant or animal, have been formed by the absorption of forces -directly or indirectly derived from the Sun; and hence the quantity -of matter raised to the form called organic, which a plant or animal -presents, is equivalent to a certain amount of force. Another amount of -force is expressed by the totality of its differentiations. A further -amount of force is that dissipated in its actions. And in these three -amounts added together, we have the whole expense of the individual -life. So, too, the whole expense of establishing each new individual -includes—first the forces latent in the substance composing it when -born or hatched; second the forces latent in the prepared nutriment -afterwards supplied; and third the forces expended in feeding and -protecting it. These two sets of forces being taken from a common fund, -it is manifest that either set can increase only by decrease of the -other. If, of the force which the parent obtains from the environment, -much is consumed in its own life, little remains to be consumed in -producing other lives; and, conversely, if there is a great consumption -in producing other lives, it can only be where comparatively little is -reserved for parental life.</p> - -<p>Hence, then, Individuation and Genesis are necessarily antagonistic. -Grouping under the word Individuation all<span class="pagenum" id="Page_430">[430]</span> processes by which -individual life is completed and maintained; and enlarging the -meaning of the word Genesis so as to include all processes aiding -the formation and perfecting of new individuals; we see that the -two are fundamentally opposed. Assuming other things to remain the -same—assuming that environing conditions as to climate, food, -enemies, &c., continue constant; then, inevitably, every higher -degree of individual evolution is followed by a lower degree of -race-multiplication, and <i>vice versâ</i>. Progress in bulk, -complexity, or activity, involves retrogress in fertility; and progress -in fertility involves retrogress in bulk, complexity, or activity.</p> - -<p>This statement needs a slight qualification. For reasons to be -hereafter assigned, the relation described is never completely -maintained; and in the small departure from it, we shall find a -remarkable self-acting tendency to further the supremacy of the -most developed types. Here, however, this hint must suffice: -explanation would carry us too far out of our line of argument. For the -present it will not lead us astray if we regard this inverse variation -of Individuation and Genesis as exact.</p> - - -<p class="p2">§ 328. Thus, then, the condition which each race must fulfil if it is -to survive, is a condition which, in the nature of things, it ever -tends to fulfil. In the last chapter we saw that a species cannot be -maintained unless the power to preserve individual life and the power -to propagate other individuals vary inversely. And here we have seen -that, irrespective of an end to be subserved, these powers cannot do -other than vary inversely. On the one hand, given a certain totality -of destroying forces with which the species has to contend; and in -proportion as its members have severally but small ability to resist -these forces, it is requisite that they should have great ability to -form new individuals, and <i>vice versâ</i>. On the other hand, given -the quantity of force, absorbed as food or otherwise, which the species -can<span class="pagenum" id="Page_431">[431]</span> use to counterbalance these destroying forces; and in proportion -as much of it is expended in preserving the individual, little of it -can be reserved for producing new individuals, and <i>vice versâ</i>. -There is thus complete accordance between the requirements considered -under each aspect. The two necessities correspond.</p> - -<p>We might rest on these deductions and their several corollaries. -Without going further we might with safety assert the general truths -that, other things equal, advancing evolution must be accompanied -by declining fertility; and that, in the highest types, fertility -must still further decrease if evolution still further increases. -We might be sure that if, other things equal, the relations between -an organism and its environment become so changed as permanently -to diminish the difficulties of self-preservation, there will be a -permanent increase in the rate of multiplication; and, conversely, that -a decrease of fertility will result where altered circumstances make -self-preservation more laborious.</p> - -<p>But we need not content ourselves with these <i>à priori</i> -inferences. If they are true, there must be an agreement between -them and the observed facts. Let us see how far such an agreement is -traceable.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_432">[432]</span></p> - -<h3>CHAPTER IV.<br /> -<span class="subhed1">DIFFICULTIES OF INDUCTIVE VERIFICATION.</span></h3></div> - - -<p>§ 329. Were all species subject to the same kinds and amounts of -destructive forces, it would be easy, by comparing different species, -to test the inverse variation of Individuation and Genesis. Or if -either the power of self-preservation or the power of multiplication -were constant, there would be little difficulty in seeing how the -other changed as the destroying forces changed. But comparisons are -nearly always partially vitiated by some want of parity. Each factor, -besides being variable as a whole, is compounded of factors that are -severally variable. Not simply is the sum of the forces destructive of -race different in every case; and not simply are both sets of forces -preservative of race unlike in their totalities in every case; but -each is made up of actions that bear such changing proportions to one -another as to prevent any positive estimation of its amount.</p> - -<p>Before dealing with the facts as well as we can, it will be best to -glance at the chief difficulties; so that we may see the kind of -verification which is alone possible.</p> - - -<p class="p2">§ 330. Either absolutely, or relatively to any species, every -environment differs more or less from every other.</p> - -<p>There are the unlikenesses of media—air, water, earth, organic matter; -severally involving special resistances to movement, and special losses -of heat. There are the contrasts<span class="pagenum" id="Page_433">[433]</span> of climate: here great expenditure -for the maintenance of temperature is needed, and there very little; -in one zone an organism is supplied with abundant light all the year -round, and in another only for a few months; this region yields an -almost unfailing supply of water, while that entails the exertion of -travelling many miles every night for a draught.</p> - -<p>Permanent differences in the natures and distributions of aliment -greatly interfere with the comparisons. The Swallow goes through -more exertion than the Sparrow in securing a given weight of food; -but then their foods are dissimilar in nutritive qualities. There is -a want of parallelism between the circumstances of those herbivores -which live where the plains are annually covered for a time with rich -herbage, but afterwards become parched up, and of those inhabiting more -temperate regions. Insects whose larvæ feed on an abundant plant, as -do several of the genus <i>Vanessa</i> on the Nettle, have practically -an environment very unlike that of insects such as <i>Deilephila -Euphorbiæ</i>, whose larvæ feed on a comparatively rare plant—the -Sea-Spurge.</p> - -<p>Again, comparisons between creatures otherwise akin in their -constitutions and circumstances, are hindered by inequalities in their -relations to enemies. Two animals, of which one is predatory and has -no foes but parasites while the other is much pursued, cannot properly -be contrasted with a view to determining the influence of size or -complexity.</p> - -<p>Without multiplying instances, it will be clear enough then that the -aggregate of destructive actions, positive and negative, which each -species has to contend with, is so undefinable in the amounts and kinds -of its components, that nothing beyond a vague idea of its relative -total can be formed.</p> - - -<p class="p2">§ 331. Besides these immense variations in the outer actions to -be counter-balanced, there are immense variations<span class="pagenum" id="Page_434">[434]</span> in the inner -actions required to counterbalance them. Even were species similarly -conditioned, self-preservation would require of them extremely unlike -expenditures of force.</p> - -<p>The cost of locomotion increases in a greater ratio than the size. In -virtue of the law that the weights of animals increase as the cubes -of their dimensions, while their powers of bearing strains increase -only as the squares of their dimensions (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect46">§ 46</a>), preservation of its -various attitudes requires a large animal to consume more substance in -proportion to its weight, than it requires a small animal to consume; -and there results, other things equal, a difficulty of self-maintenance -which augments in a more rapid ratio than the bulk. Nor must we -overlook the further complication, that among aquatic creatures the -variation of resistance of the medium tends to produce an opposite -effect.</p> - -<p>Again, the heat-consumption is a changing element in the total expense -of self-preservation. Creatures which have temperatures scarcely -above that of the air or water, may, other things equal, accumulate -more surplus nutriment than creatures which have to keep their bodies -warm spite of the continual loss by radiation and conduction. This -difference of cost is modified by the presence or absence of natural -clothing; and it is also modified by unlikenesses of size. Here the -bulky animals have the advantage: small masses cooling more rapidly -than large ones.</p> - -<p>Dissimilarities of attack and defence are also causes of variation -in the outlay for self-maintenance. A creature that has to hunt, as -compared with another that gets a sufficiency of prey by lying in wait, -or a creature that escapes by speed as compared with another that -escapes by concealment, obviously leads a life that is physiologically -more costly. Animals which protect themselves passively, as the -Hedge-hog by its spines or as the Skunk and the Musk-rat by their -intolerable odours, are relatively economical; and have the more vital -capital for other purposes.</p> - -<p>Amplification is needless. These instances will show that<span class="pagenum" id="Page_435">[435]</span> anything -beyond very general conceptions of the individual expenditures in -different cases, cannot be reached.</p> - - -<p class="p2">§ 332. Still more entangled are we among qualifying considerations -when we contrast species in their powers of multiplication. The total -cost of Genesis admits of even less definite estimation than does the -total cost of Individuation. I do not refer merely to the truth that -the degree of fertility depends on four factors—the age of commencing -reproduction, the number in each brood, the frequency of the broods, -and the time during which broods continue to be repeated. There are -many further obstacles in the way of comparisons.</p> - -<p>Were all multiplication carried on sexually, the problem would be -less involved; but there are many kinds of asexual multiplication -alternating with the sexual. This asexual multiplication is in some -cases perpetual instead of occasional; and often has more forms than -one in the same species. The result is that we have to compare what -is here a periodic process with what is elsewhere a cyclical process -partly continuous and partly periodic: the calculation of fertility in -this last case being next to impossible.</p> - -<p>We have to avoid being misled by the assumption that the cost of -Genesis is measured by the number of young produced, instead of -being measured, as it is, by the weight of nutriment abstracted to -form the young, <i>plus</i> the weight consumed in caring for them. -This total weight may be very diversely apportioned. In contrast to -the Cod with its millions of small ova spawned without protection, -we may put the <i>Hippocampus</i>, or the Pipe-fish, with its few -relatively-large ova carried about by the male in a caudal pouch, or -seated in hemispherical pits in its skin; or we may put the still more -remarkable genus <i>Arius</i>, and especially <i>Arius Boakeii</i>—a -fish some six or seven inches long, which produces ten or a dozen eggs -5–10 mm. in diameter, that are carried by the male in his mouth till -they are hatched. Here though<span class="pagenum" id="Page_436">[436]</span> the degrees of fertility, if measured -by the numbers of fertilized germs deposited, are extremely unlike, -they are less unlike if measured by the numbers of young which are -hatched and survive long enough to take care of themselves; nor will -the tax on the parent-Cod seem so immensely different from that on -the parent-<i>Arius</i>, if the masses of the ova, instead of their -numbers, are compared. Again, while sometimes the parental loss is -little else but the matter deducted to form eggs, &c., at other times -it takes the shape of a small direct deduction joined with a large -indirect outlay. The Mason-wasp furnishes a typical instance. In -journeyings hither and thither to fetch bit by bit the materials for -building a cell; in putting together these materials, as well as in -secreting glutinous matter to act as cement; and then, afterwards, in -the labour of seeking for, and carrying, the small caterpillars with -which it fills up the cell to serve its larva with food when it emerges -from the egg; the Mason-wasp expends more substance than is contained -in the egg itself. And this supplementary expenditure is manifestly so -great that but few eggs can be housed and provisioned.</p> - -<p>Estimates of the cost of Genesis are further complicated by -variations in the ratio borne by the two sexes. Among Fishes the -mass of milt approaches in size the mass of spawn; but among higher -<i>Vertebrata</i> the substance lost by the one sex in the shape of -sperm-cells is small compared with that lost by the other sex in the -shape of albumen stored-up in the eggs, or blood supplied to the fœtus, -or milk given to the young. Then there come the differences of indirect -tax on males and females. While, frequently, the fostering of the young -devolves entirely on the female, occasionally the male undertakes it -wholly or in part. After building a nest, the male Stickleback guards -the eggs till they are hatched; as does also the great <i>Silurus -glanis</i> for some forty days, during which he takes no food. And -then, among most birds, we have the male occupied in feeding the -female during<span class="pagenum" id="Page_437">[437]</span> incubation, and the young afterwards. Evidently all -these differences affect the proportion between the total cost of -reproduction and the total cost of individuation.</p> - -<p>Whether the species is monogamous or polygamous, and whether there are -marked differences of size or of structure between males and females, -are also questions not to be overlooked. If there are many females to -one male, the total quantity of assimilated matter devoted by each -generation to the production of a new generation, is greater than if -there is a male to each female. Similarly, where the requirements -are such that small males will suffice, the larger quantity of food -left for the females makes possible a greater surplus available for -reproduction. Another cause has a like effect. Where the habits of the -race render it needless that both sexes should have developed powers of -locomotion—where, as in the Glow-worm and sundry <i>Lepidoptera</i>, -the female is wingless while the male has wings—the cost of -Individuation not being so great for the species as a whole, there -arises a greater reserve for Genesis: the matter which would otherwise -have gone to the production of wings and the using of them, may go to -the production of ova.</p> - -<p>Other complications, as those which we see in Bees and Ants, might be -dwelt on; but the foregoing will amply serve the intended purpose.</p> - - -<p class="p2">§ 333. To ascertain by comparison of cases whether Individuation -and Genesis vary inversely, is thus an undertaking so beset with -difficulties, that we might despair of any satisfactory results, -were not the relation too marked a one to be hidden even by all -these complexities. Species are so extremely contrasted in their -degrees of evolution, and so extremely contrasted in their rates of -multiplication, that the law of relation between these traits becomes -unmistakable when the evidence is looked at in its <i>ensemble</i>. -This we shall soon find on ranging in order a number of typical cases.</p> - -<p>In doing this it will be convenient to neglect, temporarily,<span class="pagenum" id="Page_438">[438]</span> -all unlikenesses among the circumstances in which organisms are -placed. At the outset, we will turn our attention wholly to the -antagonism displayed between the integrative process which results in -individual evolution and the disintegrative process which results in -multiplication of individuals; and this we will consider first as we -see it under the several forms of agamogenesis, and then as we see -it under the several forms of gamogenesis. We will next look at the -antagonism between propagation and that evolution which is shown by -increased complexity. And then we will consider the remaining phase of -the antagonism, as it exists between the degree of fertility and the -degree of evolution expressed by activity.</p> - -<p>Afterwards, passing to the varying relations between organisms and -their environments, we will note how relative increase in the supply -of food, or relative decrease in the quantity of force expended by the -individual, entails relative increase in the quantity of force devoted -to multiplication, and <i>vice versâ</i>.</p> - -<p>Certain minor qualifications, together with sundry important -corollaries, may then be entered upon.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_439">[439]</span></p> - -<h3>CHAPTER V.<br /> -<span class="subhed1">ANTAGONISM BETWEEN GROWTH AND ASEXUAL GENESIS.</span></h3></div> - - -<p>§ 334. When illustrating, in Part IV, the morphological composition of -plants and animals, there were set down in groups, numerous facts which -we have here to look at from another point of view. Then we saw how, -by union of small simple aggregates, there are produced large compound -aggregates. Now we have to observe the reactive effect of this process -on the relative numbers of the aggregates. Our present subject is the -antagonism of Individuation and Genesis as seen under its simplest -form, in the self-evident truth that the same quantity of matter may -be divided into many small wholes or few large wholes; but that number -negatives largeness and largeness negatives number.</p> - -<p>In setting down some examples we may conveniently adopt the same -arrangement as before. We will look at the facts as they are presented -by vegetal aggregates of the first order, of the second order, and of -the third order; and then as they are presented by animal aggregates of -the same three orders.</p> - - -<p class="p2">§ 335. The ordinary unicellular plants are at once microscopic and -enormously prolific. The often cited <i>Sphærella nivalis</i>, which -shows its immense powers of multiplication by reddening wide tracts of -snow in a single night, does this by developing in its cavity a brood -of young cells, which, being<span class="pagenum" id="Page_440">[440]</span> presently set free by the bursting of -the parent-cell, severally grow and quickly repeat the process. The -like occurs among sundry of those kindred forms of minute <i>Algæ</i> -which, by their enormous numbers, sometimes suddenly change pools to an -opaque green. So, too, the <i>Desmidiaceæ</i> often multiply so greatly -as to colour the water; and among the <i>Diatomaceæ</i> the rate of -genesis by self-division, “is something really extraordinary. So soon -as a frustule is divided into two, each of the latter at once proceeds -with the act of self-division; so that, to use Professor Smith’s -approximative calculation of the possible rapidity of multiplication, -supposing the process to occupy, in any single instance, twenty-four -hours, ‘we should have, as the progeny of a single frustule, the -amazing number of one thousand millions in a single month.’” In these -cases the multiplication is so carried on that the parent is lost in -the offspring—the old individuality disappears either in the swarms of -zoospores it dissolves into, or in the two or four new individualities -simultaneously produced by fission. Vegetal aggregates of the first -order, have, however, a form of agamogenesis in which the parent -individuality is not lost: the young cells arise from the old cells -by external gemmation. This process, too, repeated as it is at short -intervals, results in immense fertility. The Yeast-fungus, which in a -few hours thus propagates itself throughout a large vat of wort, offers -a familiar example.</p> - -<p>In certain compound forms that must be classed as plants of the second -order of aggregation, though very minute ones, self-division similarly -increases the numbers at high rates. The <i>Sarcina ventriculi</i>, a -parasitic plant which infests the stomach and swarms afresh as fast as -previous swarms are vomited, shows us a spontaneous fission of clusters -of cells. An allied mode of increase occurs in <i>Gonium pectorale:</i> -each cell of the cluster resolving itself into a secondary cluster, -and the secondary clusters then separating. “Supposing, which is -very probable, that a young <i>Gonium</i> after twenty-four hours is -capable of development by fission, it follows<span class="pagenum" id="Page_441">[441]</span> that under favourable -conditions a single colony may on the second day develop 16, on the -third 256, on the fourth 4,096, and at the end of a week 268,435,456 -other organisms like itself.” In the <i>Volvocineæ</i> this continual -dissolution of a primary compound individual into secondary compound -individuals, is carried on endogenously, and on a modified system: -some only of the component cells giving origin to young colonies, -and the parent bursting to liberate them. The numbers arising by -this method also, are sometimes so great as to tint large bodies of -water. More fully established and organized aggregates of the second -order, such as the higher Thallophytes and the lower Archegoniates, -do not sacrifice their individualities by fission; but nevertheless, -by the kindred process of gemmation, are continually hindered in the -increase of their individualities. The gemmæ called tetraspores are -cast off in great numbers by the marine <i>Algæ</i>. Among those simple -<i>Jungermanniaceæ</i> which consist of single fronds, the young ones -that bud out grow for a time in connexion with their parents, send -rootlets from their under sides into the soil, and presently separate -themselves—a habit which augments the number of individuals in -proportion as it checks their growths.</p> - -<p>Plants of the third order of composition, arising by arrest of this -separation, exhibit a further corresponding decrease in the abundance -of the aggregates formed. Archegoniates of inferior types, in which -the axes produced by integration of fronds are but small and feeble, -are characterized by the habit of throwing off bulbils—bud-shaped -axes which, falling and taking root, add to the number of distinct -individuals. This agamic multiplication, very general among the -Mosses and their kindred, and not uncommon under a modified form -in such higher types as the Ferns, many of which produce young -ones from the surfaces of their fronds, becomes very unusual among -Phænogams. The detachment of bulbils, though not unknown among them, -is exceptional. And while it is true that some flowering plants, as -the Strawberry,<span class="pagenum" id="Page_442">[442]</span> multiply by a process allied to gemmation, yet this -is not characteristic of the class. A leading trait of these highest -groups, to which the largest members of the vegetal kingdom belong, is -that agamogenesis has so far ceased that it does not usually originate -independent plants. Though the axes which, budding one out of another, -compose a tree, are the equivalents of asexually-produced individuals; -yet the asexual production of them stops short of separation. These -vast integrations arise where spontaneous disintegration, and the -multiplication effected by it, have come to an end.</p> - -<p>Thus, not forgetting that certain Phænogams, as <i>Begonia -phyllomaniaca</i>, revert to quite primitive modes of increase, we may -hold it as beyond question that while among the most minute plants -asexual multiplication is universal, and produces enormous numbers in -short periods, it becomes step by step more restricted in range and -frequency as we advance to large and compound plants; and disappears so -generally from the highest and largest, that its occurrence is regarded -as anomalous.</p> - - -<p class="p2">§ 336. Parallel examples furnished by animals make clear the purely -quantitative nature of this relation under its original form. Among -the <i>Protozoa</i>, as among the <i>Protophyta</i>, there occurs -that process by which the individuality of the parent is wholly lost -in producing offspring—the breaking up of the parental mass into a -number of germs. Some of the <i>Infusoria</i>, as for instance those -of the genus <i>Kolpoda</i> and several allied genera, become encysted -and subsequently break up into young ones. The more familiar mode of -increase among these animal-aggregates of the first order, by fission, -though it sacrifices the parent individuality by merging it in the -individualities of the two produced, sacrifices it less completely -than does the dissolution into a great number of germs. Occurring, -however, as this fission does, very frequently, and being completed, -in some cases that<span class="pagenum" id="Page_443">[443]</span> have been observed, in the course of half-an-hour, -it results in immensely-rapid multiplication. If all its offspring -survive, and continue dividing themselves, a single <i>Paramœcium</i> -is said to be capable of thus originating 268 millions in the course of -a month.<a id="FNanchor_55" href="#Footnote_55" class="fnanchor">[55]</a> Nor is this the greatest known rate of increase. Another -animalcule, visible only under a high magnifying power, “is calculated -to generate 170 billions in four days.”<a id="FNanchor_56" href="#Footnote_56" class="fnanchor">[56]</a> And these enormous powers -of propagation are accompanied by a minuteness so extreme, that of some -species one drop of water would contain as many individuals as there -are human beings on the Earth! Even if we allow a large margin for -exaggeration in these estimates, it is beyond question that among these -smallest of animals the rate of asexual multiplication is immensely the -greatest; and this suffices for the purposes of argument.</p> - -<p>Of animal aggregates belonging to the second order, that multiply -asexually with rapidity, the familiar Polypes furnish conspicuous -examples. By gemmation in most cases, in other cases by fission, and -in some cases by both, the agamogenesis is carried on among these -tribes. As shown in Fig. <a href="#i_091">148</a>, the budding of young ones from the -parent <i>Hydra</i> is carried on so actively, that before the oldest -of them is cast off half-a-dozen or more others have reached various -stages of growth; and even while still attached, the first-formed -of the group have commenced budding out from their sides a second -generation of young ones. In the <i>Hydra tuba</i><span class="pagenum" id="Page_444">[444]</span> this gemmiparous -multiplication is from time to time interrupted by a transverse -splitting-up of the body into segments, which successively separate -and swim away: the result of the two processes being that, in the -course of a season, there are produced from a single germ great numbers -of young <i>Medusæ</i>, which are the adult or sexual forms of the -species. Respecting cœlenterate animals of this degree of composition, -it may be added that when we ascend to the larger kinds we find asexual -genesis far less active. Though comparisons are interfered with by -differences of structure and mode of life, yet the contrasts are too -striking to have their meanings much obscured. If, for instance, we -take a solitary <i>Actinozoon</i> and a solitary <i>Hydrozoon</i>, -we see that the relatively-great bulk of the first, goes along with -a relatively-slow agamogenesis. The common Sea-anemones are but -occasionally observed to undergo self-division: multiplication by -budding being in some cases largely followed, but their numbers are -not rapidly increased by either process. A higher class of secondary -aggregates exemplifies the same general truth with a difference. In the -smaller members the agamogenesis is incomplete, and in the larger it -disappears. The gemmation of the minute <i>Polyzoa</i>, though it does -not end in the separation of the young individuals, habitually goes to -the extent of producing families of partially independent individuals; -but their near ally, the <i>Phoronis</i>, which immensely exceeds them -in size, is solitary and not gemmiparous. So, too, is it with the -<i>Ascidioida</i>. And then among the true <i>Mollusca</i>, which are -relatively large, no such thing is known as fission or gemmation.</p> - -<p>Take next the <i>Annulosa</i>, including under this title the -<i>Annelida</i> and <i>Arthropoda</i>. When treating of morphological -composition, reasons were given for the belief that the annulose animal -is an aggregate of the third order, the segments of which, produced -one from another by gemmation, originally became separate; but by -progressive integration, or arrested disintegration, there resulted a -type in which many<span class="pagenum" id="Page_445">[445]</span> such segments were permanently united (<a href="#sect205">§§ 205–7</a> -and note to <a href="#sect207">§ 207</a>). Part of the evidence there assigned, is evidence -to be here repeated in illustration of the direct antagonism of Growth -and Asexual Genesis. We saw how, among the lower Annelids, the string -of segments produced by gemmation presently divides transversely into -two strings; and how, in some cases, this resolution of the elongating -string of segments into groups that are to form separate individuals, -goes on so actively that as many as six groups are found in different -stages of progress to ultimate independence—a fact implying a high -rate of fissiparous multiplication.<a id="FNanchor_57" href="#Footnote_57" class="fnanchor">[57]</a> Then we saw that, in the -superior annulose types, distinguished in the mass by including the -larger species, fission does not occur. The higher Annelids do not -propagate in this way; there is no known case of new individuals being -so formed among the <i>Myriapoda</i>; nor do the Crustaceans afford us -a single instance of this primordial mode of increase. It is, indeed, -true that while articulate animals never multiply asexually after -this simplest method, and while they are characterized in the mass by -the cessation of agamogenesis of every kind, there nevertheless occur -in a few of their small species, those higher forms of agamogenesis -known as parthenogenesis and pseudo-parthenogenesis; and that by these -some of them multiply very rapidly. Hereafter we shall find, in the -interpretation of these anomalies, further support for the general -doctrine.</p> - -<p>To the above evidence has to be added that which the <i>Vertebrata</i> -present. This may be very briefly summed up. On the one hand this -class, whether looked at in the aggregate or in its particular -species, immensely exceeds all other classes in the sizes of its -individuals; and on the other hand, agamogenesis under any form is -absolutely unknown in it. If it be said that budding occurs among the -<i>Tunicata</i> which,<span class="pagenum" id="Page_446">[446]</span> under the common title of <i>Chordata</i>, -are included in the same phylum with the <i>Vertebrata</i>, then it -may firstly be replied that those types which have no vertebræ cannot -properly be called <i>Vertebrata</i>, and secondly that if, as being -<i>Chordata</i>, they must be recognized, then the exception which they -present further illustrates the truth that agamogenetic multiplication -occurs only in creatures small in size, or low in structure, or both.</p> - - -<p class="p2">§ 337. Such are a few leading facts serving to show how deduction -is inductively verified, in so far as the antagonism between Growth -and Asexual Genesis is concerned. In whatever way we explain this -opposition of the integrative and disintegrative processes, the facts -and their implications remain the same. Indeed we need not commit -ourselves to any hypothesis respecting the physical causation. It -suffices to recognize the results under their most general aspects. We -cannot help admitting there are at work these two antagonist tendencies -to aggregation and separation; and we cannot help admitting that the -proportion between the aggregative and separative tendencies, must -in each case determine the relation between increase in bulk of the -individual and increase of the race in number.</p> - -<p>The antithesis is as manifest <i>à posteriori</i> as it is necessary -<i>à priori</i>. While the minutest organisms multiply asexually in -their billions; while the <i>Infusoria</i> thus multiply in their -millions; while the small compound types next above them thus multiply -in their thousands; while larger and more compound types thus multiply -in their hundreds and their tens; the largest types do not thus -multiply at all. Conversely, those which do not multiply asexually at -all, are a billion or a million times the size of those which thus -multiply with greatest rapidity; and are a thousand times, or a hundred -times, or ten times the size of those which thus multiply with less and -less rapidity. Without saying that this inverse proportion is regular, -which, as we shall hereafter<span class="pagenum" id="Page_447">[447]</span> see, it cannot be, we may unhesitatingly -assert its average truth. That the smallest organisms habitually -reproduce asexually with immense rapidity; that the largest organisms -never reproduce at all in this manner; and that between these extremes -there is a general decrease of asexual reproduction along with an -increase of bulk; are propositions which admit of no dispute.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_448">[448]</span></p> - -<h3>CHAPTER VI.<br /> -<span class="subhed1">ANTAGONISM BETWEEN GROWTH AND SEXUAL GENESIS.</span></h3></div> - - -<p>§ 338. In so far as it is a process of separation, sexual genesis is -like asexual genesis; and is therefore, equally with asexual genesis, -opposed to that aggregation which results in growth. Whether deduction -is made from one parent or from two, whether it is made from any part -of the body indifferently or from a specialized part, or whether it is -made directly or indirectly, it remains in any case a deduction; and in -proportion as it is great, or frequent, or both, it must restrain the -increase of the individual.</p> - -<p>Here we have to group together the leading illustrations of this truth. -We will take them in the same order as before.</p> - - -<p class="p2" id="sect339">§ 339. The lowest vegetal forms, or rather, we may say, those forms -which we cannot class as either distinctly vegetal or distinctly -animal, show us a process of sexual multiplication that differs much -less from the asexual process than in the higher forms. The common -character which distinguishes sexual from asexual genesis, is that -the mass of protoplasm whence a new generation is to arise, has been -produced by the union of two portions of matter which were before -more widely separated. I use this general expression because, among -the simplest <i>Algæ</i>, this is not invariably matter supplied by -different individuals: certain <i>Diatomaceæ</i> exhibit within a -single cell, the formation of a sporangium by a drawing<span class="pagenum" id="Page_449">[449]</span> together of -the opposite halves of the endochrome into a ball. Mostly, however, -sporangia are products of conjugation. The protoplasmic contents of -two cells unite to form the germ-mass or zygote; and these conjugating -cells may be either entirely independent, as in many <i>Desmidiaceæ</i> -and in the gametes of many <i>Confervoideæ</i>; or they may be two of -the adjacent cells forming a thread, as in some <i>Conjugateæ</i> and -the gametes of <i>Confervoideæ</i>; or they may be cells belonging -to adjacent threads, as in other <i>Conjugateæ</i>. But whether it -is originated by a single parent-cell, or by two parent-cells, the -zygote, after remaining quiescent until there recur the fit conditions -for growth, either breaks up into a multitude of spores, each of -which produces an individual that usually multiplies asexually, or -germinates directly to produce one new individual; and the fact here to -be noted is, that as the entire contents of the parent-cells unite to -form the zygote, their individualities are lost in the germs of a new -generation. In these minute simple types, sexual propagation just as -completely sacrifices the life of the parent or parents, as does that -form of asexual propagation in which the protoplasm resolves itself -directly into zoospores. And in the one case as in the other, this -sacrifice is the concomitant of a prodigious fertility. Slightly in -advance of this, but still showing us an almost equal loss of parental -life in the lives of offspring, is the process seen in such unicellular -<i>Algæ</i> as <i>Botrydium</i>, and in minute <i>Fungi</i> of the same -degree of composition. These exhibit a relatively-enormous development -of the spore-producing part, and an almost entire absorption of the -parental substance into it. As evidence of the resulting powers of -multiplication, we have but to remember that the spread of mould over -stale food, the rapid destruction of crops by mildew, and other kindred -occurrences, are made possible by the incalculably numerous spores thus -generated and universally dispersed.</p> - -<p>Plants a degree higher in composition supply a parallel series of -illustrations. We have among the larger <i>Fungi</i>, in<span class="pagenum" id="Page_450">[450]</span> which the -reproductive apparatus is relatively so enormous as to constitute -the ostensible plant, a similar subordination of the individual to -the race, and a similarly-immense fertility. Thus, as quoted by Dr. -Carpenter, Fries says—“in a single individual of <i>Reticularia -maxima</i>, I have counted (calculated?) 10,000,000 sporules.” It -needs but to note the clouds of particles, so minute as to look like -smoke, which ripe puffballs give off when they are burst, and then to -remember that each particle is a potential fungus, to be impressed -with the almost inconceivable powers of propagation which these plants -possess. The Lichens, too, furnish examples. Though they are nothing -like so prolific as the <i>Fungi</i> (the difference yielding, as we -shall hereafter see, further support to the general argument), yet -there is a great production of germs, and a proportionate sacrifice -of the parental individuality. Considerable areas of the thallus -develop into the fruit-bodies characteristic of the various fungi -which, combined with algæ, form the different lichens (various members -of the <i>Ascomycetes</i> and the <i>Basidiomycetes</i>). From these -are produced great numbers of ascospores or basidiospores, as the -case may be. Very many lichens also reproduce themselves by means of -<i>Soredia</i>, <i>i.e.</i>, little masses of algal cells closely -wrapped in a weft of fungal hyphæ. Some contrasts presented by the -higher <i>Algæ</i> may also be named as exemplifying the inverse -proportion between the size of the individual and the extent of the -generative structures. While in the smaller kinds relatively large -portions of the fronds are transformed into reproductive elements, -in the larger kinds these portions are relatively small: instance -the <i>Macrocystis pyrifera</i>, a gigantic seaweed which sometimes -attains a length of 1,500 feet, of which Dr. Carpenter remarks—“This -development of the nutritive surface takes place at the expense of the -fructifying apparatus, which is here quite subordinate.”</p> - -<p>When we turn to vegetal aggregates of the third order of composition, -facts having the same meaning are conspicuous.<span class="pagenum" id="Page_451">[451]</span> On the average -these higher plants are far larger than plants of a lower degree of -composition; and on the average their rates of sexual reproduction are -far less. Similarly if, among Archegoniates and Phænogams, we compare -the smaller types with the larger, we find them proportionately more -prolific. This is not manifest if we simply calculate the number of -seeds ripened by an individual in a single season; but it becomes -manifest if we take into account the further factor which here -complicates the result—the age at which sexual genesis commences. The -smaller Phænogams are mostly either annuals, or perennials that die -down annually; and seeding as they do annually before their deaths, or -the deaths of their reproductive parts, it results that in the course -of a year each gives origin to a multitude of potential plants, of -which every one may the next year, if preserved, give origin to an -equal multitude. Supposing but a hundred offspring to be produced the -first year, ten thousand may be produced in the second year, a million -in the third, a hundred millions in the fourth. Meanwhile, what has -been the possible multiplication of a large Phænogam? While its small -congener has been seeding and dying, and leaving multitudinous progeny -to seed and die, it has simply been growing; and may so continue to -grow for ten or a dozen years without bearing fruit. Before a Cocoa-nut -tree has ripened its first cluster of nuts, the descendants of a wheat -plant, supposing them all to survive and multiply, will have become -numerous enough to occupy the whole surface of the Earth. So that -though, when it begins to bear, a tree may annually shed as many seeds -as an herb, yet in consequence of this delay in bearing, its fertility -is incomparably less; and its relatively-small fertility becomes still -further reduced where, as in <i>Lodoicea callipyge</i>, the seeds take -two years from the date of fertilization to the date of germination.</p> - - -<p class="p2">§ 340. Some observers state that in certain <i>Protozoa</i> -there<span class="pagenum" id="Page_452">[452]</span> occurs a process of conjugation akin to that which the -<i>Protophyta</i> exhibit—a coalescence of the substance of two -individuals to form a germ-mass. This has been alleged more especially -of <i>Actinophrys</i>. If this statement should be proved true,<a id="FNanchor_58" href="#Footnote_58" class="fnanchor">[58]</a> -then of the minute forms that appear to be more animal than vegetal in -their characters, some have a mode of sexual multiplication by which -the parents are sacrificed bodily in the production of a new generation.</p> - -<p>Among small animal aggregates of the second order, the first to be -considered are of course the <i>Cœlenterata</i>. A <i>Hydra</i> -occasionally devotes a large part of its substance to sexual genesis. -In the walls of its body groups of ova, or spermatozoa, or both, take -their rise; and develop into masses greatly distorting the creature’s -form, and leaving it much diminished when they escape. Here, however, -gamogenesis is obviously supplementary to agamogenesis—the immensely -rapid multiplication by budding continues as long as food is abundant -and warmth sufficient, and is replaced by gamogenesis only at the -close of the season. A better example<span class="pagenum" id="Page_453">[453]</span> of the relation between small -size and active gamogenesis among low types of the <i>Metazoa</i> is -supplied by the <i>Rotifera</i>. Microscopic as these are, they have -a great rate of sexual increase. According to Ehrenberg, <i>Hydatina -senta</i> “is capable of a four-fold propagation every twenty-four or -thirty hours, bringing forth in this time four ova, which grow from the -embryo to maturity, and exclude their fertile ova in the same period. -The same individual, producing in ten days forty eggs, developed -with the rapidity above cited, this rate, raised to the tenth power, -gives one million of individuals from one parent, on the eleventh day -four millions, and on the twelfth day sixteen millions, and so on.” -Ehrenberg, however, characterized by Huxley as “the greatest looker and -the worst observer,” is not a safe authority, and it is better to state -the estimate of Ludwig Plate, who says that <i>Hydatina</i> lays fifty -eggs in two to three weeks—a number which, multiplying in the manner -described, will yield in the time named a much smaller total though -still an enormous total.</p> - -<p>The <i>Annulosa</i>, including among them the inferior types, have -habits and conditions of life so various that only the broadest -contrasts can be instanced in support of the proposition before us. -The differences of organization and activity greatly complicate the -inverse variation of fertility and bulk. Bearing in mind, however, -that the rate of multiplication depends much less on the number of -each brood than on the quickness with which maturity is reached and -a new generation commenced, it will be obvious that though Annelids, -relatively enormous in size, produce great numbers of ova, yet as they -do this at comparatively long intervals, their rates of increase fall -immensely below that just instanced in the Rotifers. And when at the -other extreme we come to the large articulate animals, such as the Crab -and the Lobster, the further diminution of fertility is seen in the -still longer delay which occurs before each new generation begins to -reproduce.</p> - -<p><span class="pagenum" id="Page_454">[454]</span></p> - -<p>Perhaps the best examples are supplied by vertebrate animals, and -especially those that are most familiar to us. Comparisons between -Fishes are unsatisfactory, because of our ignorance of their histories. -In some cases Fishes equal in bulk produce widely different numbers of -eggs; as the Cod which spawns millions at once, and the Salmon by which -nothing like so great a number is spawned. But then the eggs are very -unlike in size; and if the ovaria of the two fishes be compared, the -difference between their masses is comparatively moderate. There are, -indeed, contrasts which seem at variance with the alleged relation; as -that between the Cod and the Stickleback which, though so much smaller, -produces fewer ova. The Stickleback’s ova, however, are relatively -large; and their total bulk bears as great a ratio to the bulk of the -Stickleback as does the bulk of the Cod’s ova to that of the Cod. -Moreover if, as is not improbable, the reproductive age is arrived -at earlier by the Stickleback than by the Cod, the fertility of the -species may be greater notwithstanding the smaller number produced -by each individual. Evidence which admits of being tolerably well -disentangled is furnished by Birds. They differ but little in their -grades of organization; and the habits of life throughout extensive -groups of them are so similar, that comparisons may be fairly made. It -is true that, as hereafter to be shown, the differences of expenditure -which differences of bulk entail, have doubtless much to do with the -differences of fertility. But we may set down under the present head -some of those cases in which the activity, being relatively slight, -does not greatly interfere with the relation we are considering; and -may note that among such birds having similarly slight activities, the -small produce more eggs than the large, and eggs that bear in their -total mass a greater ratio to the mass of the parent. Consider, for -example, the gallinaceous birds; which are like one another and unlike -birds of most other groups in flying comparatively little. Taking -first the wild members of this order, which<span class="pagenum" id="Page_455">[455]</span> rarely breed more than -once in a season, we find that the Pheasant has from 10 to 14 eggs, -the Black-cock from 6 to 10, the Grouse 8 to 14, the Partridge 12 to -20, the Quail still more, sometimes reaching two broods of 7 to 12 in -each. Here the only exception to the relation between decreasing bulk -and increasing number of eggs, occurs in the cases of the Pheasant -and the Black-cock; and it is to be remembered, in explanation, that -the Pheasant is constitutionally adapted to a warmer region, is -better fed—often artificially—and leads a less active life. If we -pass to domesticated genera of the same order, we meet with parallel -differences. From the numbers of eggs laid, little can be inferred; -for under the favourable conditions artificially maintained, the -laying is carried on indefinitely. But though in the sizes of their -broods the Turkey and the Fowl do not greatly differ, the Fowl begins -breeding at a much earlier age than the Turkey, and produces broods -more frequently: a considerably higher rate of multiplication being -the result. Now these contrasts among domestic creatures which are -similarly conditioned, and closely-allied by constitution, may be held -to show, more clearly than most other contrasts, the inverse variation -between bulk and sexual genesis; since here the cost of activity is -diminished to a comparatively small amount. There is little expenditure -in flight—sometimes almost none; and the expenditure in walking about -is not great: there is more of standing than of actual movement. It -is true that young Turkeys commence their existence as larger masses -than chickens; but it is tolerably manifest that the total weight of -the eggs laid by a Turkey during each season, bears a less ratio to -the Turkey’s weight, than the total weight of the eggs which a Hen -lays during each season, bears to the Hen’s weight; and this is the -fairest way of making the comparison. The comparison so made shows -a greater difference than appears likely to be due to the different -costs of locomotion; considering the inertness of the creatures. -Remembering that<span class="pagenum" id="Page_456">[456]</span> the assimilating surface increases only as the -squares of the dimensions, while the mass of the fabric to be built up -by the absorbed nutriment increases as the cubes of the dimensions, -it will be seen that the expense of growth becomes relatively greater -with each increment of size; and that hence, of two similar creatures -commencing life with different sizes, the larger one in reaching its -superior adult bulk, will do this at a more than proportionate expense; -and so will either be delayed in commencing its reproduction, or will -have a diminished reserve for reproduction, or both. Other orders -of Birds, active in their habits, show more markedly the connexion -between augmenting mass and declining fertility. But in them the -increasing cost of locomotion becomes an important, and probably the -most important, factor. The evidence they furnish will therefore -come better under another head. Contrasts among Mammals, like those -which Birds present, have their meanings obscured by inequalities of -the expenditures for motion. The smaller fertility which habitually -accompanies greater bulk, must in all cases be partly ascribed to this. -Still, it may be well if we briefly note, for as much as they are -worth, the broader contrasts. While a large Mammal bears but a single -young one at a time, is several years before it commences doing this, -and then repeats the reproduction at long intervals; we find, as we -descend to the smaller members of the class, a very early commencement -of breeding, an increasing number at a birth, reaching in small Rodents -to 10 or even more, and a much more frequent recurrence of broods: the -combined result being a relatively prodigious fertility. If a specific -comparison be desired between Mammals that are similar in constitution, -in food, in conditions of life, and all other things but size, the -Deer-tribe supplies it. While the large Red-deer has but one at a -birth, the small Roe-deer has frequently two at a birth.<a id="FNanchor_59" href="#Footnote_59" class="fnanchor">[59]</a></p> - - - -<p class="p2" id="sect341">§ 341. The antagonism between growth and sexual genesis,<span class="pagenum" id="Page_457">[457]</span> visible in -these general contrasts, may also be traced in the history of each -plant and animal. So familiar is the fact that sexual genesis does not -occur early in life, and in all organisms which expend much begins only -when the limit of size is nearly reached, that we do not sufficiently -note its significance. It is a general physiological truth, however, -that while the building-up of the individual is going on rapidly, the -reproductive organs remain imperfectly developed and inactive; and that -the commencement of reproduction at once indicates a declining rate -of growth, and becomes a cause of arresting growth. As was shown in <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect78">§ 78</a>, -the exceptions to this rule are found where the limit of growth is -indefinite; either because the organism expends little or nothing in -action, or expends in action so moderate an amount that the supply of -nutriment is never equilibrated by its expenditure.</p> - -<p>We will pass over the inferior plants and, limiting ourselves to -Phænogams, will not dwell on the less conspicuous evidence with the -smaller types present. A few cases such as gardens supply will serve. -All know that a Pear-tree increases in size for years before it begins -to bear; and that, producing but few pears at first, it is long before -it fruits abundantly. A young Mulberry-tree, branching out luxuriantly -season after season, but covered with nothing but leaves, at length -blossoms sparingly and sets some small and imperfect berries, which -it drops while they are green; and it makes these futile attempts -time after<span class="pagenum" id="Page_458">[458]</span> time before it succeeds in ripening any seeds. But these -multiaxial plants, or aggregates of individuals some of which continue -to grow while others become arrested and transformed into seed-bearers, -show us the relation less definitely than certain plants that are -substantially, if not literally, uniaxial. Of these the Cocoa-nut may -be instanced. For some years it goes on shooting up without making -any sign of becoming fertile. About the sixth year it flowers; but -the flowers wither without result. In the seventh year it flowers and -produces a few nuts; but these prove abortive and drop. In the eighth -year it ripens a moderate number of nuts; and afterwards increases -the number until, in the tenth year, it comes into full bearing. -Meanwhile, from the time of its first flowering its growth begins -to diminish, and goes on diminishing till the tenth year, when it -ceases. Here we see the antagonism between growth and sexual genesis -under both its aspects—see a struggle between self-evolution and -race-evolution, in which the first for a time overcomes the last, and -the last ultimately overcomes the first. The continued aggrandizement -of the parent-individual makes abortive for two seasons the tendency to -produce new individuals; and the tendency to produce new individuals, -becoming more decided, stops any further aggrandizement of the parent -individual.</p> - -<p>Parallel illustrations occur in the animal kingdom. The eggs laid by a -pullet are relatively small and few. Similarly, it is alleged that, as -a general rule, “a bitch has fewer puppies at first, than afterwards.” -According to Burdach, as quoted by Dr. Duncan, “the elk, the bear, &c., -have at first only a single young one, then they come to have most -frequently two, and at last again only one. The young hamster produces -only from three to six young ones, while that of a more advanced age -produces from eight to sixteen. The same is true of the pig.” It is -remarked by Buffon that when a sow of less than a year old has young, -the number of the litter is small, and its members are feeble and even -imperfect.<span class="pagenum" id="Page_459">[459]</span> Here we have evidence that in animals growth checks sexual -genesis. And then, on the other hand, we have evidence that sexual -genesis checks growth. It is well known to breeders that if a filly -is allowed to bear a foal, she is thereby prevented from reaching -her proper size. And a like loss of perfection as an individual, -is suffered by a cow which breeds too early. It may be added, as a -converse fact, that castrated animals, as capons and notably cats, -often become larger than their unmutilated associates.</p> - - -<p class="p2">§ 342. Notwithstanding the way in which the inverse variation of -growth and sexual genesis is complicated with other relations, its -existence is, I think, sufficiently manifest. Individually, many of -the foregoing instances are open to criticism, and have to be taken -with qualifications; but when looked at in the mass their meaning is -beyond doubt. Comparisons between the largest with the smallest types, -whether vegetal or animal, yield results which are unmistakable. On -the one hand, remembering the fact that during its centuries of life -an Oak does not produce as many acorns as a Fungus does spores in a -single night, we see that the Fungus has a fertility exceeding that -of the Oak in a degree literally beyond our powers of calculation or -imagination. On the other hand when, taking a microscopic protophyte -which has billions of descendants in a few days, we ask how many such -would be required to build up the forest tree which is years before -it drops a seed, we are met by a parallel difficulty in conceiving -the number, if not in setting it down. Similarly, if from the minute -and prodigiously-fertile Rotifer we turn to the Elephant, which -approaches thirty years before it bears a solitary young one, we find -the connexions between small size and great fertility and between great -size and small fertility, too intensely marked to be much disguised by -the perturbing relations that have been indicated. Finally, as this -induction, reached by a survey of organisms in general, is verified by -observations on the relation<span class="pagenum" id="Page_460">[460]</span> between decreasing growth and commencing -reproduction in individual organisms, we may, I think, consider the -alleged antagonism as proved.<a id="FNanchor_60" href="#Footnote_60" class="fnanchor">[60]</a></p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_461">[461]</span></p> - -<h3>CHAPTER VII.<br /> -<span class="subhed1">THE ANTAGONISM BETWEEN DEVELOPMENT AND GENESIS, ASEXUAL AND SEXUAL.</span></h3></div> - - -<p>§ 343. By Development, as here to be dealt with apart from Growth, is -meant increase of structure as distinguished from increase of mass. As -was pointed out in <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect50">§ 50</a>, this is the biological definition of the word. -In the following sections, then, we have to note how complexity of -organization is hindered by reproductive activity, and conversely.</p> - -<p>This relation partially coincides with that which we have just -contemplated; for, as was shown in <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect44">§ 44</a>, degree of growth is to a -considerable extent dependent on degree of organization. But while the -antagonism to be illustrated in this chapter is much entangled with -that illustrated in the last chapter, it may be so far separated as to -be identified as an additional antagonism.</p> - -<p>Besides the direct opposition between that continual disintegration -which rapid genesis implies, and the fulfilment of that pre-requisite -to extensive organization—the formation of an extensive aggregate, -there is an indirect opposition which we may recognize under several -aspects. The change from homogeneity to heterogeneity takes time; -and time taken in transforming a relatively-structureless mass into -a developed individual, delays the period of reproduction. Usually -this time is merged in that taken for growth; but certain cases of -metamorphosis show us the one separate from the other. An insect, -passing from its lowly-organized caterpillar-stage<span class="pagenum" id="Page_462">[462]</span> into that of -chrysalis, is afterwards a week, a fortnight, or a longer period in -completing its structure: the re-commencement of genesis being by so -much postponed, and the rate of multiplication therefore diminished. -Further, that re-arrangement of substance which development implies, -entails expenditure. The chrysalis loses weight in the course of its -transformation; and that its loss is not loss of water only, may -be inferred from the fact that it respires, and that respiration -indicates consumption. Clearly the matter consumed is, other things -equal, a deduction from the surplus which may go to reproduction. -Yet again, the more widely and completely an organic mass becomes -differentiated, the smaller is the portion of it which retains the -relatively-undifferentiated state that admits of being moulded into -new individuals, or the germs of them. Protoplasm which has become -specialized tissue cannot be generalized afresh, and afterwards -transformed into something else; and hence the progress of structure -in an organism, by diminishing the unstructured part, diminishes the -amount available for making offspring.</p> - -<p>It is true that higher structure, like greater growth, may insure to -a species advantages which eventually further its multiplication—may -give it access to larger supplies of food, or enable it to obtain food -more economically; and we shall hereafter see how the inverse variation -we are considering is thus qualified. But here we are concerned -only with the necessary and direct effects; not with those that are -contingent and remote. These necessary and direct effects we will now -look at as exemplified.</p> - - -<p class="p2">§ 344. Speaking generally, the simpler plants propagate both -sexually and asexually; and, speaking comparatively, the complex -plants propagate only sexually: their asexual propagation is usually -incomplete—produces a united aggregate of individuals instead of -numerous distinct individuals. The Protophytes that perpetually -subdivide, the merely<span class="pagenum" id="Page_463">[463]</span> cellular <i>Algæ</i> that shed their -tetraspores, the Archegoniates that spontaneously separate their -fronds or drop their gemmæ, show us an extra mode of multiplication -which, among flowering plants, is exceptional. This extra mode of -multiplication among these simpler plants, is made easy by their -low development. Tetraspores arise only where the frond consists of -untransformed cells; gemmæ bud out and drop off only where the tissue -is comparatively homogeneous.</p> - -<p>Should it be said that this is but another aspect of the antagonism -already set forth, since these undeveloped forms are also the smaller -forms; the reply is that though in part true this is not wholly true. -Various marine <i>Algæ</i> which propagate asexually, are larger -than some Phænogams which do not thus propagate. The objection that -difference of medium vitiates this comparison, is met by the fact -that it is the same among land-plants themselves. Sundry of the -lowly-organized Liverworts which are habitually gemmiparous, exceed in -size many flowering plants. And the Ferns show us agamic multiplication -occurring in plants which, while they are inferior in complexity of -structure, are superior in bulk to numbers of annual Monocotyledons and -Dicotyledons.</p> - - -<p class="p2">§ 345. In the ability of the lowly-organized substance of a Sponge to -transform itself into multitudes of gemmules, we have an instance of -this same direct relation in the animal kingdom. Moreover, the instance -yields very distinct proof of an antagonism between development and -genesis, independent of the antagonism between growth and genesis; for -the Sponge which thus multiplies itself asexually, as well as sexually, -is far larger than hosts of more complex animals which do not multiply -asexually.</p> - -<p>Once again may be cited the creature so often brought in evidence, -the <i>Hydra</i>, as showing us how rapidity of agamic propagation -is associated with inferiority of structure. Its power to produce -young ones from nearly all parts of its body, is due to the -comparative homogeneity of its body. In<span class="pagenum" id="Page_464">[464]</span> kindred but more-organized -types, the gemmiparity is greatly restricted, or disappears. Among -the free-swimming <i>Hydrozoa</i>, multiplication by budding, when -it occurs at all, occurs only at special places. That increase of -structure apart from increase of size, is here a cause of declining -agamogenesis, we may see in the contrast between the simple -<i>Hydra</i> and the compound Hydroids. These last, along with -more-differentiated tissues, show us a gemmation which does not go -on all over the body of each polype, and much of it does not end in -separation.</p> - -<p>It is, however, among the <i>Annulosa</i> that progressing organization -is most conspicuously operative in diminishing agamogenesis. The -segments or “somites” composing an animal belonging to this class, are -primordially alike; and, as before argued (<a href="#sect205">§§ 205–7</a>), are probably -the homologues of what were originally independent individuals. The -progress from the lower to the higher types of the class, is at once -a progress towards types in which the strings of segments cease to -undergo subdivision, and towards types in which the segments, no longer -alike in their structures and functions, have become physiologically -integrated or mutually dependent. Already this group of cases has -been named as illustrating the antagonism between growth and asexual -genesis; but it is proper also to name it here, since, on the one hand, -the greater size due to the ceasing of fission, is made possible only -by the specialization of parts and the development of a co-ordinating -apparatus to combine their actions, and since, on the other hand, -specialization and co-ordination can advance only in proportion as -fission ceases.</p> - - -<p class="p2" id="sect346">§ 346. The inverse variation of development and sexual genesis is by no -means easy to follow. One or two facts indicative of it may, however, -be named.</p> - -<p>Phænogams that have but little supporting tissue may fairly be classed -as structurally inferior to those having stems with a bulky and -complex woody system; for these imply<span class="pagenum" id="Page_465">[465]</span> additional differentiations, -and constitute wider departures from the primitive type of vegetal -tissue. That the concomitant of this higher organization is a slower -gamogenesis, scarcely needs pointing out. While the herbaceous annual -is blossoming and ripening seed, the young tree is transforming its -originally-succulent axis into dense fibrous substance; and year -by year the young tree expends in doing the like, nutriment which -successive generations of the annual expend in fruit. Here the inverse -relation is between sexual reproduction and complexity, and not between -sexual reproduction and bulk, seeing that besides seeding, the annual -often grows to a size greater than that reached by the young infertile -tree in several years.</p> - -<p>Proof of the antagonism between complexity and gamogenesis in animals, -is still more difficult to disentangle. Perhaps the evidence most to -the point is furnished by the contrast between Man and certain other -Mammals approaching him in mass. To compare him with the domestic Sheep -which, though not very unlike in size, is relatively prolific, is -objectionable because of the relative inactivity of Sheep; and this, -too, may be alleged as a reason why the Ox, though far more bulky, is -also far more fertile, than Man. Further, against a comparison with -the Horse which, while both larger and more prolific, is tolerably -active, it may be urged that in his case, and the cases of herbivorous -creatures generally, the small exertion required to procure food, -joined with the great ratio borne by the alimentary organs to the -organs they have to build up and repair, vitiates the result. We may, -however, fairly draw a parallel between Man and a large carnivore. The -Lion, superior in size, and perhaps equal in activity, has a digestive -system not proportionately greater; and yet has a higher rate of -multiplication than Man. Here the only decided want of parity, besides -that of organization, is that of food. Possibly a carnivore gains an -advantage in having a surplus nutriment consisting almost wholly of -those nitrogenous materials from which the bodies<span class="pagenum" id="Page_466">[466]</span> of young ones are -mainly formed. But, allowing for all other differences, it appears not -improbable that the smallness of human fertility compared with the -fertility of large feline animals, is due to the greater complexity of -the human organization—more especially the organization of the nervous -system. Taking degree of nervous organization as the chief correlative -of mental capacity; and remembering the physiological cost of that -slow evolution whereby high mental capacity is reached; we may suspect -that nervous organization is very expensive: the inference being that -bringing it up to the level it reaches in Man, whose digestive system, -by no means large, has at the same time to supply materials for general -growth and daily waste, involves a great retardation of maturity and -sexual genesis.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_467">[467]</span></p> - -<h3>CHAPTER VIII.<br /> -<span class="subhed1">ANTAGONISM BETWEEN EXPENDITURE AND GENESIS.</span></h3></div> - - -<p>§ 347. Under this head we have to set down no evidence derived from the -vegetal kingdom. Plants are not expenders of force in such degrees as -to affect the general relations with which we are dealing. They have -not to maintain a heat above that of their environment, nor have they -to generate motion; and hence consumption for these two purposes does -not diminish the stock of material which serves on the one hand for -growth and on the other hand for propagation.</p> - -<p>It will be well, too, if we pass over the lower animals: especially -those aquatic ones which, being nearly of the same temperature as -the water, and nearly of the same specific gravity, lose but little -in evolving motion, sensible and insensible. A further reason for -excluding from consideration these inferior types, is that we do not -know enough of their rates of genesis to permit of our making, with any -satisfaction, those involved comparisons here to be entered upon.</p> - -<p>The facts on which we must mainly depend are those to be gathered -from terrestrial animals, and chiefly from those higher classes of -them which are at the same time great expenders and have rates of -multiplication about which our knowledge is tolerably definite. We -will restrict ourselves, then, to the evidence which Birds and Mammals -supply.</p> - - -<p class="p2">§ 348. Satisfactory proof that loss of substance in the<span class="pagenum" id="Page_468">[468]</span> maintenance of -heat diminishes the rapidity of propagation, is difficult to obtain. -It is, indeed, obvious that the warmblooded <i>Vertebrata</i> are less -prolific than the cold-blooded; but then they are at the same time -more vivacious. Similarly, between Mammals and Birds (which are the -warmer-blooded of the two) there is, other things equal, a parallel, -though much smaller, difference; but here, too, the unlikenesses of -muscular action complicate the evidence. Again, the annual return of -generative activity has an average correspondence with the annual -return of a warmer season, which, did it stand alone, might be taken -as evidence that a diminished cost of heat-maintenance leads to such a -surplus as makes reproduction possible. But then, this periodic rise of -temperature is habitually accompanied by an increase in the quantity -of food—a factor of equal or greater importance. We must be content, -therefore, with such few special facts as admit of being disentangled.</p> - -<p>Certain of these we are introduced to by the general relation last -named—the habitual recurrence of genesis with the recurrence of -spring. For in some cases a domesticated creature has its supplies -of food almost equalized; and hence the effect of varying nutrition -may be in great part eliminated from the comparison. The common -Fowl yields an illustration. It is fed through the cold months, but -nevertheless, in mid-winter, it either wholly leaves off laying or -lays very sparingly. And then we have the further evidence that if it -lays sparingly, it does so only on condition that the heat, as well as -the food, is artificially maintained. Hens lay in cold weather only -when they are kept warm. To which fact may be added the kindred one -that “when pigeons receive artificial heat, they not only continue to -hatch longer in autumn, but will recommence in spring sooner than they -would otherwise do.” An analogous piece of evidence is that, in winter, -inadequately sheltered Cows either cease to give milk or give it in -diminished quantity. For though giving milk is not the same thing as -bearing a young one, yet, as milk<span class="pagenum" id="Page_469">[469]</span> is part of the material from which -a young one is built up, it is part of the outlay for reproductive -purposes, and diminution of it is a loss of reproductive power. Indeed -the case aptly illustrates, under another aspect, the struggle between -self-preservation and race-preservation. Maintenance of the cow’s life -depends on maintenance of its heat; and maintenance of its heat may -entail such reduction in the supply of milk as to cause the death of -the calf.</p> - -<p>Evidence derived from the habits of the same or allied genera in -different climates, may naturally be looked for; but it is difficult -to get, and it can scarcely be expected that the remaining conditions -of existence will be so far similar as to allow of a fair comparison -being made. The only illustrative facts I have met with which seem -noteworthy, are some named by Mr. Gould in his work on <i>The Birds -of Australia</i>. He says:—“I must not omit to mention, too, the -extraordinary fecundity which prevails in Australia, many of its -smaller birds breeding three or four times in a season; but laying -fewer eggs in the early spring when insect life is less developed, -and a greater number later in the season, when the supply of insect -food has become more abundant. I have also some reason to believe -that the young of many species breed during the first season, for -among others, I frequently found one section of the Honey-eaters (the -<i>Melithrepti</i>) sitting upon eggs while still clothed in the -brown dress of immaturity; and we know that such is the case with the -introduced <i>Gallinaceæ</i> (or poultry) three or four generations of -which have been often produced in the course of a year.” Though here -Mr. Gould refers only to variation in the quantity of food as a cause -of variation in the rate of multiplication, may we not suspect that -warmth is a part-cause of the high rate which he describes as general?</p> - - -<p class="p2">§ 349. Of the inverse variation between activity and genesis, we get -clear proof. Let us begin with that which Birds furnish.</p> - -<p><span class="pagenum" id="Page_470">[470]</span></p> - -<p>First we have the average contrast, already hinted, between the -fertility of Birds and the fertility of Mammals. Comparing the large -with the large and the small with the small, we see that creatures -which continually go through the muscular exertion of sustaining -themselves in the air and propelling themselves rapidly through it, -are less prolific than creatures of equal weights which go through the -smaller exertion of moving about over solid surfaces. Predatory Birds -have fewer young ones than predatory Mammals of approximately the same -sizes. If we compare Rooks with Rats, or Finches with Mice, we find -like differences. And these differences are greater than at first -appears. For whereas among Mammals a mother is able, unaided, to bear -and suckle and rear half-way to maturity, a brood that probably weighs -more in proportion than does the brood of a Bird; a Bird, or at least -a Bird that flies much, is unable to do this. Both parents have to -help; and this indicates that the margin for reproduction in each adult -individual is smaller.</p> - -<p>Among Birds themselves occur contrasts which may be next considered. -In the Raptorial class, various species of which, differing in their -sizes, are similarly active in their habits, we see that the small -are more prolific than the large. The Golden Eagle has usually 2 -eggs: sometimes 3, sometimes only 1. As we descend to the Kites and -Falcons, the number is 2 or 3, and 3 or 4. And when we come to the -Sparrow-Hawk, 3 to 5 is the specified number. Similarly among the -Owls: while the Great Eagle-Owl has 2 or 3 eggs, the comparatively -small Common Owl has 4 or 5. As before hinted, it is impossible to say -what proportions of these differences are due to unlikenesses of bulk -merely, and what proportions are due to unlikenesses in the costs of -locomotion. But we may fairly assume that the unlikenesses in the costs -of locomotion are here the more important factors. Weights varying as -the cubes of the dimensions, while the surfaces of digestive systems -vary as the squares, the expense of flight increases more rapidly than -does the ability to take<span class="pagenum" id="Page_471">[471]</span> in nutriment; and as motion through the -air requires more effort than motion on the ground, this geometrical -progression tells more rapidly on Birds than on Mammals. Be this as -it may, however, these contrasts support the argument; as do various -others which may be set down. The Finch-family, for example, have -broods averaging about 5 in number, and have commonly 2 broods in -the season; while in the Crow-family the number of the brood is on -the average less, and there is but one brood in the season. And then -on descending to such small birds as the Wrens and the Tits, we have -8, 10, 12 to 15 eggs, and sometimes two broods in the year. One of -the best illustrations is furnished by the Swallow-tribe, throughout -which there is little or no difference in mode of life or in food. The -Sand-Martin, much the least of them, has 4 to 6 eggs and two broods; -the Swallow, somewhat larger, has 4 or 5; and the Swift (similar in -habits though unrelated), larger still, has but 2. Here we see a lower -fertility associated in part with greater size, but associated still -more conspicuously with greater expenditure. For the difference of -fertility is more than proportionate to the difference of bulk, as -shown in other cases; and for this greater difference there is the -reason, that the Swift has to support not only the cost of propelling -its larger mass through the air, but also the cost of propelling it at -a higher velocity.</p> - -<p>Omitting much evidence of like nature, let us note that disclosed by -comparisons of certain groups of birds with other groups. “Skulkers” -is the descriptive title applied to the Water-Rail, the Corn-Crake, -and their allies, which evade enemies by concealment—consequently -expending but little in locomotion. These birds have relatively large -broods—6 to 11, 8 to 12, &c. Not less instructive are the contrasts -between the Gallinaceous Birds and other Birds of like sizes but more -active habits. The Partridge and the Wood-Pigeon are about equal in -bulk and have much the same food. Yet while the one has from 12 to 20 -young ones, the other has but 2 young ones twice a-year: its annual -reproduction is less than<span class="pagenum" id="Page_472">[472]</span> one-third. It may be said that the ability -of the Partridge to bring up so large a brood, is due to that habit of -its tribe which one of its names, “Scrapers,” describes; and to the -accompanying habit of the young, which begin to get their own living as -soon as they are hatched: so saving the parents’ labour. Conversely, -it may be said that the inability of Pigeons to rear more than 2 at a -time, is caused by the necessity of fetching everything they eat. But -the alleged relation holds nevertheless. On the one hand, a great part -of the food which the Partridge chicks pick up, is food which, in their -absence, the mother would have picked up. Though each chick costs her -far less than a young Pigeon costs its parents, yet the whole of her -chicks cost her a great deal in the shape of abstinence—an abstinence -she can bear because she has to fly but little. On the other hand, -the Pigeon’s habit of laying and hatching but two eggs, must not be -referred to any foreseen necessity of going through so much labour in -supporting the young, but to a constitutional tendency established by -such labour. This is proved by the curious fact that when domesticated, -and saved from such labour by artificial feeding, Pigeons, says -Macgillivray (quoting Aitkin), “are frequently seen sitting on eggs -long before the former brood is able to leave the nest, so that the -parent bird has at the same time young birds and eggs to take care of.”</p> - - -<p class="p2">§ 350. Made to illustrate the effect of activity on fertility, most -comparisons among Mammals are objectionable: other circumstances are -not equal. A few, however, escape this criticism.</p> - -<p>One is that between the Hare and the Rabbit. These are closely-allied -species of the same genus, similar in their diet but unlike in their -expenditures for locomotion. The relatively-inert Rabbit has 6 young -ones in a litter, and four litters a-year; while the relatively-active -Hare has but 2 to 5 in a litter. This is not all. The Rabbit begins to -breed at six months old; but a year elapses before the Hare begins<span class="pagenum" id="Page_473">[473]</span> -to breed. These two factors compounded, result in a difference of -fertility far greater than can be ascribed to unlikeness of the two -creatures in size.</p> - -<p>Perhaps the most striking piece of evidence which Mammals furnish, -is the extreme infertility of our common Bat. The <i>Cheiroptera</i> -and the <i>Rodentia</i> are not very dissimilar in their internal -structures. Diversity of constitution, therefore, cannot vitiate the -comparison between Bats and Mice, which are about the same in size. -Though their diets differ, the difference is in favour of the Bat: -its food being exclusively animal while that of the Mouse is mainly -vegetal. What now are their respective rates of genesis? The Mouse has -several litters in a year of 5 to 7 in each; while the Bat produces -only one at a time. Whether the Bat repeats its one more frequently -than the Mouse repeats its 7 is not stated; but it is quite certain -that even if it does so (an absurd supposition), the more frequent -repetition cannot be such as to raise its fertility to anything like -that of the Mouse. And this relatively-low rate of multiplication we -may fairly ascribe to its relatively-high rate of expenditure.</p> - -<p>Here let us note, in passing, an interesting example of the -way in which a species which has no specially-great power of -self-preservation, while its power of multiplication is extremely -small, nevertheless avoids extinction because it has to meet an -unusually-small total of race-destroying forces. Leaving out parasites, -the only enemy of the Bat is the Owl; and the Owl is sparingly -distributed.</p> - - -<p class="p2">§ 351. These general evidences may be enforced by some special -evidences. We have few opportunities of observing how, within the -same species, variations of expenditure are related to variations of -fertility. But a fact or two showing the connexion may be named.</p> - -<p>Doctor Duncan quotes a statement to the point respecting the breeding -of dogs. Already in <a href="#sect341">§341</a> I have extracted a part of this statement, -to the effect that before her growth is complete,<span class="pagenum" id="Page_474">[474]</span> a bitch bears at a -birth fewer puppies than when she becomes full-grown. An accompanying -allegation is, that her declining vigour is shown by a decrease in the -number of puppies contained in a litter, “ending in one or two.” And -then it is further alleged that, “as regards the amount of work a dog -has to perform, so will the decline be rapid or gradual; and hence, if -a bitch is worked hard year after year, she will fail rapidly, and the -diminution of her puppies will be accordingly; but if worked moderately -and well kept, she will fail gradually, and the diminution will be less -rapid.”</p> - -<p>In this place, more fitly than elsewhere, may be added a fact of like -implication, though of a different order. Of course whether excessive -expenditure be in the continual repairs of nervo-muscular tissues or in -replacing other tissues, the reactive effects, if not quite the same, -will be similar—there will be a decrease of the surplus available for -genesis. If, then, in any animals there from time to time occur unusual -outlays for self-maintenance, we may expect the periods of such outlays -to be periods of diminished or arrested reproduction. That they are so -the moulting of birds shows us. When hens begin to moult they cease to -lay. While they are expending so much in producing new clothing, they -have nothing to expend for producing eggs.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_475">[475]</span></p> - -<h3>CHAPTER IX.<br /> -<span class="subhed1">COINCIDENCE BETWEEN HIGH NUTRITION AND GENESIS.</span></h3></div> - - -<p>§ 352. Under this head may be grouped various facts which, in another -way, tell the same tale as those contained in the last chapter. The -evidence there put together went to show that increased cost of -self-maintenance entailed decreased power of propagation. The evidence -to be set down here, will go to show that power of propagation is -augmented by making self-maintenance unusually easy. For into this may -be translated the effect of abundant food.</p> - -<p>To put the proposition more specifically—we have seen that after -individual growth, development, and daily consumption, have -been provided for, the surplus nutriment measures the rate of -multiplication. This surplus may be raised in amount by such changes in -the environment as bring a larger supply of the materials or forces on -which both parental life and the lives of offspring depend. Be there, -or be there not, any expenditure, a higher nutrition will make possible -a greater propagation. We may expect this to hold both of agamogenesis -and of gamogenesis; and we shall find that it does so.</p> - - -<p class="p2">§ 353. On multiaxial plants, the primary effect of surplus nutriment -is a production of large and numerous leaf-shoots. How this asexual -multiplication results from excessive nutrition, is well shown when the -leading axis, or a chief branch, is broken off towards its extremity. -The axillary buds below<span class="pagenum" id="Page_476">[476]</span> the breakage quickly swell and burst into -lateral shoots, which often put forth secondary shoots: two generations -of agamic individuals arise where there probably would have been none -but for the local abundance of sap, no longer drawn off. In like manner -the abnormal agamogenesis which we have in proliferous flowers, is -habitually accompanied by a general luxuriance, implying an unusual -plethora.</p> - -<p>No less conclusive is the evidence furnished by agamogenesis in -animals. Sir John Dalyell, speaking of <i>Hydra tuba</i>, and of the -period before strobilization commences, says—“It is singular how much -propagation is promoted by abundant sustenance.” This Polype goes on -budding out young polypes from its sides, with a rapidity proportionate -to the supply of materials. So, too, is it with the agamic reproduction -of the <i>Aphis</i>. As cited by Professor Huxley, Kyber “states that -he raised viviparous broods of both this species (<i>Aphis Dianthi</i>) -and <i>A. Rosæ</i> for four consecutive years, without any intervention -of males or oviparous females, and that the energy of the power of -agamic reproduction was at the end of that period undiminished. The -rapidity of the agamic proliferation throughout the whole period was -directly proportional to the amount of warmth and food supplied.”</p> - -<p>In these cases the relation is not appreciably complicated by -expenditure. The parent having reached its limit of growth, the -absorbed food goes to asexual multiplication: scarcely any being -deducted for the maintenance of parental life.</p> - - -<p class="p2">§ 354. The sexual multiplication of organisms under changed conditions, -undergoes variations conforming to a parallel law. Cultivated plants -and domesticated animals yield us proof of this.</p> - -<p>Facts showing that in cultivated plants sexual genesis increases with -nutrition, are obscured by facts showing that a less rapid asexual -genesis, and an incipient sexual genesis,<span class="pagenum" id="Page_477">[477]</span> accompany the fall from a -high to a moderate nutrition. The confounding of these two relations -has led to mistaken inferences. When treating of Genesis inductively, -we reached the generalization that “the products of a fertilized germ -go on accumulating by simple growth, so long as the forces whence -growth results are greatly in excess of the antagonist forces; but -that when diminution of the one set of forces, or increase of the -other, causes a considerable decline in this excess, and an approach -towards equilibrium, fertilized germs are again produced.” (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect78">§ 78</a>.) -It was pointed out that this holds of organisms which multiply by -heterogenesis, as well as those which multiply by homogenesis. -And plants were referred to as illustrating, both generally and -locally, the decline of agamic multiplication and commencement of -gamic multiplication, along with a lessening rate of nutrition. -Now the many cases which are given of fruitfulness caused in trees -by depletion, are really cases of this change from agamogenesis -to gamogenesis; and simply go to prove that what would naturally -arise when decreased peripheral growth had followed increased size, -may be brought about artificially by diminishing the supply of -materials for growth. Cramping its roots in a pot, or cutting them, -or ringing its branches, will make a tree bear very early: bringing -about a premature establishment of that relative innutrition which -would have spontaneously arisen in course of time. Such facts by -no means show that in plants sexual genesis increases as nutrition -diminishes. When it has once set in, sexual genesis is scanty or -imperfect unless nutrition is good. Though the starved plant may -blossom, yet many of its blossoms will fail; and such seeds as it -produces will be ill-furnished with those enveloping structures and -that store of albumen, &c., needed to give good chances of successful -germination—the number of surviving offspring will be diminished. Were -it otherwise, the manuring of fields which are to bear seed-crops, -would be not simply useless but injurious. Were it otherwise, dunging -the roots of a fruit-tree would in<span class="pagenum" id="Page_478">[478]</span> all cases be impolitic; instead -of being impolitic only where the growth of sexless axes is still -luxuriant. Were it otherwise, a tree which has borne a heavy crop -should, by the consequent depletion, be led to bear a still heavier -crop next year; whereas it is apt to be wholly or partially barren next -year—has to recover a state of tolerably-high nutrition before its -sexual genesis again becomes large.</p> - -<p>But the best illustrations are yielded by animals—those animals at -least in which we have, besides an increased supply of nutriment, a -diminished expenditure. Two classes of comparisons, alike in their -implications, may be made—comparisons between tame and wild animals of -the same species or genus, and comparisons between tame animals of the -same species differently treated.</p> - -<p>To begin with Birds, let us first contrast the farm-yard -<i>Gallinaceæ</i> with their kindred of the fields and woods. -Notwithstanding their greater size, which, other things equal, should -be accompanied by smaller fertility, the domesticated kinds have more -numerous offspring than the wild kinds. A Turkey has a dozen in a -brood, while a Pheasant has from 6 to 10. Twice or thrice in a season, -a Hen rears as many chickens as a Partridge rears once in a season. -Anserine birds show us parallel differences. The Tame Goose sits on -13 to 18 eggs and often sits a second time; but the Wild Goose sits -on 5, 6, or 7, and these are noted as considerably smaller. It is the -same with Ducks. The domesticated variety lays and hatches twice as -many eggs as the wild variety. And the like holds of Pigeons. After -remarking of the <i>Columba livia</i> that “in spring when they have -plenty of corn to pick from the newly-sown fields, they begin to -get fat and pair; and again in harvest, when the corn is cut down,” -Macgillivray goes on to say that “the same pair when tamed generally -breed four times” in the year. That between different poultry-yards -inequalities of fertility are caused by inequalities in the supplies -of food, is a familiar truth. High feeding shows its effects not only -in the continuous<span class="pagenum" id="Page_479">[479]</span> laying, but also in the sizes of the eggs. Among -directions given for obtaining eggs from pullets late in the year, -it is especially insisted on that they shall have a generous diet. -Respecting Pigeons Macgillivray writes:—“that their breeding depends -much on their having plenty of food to fatten them, seems, I think, -evident from the circumstance that, when tamed, which they easily are, -they are observed to breed in every month of the year. I do not mean -that the same pair will breed every month; but some in the flock, if -well fed, will breed at any season.” There may be added a fact of like -meaning which partially-domesticated birds yield. The Sparrow is one of -the Finch tribe that has taken to the neighbourhood of houses; and by -its boldness secures food not available to its congeners. The result -is that it has several broods in a season, while its field-haunting -kindred have none of them more than two broods, and some have only one.</p> - -<p>Equally clear proof that abundant nutriment raises the rate of -multiplication, occurs among Mammals. Compare the litters of the Dog -with the litters of the Wolf and the Fox. Whereas those of the one -range in number from 6 to 14, those of the others contain respectively -5 or 6 or occasionally 7, and 4 or 5 or rarely 6. Again, the Wild Cat -has 4 or 5 kittens; but the tame Cat has 5 or 6 kittens 2 or 3 times -a-year. So, too, is it with the Weasel tribe. The Stoat has 5 young -ones once a-year. The Ferret has 2 litters yearly, each containing -from 6 to 9; and this notwithstanding that it is the larger of the -two. Perhaps the most striking contrast is that between the wild and -tame varieties of the Pig. While the one produces, according to its -age, from 4 to 8 or 10 young ones once a year, the other produces -sometimes as many as 17 in a litter; or, in other cases, will bring -up 5 litters of 10 each in two years—a rate of reproduction which is -unparalleled in animals of as large a size.<a id="FNanchor_61" href="#Footnote_61" class="fnanchor">[61]</a> And let us not omit to -note that this excessive fertility occurs where there is the<span class="pagenum" id="Page_480">[480]</span> greatest -inactivity—where there is plenty to eat and nothing to do. There is no -less distinct evidence that among domesticated Mammals themselves, the -well-fed individuals are more prolific than the ill-fed individuals. On -the high and comparatively-infertile Cotswolds, it is unusual for ewes -to have twins; but they very commonly have twins in the adjacent rich -valley of the Severn. Similarly, among the barren hills of the west of -Scotland, two lambs will be borne by about one ewe in twenty; whereas -in England, something like one ewe in three will bear two lambs. Nay, -in rich pastures, twins are more frequent than single births; and it -occasionally happens that, after a genial autumn and consequent good -grazing, a flock of ewes will next spring yield double their number of -lambs—the triplets balancing the uniparæ. So direct is this relation, -that I have heard a farmer assert his ability to foretell, from the -high, medium, or low, condition of an ewe in the autumn, whether she -will next spring bear two, or one, or none.</p> - - - -<p class="p2" id="sect355">§ 355. An objection must here be met. Many facts may be brought to -prove that fatness is not accompanied by fertility but by barrenness; -and the inference drawn is that high feeding is unfavourable to -genesis. The premiss may be admitted while the conclusion is denied.</p> - -<p>There is a distinction between what may be called normal plethora, -and an abnormal plethora, liable to be confounded with it. The one -is a mark of constitutional wealth; but the other is a mark of -constitutional poverty. Normal plethora is a superfluity of materials -both for the building up of<span class="pagenum" id="Page_481">[481]</span> tissue and the evolution of force; and -this is the plethora which we have found to be associated with unusual -fecundity. Abnormal plethora which, as truly alleged, is accompanied by -infecundity, is a superfluity of force-evolving materials joined with -either a positive or a relative deficiency of tissue-forming materials: -the increased bulk indicating this state, being really the bulk of so -much inert or dead matter. Note, first, a few of the facts which show -us that obesity implies physiological impoverishment.</p> - -<p>Neither in brutes nor men does it ordinarily occur either in youth or -in that early maturity during which the vigour is the greatest and the -digestion the best: it does not habitually accompany the highest power -of taking up nutritive materials. When fatness arises in the prime of -life, whether from peculiarity of food or other circumstance, it is -not the sign of an increased total vitality. On the contrary, if great -muscular action has to be gone through, the fat must be got rid of; -either, as in a man, by training, or as in a horse that has grown bulky -while out at grass, by putting him on such more nutritive diet as oats. -The frequency of senile fatness, both in domesticated creatures and in -ourselves, has a similar implication. Whether we consider the smaller -ability of those who display it to withstand large demands on their -powers, or whether we consider the comparatively-inferior digestion -common among them, we see that the increased size indicates, not an -abundance of materials which the organism requires, but an abundance of -materials which it does not require. Of like meaning is the fact that -women who have had several children, and animals after they have gone -on bearing young for some time, frequently become fat; and lose their -fecundity as they do this. In such cases the fatness is not to be taken -as the cause of the infecundity; but the constitutional exhaustion -which the previous production of offspring has left, shows itself at -once in the failing fecundity and the commencing fatness. There is yet -another kind of evidence.<span class="pagenum" id="Page_482">[482]</span> Obesity not uncommonly sets in after the -system has been subject to debilitating influences. Often a serious -illness is followed by a corpulence to which there was previously no -tendency. And the prolonged administration of mercury, constitutionally -injurious as it is, sometimes produces a like effect.</p> - -<p>Closer inquiry verifies the conclusion to which these facts point. -The microscope shows that along with the increase of bulk common in -advanced life, there goes on what is called “fatty degeneration:” -oil-globules are deposited where there should be particles of flesh—or -rather, we may say, the hydrocarbonaceous molecules locally produced -by decomposition of the nitrogenous molecules, have not been replaced -by other nitrogenous molecules, as they should have been. This fatty -degeneration is, indeed, a kind of local death. For so regarding it -we have not simply the reason that an active substance has its place -occupied by an inert substance; but we have the further reason that the -flesh of dead bodies, under certain conditions, is transformed into a -fatty matter called adipocere.</p> - -<p>The infertility that accompanies fatness in domestic animals has, -however, other causes than that declining constitutional vigour which -the fatness commonly indicates. Being artificially fed, these animals -cannot always obtain what their systems need. That which is given to -them is given expressly because of its fattening quality. And since the -capacity of the digestive apparatus remains the same, the absorption -of fat-producing materials in excess, implies defect in the absorption -of materials from which the tissues are formed, and out of which young -ones are built up. Moreover, this special feeding with a view to rapid -and early fattening, continued as it is through generations, and -accompanied as it is by a selection of individuals and varieties which -fatten most readily, tends to establish a modified constitution, more -fitted for producing fat and correspondingly-less fitted for producing -flesh—a<span class="pagenum" id="Page_483">[483]</span> constitution which, from this relatively-deficient absorption -of nitrogenous matters, is likely to become infertile; as, indeed, -these varieties often do become. Hence, no conclusions respecting the -effects of high nutrition, properly so-called, can be drawn from cases -of this kind. The cases are, in truth, of a kind which could not exist -but for human agency. Under natural conditions no animal would diet -itself in the way required to produce such results. And if it did its -race would quickly disappear.<a id="FNanchor_62" href="#Footnote_62" class="fnanchor">[62]</a></p> - -<p>There is yet another mode in which accumulation of fat diminishes -fertility. Even supposing it unaccompanied by a smaller absorption of -nitrogenous materials, it is still a cause of lessening the surplus -of nitrogenous materials. For the repair of the motor tissues becomes -more costly. Fat stored-up is weight to be carried. A creature loaded -with inert matter must, other things equal, consume a greater amount -of tissue-forming substances for keeping its locomotive apparatus -in order; and thus expending more for self-maintenance can expend -less for race-maintenance. Abnormal plethora is thus antagonistic -to reproduction in a double way. It ordinarily implies a smaller -absorption of tissue-forming matters, and an increased demand on -the diminished supply. Hence fertility decreases in a geometrical -progression.</p> - -<p>The counter-conclusion drawn from facts of this class is, then, due -to a misconception of their nature—a misconception<span class="pagenum" id="Page_484">[484]</span> arising partly -from the circumstance that the increase of bulk produced by fat is -somewhat like the increase of bulk which growth of tissues causes, -and partly from the circumstance that abundance of good food normally -produces a certain quantity of fat, which, within narrow limits, is -a valuable store of force-evolving material. When, however, we limit -the phrase high nutrition to its proper meaning—an abundance of, and -due proportion among, all the substances which the organism needs—we -find that, other things equal, fertility always increases as nutrition -increases. And we see that these apparently-exceptional cases, are -cases which really show us the same thing; since they are cases of -relative innutrition.</p> - -<hr class="tb" /> - -<p>[<span class="smcap">Note.</span>—By a strange oversight when writing this chapter -in the first edition—an oversight I was on the eve of repeating in -this present edition—I omitted to bring forward the familiar and -all-important evidence furnished by the variations of genesis which -ordinarily accompany the alternations of the seasons. These variations, -in multitudinous creatures of all types, show unmistakably that -reproduction begins at those times of the year when greater warmth -and larger supplies of food render maintenance of individual life -relatively easy, and when there is therefore a surplus available for -producing new individuals. Conversely, along with the decrease of -heat and the relative deficiency of food which make it comparatively -difficult in winter to maintain individual life, there ceases to be -the power of producing other lives: the reproductive organs become -quiescent and often dwindle. With this general fact is associated -a special fact. Though among wild animals—birds, mammals, and -others—breeding ceases when Nature no longer supplies abundant food -and warmth; in domesticated mammals and birds, artificially supplied -with food and warmth, the breeding season is greatly extended and often -made continuous, as, under the same conditions, it is in Man himself.</p> - -<p>Evidence yielded by the vegetal world is less conspicuous,<span class="pagenum" id="Page_485">[485]</span> for the -reason that the cold which arrests reproductive activity also arrests -individual activity: growth of the individual and multiplication of -the race vary simultaneously with variations in the seasons. Still -there are some familiar facts showing that the external conditions -which favour nutrition also bring about reproduction. Early in the -year we are supplied with flowers from regions warmer than our own, -and by and by there come to our markets fruits and vegetables from the -south of France, the Channel Islands, and even from the Scilly Isles, -which are much in advance of those furnished by the gardens of our own -colder regions: reproduction commences earlier where the light and -heat furthering nutrition are greater. And then there is a kindred -meaning in the not unfrequent occurrence of a second flowering and even -of a second fruiting in warm, bright and prolonged autumns. Here the -abnormal re-commencement of reproduction is determined by an abnormal -increase of nutrition.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_486">[486]</span></p> - -<h3>CHAPTER X.<br /> -<span class="subhed1">SPECIALITIES OF THESE RELATIONS.</span></h3></div> - - -<p>§ 356. Tests of the general doctrines set forth in preceding chapters, -are afforded by organisms having modes of life which diverge widely -from ordinary modes. Here, as elsewhere, aberrant cases yield crucial -proofs.</p> - -<p>If certain organisms are so circumstanced that highly-nutritive matter -is supplied to them without stint, and they have nothing to do but -absorb it, we may infer that their powers of propagation will be -enormous.</p> - -<p>If there are classes of creatures which expend very little for -self-support in comparison with allied creatures, a relatively-extreme -prolificness may be expected of them.</p> - -<p>Or if, again, we find species presenting the peculiarity that while -some of their individuals have much to do and little to eat, others of -their individuals have much to eat and little to do, we may look for -great fertility in these last and comparative infertility or barrenness -in the first.</p> - -<p>These several anticipations we shall find completely verified.</p> - - -<p class="p2">§ 357. Plants which, like the <i>Rafflesiaceæ</i>, carry their -parasitism to the extent of living on the juices they absorb from -other plants, exhibit one of these relations in the vegetal kingdom. -In them the organs for self-support being needless, are rudimentary; -and the parts directly or indirectly concerned in the production and -distribution of germs, constitute the mass of the organism. That small -ratio which<span class="pagenum" id="Page_487">[487]</span> the race-preserving structures bear to the self-preserving -structures in ordinary Phænogams, is, in these Phænogams, inverted. A -like relation occurs in the common Dodder.</p> - -<p>There may be added a kindred piece of evidence which the <i>Fungi</i> -present. Those of them which grow on living plants, repeat the above -connection completely; and those of them which, though not parasitic, -nevertheless subsist on organized materials previously elaborated by -other plants, substantially repeat it. The spore-producing part is -relatively enormous; and the fertility is far greater than that of -Cryptogams of like sizes, which have to form for themselves the organic -compounds of which they and their germs consist.</p> - - -<p class="p2">§ 358. The same lesson is taught us by animal-parasites. Along with the -decreased cost of Individuation, they similarly show us an increased -expenditure for Genesis; and they show us this in the most striking -manner where the deviation from ordinary conditions of life is the -greatest.</p> - -<p>Take, among the <i>Epizoa</i>, such an instance as <i>Chondracanthus -gibbosus</i>. Belonging to the <i>Entomostraca</i>, both males -and females of this species are, in their early days, similar to -their allies; and the males, practically parasitic, though they -become greatly degraded, continue throughout life to show by their -segmentation and other external traits their original nature. The -female, however, having fixed herself where she can suck the juices -of her host, the <i>Lophius</i>, grows to twelve times the length -of the male and probably a thousand times its bulk, and becomes -utterly transformed by loss of the organs of animal life and enormous -development of the organs of reproduction. “No heart is discoverable, -and the nervous system and organs of sense (if any) are equally -undistinguishable. The interspace between the alimentary canal and -the walls of the body is almost wholly occupied by the ovarium.”<a id="FNanchor_63" href="#Footnote_63" class="fnanchor">[63]</a> -And then beyond this there are appended ovi-sacs twice the length -of the body. So that the<span class="pagenum" id="Page_488">[488]</span> germ-producing organs and their contents, -eventually acquire a total bulk many times that of all the other organs -put together. Numerous species of this type and habit, repeat this -relation between a life of inaction with high feeding, and an enormous -rate of genesis. Parasites belonging to another great division of the -animal kingdom, the <i>Platyhelminthes</i>, supply an example of an -<i>epizoon</i> in which the rate of multiplication is made great not -so much by immense development of the egg-producing organs as by the -rapidity with which generations succeed one another—a rapidity such -that each generation partially develops the next before it is itself -anything like ready for independent life. This is the <i>Gyrodactylus -elegans</i>, of which it is said that “its most remarkable feature is -that it is viviparous, and its embryos before they leave the body of -their mother have already developed their embryos inside them; and -the latter may contain their embryos, so that four generations may be -included under the cuticle of the sexually mature animal.”<a id="FNanchor_64" href="#Footnote_64" class="fnanchor">[64]</a></p> - -<p><i>Entozoa</i> yield us many examples of this causal relation, -raised to a still higher degree. The <i>Gordius</i>, or Hair-worm, -is a creature which, finding its way when young into the body of -an insect which is afterwards swallowed by a fish, there grows -rapidly, and then emerging to breed, lays as many as 8,000,000 eggs -in less than a day. Similarly with those larger types infesting the -higher animals. It has been calculated by Dr. Eschricht, as quoted -by Professor Owen, that there are “64,000,000 of ova in the mature -female <i>Ascaris lumbricoides</i>.” Very many of the <i>Entozoa</i> -belong to the <i>Platyhelminthes</i>, and among them occur examples -of fertility caused not only by great numbers of ova, but by rapid -succession of partially-developed individuals and also examples of -fertility caused by production of ova almost exceeding numeration. -Among the first the Liver-fluke may be named. Of the half-million -eggs it produces each yields a free-swimming<span class="pagenum" id="Page_489">[489]</span> ciliated embryo, and -any one of these, which finds its way into a water-snail, becomes a -sporocyst—a bag, presently occupied exclusively by masses of cells: -each mass by and by becoming a <i>Redia</i>, which makes its way out. -Like all its fellows which develop in succession, this, with the -exception of a small space occupied by the stomach, devotes the whole -of its interior partly to the formation of other <i>Rediæ</i> (which -presently escape and become similarly transformed), and partly to the -development of <i>Cercariæ</i>, into which the internal substance of -all the <i>Rediæ</i> is eventually transformed: <i>Cercariæ</i> which, -escaping from the host, become agents for infecting other creatures. -So that each ovum thus gives rise to a number of forms which severally -subserve multiplication in different ways. Of the other division of -<i>Platyhelminthes</i> referred to as carrying on its multiplication -by production of ova only, the commonest of the <i>Cestoidea</i> -furnishes the best example. Immersed as a Tape-worm is in nutritive -liquid, which it absorbs through its integument, it requires no -digestive apparatus. The room which one would occupy, and the materials -it would use up, are therefore available for germ-producing organs, -which nearly fill each segment: each segment, sexually complete in -itself, is little else than an enormous reproductive system, with just -enough of other structures to bind it together. Remembering that the -Tape-worm, retaining its hold, continues to bud out such segments as -fast as the fully-developed ones are cast off, and goes on doing this -as long as the infested individual lives; we see that here, where -there is no expenditure, where the cost of individuation is reduced to -the greatest extent while the nutrition is the highest possible, the -degree of fertility reaches its extreme. These <i>Entozoa</i> yield us -further interesting evidence. Of their various species, most if not -all undergo passive migration from animal to animal before they become -mature. Usually, the form assumed in the body of the first host is -devoid of all that part in which the reproductive structures take their -rise; and this part grows and<span class="pagenum" id="Page_490">[490]</span> develops reproductive structures, only -in some predatory animal to which its first host falls a sacrifice. -Occasionally, however, the egg gives origin to the sexual form in -the animal that originally swallowed it, but the development remains -incomplete—there is no sexual genesis, no formation of eggs in the -rudimentary segments. That these may become fertile it is needful, as -before, for the containing animal to be devoured; so that the imperfect -Tape-worm may find its way into the intestine of a higher animal. Thus -the <i>Bothriocephalus solidus</i>, found in the abdominal cavity -of the Stickleback, is barren while it remains there; but if the -Stickleback be eaten by a Water-fowl, the reproductive system of the -transferred <i>Bothriocephalus</i> (then known as <i>B. nodosus</i>) -becomes developed and active. So, too, a kind of Tape-worm which -remains infertile while in the intestine of a Mouse, becomes fertile -in the intestine of a Cat that devours the mouse. May we not regard -these facts as again showing the dependence of fertility on nutrition? -Barrenness here accompanies conditions unfavourable to the absorption -of nutriment; and it gives way to fecundity where nutriment is large in -quantity and superior in quality.</p> - - -<p class="p2">§ 359. Extremely significant are those cases of partial reversion -to primitive forms of genesis, which occur under special -conditions in some of the higher <i>Annulosa</i>. I refer to the -pseudo-parthenogenesis and metagenesis in Insects.</p> - -<p>Under what conditions do the <i>Aphides</i> exhibit this strange -deviation from the habits of their order? Why among them should -imperfect females produce, agamically, others like themselves, -generation after generation, with great rapidity? There is the obvious -explanation that they get plenty of easily-assimilated food without -exertion. Piercing the tender coats of young shoots, they sit and -suck—appropriating the nitrogenous elements of the sap and ejecting -its saccharine matter as “honey dew.” Along with a sluggishness -strongly contrasted with the activity of most insects—along<span class="pagenum" id="Page_491">[491]</span> with -a very low rate of consumption and a correlative degradation of -structure; we have here a retrogression to asexual genesis, and a -greatly-increased rate of multiplication.</p> - -<p>The recently discovered instance of internal metagenesis in the maggots -of certain Flies has a like meaning. Incredible as it at first seemed -to naturalists, it is now proved that the <i>Cecydomia</i>-larva -develops in its interior a brood of larvæ of like structure with -itself. In this case, as in the last, abundant food is combined with -low expenditure. These larvæ are found in such habitats as the refuse -of beet-root-sugar factories—masses of nitrogenous <i>débris</i> -remaining after the extraction of the saccharine matter. Each larva -has a practically-unlimited supply of sustenance imbedding it on all -sides.<a id="FNanchor_65" href="#Footnote_65" class="fnanchor">[65]</a></p> - -<p>It is true that some other maggots, as those of the Flesh-fly, -are similarly, or still better, circumstanced; and, it may be -said, ought therefore to have the same habit. But this does not -necessarily follow. Survival of the fittest will determine whether -such specially-favourable conditions result in aggrandizement of the -individual or in multiplication of the race. And in the case of the -Flesh-fly there is a reason why greater individuation rather than -more rapid genesis will occur. For a decomposing animal body lasts -so short a time, that were Flesh-fly larvae to multiply agamically, -the second generation would die from the disappearance of their food. -Hence individuals in which the excessive nutrition led to internal -metagenesis, would leave no posterity, and natural selection would -establish the variety in<span class="pagenum" id="Page_492">[492]</span> which greater growth resulted. All which -the argument requires is that when such reversion to agamogenesis -<i>does</i> take place, it shall be where the food is unusually -abundant and the expenditure unusually small; and this the cases -instanced go to show.</p> - - -<p class="p2">§ 360. The physiological lesson taught us by Bees and Ants, not quite -harmonizing with the moral lesson they are supposed to teach, is that -highly-fed idleness is favourable to fertility, and that excessive -industry has barrenness for its concomitant.</p> - -<p>The egg of a Bee develops into a small barren female or into a large -fertile female, according to the supply of food given to the larva -hatched from it. We here see that the germ-producing action is an -overflow of the surplus remaining after completion of the individual; -and that the lower feeding which the larva of a working Bee has, -results in a dwarfing of the adult and an arrested development of -the generative organs. Further, we have the fact that the condition -under which the perfect female, or mother-Bee, goes on, unlike insects -in general, laying eggs continuously, is that she has plenty of -food brought to her, is kept warm, and goes through no considerable -exertion. While, contrariwise, it is to be noted that the infertility -of the workers is associated with the ceaseless labour of bringing -materials for the combs and building them, as well as the labour of -feeding the queen, the larvæ, and themselves.</p> - -<p>Ants also show us these relations, and they are shown in a greatly -exaggerated form by what are called white ants—insects belonging to -a quite different order. The contrast in bulk between the fecund and -infecund females is here immensely greater. The mother-Ant has the -reproductive system so enormously developed, that the remainder of her -body is relatively insignificant. Entirely incapable of locomotion, -she is unable to deposit her eggs in the places where they are to be -hatched; so that they have to be carried away<span class="pagenum" id="Page_493">[493]</span> by the workers as fast -as they are extruded. Her life is thus reduced substantially to that -of a parasite—an absorption of abundant food supplied gratis, a total -absence of expenditure, and a consequent excessive rate of genesis. -“The queen-ant of the African <i>Termites</i> lays 80,000 eggs in -twenty-four hours.”</p> - - -<p class="p2">§ 361. It may be needful to say that these exceptional relations cannot -be ascribed to the assigned causes acting alone. The extreme fertility -which, among parasites and social insects, accompanies extremely high -feeding and an expenditure reduced nearly to zero, presupposes typical -structures and tendencies of suitable kinds; and these are not directly -accounted for. On creatures otherwise organized, unlimited supplies -of food and total inactivity are not followed by such results. There -of course requires a constitution fitted to the special conditions, -and the evolution of this cannot be due simply to plethora joined with -rest. These cases are given as illustrating the conditions under which -extreme exaltations of fertility become possible. Their meanings, thus -limited, are clear, and completely to the point. We see in them that -the devotion of nutriment to race-preservation, is carried furthest -where the cost of self-preservation is reduced to a minimum; and, -conversely, that nothing is devoted directly to race-preservation -by individuals on which falls an excessive expenditure for -self-preservation and preservation of other’s offspring.</p> - -<hr class="tb" /> - -<p>[<span class="smcap">Note.</span>—Among specialities of these relations may be fitly -added here a very strange one, for a description of which I am -indebted to M. Charles Julin, Professor of Comparative Anatomy in -the University of Liège. In the <i>Revue Générale des Sciences</i> -for 30th August, 1894, in an account of certain investigations of -M. Giard, he describes what he calls “la castration parasitaire”—a -castration not of a literal kind<span class="pagenum" id="Page_494">[494]</span> but one effected by the arrest of -development which follows from the depletion caused by a parasite. The -<i>Sacculina</i> is an amazingly transformed type belonging to the -<i>Cirrhipedia</i>—a type without segments or appendages and without -mouth and alimentary canal. Fixing itself, during its early locomotive -stage, under the abdomen of a decapodous crustacean, and leaving -behind its exo-skeleton, it makes its way into the interior, and there -becoming a mere bag containing the reproductive organs, obtains the -needful nutriment by developing what are practically roots and rootlets -which run everywhere among the viscera and absorb nutriment from the -surrounding tissues. Here we are concerned merely with the effect -produced upon the host by this physiological robbery. This effect is to -arrest the development not only of the primary sexual organs devoted -to the production of germs, but also of those secondary sexual organs -which characterize the male. M. Julin writes:—</p> - -<div class="blockquot"> - -<p>“Il convient cependant de dire, pour être plus exact, que, -dans les cas des Crabes infesté par des Sacculines, il n’y a -pas, en réalité, apparition de caractères femelles chez le -sexe mâle, mais plutôt absence de développement des caractères -mâles. En fait, l’animal reste à un stade jeune, non différencié -sexuellement, tout en prenant une taille plus considérable. Cela -nous porte à attribuer les modifications dont nous avons parlé à -un simple arrêt de développement, qui est plus sensible chez le -mâle, parce que chez lui les caractères sexuels secondaires sont -à l’état normal plus développés que chez la femelle.</p> - -<p>D’une manière générale, nous croyons, avec M. Giard, qu’il faut -assimiler les modifications dues à la castration parasitaire à -celles qui sont le résultat de la progenèse ou qui engendrent le -dimorphisme saisonnier.</p> - -<p>Il y a <i>progenèse</i> lorsque, chez un animal, la reproduction -sexuée s’opère d’une façon plus ou moins précoce, c’est-à-dire -lorsque les produits sexuels (œufs ou spermatozoïdes) se -forment et mûrissent avant que l’être n’ait atteint son complet -développement. On peut citer comme exemples les Axolotls et -les larves de Tritons qui, les uns normalement, les autres -accidentellement, pondent en ayant encore leurs branchies.</p> - -<p>Très souvent la progenèse n’affecte qu’un seul sexe. Tantôt, -c’est<span class="pagenum" id="Page_495">[495]</span> le sexe femelle qui mûrit à l’état larvaire comme chez -les pucerons, les <i>Stylops</i>, etc.... Tantôt c’est le -sexe mâle, comme chez la Bonellie, les mâles complémentaires -de Cirripèdes, les mâles pygmées des Rotifères, le mâle de -l’Anguille, etc. D’autres fois, enfin, l’animal présente -successivement les deux sexes avec progenèse pour l’un d’entre -eux. C’est ainsi qu’il y a <i>progenèse protandrique</i> chez -les Crustacés cymothoadiens, et, parmi les Vertébrés, chez les -Myxines, qui, mâles dans le jeune âge, deviennent femelles en -vieillissant et en achevant de prendre leur développement. Le -cas des vieilles femelles de Gallinacés à plumage et à instincts -masculins semble être, au contraire, un exemple imparfait de -<i>progenèse protogynique</i>, puisque ces femelles ont pondu -lorsqu’elles avaient encore la livrée des jeunes et qu’elles -ont continué plus tard leur développement, et présentent le -caractère des mâles sans que, cependant, l’on ait constaté la -production de spermatozoïdes.</p> - -<p>Dans les cas extrêmes de progenèse femelle, la reproduction se -fait même sans le concours de l’élément mâle, revenant ainsi -à la forme agamique primordiale. Ces cas sont connus depuis -longtemps sous le nom de <i>pédogenèse</i>. On les a observé -chez les larves de <i>Miastor</i>, de <i>Chironomus</i> et chez -certains pucerons.</p> - -<p>Chaque fois qu’il y a progenèse dans un type déterminé, on -constate soit momentanément, soit d’une façon définitive, un -arrêt de croissance et de développement: l’animal progénétique -a, par suite, l’aspect d’une larve sexuée, lorsqu’on le compare -soit à l’autre sexe, soit aux formes voisines, qui ne présentent -pas le phénomène de la progenèse.</p> - -<p>Cela est en parfaite harmonie avec le principe, si bien mis en -lumière par Herbert Spencer, de <i>l’antagonisme entre la genèse -et la croissance et entre la genèse et le développement</i>. -Cet antagonisme s’explique facilement si l’on songe que les -matériaux employés pour la reproduction ne peuvent servir à -l’accroissement de l’individu. S’il est avantageux pour un -organisme de se reproduire sans acquérir des organes inutiles, -la sélection naturelle déterminera bientôt une progenèse de plus -en plus complète. Les animaux parasites, outre qu’ils tirent de -leur hôte une nourriture abondante, n’ont guère besoin d’une -foule d’organes qui servent à leurs congénères libres dans la -vie de relation. Aussi voyons-nous qu’un très grand nombre -d’animaux parasites sont progénétiques. Les mâles progénétiques -de la Bonellie et des Cirripèdes vivent en parasites dans leurs -femelles. Chez certains types, les pucerons, la progenèse cesse -dès que, la nourriture devenant moins abondante, un déplacement -pourra être nécessaire.</p> - -<p><span class="pagenum" id="Page_496">[496]</span></p> - -<p>En résumé, l’arrêt de développement dû à la progenèse résulte -d’une dérivation des principes nourriciers au détriment -de l’animal progénétique. Dans les exemples de castration -parasitaire que nous avons examinés, le parasite joue, par -rapport à son hôte, absolument le même rôle que la glande -génitale d’un type progénétique. Il détourne, pour sa propre -subsistance, une partie des principes qui auraient servi au -développement de l’animal. Aussi les effets produits sont-ils -tout à fait de même ordre.”</p> -</div> - -<p>A phenomenon so anomalous as this, explicable upon the hypothesis set -forth but not otherwise explicable, furnishes striking verification.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_497">[497]</span></p> - -<h3>CHAPTER XI.<br /> -<span class="subhed1">INTERPRETATION AND QUALIFICATION.</span></h3></div> - - -<p>§ 362. Considering the difficulties of inductive verification, we -have, I think, as clear a correspondence between the <i>à priori</i> -and <i>à posteriori</i> conclusions, as can be expected. The many -factors co-operating to bring about the result in every case, are so -variable in their absolute and relative amounts, that we can rarely -disentangle the effect of each one, and have usually to be content -with qualified inferences. Though in the mass organisms show us an -unmistakable relation between great size and small fertility, yet -special comparisons among them are nearly always partially vitiated -by differences of structure, differences of nutrition, differences -of expenditure. Though it is beyond question that the more complex -organisms are the less prolific, yet as complexity has a certain -general connexion with bulk, and in animals with expenditure, we cannot -often identify its results as independent of these. And, similarly, -though the creatures which waste much matter in producing motion, -sensible and insensible, have lower rates of multiplication than those -which waste less, yet, as the creatures which waste much are generally -larger and more complex, we are again met by an obstacle which limits -our comparisons, and compels us to accept conclusions less definite -than are desirable.</p> - -<p>Such difficulties arise, however, only when we endeavour, as in -foregoing chapters, to prove the inverse variation<span class="pagenum" id="Page_498">[498]</span> between Genesis -and each separate element of Individuation—growth, development, -activity. We are scarcely at all hampered by qualifications when, -from contemplating these special relations, we return to the general -relation. The antagonism between Individuation and Genesis is shown -by all the facts which have been grouped under each head. We have -seen that in ascending from the lowest to the highest types, there is -a decrease of fertility so great as to be absolutely inconceivable, -and even inexpressible by figures; and whether the superiority of -type consists in relative largeness, in greater complexity, in -higher activity, or in some or all of these combined, matters not -to the ultimate inference. The broad fact, enough for us here, is -that organisms in which the integration and differentiation of -matter and motion have been carried furthest, are those in which the -rate of multiplication has fallen lowest. How much of the decline -of reproductive power is due to the greater integration of matter, -how much to its greater differentiation, how much to the larger -amounts of integrated and differentiated motions generated, it may -be impossible to say; and it is not needful to say. These are all -elements of a higher degree of life, an augmented ability to maintain -the organic equilibrium amid environing actions, an increased power -of self-preservation; and we find their invariable accompaniment -to be, a diminished expenditure of matter, or motion, or both, in -race-preservation.</p> - -<p>In brief, then, examination of the evidence shows that there -<i>does</i> exist that relation which we inferred <i>must</i> exist. -Arguing from general data, we saw that for the maintenance of a -species, the ability to produce offspring must be great, in proportion -as the ability of the individuals to contend with destroying forces is -small; and conversely. Arguing from other general data, we saw that, -derived as the self-sustaining and race-sustaining forces are from a -common stock of force, it necessarily happens that, other things equal, -increase of one involves decrease of the other. And then, turning<span class="pagenum" id="Page_499">[499]</span> to -special facts, we have found that this inverse variation is clearly -traceable throughout both the animal and vegetal kingdoms. We may -therefore set it down as a law, that every higher degree of organic -evolution, has for its concomitant a lower degree of that peculiar -organic dissolution which is seen in the production of new organisms.</p> - - -<p class="p2">§ 363. Something remains to be said in reply to the inquiry—how is the -ratio between Individuation and Genesis established in each case? This -inquiry has been but partially answered in the course of the foregoing -argument.</p> - -<p>Many specialities of the reproductive process are manifestly due to -the natural selection of favourable variations. Whether a creature -lays a few large eggs or many small ones equal in weight to the few -large, is not determined by any physiological necessity: here the only -assignable cause is the survival of varieties in which the matter -devoted to reproduction happens to be divided into portions of such -size and number as most to favour multiplication. Whether in any case -there are frequent small broods or larger broods at longer intervals, -depends wholly on the constitutional peculiarity that has arisen from -the dying out of families in which the sizes and intervals of the -broods were least suited to the conditions of life. Whether a species -of animal produces many offspring of which it takes no care or a few -of which it takes much care—that is, whether its reproductive surplus -is laid out wholly in germs or partly in germs and partly in labour on -their behalf—must have been decided by that moulding of constitution -to conditions slowly effected through the more frequent preservation -of descendants from those whose reproductive habits were best adapted -to the circumstances of the species. Given a certain surplus available -for race-preservation, and it is clear that by indirect equilibration -only, can there be established the more or less peculiar distribution -of this surplus which we see in each case. Obviously, too, survival -of the fittest<span class="pagenum" id="Page_500">[500]</span> has a share in determining the proportion between the -amount of matter that goes to Individuation and the amount that goes -to Genesis. Whether the interests of the species are most subserved -by a higher evolution of the individual joined with a diminished -fertility, or by a lower evolution of the individual joined with an -increased fertility, are questions ever being experimentally answered. -If the more-developed and less-prolific variety has a greater number of -survivors, it becomes established and predominant. If, contrariwise, -the conditions of life being simple, the larger or more-organized -individuals gain nothing by their greater size or better organization; -then the greater fertility of the less evolved ones, will insure to -their descendants an increasing predominance.</p> - -<p>But direct equilibration all along maintains the limits within which -indirect equilibration thus works. The necessary antagonism we have -traced, rigidly restricts the changes that natural selection can -produce, under given conditions, in either direction. A greater demand -for Individuation, be it a demand caused by some spontaneous variation -or by an adaptive increase of structure and function, inevitably -diminishes the supply for Genesis; and natural selection cannot, other -things remaining the same, restore the rate of Genesis while the higher -Individuation is maintained. Conversely, survival of the fittest, -acting on a species that has, by spontaneous variation or otherwise, -become more prolific, cannot again raise its lowered Individuation, so -long as everything else continues constant.</p> - - -<p class="p2">§ 364. Here, however, a qualification must be made. It was -parenthetically remarked in <a href="#sect327">§ 327</a>, that the inverse variation between -Individuation and Genesis is not exact; and it was hinted that a slight -modification of statement would be requisite at a more advanced stage -of the argument. We have now reached the proper place for specifying -this modification.</p> - -<p><span class="pagenum" id="Page_501">[501]</span></p> - -<p>Each increment of evolution entails a decrement of reproduction which -is not accurately proportionate, but somewhat less than proportionate. -The gain in the one direction is not wholly cancelled by a loss in -the other direction, but only partially cancelled: leaving a margin -of profit to the species. Though augmented power of self-maintenance -habitually necessitates diminished power of race-propagation, yet the -product of the two factors is greater than before; so that the forces -preservative of race become, thereafter, in excess of the forces -destructive of race, and the race spreads. We shall soon see why this -happens.</p> - -<p>Every advance in evolution implies an economy. That any increase in -bulk, or structure, or activity, may become established, the life of -the organism must be to some extent facilitated by the change—the -cost of self-support must be, on the average, reduced. If the greater -complexity, or the larger size, or the more agile movement, entails -on the individual an outlay that is not repaid in food more-easily -obtained, or danger more-easily escaped; then the individual will -be at a relative disadvantage, and its diminished posterity will -disappear. If the extra outlay is but just made good by the extra -advantage, the modified individual will not survive longer, or leave -more descendants, than the unmodified individuals. Consequently, it -is only when the expense of greater individuation is out-balanced by -a subsequent saving, that it can tend to subserve the preservation of -the individual, and, by implication, the preservation of the race. -The vital capital invested in the alteration must bring a more than -equivalent return. A few instances will show that, whether the change -results from direct equilibration or from indirect equilibration, this -must happen. Suppose a creature takes to performing some act in an -unusual way—leaps where ordinarily its kindred crawl, eludes pursuit -by diving instead of, like others of its kind, by swimming along the -surface, escapes by doubling instead of by speed. Clearly, perseverance -in the modified habit will, other<span class="pagenum" id="Page_502">[502]</span> things equal, imply that it takes -less effort. The creature’s sensations will ever prompt desistance from -the more laborious course; and hence a congenital habit is not likely -to be diverged from unless an economy of force is achieved by the -divergence. Assuming, then, that the new method has no advantage over -the old in directly diminishing the chances of death, the establishment -of it, and of the structural complications involved, nevertheless -implies a physiological gain. Suppose, again, that an animal takes -to some abundant food previously refused by its kind. It is likely -to persist only if the comparative ease in obtaining this food, more -than compensates for any want of adaptation to its digestive organs; -so that superposed modifications of the digestive organs are likely -to arise only when an average economy results. What now must be the -influence on the creature’s system as a whole? Diminished expenditure -in any direction, or increased nutrition however effected, will leave -a greater surplus of materials. The animal will be physiological -richer. Part of its augmented wealth will go towards its own greater -individuation—its size, or its strength, or both, will increase; while -another part will go towards more active genesis. Just as a state of -plethora directly produced enhances fertility; so will such a state -indirectly produced.</p> - -<p>In another way, the same thing must result from those additions -to bulk or complexity or activity that are due to survival of the -fittest. Any change which prolongs individual life will, other things -remaining the same, further the production of offspring. Even when it -is not, like the foregoing, a means of economizing the forces of the -individual, still, if it increases the chances of escaping destruction, -it increases the chances of leaving posterity. Any further degree of -evolution, therefore, will be established only where the cost of it -is more than repaid: part of the gain being shown in the lengthened -life of the individual, and part in the greater production of other -individuals.</p> - -<p><span class="pagenum" id="Page_503">[503]</span></p> - -<p>We have here the solution of various minor anomalies by which the -inverse variation of Individuation and Genesis is obscured. Take as an -instance the fertility of the Blackbird as compared with that of the -Linnet. Both birds lay five eggs, and both usually have two broods. Yet -the Blackbird is far the larger of the two, and ought, according to the -general law, to be much less prolific. What causes this nonconformity? -We shall find an answer in their respective foods and habits. Except -during the time that it is rearing its young, the Linnet collects only -vegetal food—lives during the winter on the seeds it finds in the -fields, or, when hard pressed, picks up around farms; and to obtain -this spare diet is continually flying about. The result, if it survives -the frost and snow, is a considerable depletion; and it recovers its -condition only after some length of spring weather. The Blackbird, on -the other hand, is omnivorous. While it eats grain and fruit when they -come in its way, it depends largely on animal food. It cuts to pieces -and devours the dew-worms which, morning and evening, it finds on the -surface of a lawn, and, even discovering where they are, unearths -them; it swallows slugs, and breaking snail-shells, either with its -beak or by hammering them against stones, tears out their tenants; and -it eats beetles and larvæ. Thus the strength of the Blackbird opens -to it a store of good food, much of which is inaccessible to so small -and weak a bird as a Linnet—a store especially helpful to it during -the cold months, when the hybernating snails in hedge-bottoms yield -it abundant provision. The result is that the Blackbird is ready to -breed very early in spring, and is able during the summer to rear -a second, and sometimes even a third, brood. Here, then, a higher -degree of Individuation secures advantages so great, as to much more -than compensate its cost. It is not that the decline of Genesis is -less than proportionate to the increase of Individuation, but there -is no decline at all. Comparison of the Rat with the Mouse yields a -parallel result. Though they differ greatly in size, yet the one is as -prolific<span class="pagenum" id="Page_504">[504]</span> as the other. This absence of difference cannot be ascribed -to their unlike degrees of activity. We must seek its cause in some -facility of living secured to the Rat by its greater intelligence, -greater power and courage, greater ability to utilize what it finds. -The Rat is notoriously cunning; and its cunning gives success to its -foraging expeditions. It is not, like the Mouse, limited mainly to -vegetal food; but while it eats grain and beans like the Mouse, it also -eats flesh and carrion, devours young poultry and eggs. The result is -that, without a proportionate increase of expenditure, it gets a far -larger supply of nourishment than the Mouse; and relative excess of -nourishment makes possible a larger size without a smaller rate of -multiplication. How clearly this is the cause, we see in the contrast -between the common Rat and the Water-Rat. While the common Rat has -ordinarily several broods a-year of from 10 to 12 each, the Water-Rat, -though somewhat smaller, has but 5 or 6 in a brood, and but one brood, -or sometimes two broods, a-year. But the Water-Rat lives on vegetal -food, and it lacks all that its bold, sagacious, omnivorous congener -gains from the warmth as well as the abundance which men’s habitations -yield.</p> - -<p>The inverse variation of Individuation and Genesis is, therefore, but -approximate. Recognizing the truth that every increment of evolution -which is appropriate to the circumstances of an organism, brings an -advantage somewhat in excess of its cost; we see the general law, as -more strictly stated, to be that Genesis decreases not quite so fast -as Individuation increases. Whether the greater Individuation takes -the form of a larger bulk and accompanying access of strength; whether -it be shown in higher speed or agility; whether it consists in a -modification of structure which facilitates some habitual movement, -or in a visceral change that helps to utilize better the absorbed -aliment; the ultimate effect is identical. There is either a more -economical performance of the same actions, internal or external, or -there is a securing of greater advantages by modified actions, which<span class="pagenum" id="Page_505">[505]</span> -cost no more, or have an increased cost less than the increased gain. -In any case the result is a greater surplus of vital capital, part -of which goes to the aggrandizement of the individual, and part to -the formation of new individuals. While the higher tide of nutritive -matters, everywhere filling the parent-organism, adds to its power of -self-maintenance, it also causes a reproductive overflow larger than -before.</p> - -<p>Hence every type which is best adapted to its conditions, (and this -on the average means every higher type), has a rate of multiplication -that insures a tendency to predominate. Survival of the fittest, acting -alone, is ever replacing inferior species by superior species. But -beyond the longer survival, and therefore greater chance of leaving -offspring, which superiority gives, we see here another way in which -the spread of the superior is insured. Though the more-evolved organism -is the less fertile absolutely, it is the more fertile relatively.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_506">[506]</span></p> - -<h3>CHAPTER XII.<br /> -<span class="subhed1">MULTIPLICATION OF THE HUMAN RACE.</span></h3></div> - - -<p id="sect365">§ 365. The relative fertility of Man considered as a species, and -those changes in Man’s fertility which occur under changed conditions, -must conform to the laws which we have traced thus far. As a matter -of course, the inverse variation between Individuation and Genesis -holds of him as of all other organized beings. His extremely low rate -of multiplication—far below that of all terrestrial Mammals except -the Elephant, (which though otherwise less evolved is, in extent -of integration, more evolved)—we shall recognize as the necessary -concomitant of his much higher evolution. And the causes of increase or -decrease in his fertility, special or general, temporary or permanent, -we shall expect to find in those changes of bulk, of structure, or of -expenditure, which we have in all other cases seen associated with such -effects.</p> - -<p>In the absence of detailed proof that these parallelisms exist, it -might suffice to contemplate the several communities between the -reproductive function in human beings and other beings. I do not refer -simply to the fact that genesis proceeds in a similar manner; but I -refer to the similarity of the relation between the generative function -and the functions which have for their joint end the preservation -of the individual. In Man, as in other creatures that expend much, -genesis commences only when growth and development are declining in -rapidity and approaching their termination. Among the higher organisms -in general, the reproductive<span class="pagenum" id="Page_507">[507]</span> activity, continuing during the prime -of life, ceases when the vigour declines, leaving a closing period of -infertility; and in like manner among ourselves, barrenness supervenes -when middle age brings the surplus vitality to an end. So, too, it is -found that in Man, as in beings of lower orders, there is a period -at which fecundity culminates. In <a href="#sect341">§ 341</a>, facts were cited showing -that at the commencement of the reproductive period, animals bear -fewer offspring than afterwards; and that towards the close of the -reproductive period, there is a decrease in the number produced. In -like manner it is shown by the tables of Dr. Duncan’s recent work, -that the fecundity of women increases up to the age of about 25 -years, and continuing high with but slight diminution till after 30, -then gradually wanes. It is the same with the sizes and weights of -offspring. Infants born of women from 25 to 29 years of age, are both -longer and heavier than infants born of younger or older women; and -this difference has the same implication as the greater total weight -of the offspring produced at a birth, during the most fecund age of -a pluriparous animal. Once more, there is the fact that a too-early -bearing of young produces on a woman the same injurious effects as -on an inferior creature—an arrest of growth and an enfeeblement of -constitution.</p> - -<p>Considering these general and special parallelisms, we might safely -infer that variations of human fertility conform to the same laws -as do variations of fertility in general. But it is not needful to -content ourselves with an implication. Evidence is assignable that -what causes increase or decrease of genesis in other creatures, causes -increase or decrease of genesis in Man. It is true that, even more -than hitherto, our reasonings are beset by difficulties. So numerous -are the inequalities in the conditions, that but few unobjectionable -comparisons can be made. The human races differ considerably in their -sizes, and notably in their degrees of cerebral development. The -countries they inhabit entail on them widely different consumptions -of matter for maintenance of<span class="pagenum" id="Page_508">[508]</span> temperature. Both in their qualities -and quantities the foods they live on are unlike; and the supply is -here regular and there very irregular. Their expenditures in bodily -action are extremely unequal; and even still more unequal are their -expenditures in mental action. Hence the factors, varying so much in -their amounts and combinations, can scarcely ever have their respective -effects identified. Nevertheless there are a few comparisons the -results of which may withstand criticism.</p> - - -<p class="p2" id="sect366">§ 366. The increase of fertility caused by a nutrition that is greatly -in excess of the expenditure, is to be detected by contrasting -populations of the same race, or allied races, one of which obtains -good and abundant sustenance much more easily than the other. Three -cases may here be set down.</p> - -<p>The traveller Barrow, describing the Cape-Boers, says:—“Unwilling -to work and unable to think,” ... “indulging to excess in the -gratification of every sensual appetite, the African peasant grows to -an unwieldy size;” and respecting the other sex, he adds—“the women -of the African peasantry lead a life of the most listless inactivity,” -Then, after illustrating these statements, he goes on to note “the -prolific tendency of all the African peasantry. Six or seven children -in a family are considered as very few; from a dozen to twenty are -not uncommon.” The native races of this region yield evidence to the -same effect. Speaking of the cruelly-used Hottentots (he is writing -a century ago), who, while they are poor and ill-fed, have to do all -the work for the idle Boers, Barrow says that they “seldom have more -than two or three children; and many of the women are barren.” This -unusual infertility stands in remarkable contrast with the unusual -fertility of the Kaffirs, of whom he afterwards gives an account. -Rich in cattle, leading easy lives, and living almost exclusively on -animal food (chiefly milk with occasional flesh), these people were -then reputed<span class="pagenum" id="Page_509">[509]</span> to have a very high rate of multiplication. Barrow -writes:—“They are said to be exceedingly prolific; that twins are -almost as frequent as single births, and that it is no uncommon -thing for a woman to have three at a time.” Probably both these -statements are in excess of the truth; but there is room for large -discounts without destroying the extreme difference. A third instance -is that of the French-Canadians. “<i>Nous sommes terribles pour les -enfants!</i>” observed one of them to Prof. Johnston, who tells us -that the man who said this “was one of fourteen children—was himself -the father of fourteen, and assured me that from eight to sixteen was -the usual number of the farmers’ families. He even named one or two -women who had brought their husbands five-and-twenty, and threatened -‘<i>le vingt-sixième pour le prêtre</i>.’” From these large families, -joined with the early marriages and low rate of mortality, it results -that, by natural increase, “there are added to the French-Canadian -population of Lower Canada four persons for every one that is added to -the population of England.” Now these French-Canadians are described -by Prof. Johnston as home-loving, contented, unenterprising; and as -living in a region where “land and subsistence are easily obtained.” -Very moderate industry brings to them liberal supplies of necessaries; -and they pass a considerable portion of the year in idleness. Hence -the cost of Individuation being much reduced, the rate of Genesis -is much increased. That this uncommon fertility is not due to any -direct influence of the locality, is implied by the fact that along -with the “restless, discontented, striving, burning energy of their -Saxon neighbours,” no such rate of multiplication is observed; while -further south, where the physical circumstances are more favourable if -anything, the Anglo-Saxons, leading lives of excessive activity, have a -fertility below the average. And that the peculiarity is not a direct -effect of race, is proved by the fact that in Europe, the rural French -are certainly not more prolific than the rural English.</p> - -<p><span class="pagenum" id="Page_510">[510]</span></p> - -<p>To every reader there will probably occur the seemingly-adverse -evidence furnished by the Irish; who, though not well fed, multiply -fast. Part of this more rapid increase is due to the earlier marriages -common among them, and consequent quicker succession of generations—a -factor which, as we have seen, has a larger effect than any other on -the rate of multiplication. Part of it is due to the greater generality -of marriage—to the comparative smallness of the number who die without -having had the opportunity of producing offspring. The effects of -these causes having been deducted, we may doubt whether the Irish, -individually considered, would be found more prolific than the English. -Perhaps, however, it will be said that, considering their diet, they -ought to be less prolific. This is by no means obvious. It is not -simply a question of nutriment absorbed. It is a question of how much -remains after the expenditure in self-maintenance. Now a notorious -peculiarity in the life of the Irish peasant is, that he obtains a -return of food which is large in proportion to his outlay in labour. -The cultivation of his potatoe-ground occupies each cottager but a -small part of the year; and the domestic economy of his wife is not of -a kind to entail on her much daily exertion. Consequently the crop, -tolerably abundant in quantity though innutritive in quality, possibly -suffices to meet the comparatively-low expenditure, and to leave a good -surplus for genesis—perhaps a greater surplus than remains to the -males and females of the English peasantry, who, though fed on better -food, are harder worked.</p> - -<p>We conclude, then, that in the human race, as in all other races, such -absolute or relative abundance of nutriment as leaves a large excess -after defraying the cost of carrying on parental life, is accompanied -by a high rate of genesis.<a id="FNanchor_66" href="#Footnote_66" class="fnanchor">[66]</a></p> - - -<p class="p2" id="sect367">§ 367. Evidence of the converse truth, that relative increase<span class="pagenum" id="Page_511">[511]</span> of -expenditure, leaving a diminished surplus, reduces the degree of -fertility, is not wanting. Some of it has been set down for the sake of -antithesis in the foregoing section. Here may be grouped a few facts of -a more special kind having the same implication.</p> - -<p>To prove that much bodily labour renders women less prolific, requires -more evidence than has at present been collected. Nevertheless it may -be noted that De Boismont in France and Dr. Szukits in Austria, have -shown by extensive statistical comparisons, that the reproductive -age is reached a year later by women of the labouring class than by -middle-class women; and while ascribing this delay in part to inferior<span class="pagenum" id="Page_512">[512]</span> -nutrition, we may suspect that it is in part due to greater muscular -expenditure. A kindred fact, admitting of a kindred interpretation, -may be added. Though the comparatively-low rate of increase in France -is attributed to other causes, yet, very possibly, one of its causes -is the greater proportion of hard work entailed on French women, by -the excessive abstraction of men for non-productive occupations, -military and civil. The higher rate of multiplication in England than -in continental countries generally, is not improbably furthered by the -easier lives which English women lead.</p> - -<p>That absolute or relative infertility is commonly produced in women -by mental labour carried to excess, is more clearly shown. Though the -regimen of upper-class girls is not what it should be, yet, considering -that their feeding is better than that of girls belonging to the poorer -classes, while, in most other respects, their physical treatment is -not worse, the<span class="pagenum" id="Page_513">[513]</span> deficiency of reproductive power among them may be -reasonably attributed to the overtaxing of their brains—an overtaxing -which produces a serious reaction on the physique. This diminution -of reproductive power is not shown only by the greater frequency of -absolute sterility; nor is it shown only in the earlier cessation of -child-bearing; but it is also shown in the very frequent inability of -such women to suckle their infants. In its full sense, the reproductive -power means the power to bear a well-developed infant and to supply -that infant with the natural food for the natural period. Most of the -flat-chested girls who survive their high-pressure education, are -incompetent to do this. Were their fertility measured by the number -of children they could rear without artificial aid, they would prove -relatively very infertile.</p> - -<p>The cost of reproduction to males being so much less than it is to -females, the antagonism between Genesis and Individuation is not often -shown in men by suppression of generative power consequent on unusual -expenditure in bodily action. Nevertheless, there are indications that -this results in extreme cases. We read that the ancient <i>athletæ</i> -rarely had children; and among such of their modern representatives as -acrobats, an allied relation of cause and effect is alleged. Indirectly -this truth, or rather its converse, appears to have been ascertained -by those who train men for feats of strength—they find it needful to -insist on continence.</p> - -<p>Special proofs that in men great cerebral expenditure diminishes or -destroys generative power, are difficult to obtain. It is, indeed, -asserted that intense application to mathematics, requiring as it does -extreme concentration of thought, is apt to have this result; and it is -asserted, too, that this result is produced by the excessive emotional -excitement of gambling. Then, again, it is a matter of common remark -how frequently men of unusual mental activity leave no offspring. But -facts of this kind admit of another interpretation. The reaction of -the brain on the body is so violent—the<span class="pagenum" id="Page_514">[514]</span> overtaxing of the nervous -system is so apt to prostrate the heart and derange the digestion; that -the incapacities caused in these cases, are probably often due more to -constitutional disturbance than to the direct deduction which excessive -action entails. Such instances harmonize with the hypothesis; but how -far they yield it positive support we cannot say.</p> - - -<p class="p2">§ 368. An objection must here be guarded against. It is likely to -be urged that since the civilized races are, on the average, larger -than many of the uncivilized races; and since they are also somewhat -more complex as well as more active; they ought, in conformity with -the alleged general law, to be less prolific. There is, however, no -evidence to prove that they are so: on the whole, they seem rather the -reverse.</p> - -<p>The reply is that were all other things equal, these superior varieties -of men should have inferior rates of increase. But other things are not -equal; and it is to the inequality of other things that this apparent -anomaly is attributable. Already we have seen how much more fertile -domesticated animals are than their wild kindred; and the causes of -this greater fertility are also the causes of the greater fertility, -relative or absolute, which civilized men exhibit when compared with -savages.</p> - -<p>There is the difference in amount of food. Australians, Fuegians, and -sundry races that might be named as having low rates of multiplication, -are obviously underfed. The sketches of natives contained in the -volumes of Livingstone, Baker, and others, yield clear proofs of the -extreme depletion common among the uncivilized. In quality as well -as in quantity, their feeding is bad. Wild fruits, insects, larvæ, -vermin, &c., which we refuse with disgust, often enter largely into -their dietary. Much of this inferior food they eat uncooked; and they -have not our elaborate appliances for mechanically-preparing it, and -rejecting its useless parts. So that they live on matters of less -nutritive value, which<span class="pagenum" id="Page_515">[515]</span> cost more both to masticate and to digest. -Further, to uncivilized men supplies of food come very irregularly. -Long periods of scarcity are divided by short periods of abundance. -And though by gorging when opportunity occurs, something is done -towards compensating for previous fasting, yet the effects of prolonged -starvation cannot be neutralized by occasional enormous meals. Bearing -in mind, too, that improvident as they are, savages often bestir -themselves only under pressure of hunger, we may fairly consider them -as habitually ill-nourished—may see that even the poorer classes of -civilized men, making regular meals on food separated from innutritive -matters, easy to masticate and digest, tolerably good in quality and -adequate if not abundant in quantity, are much better nourished.</p> - -<p>Then, again, though a greater consumption in muscular action appears -to be undergone by civilized men than by savages; and though it is -probably true that among our labouring people the daily repairs cost -more; yet in many cases there does not exist so much difference as we -are apt to suppose. The chase is very laborious; and great amounts of -exertion are gone through by the lowest races in seeking and securing -the odds and ends of wild food on which they largely depend. We -naturally assume that because barbarians are averse to regular labour, -their muscular action is less than our own. But this is not necessarily -true. The monotonous toil is what they cannot tolerate; and they may -be ready to go through as much or more exertion when it is joined with -excitement. If we remember that the sportsman who gladly scrambles -up and down rough hill-sides all day after grouse or deer, would -think himself hardly used had he to spend as much effort and time in -digging; we shall see that a savage who is the reverse of industrious, -may nevertheless be subject to a muscular waste not very different in -amount from that undergone by the industrious. When it is added that a -larger physiological expenditure is entailed on the uncivilized than -on the<span class="pagenum" id="Page_516">[516]</span> civilized by the absence of good appliances for shelter and -protection—that in some cases they have to make good a greater loss -of heat, and in other cases suffer much wear from irritating swarms of -insects; we shall see that the total cost of self-maintenance among -them is probably in many cases little less, and in some cases more, -than it is among ourselves.</p> - -<p>So that though, on the average, the civilized are probably larger than -the savage; and though they are, in their nervous systems at least, -somewhat more complex; and though, other things equal, they ought to -be the less prolific; yet other things are so unequal as to make it -quite conformable to the general law that they should be more prolific. -In <a href="#sect365">§ 365</a> we observed how, among inferior animals, higher evolution -sometimes makes self-preservation far easier, by opening the way to -resources previously unavailable: so involving an undiminished, or -even an increased, rate of genesis. And similarly we may expect that -among races of men, those whose slight further developments have been -followed by habits and arts which immensely facilitate life, will not -exhibit a lower degree of fertility, and may even exhibit a higher.</p> - - -<p class="p2">§ 369. One more objection has to be met—a kindred objection to which -there is a kindred reply. Cases may be named of men conspicuous -for activity, bodily and mental, who were also noted, not for less -generative power than usual, but for more. As their superiorities -indicate higher degrees of evolution, it may be urged that such men -should, according to the theory, have lower degrees of reproductive -activity. The fact that here, along with increased powers of -self-preservation, there go increased powers of race-propagation, -seems irreconcilable with the general doctrine. Reconciliation is not -difficult however.</p> - -<p>The cases are analogous to some before named, in which more abundant -food simultaneously aggrandizes the individual<span class="pagenum" id="Page_517">[517]</span> and adds to the -production of new individuals: the difference between the cases -being, that instead of a better external supply of materials there -is a better internal utilization of materials. Creatures of the same -species notoriously differ in goodness of constitution. Here there -is some visceral defect, showing itself in feebleness of all the -functions; while here some peculiarity of organic balance, some high -quality of tissue, some abundance or potency of the digestive juices, -gives to the system a perpetual high tide of rich blood, which serves -at once to enhance the vital activities and to raise the power of -propagation. Such variations, however, are independent of changes in -the <i>proportion</i> between Individuation and Genesis. This remains -the same, while both are increased or decreased by the increase or -decrease of the common stock of materials.</p> - -<p>An illustration will best clear up any perplexity. Let us say that -the fuel burnt in the furnace of a locomotive steam-engine, answers -to the food which a man consumes. Let us say that the produced steam -expended in working the engine, corresponds to that portion of absorbed -nutriment which carries on the man’s functions and activities. And -let us say that the steam blowing off at the safety-valve, answers to -that portion of the absorbed nutriment which goes to the propagation -of the race. Such being the conditions of the case, several kinds of -variations are possible. All other circumstances remaining the same, -there may be changes of proportion between the steam used for working -the engine and the steam that escapes by the safety-valve. There may -be a structural or organic change of proportion. By enlarging the -safety-valve or weakening its spring, while the cylinders are reduced -in size, there may be established a constitutionally-small power of -locomotion and a constitutionally-large amount of escape-steam; and -inverse variations so produced, will answer to the inverse variations -between Individuation and Genesis which different types of organisms<span class="pagenum" id="Page_518">[518]</span> -show us. Again, there may be a functional change of proportion. If the -engine has to draw a considerable load, the abstraction of steam by -the cylinders greatly reduces the discharge by the safety-valve; and -if a high velocity is kept up, the discharge from the safety-valve -entirely ceases. Conversely, if the velocity is low, the escape-steam -bears a large ratio to the steam consumed by the motor apparatus; -and if the engine becomes stationary the whole of the steam escapes -by the safety-valve. This inverse variation answers to that which -we have traced between Expenditure and Genesis, as displayed in the -contrasts between species of the same type but unlike activities, -and in the contrasts between active and inactive individuals of the -same species. But now beyond these inverse variations between the -quantities of consumed steam and escape-steam, which are structurally -and functionally caused, there are coincident variations, producible -in both by changes in the quantity of steam supplied—changes which -may be caused in several ways. In the first place, the fuel thrown -into the furnace may be increased or made better. Other things equal, -there will result a more active locomotion as well as a greater escape; -and this will answer to that simultaneous addition to its individual -vigour and its reproductive activity, caused in an animal by a larger -quantity, or a superior quality, of food. In the second place, the -steam generated may be economized. Loss by radiation from the boiler -may be lessened by a covering of non-conducting substances; and part -of the steam thus prevented from condensing, will go to increase the -working power of the engine, while part will be added to the quantity -blowing off. This variation corresponds to that simultaneous addition -to bodily vigour and propagative power, which results in animals -that have to expend less in keeping up their temperatures. In the -third place, by improvement of the steam-generating apparatus, more -steam may be obtained from a given weight of fuel. A better-formed -evaporating surface, or boiler tubes which conduct more rapidly, or -an increased number of them<span class="pagenum" id="Page_519">[519]</span> may cause a larger absorption of heat -from the burning mass or the hot gases it gives off; and the extra -steam generated by this extra heat will, as before, augment both the -motive force and the emission through the safety-valve. And this last -case of coincident variation, is parallel to the case with which we -are here concerned—the augmentation of individual expenditure and of -reproductive energy, that may be caused by a superiority of some organ -on which the utilizing or economizing of materials depends.</p> - -<p>Manifestly, therefore, an increased expenditure for Genesis, or an -increased expenditure for Individuation, may arise in one of two quite -different ways—either by diminution of the antagonistic expenditure, -or by addition to the store which supplies both expenditures; and -confusion results from not distinguishing between these. Given the -ratio 4 to 20, as expressive of the relative costs of Genesis and -Individuation; then the expenditure for Genesis may be raised to 5 -while the expenditure for Individuation is raised to 25, without any -alteration of type, merely by favourable circumstances or superiority -of constitution. On the other hand, circumstances remaining the same, -the expenditure for Genesis may be raised from 4 to 5, by lowering the -expenditure for Individuation from 20 to 19: which change of ratio may -be either functional and temporary, or structural and permanent. And -only when it is the last does it illustrate that inverse variation -between degree of evolution and degree of procreative dissolution, -which we have everywhere seen.</p> - - -<p class="p2">§ 370. There is no reason to suppose, then, that the laws of -multiplication which hold of other beings, do not hold of the human -being. On the contrary, there are special facts which unite with -general implications to show that these laws do hold of the human -being. The absence of direct evidence in some cases where it might be -looked for, we find fully explained when all the factors are taken into -account. And certain seemingly-adverse facts prove, on examination,<span class="pagenum" id="Page_520">[520]</span> to -be facts belonging to a different category from that in which they are -placed, and harmonize with the rest when rightly interpreted.</p> - -<p>The conformity of human fertility to the laws of multiplication in -general, being granted, it remains to inquire what effects must be -caused by permanent changes in men’s natures and circumstances. Thus -far we have observed how, by their exceptionally-high evolution and -exceptionally-low fertility, mankind display the inverse variation -between Individuation and Genesis, in one of its extremes. And we have -also observed how mankind, like other kinds, are functionally changed -in their rates of multiplication by changes of conditions. But we have -not observed how alteration of structure in Man entails alteration -of fertility. The influence of this factor is so entangled with the -influences of other factors which are for the present more potent, that -we cannot recognize it. Here, if we proceed at all, we must proceed -deductively.</p> - -<hr class="tb" /> - -<p>[<span class="smcap">Note.</span>—From among the publications of the American Academy of -Political and Social Science, there was sent to me some years ago an -essay entitled “The Significance of a Decreasing Birth Rate” by (Miss) -J. L. Brownell, Fellow in Political Science, Bryn Mawr College. This -essay contains a number of elaborate comparisons drawn from the vital -statistics of the tenth United States Census. The results of these -comparisons are thus summed up:—</p> - -<div class="blockquot"> - -<p>“1. Whether or not it be true that the means spoken of by Dr. -Billings, M. Dumont, M. Levasseur, and Dr. Edson has become an -important factor in the diminishing birth-rate of civilized -countries, it is evident that it is not the only factor, and -that, quite apart from voluntary prevention, there is a distinct -problem to be investigated. This is shown by the fact that the -white and the colored birth-rate vary together.</p> - -<p>“2. Mr. Spencer’s generalization that the birth-rate diminishes -as the rate of individual evolution increases is confirmed by a -comparison of the birth-rates with the death-rates from nervous -diseases, and also<span class="pagenum" id="Page_521">[521]</span> with the density of population, the values -of agricultural and manufactured products, and the mortgage -indebtedness.”</p> -</div> - -<p>Of course multitudinous differences of race, class, mode of living, -occupation, locality, make it difficult to draw positive inferences -from the data; but the inferences above drawn are held to remain -outstanding after allowing for all the qualifying conditions.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_522">[522]</span></p> - -<h3>CHAPTER XIII.<br /> -<span class="subhed1">HUMAN POPULATION IN THE FUTURE.</span></h3></div> - - -<p>§ 371. Any further evolution in the most highly-evolved of terrestrial -beings, Man, must be of the same nature as evolution in general. -Structurally considered, it may consist in greater integration, -or greater differentiation, or both—augmented bulk, or increased -heterogeneity and definiteness, or a combination of the two. -Functionally considered, it may consist in a larger sum of actions, -or more multiplied varieties of actions, or both—a larger amount of -sensible and insensible motion generated, or motions more numerous in -their kinds and more intricate and exact in their co-ordinations, or -motions that are greater alike in quantity, complexity, and precision.</p> - -<p>Expressing the change in terms of that more special evolution displayed -by organisms; we may say that it must be one which further adapts the -moving equilibrium of organic actions. As was pointed out in <i>First -Principles</i>, § 173, “the maintenance of such a moving equilibrium, -requires the habitual genesis of internal forces corresponding in -number, directions, and amounts to the external incident forces—as -many inner functions, single or combined, as there are single or -combined outer actions to be met.” And it was also pointed out that -“the structural complexity accompanying functional equilibration, is -definable as one in which there are as many specialized parts as are -capable, separately and jointly, of counteracting the separate and -joint forces<span class="pagenum" id="Page_523">[523]</span> amid which the organism exists.” Clearly, then, since -all incompletenesses in Man as now constituted, are failures to meet -certain of the outer actions (mostly involved, remote, irregular), to -which he is exposed; every advance implies additional co-ordinations of -actions and accompanying complexities of organization.</p> - -<p>Or, to specialize still further this conception of future progress, we -may consider it as an advance towards completion of that continuous -adjustment of internal to external relations, which Life shows us. -In Part I. of this work, where it was shown that the correspondence -between inner and outer actions which under its phenomenal aspect, -we call Life, is a particular kind of what, in terms of Evolution, -we called a moving equilibrium; it was shown that the degree of life -varies as the degree of correspondence. Greater evolution or higher -life implies, then, such modifications of human nature as shall make -more exact the existing correspondences, or shall establish additional -correspondences, or both. Connexions of phenomena of a rare, distant, -unobtrusive, or intricate kind, which we either suffer from or do not -take advantage of, have to be responded to by new connexions of ideas, -and acts properly combined and proportioned: there must be increase -of knowledge, or skill, or power, or of all these. And to effect this -more extensive, more varied, and more accurate, co-ordination of -actions, there must be organization of still greater heterogeneity and -definiteness.</p> - - -<p class="p2">§ 372. Let us, before proceeding, consider in what particular ways this -further evolution, this higher life, this greater co-ordination of -actions, may be expected to show itself.</p> - -<p>Will it be in strength? Probably not to any considerable degree. -Mechanical appliances are fast supplanting brute force, and doubtless -will continue doing this. Though at present civilized nations largely -depend for self-preservation on vigour of limb, and are likely to do -so while wars continue;<span class="pagenum" id="Page_524">[524]</span> yet that progressive adaptation to the social -state which must at last bring wars to an end, will leave the amount -of muscular power to adjust itself to the requirements of a peaceful -<i>regime</i>. Though, taking all things into account, the muscular -power then required may not be less than now, there seems no reason why -more should be required.</p> - -<p>Will it be swiftness or agility? Probably not. In savages these are -important elements of the ability to maintain life; but in civilized -men they aid self-preservation in quite minor degrees, and there -seems no circumstance likely to necessitate an increase of them. -By games and gymnastic competitions, such attributes may indeed be -artificially increased; but no artificial increase which does not bring -a proportionate advantage can be permanent; since, other things equal, -individuals and societies that devote the same amounts of energy in -ways which subserve life more effectually, must by and by predominate.</p> - -<p>Will it be in mechanical skill, that is, in the better-co-ordination -of complex movements? Most likely in some degree. Awkwardness is -continually entailing injuries and deaths. Moreover the complicated -tools which civilization brings into use, are constantly requiring -greater delicacy of manipulation. All the arts, industrial and -æsthetic, as they develop, imply a corresponding development of -perceptive and executive faculties in men: the two act and react.</p> - -<p>Will it be in intelligence? Largely, no doubt. There is ample room -for advance in this direction, and ample demand for it. Our lives are -universally shortened by our ignorance. In attaining complete knowledge -of our own natures and of the natures of surrounding things—in -ascertaining the conditions of existence to which we must conform, -and in discovering means of conforming to them under all variations -of seasons and circumstances; we have abundant scope for intellectual -progress.</p> - -<p>Will it be in morality, that is, in greater power of self-regulation?<span class="pagenum" id="Page_525">[525]</span> -Largely also: perhaps most largely. Right conduct is usually come short -of more from defect of will than defect of knowledge. For the right -co-ordination of those complex actions which constitute human life in -its civilized form, there goes not only the pre-requisite—recognition -of the proper course; but the further pre-requisite—a due impulse to -pursue that course. On calling to mind our daily failures to fulfil -often-repeated resolutions, we shall perceive that lack of the needful -desire, rather than lack of the needful insight, is the chief cause of -faulty action. A further endowment of those feelings which civilization -is developing in us—sentiments responding to the requirements of the -social state—emotive faculties that find their gratifications in the -duties devolving on us—must be acquired before the crimes, excesses, -diseases, improvidences, dishonesties, and cruelties, that now so -greatly diminish the duration of life, can cease.</p> - -<p>Thus, looking at the several possibilities, and asking what direction -this further evolution, this more complete moving equilibrium, this -better adjustment of inner to outer relations, this more perfect -co-ordination of actions, is likely to take; we conclude that it must -take mainly the direction of a higher intellectual and emotional -development.</p> - - -<p class="p2">§ 373. This conclusion we shall find equally forced on us if we -inquire for the causes which are to bring about such results. No -more in the case of Man than in the case of any other being, can -we presume that evolution has taken place, or will hereafter take -place, spontaneously. In the past, at present, and in the future, all -modifications, functional and organic, have been, are, and must be, -immediately or remotely consequent on surrounding conditions. What, -then, are those changes in the environment to which, by direct or -indirect equilibration, the human organism has been adjusting itself, -is adjusting itself now, and will continue to<span class="pagenum" id="Page_526">[526]</span> adjust itself? And how -do they necessitate a higher evolution of the organism?</p> - -<p>Civilization, everywhere having for its antecedent the increase -of population, and everywhere having for one of its consequences -a decrease of certain race-destroying forces, has for a further -consequence an increase of certain other race-destroying forces. Danger -of death from predatory animals lessens as men grow more numerous. -Though, as they spread over the Earth and divide into tribes, men -become wild beasts to one another, yet the danger of death from this -cause also diminishes as tribes coalesce into nations. But the danger -of death which does not diminish, is that produced by augmentation of -numbers itself—the danger from deficiency of food. Supposing human -nature to remain unchanged, the mortality hence resulting would, on -the average, rise as human beings multiplied. If mortality, under -such conditions, does not rise, it must be because the supply of food -also augments; and this implies some change in human habits wrought -by stress of human needs. Here, then, is the permanent cause of -modification to which civilized men are exposed. Though the intensity -of its action is ever being mitigated in one direction by greater -production of food, it is, in the other direction, ever being added -to by the greater production of individuals. Manifestly, the wants of -their redundant numbers constitute the only stimulus mankind have to -obtain more necessaries of life. Were not the demand beyond the supply, -there would be no motive to increase the supply. And manifestly, this -excess of demand over supply is perennial: this pressure of population, -of which it is the index, cannot be eluded. Though by the emigration -that takes place when the pressure arrives at a certain intensity, -temporary relief is from time to time obtained; yet as, by this -process, all habitable countries must become peopled, it follows that -in the end the pressure, whatever it may then be, must be borne in full.</p> - -<p>This constant increase of people beyond the means of subsistence<span class="pagenum" id="Page_527">[527]</span> -causes, then, a never-ceasing requirement for skill, intelligence, and -self-control—involves, therefore, a constant exercise of these and -gradual growth of them. Every industrial improvement is at once the -product of a higher form of humanity, and demands that higher form of -humanity to carry it into practice. The application of science to the -arts, is the bringing to bear greater intelligence for satisfying our -wants, and implies continued progress of that intelligence. To get more -produce from the acre, the farmer must study chemistry, must adopt new -mechanical appliances, and must, by the multiplication of processes, -cultivate both his own powers and the powers of his labourers. To -meet the requirements of the market, the manufacturer is perpetually -improving his old machines and inventing new ones; and by the -premium of high wages incites artizans to acquire greater skill. The -daily-widening ramifications of commerce entail on the merchant a need -for more knowledge and more complex calculations; while the lessening -profits of the ship-owner force him to build more scientifically, to -get captains of higher intelligence and better crews. In all cases -pressure of population is the original cause. Were it not for the -competition this entails, more thought and energy would not daily be -spent on the business of life; and growth of mental power would not -take place. Difficulty in getting a living is alike the incentive to a -higher education of children, and to a more intense and long-continued -application in adults. In the mother it prompts foresight, economy, -and skilful house-keeping; in the father, laborious days and constant -self-denial. Nothing but necessity could make men submit to this -discipline; and nothing but this discipline could produce a continued -progression.</p> - -<p>In this case, as in many others, Nature secures each step in advance by -a succession of trials; which are perpetually repeated, and cannot fail -to be repeated, until success is achieved. All mankind in turn subject -themselves more or<span class="pagenum" id="Page_528">[528]</span> less to the discipline described; they either may -or may not advance under it; but, in the nature of things, only those -who <i>do</i> advance under it eventually survive. For, necessarily, -families and races whom this increasing difficulty of getting a living -which excess of fertility entails, does not stimulate to improvements -in production—that is, to greater mental activity—are on the high -road to extinction; and must ultimately be supplanted by those whom -the pressure does so stimulate. This truth we have recently seen -exemplified in Ireland. And here, indeed, without further illustration, -it will be seen that premature death, under all its forms and from all -its causes, cannot fail to work in the same direction. For as those -prematurely carried off must, in the average of cases, be those in whom -the power of self-preservation is the least, it unavoidably follows -that those left behind to continue the race, must be those in whom the -power of self-preservation is the greatest—must be the select of their -generation. So that, whether the dangers to existence be of the kind -produced by excess of fertility, or of any other kind, it is clear that -by the ceaseless exercise of the faculties needed to contend with them, -and by the death of all men who fail to contend with them successfully, -there is ensured a constant progress towards a higher degree of skill, -intelligence, and self-regulation—a better co-ordination of actions—a -more complete life.<a id="FNanchor_67" href="#Footnote_67" class="fnanchor">[67]</a></p> - - -<p class="p2">§ 374. The proposition at which we have thus arrived is, then, that -excess of fertility, through the changes it is ever<span class="pagenum" id="Page_529">[529]</span> working in Man’s -environment, is itself the cause of Man’s further evolution; and the -obvious corollary here to be drawn is, that Man’s further evolution so -brought about, itself necessitates a decline in his fertility.</p> - -<p>All future progress in civilization which the never-ceasing pressure -of population must produce, will be accompanied by an enhanced cost of -Individuation, both in structure and function; and more especially in -nervous structure and function. The peaceful struggle for existence in -societies ever growing more crowded and more complicated, must have -for its concomitant an increase of the great nervous centres in mass, -in complexity, in activity. That larger body of emotion needed as a -fountain of energy for men who have to hold their places and rear their -families under the intensifying competition of social life, is, other -things equal, the correlative of larger brain. Those higher feelings -presupposed by the better self-regulation which, in a better society, -can alone enable the individual to leave a persistent posterity, are, -other things equal, the correlatives of a more complex brain; as are -also those more numerous, more varied, more general, and more abstract -ideas, which must also become increasingly requisite for successful -life as society advances. And the genesis of this larger quantity of<span class="pagenum" id="Page_530">[530]</span> -feeling and thought, in a brain thus augmented in size and developed -in structure, is, other things equal, the correlative of a greater -wear of nervous tissue and greater consumption of materials to repair -it. So that both in original cost of construction and in subsequent -cost of working, the nervous system must become a heavier tax on the -organism. Already the brain of the civilized man is larger by nearly -thirty per cent. than the brain of the savage. Already, too, it -presents an increased heterogeneity—especially in the distribution -of its convolutions. And further changes like these which have taken -place under the discipline of civilized life, we infer will continue -to take place. But everywhere and always, evolution is antagonistic -to procreative dissolution. Whether it be in greater growth of the -organs which subserve self-maintenance, whether it be in their added -complexity of structure, or whether it be in their higher activity, -the abstraction of the required materials implies a diminished reserve -of materials for race-maintenance. And we have seen reason to believe -that this antagonism between Individuation and Genesis, becomes -unusually marked where the nervous system is concerned, because of the -costliness of nervous structure and function. In <a href="#sect346">§ 346</a> was pointed out -the apparent connexion between high cerebral development and prolonged -delay of sexual maturity; and in <a href="#sect366">§§ 366</a>, <a href="#sect367">367</a>, the evidence went to show -that where exceptional fertility exists there is sluggishness of mind, -and that where there has been during education excessive expenditure -in mental action, there frequently follows a complete or partial -infertility. Hence the particular kind of further evolution which Man -is hereafter to undergo, is one which, more than any other, may be -expected to cause a decline in his power of reproduction.</p> - -<p>The higher nervous development and greater expenditure in nervous -action, here described as indirectly brought about by increase of -numbers, and as thereafter becoming a check on the increase of numbers, -must not be taken to imply<span class="pagenum" id="Page_531">[531]</span> an intenser strain—a mentally-laborious -life. The greater emotional and intellectual power and activity above -contemplated, must be understood as becoming, by small increments, -organic, spontaneous, and pleasurable. As, even when relieved from -the pressure of necessity, large-brained Europeans voluntarily enter -on enterprises and activities which the savage could not keep up even -to satisfy urgent wants; so, their still larger-brained descendants -will, in a still higher degree, find their gratifications in careers -entailing still greater mental expenditures. This enhanced demand for -materials to establish and carry on the psychical functions, will be a -constitutional demand. We must conceive the type gradually so modified, -that the more-developed nervous system irresistibly draws off, for its -normal and unforced activities, a larger proportion of the common stock -of nutriment; and while so increasing the intensity, completeness, and -length of the individual life, necessarily diminishing the reserve -applicable to the setting up of new lives—no longer required to be so -numerous.</p> - -<p>Though the working of this process will doubtless be interfered -with and modified in the future, as it has been in the past, by the -facilitations of living which civilization brings; yet nothing beyond -temporary interruptions can so be caused. However much the industrial -arts may be improved, there must be a limit to the improvement; while, -with a rate of multiplication in excess of the rate of mortality, -population must continually tread on the heels of production. So that -though, during the earlier stages of civilization, an increased amount -of food may accrue from a given amount of labour, there must come a -time when this relation will be reversed, and when every additional -increment of food will be obtained by a more than proportionate labour: -the disproportion growing ever higher, and the diminution of the -reproductive power becoming greater.</p> - - -<p class="p2">§ 375. There now remains but to inquire towards what<span class="pagenum" id="Page_532">[532]</span> limit this -progress tends. So long as the fertility of the race is more than -sufficient to balance the diminution by deaths, population must -continue to increase. So long as population continues to increase, -there must be pressure on the means of subsistence. And so long -as there is pressure on the means of subsistence, further mental -development must go on, and further diminution of fertility must -result; provided that the actions and reactions which have been -described are not artificially interfered with. I append this -qualifying clause advisedly, and especially emphasize it, because -these actions and reactions have been hitherto, and are now, -greatly interfered with by governments, and the continuance of the -interferences may retard, if not stop, that further evolution which -would else go on.</p> - -<p>I refer to those hindrances to the survival of the fittest which -in earlier times resulted from the undiscriminating charities of -monasteries and in later times from the operation of Poor Laws. Of -course if the competition which increasing pressure of population -entails, is prevented from acting on a considerable part of the -community, such part, saved from the needed intellectual and moral -stress, will not undergo any further mental development; and must -ever tend to leave a posterity, and an increasing posterity, in which -none of that higher individuation which checks genesis takes place. -Such State-meddlings with the natural play of actions and reactions -produce a further evil equally great or greater. For those who are -not self-maintained, or but partially self-maintained, are supplied -with the means they lack by the better members of the community; and -these better members have thus not only to support themselves and -their offspring, but also to support or aid the inferior members and -their offspring. The under-working of one part is accompanied by the -over-working of the other part—by a working which at each stage of -progress exceeds that which the normal conditions necessitate, and -results sometimes in illness, premature age, or death, or in lessened<span class="pagenum" id="Page_533">[533]</span> -number of children, or in imperfect rearing of children: the bad are -fostered and the good are repressed.</p> - -<p>It does not follow that the struggle for life and the survival of the -fittest must be left to work out their effects without mitigation. It -is contended only that there shall not be a forcible burdening of the -superior for the support of the inferior. Such aid to the inferior as -the superior voluntarily yield, kept as it will be within moderate -limits, may be given with benefit to both—relief to the one, moral -culture to the other. And aid willingly given (little to the least -worthy and more to the most worthy) will usually be so given as not -to further the increase of the unworthy. For in proportion as the -emotional nature becomes more evolved, and there grows up a higher -sense of parental responsibility, the begetting of children that cannot -be properly reared will be universally held intolerable. If, as we -see, public opinion in many places and times becomes coercive enough -to force men to fight duels, we can scarcely doubt that at a higher -stage of evolution it may become so coercive as to prevent men from -marrying improvidently. If the frowns of their fellows can make men -commit immoral acts, surely they may make men refrain from immoral -acts—especially when the actors themselves feel that the threatened -frowns would be justified. Hence with a higher moral nature will come a -restriction on the multiplication of the inferior.</p> - -<p>In brief, the sole requirement is that there shall be no extensive -suspension of that natural relation between merit and benefit which -constitutes justice. Holding, then, that this all-essential condition -will itself come to be recognized and enforced by a more evolved -humanity, let us consider what is the goal towards which the restraint -on genesis by individuation progresses.</p> - - -<p class="p2">§ 375<i>a</i>. Supposing the Sun’s light and heat, on which all -terrestrial life depends, to continue abundant for a period long -enough to allow the entire evolution we are contemplating;<span class="pagenum" id="Page_534">[534]</span> there are -still certain changes which must prevent such complete adjustment of -human nature to surrounding conditions, as would permit the rate of -multiplication to become equal to the rate of mortality. As before -pointed out (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect148">§ 148</a>), during an epoch of 21,000 years each hemisphere -goes through a cycle of temperate seasons and seasons extreme in their -heat and cold—variations which are themselves alternately exaggerated -and mitigated in the course of far longer cycles; and we saw that -these cause perpetual ebbings and flowings of species over different -parts of the Earth’s surface. Further, by slow but inevitable geologic -changes, especially those of elevation and subsidence, the climate and -physical characters of every habitat are modified; while old habitats -are destroyed and new are formed. This, too, we noted as a constant -cause of migrations and of resulting alterations of environment. Now -though the human race differs from other races in having a power of -artificially counteracting external changes, yet there are limits to -this power; and, even were there no limits, the changes could not -fail to work their effects indirectly, if not directly. If, as is -thought probable, these astronomic cycles entail recurrent glacial -periods in each hemisphere, then parts of the Earth which are at one -time thickly peopled, will at another time be almost deserted, and -<i>vice versâ</i>. The geologically-caused alterations of climate and -surface, must produce further slow re-distributions of population; -and other currents of people, to and from different regions, will be -necessitated by the rise of successive centres of higher civilization. -Consequently, mankind cannot but continue to undergo changes of -environment, physical and moral, analogous to those which they have -thus far been undergoing. Such changes may eventually become slower -and less marked; but they can never cease. And if they can never cease -there can never arise a perfect adaptation of human nature to its -conditions of existence. To establish that complete correspondence -between inner and outer actions which constitutes the highest life -and<span class="pagenum" id="Page_535">[535]</span> greatest power of self-preservation, there must be a prolonged -converse between the organism and circumstances which remain the -same. If the external relations are being altered while the internal -relations are being adjusted to them, the adjustment can never become -exact. And in the absence of exact adjustment, there cannot exist that -theoretically-highest power of self-preservation with which there would -co-exist the theoretically-lowest power of race-production.</p> - -<p>Hence though the number of premature deaths may ultimately become very -small, it can never become so small as to allow the average number of -offspring from each pair to fall so low as two. Some average number -between two and three may be inferred as the limit—a number, however, -which is not likely to be quite constant, but may be expected at -one time to increase somewhat and afterwards to decrease somewhat, -according as variations in physical and social conditions lower or -raise the cost of self-preservation.</p> - -<p>To this qualification must be added a further qualification. The -foregoing argument tacitly assumes that the causes described will -continuously operate on all mankind; whereas a survey of the facts -makes it clear that some parts only of the Earth’s surface are capable -of bearing high types of civilization, and consequently high types -of Man. There must remain hereafter, as there are now, considerable -parts of its surface which can support only groups of nomads, or other -groups obliged by their habitats to lead simple and inferior kinds of -life. Only by subjection to the discipline we have been contemplating -can there be produced the fully-developed Man; and evidently in many -parts of the world this discipline will continue to be eluded. Not -only must we conclude that the varieties of our race now living in -desert regions and arctic climates will continue hereafter to do so, -but we may conclude that always, as now, a certain proportion of men -who are born in civilized societies, impatient of the stress which -pressure of population puts on them, will escape into unoccupied or -sparsely-peopled<span class="pagenum" id="Page_536">[536]</span> regions, where they can lead unrestrained lives -though lives of hardship. Recognizing as we must the probability -that in common with all other things, humanity will continue to -differentiate and produce a more heterogeneous assemblage of types, -we must infer that only in some of the highest of these will the -antagonism of individuation and genesis have the anticipated effects.</p> - -<p>Restricting ourselves to these, then, we may conclude that in the -end, pressure of population and its accompanying evils will almost -disappear; and will leave a state of things requiring from each -individual little more than a normal and pleasurable activity. -Cessation in the decrease of fertility implies cessation in the -development of the nervous system; and this implies a nervous system -which has become equal to all that is demanded of it—has not to do -more than is natural to it. But that exercise of faculties which does -not exceed what is natural, constitutes gratification.</p> - -<p>The necessary antagonism of Individuation and Genesis, not only, -then, fulfils the <i>à priori</i> law of maintenance of race, from -the monad up to Man, but ensures final attainment of the highest form -of this maintenance—a form in which the amount of life shall be the -greatest possible and the births and deaths the fewest possible. From -the beginning pressure of population has been the proximate cause of -progress. It produced the original diffusion of the race. It compelled -men to abandon predatory habits and take to agriculture. It led to -the clearing of the Earth’s surface. It forced men into the social -state; made social organization inevitable; and has developed the -social sentiments. It has stimulated to progressive improvements -in production, and to increased skill and intelligence. It is -daily thrusting us into closer contact and more mutually-dependent -relationships. And after having caused, as it ultimately must, the due -peopling of the globe, and the raising of its habitable parts into the -highest state of culture—after having perfected all processes for the -satisfaction of human wants—after<span class="pagenum" id="Page_537">[537]</span> having, at the same time, developed -the intellect into competence for its work, and the feelings into -fitness for social life—after having done all this, the pressure of -population must gradually approach to an end—an end, however, which -for the reasons given it cannot absolutely reach.</p> - - -<p class="p2">§ 377. In closing the argument let us not overlook the -self-sufficingness of those universal processes by which the results -reached thus far have been wrought out, and which may be expected to -work out these future results.</p> - -<p>Evolution under all its aspects, general and special, is an advance -towards equilibrium. We have seen that the theoretical limit towards -which the integration and differentiation of every aggregate advances, -is a state of balance between all the forces to which its parts are -subject, and the forces which its parts oppose to them (<i>First -Prin.</i> § 170). And we have seen that organic evolution is a progress -towards a moving equilibrium completely adjusted to environing actions.</p> - -<p>It has been also pointed out that, in civilized Man, there is going -on a new class of equilibrations—those between his actions and the -actions of the societies he forms (<i>First Prin.</i> § 175). Social -restraints and requirements are ever altering his activities and by -consequence his nature; and as fast as his nature is altered, social -restraints and requirements undergo more or less re-adjustment. Here -the organism and the conditions are both modifiable; and by successive -conciliations of the two, there is effected a progress towards -equilibrium.</p> - -<p>More recently we have seen that in every species, there establishes -itself an equilibrium of an involved kind between the total -race-destroying forces and the total race-preserving forces—an -equilibrium which implies that where the ability to maintain individual -life is small, the ability ta propagate must be great, and <i>vice -versâ</i>. Whence it follows that the evolution of a race more in -equilibrium with the environment, is also the evolution of a race in -which there is a correlative<span class="pagenum" id="Page_538">[538]</span> approach towards equilibrium between the -number of new individuals produced and the number which survive and -propagate.</p> - -<p>The final result to be observed is that in Man, all these -equilibrations between constitution and conditions, between the -structure of society and the nature of its members, between fertility -and mortality, advance simultaneously towards a common climax. In -approaching an equilibrium between his nature and the ever-varying -circumstances of his inorganic environment, and in approaching an -equilibrium between his nature and all the requirements of the social -state, Man is at the same time approaching that lowest limit of -fertility at which the equilibrium of population is maintained by the -addition of as many infants as there are subtractions by death in old -age. But in a universe of which all parts are in motion and every -part is consequently subject to change of conditions, neither this -equilibrium nor any other equilibrium can become complete.</p> - - -<p class="center p-left sm p4">THE END.</p> - -<p><span class="pagenum" id="Page_539">[539]</span></p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_541">[541]</span></p> - -<h2>APPENDICES.</h2> -</div> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> - -<h3>APPENDIX A.<br /> -<span class="subhed1">SUBSTITUTION OF AXIAL FOR FOLIAR ORGANS IN PLANTS.</span></h3></div> - - -<p>I append here the evidences referred to in <a href="#sect190">§ 190</a>. The most numerous and -striking I have met with among the <i>Umbelliferæ</i>. Monstrosities -having the alleged implication, are frequent in the common -Cow-Parsnep—so frequent that they must be familiar to botanists; and -wild Angelica supplies many over-developments of like meaning. Omitting -numerous cases of more or less significance, I will limit myself to two.</p> - - <div class="figcenter" id="i_541"> - <img - class="p2" - src="images/i_541.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 69.</p> - </div> - -<p class="p2">One of them is that of a terminal umbel, in which nine of the outer -umbellules are variously transformed—here a single flower being -made monstrous by the development of some of its members into buds; -there several such malformed flowers being associated with rays that -bear imperfect umbellules; and elsewhere, flowers being replaced by -umbellules: some of which are perfect, and others imperfect only in the -shortness of the flower-stalks. The annexed Fig. <a href="#i_541">69</a>, representing in -a somewhat conventionalized way, a part of<span class="pagenum" id="Page_542">[542]</span> the dried specimen, will -give an idea of this Angelica. At <i>a</i> is shown a single flower -partially changed; in the umbellule marked <i>b</i>, one of the rays -bears a secondary umbellule; and there may be seen at <i>c</i> and -<i>d</i>, several such over-developments.</p> - -<p>But the most conclusive instance is that of a Cow-Parsnep, in which a -single terminal umbel, besides the transformations already mentioned, -exhibits higher degrees of such transformations.<a id="FNanchor_68" href="#Footnote_68" class="fnanchor">[68]</a> The components -of this complex growth are;—three central umbellules, abnormal only -in minor points; one umbellule, external to these, which is partially -changed into an umbel; one rather more out of the centre, which is -so far metamorphosed as to be more an umbel than an umbellule: nine -peripheral clusters formed by the development of umbellules into -umbels, some of which are partially compounded still further. Examined -in detail, these structures present the following facts:—1. The -innermost umbellule is normal, save in having a peripheral flower of -which one member (apparently a petal) is transformed into a flower-bud. -2. The next umbellule, not quite so central, has one of its peripheral -flowers made monstrous by the growth of a bud from the base of the -calyx. 3. The third of the central umbellules has two abnormal outer -flowers. One of them carries a flower-bud on its edge, in place of -a foliar member. The other is half flower and half umbellule: being -composed of three petals, three stamens, and five flower-buds growing -where the other petals and stamens should grow. 4. Outside of these -umbellules comes one of the mixed clusters. Its five central flowers -are normal. Surrounding these are several flowers transformed in -different degrees: one having a stamen partially changed into a flower -bud. And then, at the periphery of this mixed cluster, come three -complete umbellules and an incomplete one in which some petals and -stamens of the original flower remain. 5. A mixed cluster, in which -the umbel-structure predominates, stands next. Its three central -flowers are normal. Surrounding them are five flowers over-developed in -various ways, like those already described. And on its periphery are -seven complete umbellules in place of flowers; besides an incomplete -umbellule that contains traces of the original flower, one of them -being a petal imperfectly twisted up into a bud. 6. Of the nine -external clusters, in which the development of simple into compound -umbels is most decided, nearly all present anomalies. Three of them -have each a central flower untransformed; and in others, the central<span class="pagenum" id="Page_543">[543]</span> -umbellule is composed of two, three, or four flowers. 7. But the most -remarkable fact is, that in sundry of these peripheral clusters, -resulting from the metamorphosis of simple umbels into compound umbels, -the like metamorphosis is carried a stage higher. Some of the component -rays, are themselves the bearers of compound umbels instead of simple -umbels. In Fig. <a href="#i_543">70</a>, a portion of the dried specimen is represented. -Two of the central umbellules are marked <i>a</i> and <i>b</i>; those -marked <i>c</i> and <i>d</i> are mixed clusters; at <i>e</i> and -<i>f</i> are compound umbels replacing simple ones; and <i>g</i> shows -one of the rays on which the over-development goes still further.</p> - - <div class="figcenter" id="i_543"> - <img - class="p2" - src="images/i_543.jpg" - alt="" /> - <p class="p0 center p-left">Fig. 70.</p> - </div> - -<p class="p2">Does not this evidence, enforced as it is by much more of like kind, -go far to prove that foliar organs may be developed into axial organs? -Even were not the transitional forms traceable, there would still, -I think, be no other legitimate interpretation of the facts last -detailed. The only way of eluding the conclusion here drawn, is by -assuming that where a cluster of flowers replaces a single flower, -it is because the axillary buds which hypothetically belong to the -several foliar organs of the flower, become developed into axes; and -assuming this, is basing an hypothesis on another hypothesis that -is directly at variance with facts. The foliar organs of flowers do -<i>not</i> bear buds in their axils; and it would never have been -supposed that such buds are typically present, had it not been for -that mistaken conception of “type” which has led to many other errors -in Biology. Goethe writes: “Now as we cannot realize the idea of a -leaf apart from the node out of which it springs, or of a node without -a bud, we may venture to infer,” &c. See here an example of a method -of philosophizing not uncommon among the Germans.<span class="pagenum" id="Page_544">[544]</span> The method is -this—Survey a portion of the facts, and draw from them a general -conception; project this general conception back into the objective -world, as a mould in which Nature casts her products; expect to find it -everywhere fulfilled; and allege potential fulfilment where no actual -fulfilment is visible.</p> - -<p>If instead of imposing our ideal forms on Nature, we are content to -generalize the facts as Nature presents them, we shall find no warrant -for the morphological doctrine above enunciated. The only conception -of type justified by the logic of science, is—that correlation -of parts which remains constant under all modifications of the -structure to be defined. To ascertain this, we must compare all these -modifications, and note what traits are common to them. On doing so -with the successive segments of a phænogamic axis, we are brought to -a conclusion widely different from that of Goethe. Axillary buds are -almost universally absent from the cotyledons; they are habitually -present in the axils of fully-developed leaves higher up the axis; they -are often absent from leaves that are close to the flower; they are -nearly always absent from the bracts; absent from the sepals; absent -from the petals; absent from the stamens; absent from the carpels. -Thus, out of eight leading forms which folia assume, one has the -axillary bud and seven are without it. With these facts before us, it -seems to me not difficult to “realize the idea” “of a node without a -bud.” If we are not possessed by a foregone conclusion, the evidence -will lead us to infer, that each node bears a foliar appendage and -<i>may</i> bear an axillary bud.</p> - -<p>Even, however, were it granted that the typical segment of a Phænogam -includes an axillary bud, which must be regarded as always potentially -present, no legitimate counter-interpretation of the monstrosities -above described could thence be drawn. If when an umbellule is -developed in place of a flower, the explanation is, that its component -rays are axillary to the foliar organs of the flower superseded; we may -fairly require that these foliar organs to which they are axillary, -shall be shown. But there are none. In the last specimen figured, -the inner rays of each such umbellule are without them; most of the -outer rays are also without them; and in one cluster, only a single -ray has a bract at its point of origin. There is a rejoinder ready, -however: the foliar organs are said to be suppressed. Though Goethe -could not “realize the idea” “of a node without a bud,” those who -accept his typical form appear to find no difficulty in realizing the -idea of an axillary bud without anything to which it is axillary. But -letting this pass, suppose we ask what is the warrant for this assumed -suppression. Axillary buds normally occur where the nutrition is high -enough to produce fully-developed leaves; and when axillary buds are -demonstrably present in flowers, they accompany foliar organs that -are more leaf-like than usual—always greener if not always larger. -That is to<span class="pagenum" id="Page_545">[545]</span> say, the normal and the abnormal axillary buds, are -alike the concomitants of foliar organs coloured by that chlorophyll -which habitually favours foliar development. How, then, can it be -supposed that when, out of a flower there is developed a cluster -of flower-bearing rays, the implied excess of nutrition causes the -foliar organs to abort? It is true that very generally in a branched -inflorescence, the bracts of the several flower-branches are very -small (their smallness being probably due to that defective supply of -certain chlorophyll-forming matters, which is the proximate cause of -flowering); and it is true that, under these conditions, a flowering -axis of considerable size, for the development of which chlorophyll is -less needful, grows from the axil of a dwarfed leaf. But the inference -that the foliar organ may therefore be entirely suppressed, seems to me -irreconcilable with the fact, that the foliar organ is always developed -to some extent <i>before</i> the axillary bud appears. Until it has -been shown that in some cases a lateral bud first appears, and a foliar -organ <i>afterwards</i> grows out beneath it, to form its axil, the -conception of an axillary bud of which the foliar organ is suppressed, -will remain at variance with the established truths of development.</p> - -<hr class="tb" /> - -<p>The above originally formed a portion of <a href="#sect190">§ 190</a>. I have transferred it -to the Appendix, partly because it contains too much detail to render -it fit for the general argument, and partly because the interpretations -being open to some question, it seemed undesirable to risk compromising -that argument by including them. The criticisms passed upon these -interpretations have not, however, sufficed to convince me of their -incorrectness. Unfortunately, I have since had no opportunity of -verifying the above statements by microscopic examinations, as I had -intended.</p> - -<p>Though unable to enforce the inference drawn by further facts more -minutely looked into, I may add some arguments based on facts that are -well known. One of these is the fact that the so-called axillary bud -is not universally axillary—is not universally seated in the angle -made by the axis and an appended foliar organ. In certain plants the -axillary bud is placed far above the node, half-way between it and the -succeeding node. So that not only may a segment of a phæenogamic axis -be without the axillary bud, but the axillary bud, when present, may be -removed from that place in which, according to Goethe, it necessarily -exists. Another fact not congruous with the current doctrine, is the -common occurrence of “adventitious” buds—the buds that are put out -from roots and from old stems or branches bare of leaves. The name -under which they are thus classed, is meant to imply that they may be -left out of consideration. Those, however, who have not got a theory to -save by<span class="pagenum" id="Page_546">[546]</span> putting anomalies out of sight, may be inclined to think that -the occurrence of buds where they are avowedly unconnected with nodes, -and are axillary to nothing, tells very much against the assumption -that every bud implies a node and a corresponding foliar organ. And -they may also see that the development of these adventitious buds at -places where there is excess of nutritive materials, favours the view -above set forth. For if a bud thus arises at a place where it is not -morphologically accounted for, simply because there happens to be at -that place an abundance of unorganized protoplasm; then, clearly, it is -likely that if the mass of protoplasm from which a leaf would usually -arise, is greatly increased in mass by excess of nutrition, it may -develop into an axis instead of a leaf.</p> - -<hr class="tb" /> - -<p>Many years after this work was published, I discovered among my papers -a memorandum which unfortunately I had overlooked, containing further -evidence in support of the foregoing conclusion. With the omission of -an error concerning the species of plant, I reproduce this memorandum -just as it stood:—</p> - -<p>“I found at Dieppe, July 1, 1860, in a garden near the sea a sample of -cultivated wild flower (I thought it was grown as an ornamental flower) -in which some of the single flowers of the umbel were developed into -groups of flowers thus:—</p> - - <div class="figcenter" id="i_546"> - <img - class="p2" - src="images/i_546.jpg" - alt="" /> - <p class="p0 center p-left"></p> - </div> - -<p class="p2">“In the case where the transformation was fully effected the umbellule -had <i>six</i> flowers, answering to the <i>six petals</i> of the -original flowers. In other cases the transformation was incomplete. -There were instances where but <i>two</i> of the petals were developed -into flowers; and the other petals remained unchanged. Others in which -<i>three</i> were developed; and others where four were developed. -In some cases, too, the development of a petal into a flower was -imperfect, in the absence of the flower-stalk—the flowers were sessile -in the place where the petals would have been. In one case there was an -<i>imperfect</i> flower sessile; another <i>imperfect</i> flower on a -short stalk; and three perfect flowers on long stalks.</p> - -<p><span class="pagenum" id="Page_547">[547]</span></p> - -<p>“I was in some doubt whether the petals or the stamens were developed. -In cases of imperfect transformation the petals at the base of the -umbellule seemed to stand in the position of calyx or involucrum, -giving the idea that the stamens were developed into flowers. But in -the case where there were <i>six</i> flowers developed there were no -petals at the base.</p> - -<p>“That it was a matter of extra nutrition was shown by this:—</p> - -<p>“1. That they were cultivated as garden flowers.</p> - -<p>“2. That where there was one perfectly developed umbellule, it was the -only one in the umbel.</p> - -<p>“3. That where there were three umbellules they were all imperfect.</p> - -<p>“4. That in this imperfect umbellule the perfect flowers were on long -stalks and the imperfect ones sessile.</p> - -<p>“5. That the umbellules were on stalks both longer and thicker than -those of single flowers.”</p> - -<hr class="tb" /> - -<p>[Concerning the foregoing argument at large an expert writes:—“The -abnormalities you describe certainly show that an axis may arise -abnormally in the place of a normal leaf-structure, and every modern -botanist would be in agreement with you in your criticism of the -older form of the doctrine of axillary buds. I think we are largely -emancipated from the dextrous juggling with the arrangements and -relations of organs which used to pass current as morphology.</p> - -<p>“You have quoted sufficient evidence in the text (<a href="#sect190">§ 190</a>) to establish -the conclusion that no sharp line can be drawn between axes and -leaf-structure; and a very great deal more could be added in the same -sense. Petioles for instance, exist which the most highly trained -histological observer could not distinguish from stems.</p> - -<p>“But I must demur to the suggestion that the replacement of one by the -other is primarily a question of nutrition. We are as ignorant as ever -of the proximate cause of the production of a leaf or a shoot at a -certain spot in meristematic tissue.”</p> - -<p>To this last remark I had at first made only the reply that the plants -exhibiting the abnormalities were in all cases excessively luxuriant in -their growths; but to this I am now able to add a more definite reply. -The expert from whom I have just quoted, had read this appendix before -there had been made to it the above addition describing the flower -from Dieppe; and I was not myself aware, until I came to read over -this addition, what clear evidence it contains that extra nutrition -was the cause of these transformations of foliar structures into axial -structures; but the above paragraphs 1, 2, 3, 4, 5, contain different -evidences conspiring to prove this.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_548">[548]</span></p> - -<h3>APPENDIX B.<br /> -<span class="subhed1">A CRITICISM ON PROF. OWEN’S THEORY OF THE VERTEBRATE SKELETON.</span></h3></div> - -<p>[<i>From the</i> <span class="smcap">British & Foreign Medico-Chirurgical Review for -Oct., 1858.</span>]</p> - -<hr class="full" /> - -<div class="blockquot"> - -<p class="hangingindent">I. <i>On the Archetype and Homologies of the Vertebrate -Skeleton.</i> <i>By</i> <span class="smcap">Richard Owen</span>, -<i>F.R.S.</i>—<i>London</i>, 1848. <i>pp.</i> 172.</p> - -<p class="hangingindent">II. <i>Principes d’Ostéologie Comparée, ou Recherches sur -l’Archétype et les Homologies du Squelette Vertébré.</i> -<i>Par</i> <span class="smcap">Richard Owen</span>.—<i>Paris.</i></p> - -<p class="hangingindent"><i>Principles of Comparative Osteology; or, Researches on the -Archetype and the Homologies of the Vertebrate Skeleton.</i> -<i>By</i> <span class="smcap">Richard Owen</span>.</p> - -<p class="hangingindent">III. <i>On the Nature of Limbs. A Discourse delivered on Friday, -February 9, at an Evening Meeting of the Royal Institution -of Great Britain.</i> <i>By</i> <span class="smcap">Richard Owen</span>, -<i>F.R.S.</i>—<i>London</i>, 1849. <i>pp.</i> 119.</p> -</div> - -<p>Judging whether another proves his position is a widely different thing -from proving your own. To establish a general law requires an extensive -knowledge of the phenomena to be generalized; but to decide whether an -alleged general law is established by the evidence assigned, requires -merely an adequate reasoning faculty. Especially is such a decision -easy where the premises do <i>not</i> warrant the conclusion. It may -be dangerous for one who has but little previous acquaintance with the -facts, to say that a generalization is demonstrated; seeing that the -argument may be one-sided: there may be many facts unknown to him which -disprove it. But it is not dangerous to give a negative verdict when -the alleged demonstration<span class="pagenum" id="Page_549">[549]</span> is manifestly insufficient. If the data put -before him do not bear out the inference, it is competent for every -logical reader to say so.</p> - -<p>From this standpoint, then, we venture to criticize some of Professor -Owen’s osteological theories. For his knowledge of comparative -osteology we have the highest respect. We believe that no living man -has so wide and detailed an acquaintance with the bony structure of -the <i>Vertebrata</i>. Indeed, there probably has never been any one -whose information on the subject was so nearly exhaustive. Moreover, we -confess that nearly all we know of this department of biology has been -learnt from his lectures and writings. We pretend to no independent -investigations, but merely to such knowledge of the phenomena as he has -furnished us with. Our position, then, is such that, had Professor Owen -simply enunciated his generalizations, we should have accepted them on -his authority. But he has brought forward evidence to prove them. By -so doing he has tacitly appealed to the judgments of his readers and -hearers—has practically said, “Here are the facts; do they not warrant -these conclusions?” And all we propose to do, is to consider whether -the conclusions <i>are</i> warranted by the facts brought forward.</p> - -<p>Let us first limit the scope of our criticisms. On that division -of comparative osteology which deals with what Professor Owen -distinguishes as “special homologies,” we do not propose to enter. That -the wing of a bird is framed upon bones essentially parallel to those -of a mammal’s fore-limb; that the cannon-bone of a horse’s leg answers -to the middle metacarpal of the human hand; that various bones in the -skull of a fish are homologous with bones in the skull of a man—these -and countless similar facts, we take to be well established. It may -be, indeed, that the doctrine of special homologies is at present -carried too far. It may be that, just as the sweeping generalization -at one time favoured, that the embryonic phases of the higher animals -represent the adult forms of lower ones, has been found untrue in a -literal sense, and is acceptable only in a qualified sense; so the -sweeping generalization that the skeletons of all vertebrate animals -consist of homologous parts, will have to undergo some modification. -But that this generalization is substantially true, all comparative -anatomists agree.</p> - -<p>The doctrine which we are here to consider, is quite a separate -one—that of “general homologies.” The truth or falsity of this may -be decided on quite apart from that of the other. Whether certain -bones in one vertebrate animal’s skeleton correspond with certain -bones in another’s, or in every other’s, is one question; and whether -the skeleton of every vertebrate animal is divisible into a series of -segments, each of which is modelled after the same type, is another -question. While the first is answered in the affirmative,<span class="pagenum" id="Page_550">[550]</span> the last -may be answered in the negative; and we propose to give reasons why it -should be answered in the negative.</p> - -<hr class="tb" /> - -<p>In so far as his theory of the skeleton is concerned, Professor Owen -is an avowed disciple of Plato. At the conclusion of his <i>Archetype -and Homologies of the Vertebrate Skeleton</i>, he quotes approvingly -the Platonic hypothesis of ἰδέαι, “a sort of models, or moulds in -which matter is cast, and which regularly produce the same number -and diversity of species.” The vertebrate form in general (see -diagram of the <i>Archetypus</i>), or else the form of each kind of -vertebrate animal (see p. 172, where this seems implied), Professor -Owen conceives to exist as an “idea”—an “archetypal exemplar on which -it has pleased the Creator to frame certain of his living creatures.” -Whether Professor Owen holds that the typical vertebra also exists as -an “idea,” is not so certain. From the title given to his figure of -the “ideal typical vertebra,” it would seem that he does; and at p. -40 of his <i>Nature of Limbs</i>, and indeed throughout his general -argument, this supposition is implied. But on the last two pages of the -<i>Archetype and Homologies</i>, it is distinctly alleged that “the -repetition of similar segments in a vertebral column, and of similar -elements in a vertebral segment, is analogous to the repetition of -similar crystals as the result of polarizing force in the growth of an -inorganic body;” it is pointed out that, “as we descend the scale of -animal life, the forms of the repeated parts of the skeleton approach -more and more to geometrical figures;” and it is inferred that “the -Platonic ἰδέα or specific organizing principle or force, would seem to -be in antagonism with the general polarizing force, and to subdue and -mould it in subserviency to the exigencies of the resulting specific -form.” If Professor Owen’s doctrine is to be understood as expressed -in these closing paragraphs of his <i>Archetype and Homologies</i>—if -he considers that “the ἰδέα” “which produces the diversity of form -belonging to living bodies of the same materials,” is met by the -“counter-operation” of “the polarizing force pervading all space,” -which produces “the similarity of forms, the repetition of parts, -the signs of unity of organization,” and which is “<i>subdued</i>” -as we ascend “in the scale of being;” then we may pass on with the -remark that the hypothesis is too cumbrous and involved to have much -<i>vraisemblance</i>. If, on the other hand, Professor Owen holds, as -every reader would suppose from the general tenor of his reasonings, -that not only does there exist an archetypal or ideal vertebrate -skeleton, but that there also exists an archetypal or ideal vertebra; -then he carries the Platonic hypothesis much further than Plato does. -Plato’s argument, that before any species of object was created it -must have existed as an idea of the Creative Intelligence, and that -hence all objects of such species must be<span class="pagenum" id="Page_551">[551]</span> copies of this original -idea, is tenable enough from the anthropomorphic point of view. But -while those who, with Plato, think fit to base their theory of creation -upon the analogy of a carpenter designing and making a table, must -yield assent to Plato’s inference, they are by no means committed -to Professor Owen’s expansion of it. To say that before creating a -vertebrate animal, God must have had the conception of one, does not -involve saying that God gratuitously bound himself to make a vertebrate -animal out of segments all moulded after one pattern. As there is -no conceivable advantage in this alleged adhesion to a fundamental -pattern—as, for the fulfilment of the intended ends, it is not only -needless, but often, as Professor Owen argues, less appropriate than -some other construction would be (see <i>Nature of Limbs</i>, pp. 39, -40), to suppose the creative processes thus regulated, is not a little -startling. Even those whose conceptions are so anthropomorphic as to -think they honour the Creator by calling him “the Great Artificer,” -will scarcely ascribe to him a proceeding which, in a human artificer, -they would consider a not very worthy exercise of ingenuity.</p> - -<p>But whichever of these alternatives Professor Owen contends -for—whether the typical vertebra is that more or less crystalline -figure which osseous matter ever tends to assume in spite of “the ἰδέα -or organizing principle,” or whether the typical vertebra is itself -an “ἰδέα or organizing principle”—there is alike implied the belief -that the typical vertebra has an abstract existence apart from actual -vertebræ. It is a form which, in every endo-skeleton, strives to embody -itself in matter—a form which is potentially present in each vertebra; -which is manifested in each vertebra with more or less clearness; but -which, in consequence of antagonizing forces, is nowhere completely -realized. Apart from the philosophy of this hypothesis, let us here -examine the evidence which is thought to justify it.</p> - -<hr class="tb" /> - -<p>And first as to the essential constituents of the “ideal typical -vertebra.” Exclusive of “<i>diverging appendages</i>” which it -“may also support,” “it consists in its typical completeness of -the following elements and parts”:—A <i>centrum</i> round which -the rest are arranged in a somewhat radiate manner; above it two -<i>neurapophyses</i>—converging as they ascend, and forming with the -centrum a trianguloid space containing the neural axis; a <i>neural -spine</i>, surmounting the two neurapophyses, and with them completing -the neural arch; below the centrum two <i>hæmapophyses</i> and a -<i>hæmal spine</i>, forming a hæmal arch similar to the neural arch -above, and enclosing the hæmal axis; two <i>pleurapophyses</i> -radiating horizontally from the sides of the centrum; and -two <i>parapophyses</i> diverging from the centrum below the -pleurapophyses. “These,” says Professor Owen, “being usually developed -from distinct and independent<span class="pagenum" id="Page_552">[552]</span> centres, I have termed ‘autogenous -elements.’” The remaining elements, which he classes as “exogenous,” -because they “shoot out as continuations from some of the preceding -elements,” are the <i>diapophyses</i> diverging from the upper part of -the centrum as the parapophyses do below, and the <i>zygapophyses</i> -which grow out of the distal ends of the neurapophyses and hæmapophyses.</p> - -<p>If, now, these are the constituents of the vertebrate segment “in its -typical completeness;” and if the vertebrate skeleton consists of a -succession of such segments; we ought to have in these constituents, -representatives of all the elements of the vertebrate skeleton—at -any rate, all its essential elements. Are we then to conclude -that the “diverging appendages,” which Professor Owen regards as -rudimental limbs, and from certain of which he considers actual -limbs to be developed, are typically less important than some of the -above-specified exogenous parts—say the zygapophyses?</p> - -<p>That the meaning of this question may be understood, it will be -needful briefly to state Professor Owen’s theory of <i>The Nature -of Limbs</i>; and such criticisms as we have to make on it must be -included in the parenthesis. In the first place, he aims to show that -the scapular and pelvic arches, giving insertion to the fore and -hind limbs respectively, are displaced and modified hæmal arches, -originally belonging in the one case to the occipital vertebra, and -in the other case to some trunk-vertebra not specified. In support of -this assumption of displacement, carried in some cases to the extent of -<i>twenty-seven</i> vertebræ, Professor Owen cites certain acknowledged -displacements which occur in the human skeleton to the extent of half -a vertebra—a somewhat slender justification. But for proof that such -a displacement <i>has</i> taken place in the scapular arch, he chiefly -relies on the fact that in fishes, the pectoral fins, which are the -homologues of the fore-limbs, are directly articulated to certain bones -at the back of the head, which he alleges are parts of the occipital -vertebra. This appeal to the class of fishes is avowedly made on -the principle that these lowest of the <i>Vertebrata</i> approach -closest to archetypal regularity, and may therefore be expected to -show the original relations of the bones more nearly. Simply noting -the facts that Professor Owen does not give us any transitional forms -between the alleged normal position of the scapular arch in fishes, -and its extraordinary displacement in the higher <i>Vertebrata</i>; -and that he makes no reference to the embryonic phases of the higher -<i>Vertebrata</i>, which might be expected to exhibit the progressive -displacement; we go on to remark that, in the case of the pelvic -arch, he abandons his principle of appealing to the lowest vertebrate -forms for proof of the typical structure. In fishes, the rudimentary -pelvis, widely removed from the spinal column, shows no signs of -having belonged to any vertebra; and here Professor Owen instances -the perennibranchiate <i>Batrachia</i> as<span class="pagenum" id="Page_553">[553]</span> exhibiting the typical -structure: remarking that “mammals, birds, and reptiles show the -rule of connexion, and fishes the exception.” Thus in the case of -the scapular arch, the evidence afforded by fishes is held of great -weight, <i>because</i> of their archetypal regularity; while in the -case of the pelvic arch, their evidence is rejected as exceptional. But -now, having, as he considers, shown that these bony frames to which -the limbs are articulated are modified hæmal arches, Professor Owen -points out that the hæmal arches habitually bear certain “diverging -appendages;” and he aims to show that the “diverging appendages” of the -scapular and pelvic arches respectively, are developed into the fore -and hind limbs. There are several indirect ways in which we may test -the probability of this conclusion. If these diverging appendages are -“rudimental limbs”—“future possible or potential arms, legs, wings, -or feet,” we may fairly expect them always to bear to the hæmal arches -a relation such as the limbs do. But they by no means do this. “As the -vertebræ approach the tail, these appendages are often transferred -gradually from the pleurapophysis to the parapophysis, or even to the -centrum and neural arch.” (<i>Arch. and Hom.</i>, p. 93.) Again, it -might naturally be assumed that in the lowest vertebrate forms, where -the limbs are but little developed, they would most clearly display -their alliance with the appendages, or “rudimental limbs,” by the -similarity of their attachments. Instead of this, however, Professor -Owen’s drawings show that whereas the appendages are habitually -attached to the pleurapophyses, the limbs, in their earliest and lowest -phase, alike in fishes and in the <i>Lepidosiren</i>, are articulated -to the hæmapophyses. Most anomalous of all, however, is the process -of development. When we speak of one thing as being developed out of -another, we imply that the parts next to the germ are the first to -appear, and the most constant. In the evolution of a tree out of a -seed, there come at the outset the stem and the radicle; afterwards -the branches and divergent roots; and still later the branchlets and -rootlets; the remotest parts being the latest and most inconstant. If, -then, a limb is developed out of a “diverging appendage” of the hæmal -arch, the earliest and most constant bones should be the humerus and -femur; next in order of time and constancy should come the coupled -bones based on these; while the terminal groups of bones should be the -last to make their appearance, and the most liable to be absent. Yet, -as Professor Owen himself shows, the actual mode of development is the -very reverse of this. At p. 16 of the <i>Archetype and Homologies</i>, -he says:—</p> - -<div class="blockquot"> - -<p>“The earlier stages in the development of all locomotive -extremities are permanently retained or represented in the -paired fins of fishes. First the essential part of the member, -the hand or foot, appears: then the fore-arm or leg, both much -shortened, flattened, and expanded, as in all fins and all -embryonic rudiments of limbs: finally come the humeral and -femoral segments; but this stage I have not found attained in -any fish.”</p> -</div> - -<p><span class="pagenum" id="Page_554">[554]</span></p> - -<p>That is to say, alike in ascending through the <i>Vertebrata</i>, -generally, and in tracing up the successive phases of a mammalian -embryo, the last-developed and least constant division of the limb, is -that basic one by which it articulates with the hæmal arch. It seems to -us that, so far from proving his hypothesis, Professor Owen’s own facts -tend to show that limbs do not belong to the vertebræ at all: that they -make their first appearance peripherally; that their development is -centripetal; and that they become fixed to such parts of the vertebrate -axis as the requirements of the case determine.</p> - -<p>But now, ending here this digressive exposition and criticism, -and granting the position that limbs “are developments of costal -appendages,” let us return to the question above put—Why are not -these appendages included as elements of the “ideal typical vertebra?” -It cannot be because of their comparative inconstancy; for judging -from the illustrative figures, they seem to be as constant as the -hæmal spine, which is one of the so-called autogenous elements: in -the diagram of the <i>Archetypus</i>, the appendage is represented as -attached to every vertebrate segment of the head and trunk, which the -hæmal spine is not. It cannot be from their comparative unimportance; -seeing that as potential limbs they are essential parts of nearly all -the <i>Vertebrata</i>—much more obviously so than the diapophyses -are. If, as Professor Owen argues, “the divine mind which planned the -archetype also foreknew all its modifications;” and if, among these -modifications, the development of limbs out of diverging appendages -was one intended to characterize all the higher <i>Vertebrata</i>; -then, surely, these diverging appendages must have been parts of the -“ideal typical vertebra.” Or, if the “ideal typical vertebra” is to -be understood as a crystalline form in antagonism with the organizing -principle; then why should not the appendages be included among its -various offshoots? We do not ask this question because of its intrinsic -importance. We ask it for the purpose of ascertaining Professor Owen’s -method of determining what are true vertebral constituents. He presents -us with a diagram of the typical vertebra, in which are included -certain bones, and from which are excluded certain others. If relative -constancy is the criterion, then there arises the question—What degree -of constancy entitles a bone to be included? If relative importance -is the criterion, there comes not only the question—What degree of -importance suffices? but the further question—How is importance to -be measured? If neither of these is the criterion, then what is it? -And if there is no criterion, does it not follow that the selection is -arbitrary?</p> - -<hr class="tb" /> - -<p>This question serves to introduce a much wider one:—Has the “ideal -typical vertebra” any essential constituents at all? It might<span class="pagenum" id="Page_555">[555]</span> -naturally be supposed that though some bones are so rarely developed -as not to seem worth including, and though some that are included are -very apt to be absent, yet that certain others are invariable: forming, -as it were, the basis of the ideal type. Let us see whether the facts -bear out this supposition. In his “summary of modifications of corporal -vertebræ” (p. 96), Professor Owen says—“The <i>hæmal spine</i> is much -less constant as to its existence, and is subject to a much greater -range of variety, when present, than its vertical homotype above, which -completes the neural arch.” Again he says—“The <i>hæmapophyses</i>, -as osseous elements of a vertebra, are less constant than the -pleurapophyses.” And again—“The <i>pleurapophyses</i> are less -constant elements than the neurapophyses.” And again—“Amongst -air-breathing vertebrates the <i>pleurapophyses</i> of the trunk -segments are present only in those species in which the septum of -the heart’s ventricle is complete and imperforate, and here they -are exogenous and confined to the cervical and anterior thoracic -vertebræ.” And once more, both the <i>neurapophyses</i> and the -<i>neural spine</i> “are absent under both histological conditions, -at the end of the tail in most air-breathing vertebrates, where the -segments are reduced to their central elements.” That is to say, of -all the peripheral elements of the “ideal typical vertebra,” there is -not one which is always present. It will be expected, however, that -at any rate the <i>centrum</i> is constant: the bone which “forms the -axis of the vertebral column, and commonly the central bond of union -of the peripheral elements of the vertebrate (p. 97), is of course an -invariable element. No: not even this is essential.</p> - -<div class="blockquot"> - -<p>“The centrums do not pass beyond the primitive stage of the -notochord (undivided column) in the existing lepidosiren, and -they retained the like rudimental state in every fish whose -remains have been found in strata earlier than the permian -æra in Geology, though the number of vertebræ is frequently -indicated in Devonian and Silurian ichthyolites by the -fossilized neur-and hæmapophyses and their spines” (p. 96).</p> -</div> - -<p>Indeed, Professor Owen himself remarks that “the neurapophyses are -more constant as osseous or cartilaginous elements of the vertebræ -than the centrums” (p. 97). Thus, then, it appears that the several -elements included in the “ideal typical vertebra” have various degrees -of constancy, and that no one of them is essential. There is no one -part of a vertebra which invariably answers to its exemplar in the -pattern-group. How does this fact consist with the hypothesis? If -the Creator saw fit to make the vertebrate skeleton out of a series -of segments, all formed on essentially the same model—if, for the -maintenance of the type, one of these bony segments is in many cases -formed out of a coalesced group of pieces, where, as Professor Owen -argues, a single piece would have served as well or better; then we -ought to find this typical repetition of parts<span class="pagenum" id="Page_556">[556]</span> uniformly manifested. -Without any change of shape, it would obviously have been quite -possible for every actual vertebra to have contained all the parts -of the ideal one—rudimentally where they were not wanted. Even one -of the terminal bones of a mammal’s tail might have been formed -out of the nine autogenous pieces, united by suture but admitting -of identification. As, however, there is no such uniform typical -repetition of parts, it seems to us that to account for the typical -repetition which <i>does</i> occur, by supposing the Creator to have -fixed on a pattern-vertebra, is to ascribe to him the inconsistency of -forming a plan and then abandoning it.</p> - -<p>If, on the other hand, Professor Owen means that the “ideal typical -vertebra” is a crystalline form in antagonism with “the idea or -organizing principle;” then we might fairly expect to find it -most clearly displaying its crystalline character, and its full -complement of parts, in those places where the organizing principle -may be presumed to have “subdued” it to the smallest extent. Yet -in the <i>Vertebrata</i> generally, and even in Professor Owen’s -<i>Archetypus</i>, the vertebræ of the tail, which must be considered -as, if anything, less under the influence of the organizing principle -than those of the trunk, do not manifest the ideal form more -completely. On the contrary, as we approach the end of the tail, the -successive segments not only lose their remaining typical elements, but -become as uncrystalline-looking as can be conceived.</p> - -<hr class="tb" /> - -<p>Supposing, however, that the assumption of suppressed or undeveloped -elements be granted—supposing it to be consistent with the hypothesis -of an “ideal typical vertebra,” that the constituent parts may -severally be absent in greater or less number, sometimes leaving only -a single bone to represent them all; may it not be that such parts -as <i>are</i> present, show their respective typical natures by some -constant character: say their mode of ossification?</p> - -<p>To this question some parts of the <i>Archetype and Homologies</i> seem -to reply, “Yes;” while others clearly answer, “No.” Criticising the -opinions of Geoffrey St. Hilaire and Cuvier, who agreed in thinking -that ossification from a separate centre was the test of a separate -bone, and that thus there were as many elementary bones in the skeleton -as there were centres of ossification, Professor Owen points out that, -according to this test, the human femur, which is ossified from four -centres, must be regarded as four bones; while the femur in birds and -reptiles, which is ossified from a single centre, must be regarded as -a single bone. Yet, on the other hand, he attaches weight to the fact -that the skull of the human fœtus presents “the same ossific centres” -as do those of the embryo kangaroo and the young bird. (<i>Nature of -Limbs</i>, p. 40.) And at p. 104 of the <i>Homologies</i>, after giving -a number of instances, he says—</p> - -<div class="blockquot"> - -<p>“These and the like correspondences between the points of -ossification of<span class="pagenum" id="Page_557">[557]</span> the human fœtal skeleton, and the separate -bones of the adult skeletons of inferior animals, are pregnant -with interest, and rank among the most striking illustrations of -unity of plan in the vertebrate organization.”</p> -</div> - -<p>It is true that on the following page he seeks to explain this seeming -contradiction by distinguishing</p> - -<div class="blockquot"> - -<p>“between those centres of ossification that have homological -relations, and those that have teleological ones—<i>i.e.</i>, -between the separate points of ossification of a human bone -which typify vertebral elements, often permanently distinct -bones in the lower animals; and the separate points which, -without such signification, facilitate the progress of -osteogeny, and have for their obvious final cause the well-being -of the growing animal.”</p> -</div> - -<p>But if there are thus centres of ossification which have homological -meanings, and others which have not, there arises the question—How are -they always to be distinguished? Evidently independent ossification -ceases to be a homological test, if there are independent ossifications -that have nothing to do with the homologies. And this becomes the -more evident when we learn that there are cases where neither a -homological nor a teleological meaning can be given. Among various -modes of ossification of the centrum, Professor Owen points out -that “the body of the human atlas is sometimes ossified from two, -rarely from three, distinct centres placed side by side” (p. 89); -while at p. 87 he says:—“In osseous fishes I find that the centrum -is usually ossified from six points.” It is clear that this mode of -ossification has here no homological signification; and it would be -difficult to give any teleological reason why the small centrum of a -fish should have more centres of ossification than the large centrum -of a mammal. The truth is, that as a criterion of the identity or -individuality of a bone, mode of ossification is quite untrustworthy. -Though, in his “ideal typical vertebra,” Professor Owen delineates -and classifies as separate “autogenous” elements, those parts which -are “usually developed from distinct and independent centres;” and -though by doing so he erects this characteristic into some sort -of criterion; yet his own facts show it to be no criterion. The -parapophyses are classed among the autogenous elements; yet they are -autogenous in fishes alone, and in these only in the trunk vertebræ, -while in all air-breathing vertebrates they are, when present at -all, exogenous. The neurapophyses, again, “lose their primitive -individuality by various kinds and degrees of confluence:” in the -tails of the higher <i>Vertebrata</i> they, in common with the neural -spine, become exogenous. Nay, even the centrum may lose its autogenous -character. Describing how, in some batrachians, “the ossification of -the centrum is completed by an extension of bone from the bases of -the neurapophyses, which effects also the coalescence of these with -the centrum,” Professor Owen adds:—“In <i>Pelobates fuscus</i> and -<i>Pelobates cultripes</i>, Müller found the entire<span class="pagenum" id="Page_558">[558]</span> centrum ossified -from this source, without any independent points of ossification” (p. -88). That is to say, the centrum is in these cases an exogenous process -of the neurapophyses. We see, then, that these so-called typical -elements of vertebræ have no constant developmental character by which -they can be identified. Not only are they undistinguishable by any -specific test from other bones not included as vertebral elements; not -only do they fail to show their typical characters by their constant -presence; but, when present, they exhibit no persistent marks of -individuality. The central element may be ossified from six, four, -three, or two points; or it may have no separate point of ossification -at all: and similarly with various of the peripheral elements. The -whole group of bones forming the “ideal typical vertebra” may severally -have their one or more ossific centres; or they may, as in a mammal’s -tail, lose their individualities in a single bone ossified from one or -two points.</p> - -<hr class="tb" /> - -<p>Another fact which seems very difficult to reconcile with the -hypothesis of an “ideal typical vertebra,” is the not infrequent -presence of some of the typical elements in duplicate. Not only, as -we have seen, may they severally be absent, but they may severally be -present in greater number than they should be. When we see, in the -ideal diagram, one centrum, two neurapophyses, two pleurapophyses, -two hæmapophyses, one neural spine, and one hæmal spine, we naturally -expect to find them always bearing to each other these numerical -relations. Though we may not be greatly surprised by the absence of -some of them, we are hardly prepared to find others multiplied. Yet -such cases are common. Thus the neural spine “is double in the anterior -vertebræ of some fishes” (p. 98). Again, in the abdominal region of -extinct saurians, and in crocodiles, “the freely-suspended hæmapophyses -are compounded of two or more overlapping bony pieces” (p. 100). -Yet again, at p. 99, we read—“I have observed some of the expanded -pleurapophyses in the great <i>Testudo elephantopus</i> ossified from -two centres, and the resulting divisions continuing distinct, but -united by suture.” Once more “the neurapophyses, which do not advance -beyond the cartilaginous stage in the sturgeon, consist in that fish -of two distinct pieces of cartilage; and the anterior pleurapophyses -also consist of two or more cartilages, set end on end” (p. 91). And -elsewhere referring to this structure, he says:—</p> - -<div class="blockquot"> - -<p>“Vegetative repetition of perivertebral parts not only manifests -itself in the composite neurapophyses and pleurapophyses, but -in a small accessory (interneural) cartilage, at the fore and -back part of the base of the neurapophysis; and by a similar -(interhæmal) one at the fore and back part of most of the -parapophyses” (p. 87).</p> -</div> - -<p>Thus the neural and hæmal spines, the neurapophyses, the -pleurapophyses,<span class="pagenum" id="Page_559">[559]</span> the hæmapophyses, may severally consist of two or more -pieces. This is not all: the like is true even of the centrums.</p> - -<div class="blockquot"> - -<p>“In <i>Heptanchus</i> (<i>Squalus cinereus</i>) the vertebral -centres are feebly and vegetatively marked out by numerous -slender rings of hard cartilage in the notochordal capsule, -the number of vertebræ being more definitely indicated by -the neurapophyses and parapophyses.... In the piked dog-fish -(<i>Acanthias</i>) and the spotted dog-fish (<i>Scyllium</i>) -the vertebral centres coincide in number with the neural arches” -(p. 87).</p> -</div> - -<p>Is it not strange that the pattern-vertebra should be so little adhered -to, that each of its single typical pieces may be transformed into two -or three?</p> - -<p>But there are still more startling departures from the alleged type. -The numerical relations of the elements vary not only in this way, but -in the opposite way. A given part may be present not only in greater -number than it should be, but also in less. In the tails of homocercal -fishes, the centrums “are rendered by centripetal shortening and bony -confluence fewer in number than the persistent, neural, and hæmal -arches of that part”—that is, there is only a fraction of a centrum to -each vertebra. Nay, even this is not the most heteroclite structure. -Paradoxical as it may seem, there are cases in which the same vertebral -element is, considered under different aspects, at once in excess and -defect. Speaking of the hæmal spine, Professor Owen says:—</p> - -<div class="blockquot"> - -<p>“The horizontal extension of this vertebral element is -sometimes accompanied by a median division, or in other words, -it is ossified from two lateral centres; this is seen in the -development of parts of the human sternum; the same vegetative -character is constant in the broader thoracic hæmal spines of -birds; though, sometimes, as <i>e.g.</i>, in the struthionidæ, -<i>ossification extends from the same lateral centre -lengthwise—i.e., forwards and backwards, calcifying the connate -cartilaginous homologues of halves of four or five hæmal spines, -before these finally coalesce with their fellows at the median -line</i>” (p. 101).</p> -</div> - -<p>So that the sternum of the ostrich, which according to the hypothesis, -should, in its cartilaginous stage, have consisted of <i>four or five -transverse</i> pieces, answering to the vertebral segments, and should -have been ossified from four or five centres, one to each cartilaginous -piece, shows not a trace of this structure; but instead, consists -of <i>two longitudinal</i> pieces of cartilage, each ossified from -one centre, and finally coalescing on the median line. These four or -five hæmal spines have at the same time doubled their individualities -transversely, and entirely lost them longitudinally!</p> - -<hr class="tb" /> - -<p>There still remains to be considered the test of relative position. -It might be held that, spite of all the foregoing anomalies, if the -typical parts of the vertebræ always stood towards each other in the -same relations—always preserved the same connexions, something like a -case would be made out. Doubtless, relative position<span class="pagenum" id="Page_560">[560]</span> is an important -point; and it is one on which Professor Owen manifestly places great -dependence. In his discussion of “moot cases of special homology,” it -is the general test to which he appeals. The typical natures of the -alisphenoid, the mastoid, the orbito-sphenoid, the prefrontal, the -malar, the squamosal, &c. he determines almost wholly by reference to -the adjacent nerve-perforations and the articulations with neighbouring -bones (see pp. 19 to 72): the general form of the argument being—This -bone is to be classed as such or such, <i>because</i> it is connected -thus and thus with these others, which are so and so. Moreover, by -putting forth an “ideal typical vertebra,” consisting of a number of -elements standing towards each other in certain definite arrangement, -this persistency of relative position is manifestly alleged. The -essential attribute of this group of bones, considered as a typical -group, is the constancy in the connexions of its parts: change the -connexions, and the type is changed. But the constancy of relative -position thus tacitly asserted, and appealed to as a conclusive test -in “moot cases of special homology,” is clearly negatived by Professor -Owen’s own facts. For instance, in the “ideal typical vertebra,” the -hæmal arch is represented as formed by the two hæmapophyses and the -hæmal spine; but at p. 91 we are told that</p> - -<div class="blockquot"> - -<p>“The contracted hæmal arch in the caudal region of the body -may be formed by different elements of the typical vertebra: -<i>e.g.</i>, by the parapophyses (fishes generally); by -the pleurapophyses (lepidosiren); by both parapophyses and -pleurapophyses (<i>Sudis</i>, <i>Lepidosteus</i>), and by -hæmapophyses, shortened and directly articulated with the -centrums (reptiles and mammals).”</p> -</div> - -<p>And further, in the thorax of reptiles, birds, and mammals, “the -hæmapophyses are removed from the centrum, and are articulated to -the distal ends of the pleurapophyses; the bony hoop being completed -by the intercalation of the hæmal spine” (p. 82). So that there are -<i>five</i> different ways in which the hæmal arch may be formed—four -modes of attachment of the parts different from that shown in the -typical diagram! Nor is this all. The pleurapophyses “may be quite -detached from their proper segment, and suspended to the hæmal arch of -another vertebra;” as we have already seen, the entire hæmal arch may -be detached and removed to a distance, sometimes reaching the length -of twenty-seven vertebræ; and, even more remarkable, the ventral fins -of some fishes, which theoretically belong to the pelvic arch, are so -much advanced forward as to be articulated to the scapular arch—“the -ischium elongating to join the coracoid.” With these admissions it -seems to us that relative position and connexions cannot be appealed to -as tests of homology, nor as evidence of any original type of vertebra.</p> - -<p>In no class of facts, then, do we find a good foundation for the -hypothesis of an “ideal typical vertebra.” There is no one conceivable<span class="pagenum" id="Page_561">[561]</span> -attribute of this archetypal form which is habitually realised by -actual vertebræ. The alleged group of true vertebral elements is not -distinguished in any specified way from bones not included in it. Its -members have various degrees of inconstancy; are rarely all present -together; and no one of them is essential. They are severally developed -in no uniform way: each of them may arise either out of a separate -piece of cartilage, or out of a piece continuous with that of some -other element; and each may be ossified from many independent points, -from one, or from none. Not only may their respective individualities -be lost by absence, or by confluence with others; but they may be -doubled, or tripled, or halved, or may be multiplied in one direction -and lost in another. The entire group of typical elements may coalesce -into one simple bone representing the whole vertebra; and even, as in -the terminal piece of a bird’s tail, half-a-dozen vertebræ, with all -their many elements, may become entirely lost in a single mass. Lastly, -the respective elements, when present, have no fixity of relative -position: sundry of them are found articulated to various others than -those with which they are typically connected; they are frequently -displaced and attached to neighbouring vertebræ; and they are even -removed to quite remote parts of the skeleton. It seems to us that if -this want of congruity with the facts does not disprove the hypothesis, -no such hypothesis admits of disproof.</p> - -<hr class="tb" /> - -<p>Unsatisfactory as is the evidence in the case of the trunk and tail -vertebræ, to which we have hitherto confined ourselves, it is far worse -in the case of the alleged cranial vertebræ. The mere fact that those -who have contended for the vertebrate structure of the skull, have -differed so astonishingly in their special interpretations of it, is -enough to warrant great doubt as to the general truth of their theory. -From Professor Owen’s history of the doctrine of general homology, we -gather that Duméril wrote upon “la tête considérée comme <i>une</i> -vertèbre;” that Kielmeyer, “instead of calling the skull a vertebra, -said each vertebra might be called a skull;” that Oken recognized in -the skull <i>three</i> vertebræ and a rudiment; that Professor Owen -himself makes out <i>four</i> vertebræ; that Goethe’s idea, adopted -and developed by Carus, was, that the skull is composed of <i>six</i> -vertebræ; and that Geoffrey St. Hilaire divided it into <i>seven</i>. -Does not the fact that different comparative anatomists have arranged -the same group of bones into <i>one</i>, <i>three</i>, <i>four</i>, -<i>six</i>, and <i>seven</i> vertebral segments, show that the mode of -determination is arbitrary, and the conclusions arrived at fanciful? -May we not properly entertain great doubts as to any one scheme being -more valid than the others? And if out of these conflicting schemes -we are asked to accept one, ought we not to accept it only on the -production of some thoroughly conclusive proof—some<span class="pagenum" id="Page_562">[562]</span> rigorous test -showing irrefragably that the others must be wrong and this alone -right? Evidently where such contradictory opinions have been formed by -so many competent judges, we ought, before deciding in favour of one of -them, to have a clearness of demonstration much exceeding that required -in any ordinary case. Let us see whether Professor Owen supplies us -with any such clearness of demonstration.</p> - -<p>To bring the first or occipital segment of the skull into -correspondence with the “ideal typical vertebra,” Professor -Owen argues, in the case of the fish, that the parapophyses are -<i>displaced</i>, and wedged between the neurapophyses and the neural -spine—removed from the hæmal arch and built into the upper part of -the neural arch. Further, he considers that the pleurapophyses are -<i>teleologically compound</i>. And then, in all the higher vertebrata, -he alleges that the hæmal arch is <i>separated</i> from its centrum, -taken to a distance, and transformed into the scapular arch. Add to -which, he says that in mammals the displaced parapophyses are mere -processes of the neurapophyses (p. 133): these vertebral elements, -typically belonging to the lower part of the centrum, and in nearly -all cases confluent with it, are not only removed to the far ends of -elements placed above the centrum, but have become exogenous parts of -them!</p> - -<p>Conformity of the second or parietal segment of the cranium with the -pattern-vertebra, is produced thus:—The petrosals are <i>excluded</i> -as being partially-ossified sense-capsules, not forming parts of the -true vertebral system, but belonging to the “splanchno-skeleton.” A -centrum is <i>artificially</i> obtained by sawing in two the bone which -serves in common as centrum to this and the preceding segment; and -this though it is admitted that in fishes, where their individualities -ought to be best seen, these two hypothetical centrums are not simply -coalescent, but connate. Next, a similar <i>arbitrary bisection</i> is -made of certain elements of the hæmal arches. And then, “the principle -of <i>vegetative repetition</i> is still more manifest in this arch -than in the occipital one:” each pleurapophysis is double; each -hæmapophysis is double; and the hæmal spine consists of six pieces!</p> - -<p>The interpretation of the third and fourth segments being of the -same general character, need not be detailed. The only point calling -for remark being, that in addition to the above various modes of -getting over anomalies, we find certain bones referred to the -<i>dermo-skeleton</i>.</p> - -<p>Now it seems to us, that even supposing no antagonist interpretations -had been given, an hypothesis reconcilable with the facts only by -the aid of so many questionable devices, could not be considered -satisfactory; and that when, as in this case, various comparative -anatomists have contended for other interpretations, the character -of this one is certainly not of a kind to warrant the rejection of -the others in its favour; but rather of a kind to make<span class="pagenum" id="Page_563">[563]</span> us doubt the -possibility of all such interpretations. The question which naturally -arises is, whether by proceeding after this fashion, groups of bones -might not be arranged into endless typical forms. If, when a given -element was not in its place, we were at liberty to consider it as -<i>suppressed</i>, or <i>connate</i> with some neighbouring element, -or <i>removed</i> to some more or less distant position;—if, on -finding a bone in excess, we might consider it, now as part of the -<i>dermo-skeleton</i>, now as part of the <i>splanchno-skeleton</i>, -now as <i>transplanted</i> from its typical position, now as resulting -from <i>vegetative repetition</i>, and now as a bone <i>teleologically -compound</i> (for these last two are intrinsically different, though -often used by Professor Owen as equivalents);—if, in other cases, -a bone might be regarded as <i>spurious</i> (p. 91), or again as -having <i>usurped</i> the place of another;—if, we say, these various -liberties were allowed us, we should not despair of reconciling the -facts with various diagrammatic types besides that adopted by Professor -Owen.</p> - -<p>When, in 1851, we attended a course of Professor Owen’s lectures -on Comparative Osteology, beginning though we did in the attitude -of discipleship, our scepticism grew as we listened, and reached -its climax when we came to the skull; the reduction of which to the -vertebrate structure, reminded us very much of the interpretation of -prophecy. The delivery, at the Royal Society, of the Croonian Lecture -for 1858, in which Professor Huxley, confirming the statements of -several German anatomists, has shown that the facts of embryology do -not countenance Professor Owen’s views respecting the formation of the -cranium, has induced us to reconsider the vertebral theory as a whole. -Closer examination of Professor Owen’s doctrines, as set forth in his -works, has certainly not removed the scepticism generated years ago -by his lectures. On the contrary, that scepticism has deepened into -disbelief. And we venture to think that the evidence above cited shows -this disbelief to be warranted.</p> - -<hr class="tb" /> - -<p>There remains the question—What general views are we to take -respecting the vertebrate structure? If the hypothesis of an “ideal -typical vertebra” is not justified by the facts, how are we to -understand that degree of similarity which vertebræ display?</p> - -<p>We believe the explanation is not far to seek. All that our space will -here allow, is a brief indication of what seems to us the natural view -of the matter.</p> - -<p>Professor Owen, in common with other comparative anatomists, regards -the divergences of individual vertebræ from the average form, as due -to adaptive modifications. If here one vertebral element is largely -developed, while elsewhere it is small—if now the form, now the -position, now the degree of coalescence, of a given part varies; it -is that the local requirements have involved this change. The entire -teaching of comparative osteology implies that<span class="pagenum" id="Page_564">[564]</span> differences in the -conditions of the respective vertebræ necessitate differences in their -structures.</p> - -<p>Now, it seems to us that the first step towards a right conception -of the phenomena, is to recognize this general law in its converse -application. If vertebræ are unlike in proportion to the unlikeness -of their circumstances, then, by implication, they will be like in -proportion to the likeness of their circumstances. While successive -segments of the same skeleton, and of different skeletons, are all in -some respects more or less differently acted on by incident forces, -and are therefore required to be more or less different; they are all, -in other respects, similarly acted on by incident forces, and are -therefore required to be more or less similar. It is impossible to -deny that if differences in the mechanical functions of the vertebræ -involve differences in their forms; then, community in their mechanical -functions, must involve community in their forms. And as we know that -throughout the <i>Vertebrata</i> generally, and in each vertebrate -animal, the vertebræ, amid all their varying circumstances, <i>have</i> -a certain community of function, it follows necessarily that they will -have a certain general resemblance—there will recur that average shape -which has suggested the notion of a pattern-vertebra.</p> - -<p>A glance at the facts at once shows their harmony with this conclusion. -In an eel or a snake, where the bodily actions are such as to involve -great homogeneity in the mechanical conditions of the vertebræ, the -series of them is comparatively homogeneous. On the contrary, in a -mammal or a bird, where there is considerable heterogeneity in their -circumstances, their similarity is no longer so great. And if, instead -of comparing the vertebral columns of different animals, we compare -the successive vertebræ of any one animal, we recognize the same law. -In the segments of an individual spine, where is there the greatest -divergence from the common mechanical conditions? and where may we -therefore expect to find the widest departure from the average form? -Obviously at the two extremities. And accordingly it is at the two -extremities that the ordinary structure is lost.</p> - -<p>Still clearer becomes the truth of this view, when we consider the -genesis of the vertebral column as displayed throughout the ascending -grades of the <i>Vertebrata</i>. In its first embryonic stage, the -spine is an undivided column of flexible substance. In the early -fishes, while some of the peripheral elements of the vertebræ were -marked out, the central axis was still a continuous unossified cord. -And thus we have good reason for thinking that in the primitive -vertebrate animal, as in the existing <i>Amphioxus</i>, the notochord -was persistent. The production of a higher, more powerful, more -active creature of the same type, by whatever method it is conceived -to have taken place, involved a change in the notochordal structure. -Greater muscular endowments presupposed a firmer internal fulcrum<span class="pagenum" id="Page_565">[565]</span> -—a less yielding central axis. On the other hand, for the central -axis to have become firmer while remaining continuous, would have -entailed a stiffness incompatible with the creature’s movements. Hence, -increasing density of the central axis necessarily went hand in hand -with its segmentation: for strength, ossification was required; for -flexibility, division into parts. The production of vertebræ resulting -thus, there obviously would arise among them a general likeness, due -to the similarity in their mechanical conditions, and more especially -the muscular forces bearing on them. And then observe, lastly, that -where, as in the head, the terminal position and the less space -for development of muscles, entailed smaller lateral bendings, the -segmentation would naturally be less decided, less regular, and would -be lost as we approached the front of the head.</p> - -<p>But, it may be replied, this hypothesis does not explain all the -facts. It does not tell us why a bone whose function in a given animal -requires it to be solid, is formed not of a single piece, but by the -coalescence of several pieces, which in other creatures are separate; -it does not account for the frequent manifestations of unity of plan -in defiance of teleological requirements. This is quite true. But it -is not true, as Professor Owen argues respecting such cases, that -“if the principle of special adaptation fails to explain them, and -we reject the idea that these correspondences are manifestations of -some archetypal exemplar, on which it has pleased the Creator to frame -certain of his living creatures, there remains only the alternative -that the organic atoms have concurred fortuitously to produce such -harmony.” This is not the only alternative: there is another, which -Professor Owen has overlooked. It is a perfectly tenable supposition -that all higher vertebrate forms have arisen by <i>the superposing -of adaptations upon adaptations</i>. Either of the two antagonist -cosmogonies consists with this supposition. If, on the one hand, we -conceive species to have resulted from acts of special creation; then -it is quite a fair assumption that to produce a higher vertebrate -animal, the Creator did not begin afresh, but took a lower vertebrate -animal, and so far modified its pre-existing parts as to fit them for -the new requirements; in which case the original structure would show -itself through the superposed modifications. If, on the other hand, we -conceive species to have resulted by gradual differentiations under the -influence of changed conditions; then, it would manifestly follow that -the higher, heterogeneous forms, would bear traces of the lower and -more homogeneous forms from which they were evolved.</p> - -<p>Thus, besides finding that the hypothesis of an “ideal typical -vertebra” is irreconcilable with the facts, we find that the facts are -interpretable without gratuitous assumptions. The average community of -form which vertebræ display, is explicable as resulting<span class="pagenum" id="Page_566">[566]</span> from natural -causes. And those typical similarities which are traceable under -adaptive modifications, must obviously exist if, throughout creation in -general, there has gone on that continuous superposing of modifications -upon modifications which goes on in every unfolding organism.</p> - -<hr class="tb" /> - -<p>[I might with propriety have added to the foregoing criticisms, the -remark that Professor Owen has indirectly conferred a great benefit by -the elaborate investigations he has made with the view of establishing -his hypothesis. He has himself very conclusively proved that the -teleological interpretation is quite irreconcilable with the facts. -In gathering together evidence in support of his own conception of -archetypal forms, he has disclosed adverse evidence which I think shows -his conception to be untenable. The result is that the field is left -clear for the hypothesis of Evolution as the only tenable one.]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_567">[567]</span></p> - -<h3>APPENDIX C.</h3> -</div> - -<p>[<i>From the</i> <span class="smcap">Transactions of the Linnean Society, vol. -xxv</span>.]</p> - -<hr class="full" /> - -<div class="blockquot"> - -<p>XV. <i>On Circulation and the Formation of Wood in Plants. -By</i> <span class="smcap">Herbert Spencer</span>, <i>Esq. Communicated by</i> -<span class="smcap">George Busk</span>, <i>Esq., F.R.S., Sec. L.S.</i></p> -</div> - -<p class="center p-left p2">Read March 1st, 1866.</p> - -<p>Opinions respecting the functions of the vascular tissues in plants -appear to make but little progress towards agreement. The supposition -that these vessels and strings of partially-united cells, lined with -spiral, annular, reticulated, or other frameworks, are carriers of the -plant-juices, is objected to on the ground that they often contain -air: as the presence of air arrests the movement of blood through -arteries and veins, its presence in the ducts of stems and petioles -is assumed to unfit them as channels for sap. On the other hand, that -these structures have a respiratory office, as some have thought, is -certainly not more tenable, since, if the presence of air in them -negatives the belief that their function is to distribute liquid, the -presence of liquid in them equally negatives the belief that their -function is to distribute air. Nor can any better defence be made for -the hypothesis which I find propounded, that these parts serve “to give -strength to the parenchyma.” Tubes with fenestrated and reticulated -internal skeletons have, indeed, some power of supporting the tissue -through which they pass; but tubes lined with spiral threads can yield -extremely little support, while tubes lined with annuli, or spirals -alternating with annuli, can yield no support whatever. Though all -these types of internal framework are more or less efficient for -preventing closure by lateral pressure, they are some of them quite -useless for holding up the mass through which the vessels pass; and the -best of them are for this purpose mechanically inferior to the simple -cylinder. The same quantity of matter made into a continuous tube would -be more effective in giving stiffness to the cellular tissue around it.</p> - -<p>In the absence of any feasible alternative, the hypothesis that these -vessels are distributors of sap claims reconsideration. The objections -are not, I think, so serious as they seem. The habitual<span class="pagenum" id="Page_568">[568]</span> presence of -air in the ducts that traverse wood, can scarcely be held anomalous if -when the wood is formed their function ceases. The canals which ramify -through a Stag’s horn, contain air after the Stag’s horn is fully -developed; but it is not thereby rendered doubtful whether it is the -function of arteries to convey blood. Again, that air should frequently -be found even in the vessels of petioles and leaves, will not appear -remarkable when we call to mind the conditions to which a leaf is -subject. Evaporation is going on from it. The thinner liquids pass -by osmose out of the vessels into the tissues containing the liquids -thickened by evaporation. And as the vessels are thus continually -drained, a draught is made upon the liquid contained in the stem and -roots. Suppose that this draught is unusually great, or suppose that -around the roots there exists no adequate supply of moisture. A state -of capillary tension must result—a tendency of the liquid to pass into -the leaves resisted below by liquid cohesion. Now, had the vessels -impermeable coats, only their upper extremities would under these -conditions be slowly emptied. But their coats, in common with all the -surrounding tissues, are permeable by air. Hence, under this state -of capillary tension, air will enter; and as the upper ends of the -tubes, being both smaller in diameter and less porous than the lower, -will retain the liquids with greater tenacity, the air will enter the -wider and more porous tubes below—the ducts of the stem and branches. -Thus the entrance of air no more proves that these ducts are not -sap-carriers, than does the emptiness of tropical river-beds in the dry -season prove that they are not channels for water. There is, however, a -difficulty which seems more serious. It is said that air, when present -in these minute canals, must be a great obstacle to the movement of sap -through them. The investigations of Jamin have shown that bubbles in a -capillary tube resist the passage of liquid, and that their resistance -becomes very great when the bubbles are numerous—reaching, in some -experiments, as much as three atmospheres. Nevertheless the inference -that any such resistance is offered by the air-bubbles in the vessels -of a plant, is, I think, an erroneous one. What happens in a capillary -tube having impervious sides, with which these experiments were made, -will by no means happen in a capillary tube having pervious sides. -Any pressure brought to bear on the column of liquid contained in the -porous duct of a plant, must quickly cause the expulsion of a contained -air-bubble through the minute openings in the coats of the duct. The -greater molecular mobility of gases than liquids, implies that air will -pass out far more readily than sap. Whilst, therefore, a slight tension -on the column of sap will cause it to part and the air to enter, a -slight pressure upon it will force out the air and reunite the divided -parts of the column.</p> - -<p>To obtain data for an opinion on this vexed question, I have<span class="pagenum" id="Page_569">[569]</span> lately -been experimenting on the absorption of dyes by plants. So far as I can -learn, experiments of this kind have most, if not all of them, been -made on stems, and, as it would seem from the results, on stems so far -developed as to contain all their characteristic structures. The first -experiments I made myself were on such parts, and yielded evidence that -served but little to elucidate matters. It was only after trying like -experiments with leaves of different ages and different characters, -and with undeveloped axes, as well as with axes of special kinds, that -comprehensible results were reached; and it then became manifest that -the appearances presented by ordinary stems when thus tested, are in a -great degree misleading. Let me briefly indicate the differences.</p> - -<p>If an adult shoot of a tree or shrub be cut off, and have its lower -end placed in an alumed decoction of logwood or a dilute solution of -magenta,<a id="FNanchor_69" href="#Footnote_69" class="fnanchor">[69]</a> the dye will, in the course of a few hours, ascend to a -distance varying according to the rate of evaporation from the leaves. -On making longitudinal sections of the part traversed by it, the dye is -found to have penetrated extensive tracts of the woody tissue; and on -making transverse sections, the openings of the ducts appear as empty -spaces in the midst of a deeply-coloured prosenchyma. It would thus -seem that the liquid is carried up the denser parts of the vascular -bundles; neglecting the cambium layer, neglecting the central pith, -and neglecting the spiral vessels of the medullary sheath. Apparently -the substance of the wood has afforded the readiest channel. When, -however, we examine these appearances critically, we find reasons for -doubting this conclusion. If a transverse section of the lower part, -into which the dye passed first and has remained longest, be compared -with a transverse section of the part which the dye has but just -reached, a marked difference is visible. In the one case the whole of -the dense tissue is stained; in the other case it is not. This uneven -distribution of stain in the part which the dye has incompletely -permeated is not at random; it admits of definite description. A -tolerably regular continuous ring of colour distinguishes the outer -part of the wood from the inner mass, implying a passage of liquid -up the elongated cells next the cambium layer. And the inner mass is -coloured more round the mouths of the pitted ducts than elsewhere: the -dense tissue is darkest close to the edges of these ducts; the colour -fades away gradually on receding from their edges; there is most colour -where there are several ducts together; and the dense tissue which<span class="pagenum" id="Page_570">[570]</span> -is fully dyed for some space, is that which lies between two or more -ducts. These are indications that while the layer of pitted cells -next the cambium has served as a channel for part of the liquid, the -rest has ascended the pitted ducts, and oozed out of these into the -prosenchyma around. And this conclusion is confirmed by the contrast -between the appearances of the lowest part of a shoot under different -conditions. For if, instead of allowing the dye time for oozing through -the prosenchyma, the end of the shoot be just dipped into the dye and -taken out again, we find, on making transverse sections of the part -into which the dye has been rapidly taken up, that, though it has -diffused to some distance round the ducts, it has left tracts of wood -between the ducts uncoloured—a difference which would not exist had -the ascent been through the substance of the wood. Even still stronger -is the confirmation obtained by using one dye after another. If a shoot -that has absorbed magenta for an hour be placed for five minutes in the -logwood decoction, transverse sections of it taken at a short distance -from its end show the mouths of the ducts surrounded by dark stains in -the midst of the much wider red stains.</p> - -<p>Based on these comparisons only, the inference pointed out has little -weight; but its weight is increased by the results of experiments on -quite young shoots, and shoots that develope very little wood. The -behaviour of these corresponds perfectly with the expectation that a -liquid will ascend capillary tubes in preference to simple cellular -tissue or tissue not differentiated into continuous canals. The -vascular bundles of the medullary sheath are here the only channels -which the coloured liquid takes. In sections of the parts up to which -the dye has but just reached, the spiral, fenestrated, scalariform, -or other vessels contained in these bundles are alone coloured, and -lower down it is only after some hours that such an exudation of dye -takes place as suffices partially to colour the other substances of the -bundle. Further, it is to be noted that at the terminations of shoots, -where the vessels are but incompletely formed out of irregularly-joined -fibrous cells which still retain their original shapes, the dye runs up -the incipient vessels and does not colour in the smallest degree the -surrounding tissue.</p> - -<p>Experiments with leaves bring out parallel facts. On placing in a dye -a petiole of an adult leaf of a tree, and putting it before the fire -to accelerate evaporation, the dye will be found to ascend the mid-rib -and veins at various rates, up even to a foot per hour. At first it -is confined to the vessels; but by the time it has reached the point -of the leaf, it will commonly be seen that at the lower part it has -diffused itself into the sheaths of the vessels. In a quite young leaf -from the same shoot, we find a much more rigorous restriction of the -dye to the vessels. On making oblique sections of its petiole, mid-rib, -and veins, the vessels have the appearance of groups of<span class="pagenum" id="Page_571">[571]</span> sharply -defined coloured rods imbedded in the green prosenchyma; and this -marked contrast continues with scarcely an appreciable change after -plenty of time has been allowed for exudation.</p> - -<p>The facts thus grouped and thus contrasted seem, at first sight, to -imply that while they are young the coats of these ramifying canals -lined with spiral or allied structures are not readily permeable, -but that, becoming porous as they grow old, they allow the liquids -they carry to escape with increasing facility; and hence a possible -interpretation of the fact that, in the older parts, the staining of -the tissue around the vessels is so rapid as to suggest that the dye -has ascended directly through this tissue, whereas in the younger -parts the reverse appearance necessitates the reverse conclusion. But -now, is this difference determined by difference of age, or is it -otherwise determined? The evidence as presented in ordinary stems and -leaves shows us that the parts of the vascular system at which there -is a rapid escape of dye are not simply older parts, but are parts -where a deposit of woody matter is taking place. Is it, then, that -the increasing permeability of the ducts, instead of being directly -associated with their increasing age, is directly associated with the -increasing deposit of dense substance around them?</p> - -<p>To get proof that this last connexion is the true one, we have but -to take a class of cases in which wood is formed only to a small -extent. In such cases experiments show us a far more general and -continued limitation of the dye to the vessels. Ordinary herbs and -vegetables, when contrasted with shrubs and trees, illustrate this; -as instance the petioles of Celery, or of the common Dock, and the -leaves of Cabbages or Turnips. And then in very succulent plants, such -as <i>Bryophyllum calycinum</i>, <i>Kalanchoë rotundifolia</i>, the -various species of <i>Crassula</i>, <i>Cotyledon</i>, <i>Kleinia</i>, -and others of like habit, the ducts of old and young leaves alike -retain the dye very persistently: the concomitant in these cases being -the small amount of prosenchyma around the ducts, or the small amount -of deposit in it, or both. More conclusive yet is the evidence which -meets us when we turn from very succulent leaves to very succulent -axes. The tender young shoots of <i>Kleinia ante-euphorbium</i>, or -<i>Euphorbia Mauritanica</i>, which for many inches of their lengths -have scarcely any ligneous fibres, show us scarcely any escape of -the coloured liquid from the vessels of the medullary sheath. So, -too, is it with <i>Stapelia Buffonia</i>, a plant of another order, -having soft swollen axes. And then we have a repetition of the like -connexion of facts throughout the <i>Cactaceæ</i>: the most succulent -showing us the smallest permeability of the vessels. In two species of -<i>Rhipsalis</i>, in two species of <i>Cereus</i>, and in two species -of <i>Mammillaria</i>, which I have tried, I have found this so. -<i>Mammillaria gracilis</i> may be named as exemplifying the relation -under its extreme form. Into one of these small spheroidal masses, the -dye ascends through the large bundles<span class="pagenum" id="Page_572">[572]</span> of spiral or annular ducts, or -cells partially united into such ducts, colouring them deeply, and -leaving the feebly-marked sheath of prosenchyma, together with the -surrounding watery cellular tissue, perfectly uncoloured.</p> - -<p>The most conclusive evidence, however, is furnished by those -<i>Cactaceæ</i> in which the transition from succulent to dense tissue -takes place variably, according as local circumstances determine. -<i>Opuntia</i> yields good examples. If a piece of it including one of -the joints at which wood is beginning to form, be allowed to absorb -a coloured liquid, the liquid, running up the irregular bundles of -vessels and into many of their minute ramifications, is restricted to -these where they pass through the parenchyma forming the mass of the -stem; but near the joints the hardened tissue around the vessels is -coloured. In one of these fleshy growths we get clear evidence that -the escape of the dye has no immediate dependence on the age of the -vessels, since, in parts of the stem that are alike in age, some of -the vessels retain their contents while others do not. Nay, we even -find that the younger vessels are more pervious than the older ones, if -round the younger ones there is a formation of wood.</p> - -<p>Thus, then, is confirmed the inference before drawn, that in ordinary -stems the staining of the wood by an ascending coloured liquid is due, -not to the passage of the coloured liquid up the substance of the wood, -but to the permeability of its ducts and such of its pitted cells as -are united into irregular canals. And the facts showing this, at the -same time indicate with tolerable clearness the process by which wood -is formed. What in these cases is seen to take place with a dye, may -be fairly presumed to take place with sap. Where the dye exudes but -slowly, we may infer that the sap exudes but slowly; and it is a fair -inference that where the dye leaks rapidly out of the vessels, the sap -does the same. Inferring, thus, that where-ever there is a considerable -formation of wood there is a considerable escape of the sap, we see -in the one the result of the other. The thickening of the prosenchyma -is proportionate to the quantity of nutritive liquid passing into it; -and this nutritive liquid passes into it from the vessels, ducts, and -irregular canals it surrounds.</p> - -<p>But an objection is made to such experiments as the foregoing, and to -all the inferences drawn from them. It is said that portions of plants -cut off and thus treated, have their physiological actions arrested, -or so changed as may render the results misleading; and it is said -that when detached shoots and leaves have their cut ends placed in -solutions, the open mouths of their vessels and ducts are directly -presented with the liquids to be absorbed, which does not happen in -their natural states. Further, making these objections look serious, it -is alleged that when solutions are absorbed through the roots, quite -different results are obtained: the absorbed matters are found in the -tissues and not in the vessels. Clearly, were the experiments<span class="pagenum" id="Page_573">[573]</span> yielding -these adverse results conducted in unobjectionable ways, the conclusion -implied by them would negative the conclusions above drawn. But these -experiments are no less objectionable than those to which they are -opposed. Such mineral matters as salts of iron, solutions of which -have in some cases been supplied to the roots for their absorption, -are obviously so unlike the matters ordinarily absorbed, that they -are likely to interfere fatally with the physiological actions. If -experiments of this kind are made by immersing the roots in a dye, -there is, besides the difficulty that the mineral mordant contained -by the dye is injurious to the plant, the further difficulty that the -colouring matter, being seized by the substances for which it has an -affinity, is left behind in the first layers of root-tissues passed -through, and that the decolorized water passing up into the plant is -not traceable. To be conclusive, then, an experiment on absorption -through roots must be made with some solution which will not seriously -interfere with the plant’s vital processes, and which will not have -its distinctive element left behind. To fulfil these requirements I -adopted the following method. Having imbedded a well-soaked broad-bean -in moist sand, contained in an inverted cone of cardboard with its -apex cut off for the radicle to come through—having placed this in -a wide-mouthed dwarf bottle, partly filled with water, so that the -protruding radicle dipped into the water—and having waited until the -young bean had a shoot some three or more inches high, and a cluster -of secondary rootlets from an inch to an inch and a-half long—I -supplied for its absorption a simple decoction of logwood, which, -being a vegetal matter, was not likely to do it much harm, and which, -being without a mordant, would not leave its suspended colour in the -first tissues passed through. To avoid any possible injury, I did not -remove the plant from the bottle, but slightly raising the cone out of -its neck, I poured away the water through the crevice and then poured -in the logwood decoction; so that there could have been no broken end -or abraded surface of a rootlet through which the decoction might -enter. Being prepared with some chloride of tin as a mordant, I cut -off, after some three hours, one of the lowest leaves, expecting that -the application of the mordant to the cut surface would bring out -the characteristic colour if the logwood decoction had risen to that -height. I got no reaction, however. But after eight hours I found, on -cutting off another leaf, that the vessels of its petiole were made -visible as dark streaks by the colour with which they were charged—a -colour differing, as was to be expected, from that of the logwood -decoction, which spontaneously changes even by simple exposure. It was -then too late in the day to pursue the observations; but next morning -the vessels of the whole plant, as far as the petioles of its highest -unfolded leaves, were full of the colouring matter; and on applying -chloride of tin to the cut surfaces, the vessels assumed that purplish<span class="pagenum" id="Page_574">[574]</span> -red which this mordant produces when directly mixed with the logwood -decoction. Subsequently, when one of the cotyledons was cut open -by Prof. Oliver, to whom, in company with Dr. Hooker, I showed the -specimen, we found that the whole of its vascular system was filled -with the decoction, which everywhere gave the characteristic reaction. -And it became manifest that the liquid absorbed through the rootlets, -in the central vessels of which it was similarly traceable, had part -of it passed directly up the vessels of the axis, while part of it -had passed through other vessels into the cotyledon, out of which, no -doubt, the liquid ordinarily so carried returns charged with a supply -of the stored nutriment. I have since obtained a verification by -varying the method. Digging up some young plants (Marigolds happened -to afford the best choice) with large masses of soil round them, -placing them in water, so as gradually to detach the soil without -injuring the rootlets, planting them afresh in a flower-pot full of -washed sand, and then, after a few days, watering them with a logwood -decoction, I found, as before, that in less than twenty-four hours the -colouring matter had run up into the vessels of the leaves. Though the -reaction produced by the mordant was not so strong as before, it was -marked enough to be quite unquestionable.</p> - -<p>As these experiments were so conducted that there was no access to -the vessels except through the natural channels, and as the vital -actions of the plants were so little interfered with that at the end -of twenty-four hours they showed no traces of disturbance, I think the -results must be held conclusive.</p> - -<p>Taking it, then, as a fact that in plants possessing them the vessels -and ducts are the channels through which sap is distributed, we come -now to the further question—What determines the varying permeability -of the walls of the vessels and ducts, and the consequent varying -formation of wood? To this question I believe the true reply is—The -exposure of the parts to intermittent mechanical strains, actual or -potential, or both. By actual strains I of course mean those which the -plant experiences in the course of its individual life. By potential -strains I mean those which the form, attitude, and circumstances -common to its kind involve, and which its inherited structure is -adapted to meet. In plants with stems, petioles, and leaves, having -tolerably constant attitudes, the increasing porosity of the tubes and -consequent deposit of dense tissue takes place in anticipation of the -strains to which the parts of the individual are liable, but takes -place at parts which have been habitually subject to such strains -in ancestral individuals. But though in such plants the tendency to -repeat that distribution of dense tissue caused by mechanical actions -on past generations, goes on irrespective of the mechanical actions -to which the developing individual is subject, these direct actions, -while they greatly aid the assumption of the typical structure, are -the sole causes of those deviations in the relative<span class="pagenum" id="Page_575">[575]</span> thickenings of -parts which distinguish the individual from others of its kind. And -then, in certain irregularly growing plants, such as Cactuses and -Euphorbias, where the strains fall on parts that do not correspond in -successive individuals, we distinctly trace a direct relation between -the degrees of strain and the rates of these changes which result in -dense tissue. I will not occupy space in detailing the evidence of this -relation, which is conspicuous in the orders named, but will pass to -the question—What are the physical processes by which intermittent -mechanical strains produce this deposit of resistant substance at -places where it is needed to meet the strains? We have not to seek far -for an answer. If a trunk, a bough, a shoot, or a petiole, is bent -by a gust of wind, the substance of its convex side is subject to -longitudinal tension: the substance of its concave side being at the -same time compressed. This is the primary mechanical effect. There is, -however, a secondary mechanical effect, which here chiefly concerns -us. That bend by which the tissues of the convex side are stretched, -also produces lateral compression of them. Buttoning on a tight -glove and then closing the hand, will make this necessity clear: the -leather, while it is strained along the backs of the fingers, presses -with considerable force on the knuckles. It is demonstrable that the -tensions of the outer layer of a mass made convex by bending, must, -by composition of forces, produce at every point a resultant at right -angles to the layer beneath it; that, similarly, the joint tensions -of these two layers must throw a pressure on the next deeper layer; -and so on. Hence, if at some little distance beneath the surface of a -stem, twig, or leaf-stalk, there exist longitudinal tubes, these tubes -must be squeezed each time the side of the branch they are placed on -becomes convex. Modifying the illustration just drawn from the clenched -hand will make this clear. When, on forcibly grasping something, the -skin is drawn tightly over the back of the hand, the whitening of -the knuckles shows how the blood is expelled from the vessels below -the surface by the pressure of the tightened skin. If, then, the -sap-vessels must be thus compressed, what will happen to the liquid -they contain? It will move away along the lines of least resistance. -Part, and probably the greater part, will escape lengthways from the -place of greatest pressure: some of it being expelled downwards, and -some of it upwards. But, at the same time, part of it will be likely -to ooze through the walls of the tubes. If these walls are so perfect -as to permit the passage of liquid only by osmose, it may still be -inferred that the osmose will increase under pressure; and probably, -under recurrent pressure, the places at which the osmotic current -passes most readily will become more and more permeable, until they -eventually form pores. At any rate it is manifest that where pores -and slits exist, whether thus formed or formed in any other way, the -escape of sap into the adjacent tissue at each bend<span class="pagenum" id="Page_576">[576]</span> will become easy -and rapid. What further must happen? When the branch or shoot recoils, -the vessels on the side that was convex, being relieved from pressure, -will tend to resume their previous diameters; and will be helped to do -this by the elasticity of the surrounding tissue, as well as by those -spiral, annular, and allied structures which they contain. But this -resumption of their previous diameters must cause an immediate rush -of sap back into them. Whence will it come? Not to any considerable -extent from the surrounding tissues into which part of it has been -squeezed, seeing that the resistance to the return of liquid through -small pores will be greater than the resistance to its return along the -vessels themselves. Manifestly the sap which was thrust up and down -the vessels from the place of compression will return—the quantities -returning from above and from below varying, as we shall hereafter -see, according to circumstances. But this is not all. From some side a -greater quantity must come back than was sent away; for the amount that -has escaped out of the tube into the prosenchyma has to be replaced. -Thus during the time when the side of the branch or twig becomes -concave, more sap returns from above or below than was expelled upwards -or downwards during the previous compression. The refilled vessels, -when the next bend renders their side convex, again have part of their -contents forced through their parietes, and are again refilled in the -same way. There is thus set up a draught of sap to the place where -these intermittent strains are going on, an exudation proportionate -to the frequency and intensity of the strains, and a proportionate -nutrition or thickening of the wood-cells, fitting them to resist the -strains. A rude idea of this action may be obtained by grasping in one -hand a damp sponge, having its lower end in water, while holding a -piece of blotting-paper in contact with its upper end, and then giving -the sponge repeated squeezes. At each squeeze some of the water will -be sent into the blotting-paper; at each relaxation the sponge will -refill from below, to give another portion of its contents to the -blotting-paper when again squeezed.</p> - -<p>But how does this explanation apply to roots? If the formation of -wood is due to intermittent transverse strains, such as are produced -in the aërial parts of upright plants by the wind, how does it happen -that woody matter is deposited in roots, where there are no lateral -oscillations, no transverse strains? The answer is, that longitudinal -strains also are capable of causing the effects described. It is -true that perfectly straight fibres united into a bundle and pulled -lengthways would not exert on one another any lateral pressure, and -would not laterally compress any similarly-straight canals running -along with them. But if the fibres united into a bundle are variously -bent or twisted, they cannot be longitudinally strained without -compressing one another and structures imbedded in them. It needs<span class="pagenum" id="Page_577">[577]</span> but -to watch a wet rope drawn tight by a capstan, to see that an action -like that which squeezes the water out of its strands, will squeeze the -sap out of the vessels of a root into the surrounding tissue, as often -as the root is pulled by the swaying of the plant it belongs to. Here, -too, as before, the vessels will refill when the pull intermits; and -so, in the roots as in the branches, this rude pumping process will -produce a growth of hard tissue proportionate to the stress to be borne.</p> - -<p>These conclusions are supported by the evidence which exceptional -cases supply. If intermittent mechanical strains thus cause the -formation of wood where wood is found, then where it is not found, -there should be an absence of intermittent mechanical strains. There -is such an absence. Vascular plants characterized by little or no -deposit of dense substance, are those having vessels so conditioned -that no considerable pressures are borne by them. The more succulent a -petiole or leaf becomes, the more do the effects of transverse strains -fall on its outer layers of cells. Its mechanical support is chiefly -derived from the ability of these minute vesicles, full of liquid, to -resist bursting and tearing under the compressions and tensions they -are exposed to. And just as fast as this change from a thin leaf or -foot-stalk to a thick one entails increasing stress on the superficial -tissue, so fast does it diminish the stress on the internally-seated -vascular tissue. The succulent leaf cannot be swayed about by the wind -as much as an ordinary leaf; and such small bends as can be given to -it and its foot-stalk are prevented from affecting in any considerable -degree the tubes running through its interior. Hence the retentiveness -of the vessels in these fleshy leaves, as shown by the small exudation -of dye; and hence the small thickening of their surrounding prosenchyma -by woody deposit. Still more conspicuously is this connexion of facts -shown when, from the soft thick leaves before named and such others -as those of <i>Echeveria</i>, <i>Rochea</i>, <i>Pereskia</i>, we turn -to the thick leaves that have strong exo-skeletons. <i>Gasteria</i> -serves as an illustration. The leathery or horny skin here evidently -bears the entire weight of the leaf, and is so stiff as to prevent -any oscillation. Here, then, the vessels running inside are protected -from all mechanical stress; and accordingly we find that the cells -surrounding them are not appreciably thickened.</p> - -<p>Equally clear, and more striking because more obviously exceptional, is -the evidence given by succulent stems which are leafless. <i>Stapelia -Buffonia</i>, having soft procumbent axes not liable to be bent -backwards and forwards in any considerable degree by the wind, has, -ramifying through its tissue, vessels that allow but an extremely slow -escape of dye and have unthickened sheaths. Such of the Euphorbias as -have acquired the fleshy character while retaining the arborescent -growth, like <i>Euphorbia Canariensis</i>, teach us the same truth -in another way. In them the formation of wood around the<span class="pagenum" id="Page_578">[578]</span> vessels is -inconspicuous where the intermittent strains are but slight; but it -is conspicuous at those joints on which lateral oscillations of the -attached branches throw great extensions and compressions of tissue. -Throughout the <i>Cactaceæ</i> we find varied examples of the alleged -relation. <i>Mammillaria</i> furnishes a very marked one. The substance -of one of these globular masses, resting on the ground, admits of no -bending from side to side; and accordingly its large bundles of spiral -and annular vessels, or partially-united cells, have very feebly-marked -sheaths not at all thickened. In such types as <i>Cereus</i> and -<i>Opuntia</i> we see, as in the Euphorbias, that where little stress -falls on the vessels, little deposit takes place around them; while -there is much deposit where there is much stress. Here let me add -a confirmation obtained since writing the above. After observing -among the Cactuses the very manifest relation between strain and the -formation of wood, I inquired of Mr. Croucher, the intelligent foreman -of the Cactus-house at Kew, whether he found this relation a constant -one. He replied that he did, and that he had frequently tested it by -artificially subjecting parts of them to strains. Neglecting at the -time to inquire how he had done this, it afterwards occurred to me -that if he had so done it as to cause constant strains, the observed -result would not tell in favour of the foregoing interpretation. -Subsequently, however, I learned that he had produced the strains by -placing the plants in inclined attitudes—a method which, by permitting -oscillations of the strained joints, allowed the strains to intermit. -And then, making the proof conclusive, Mr. Croucher volunteered the -statement that where he had produced constant strains by tying, no -formation of wood took place.</p> - -<p>Aberrant growths of another class display the same relations of -phenomena. Take first the underground stems, such as the Potato and -the Artichoke. The vessels which run through these, slowly take up -the dye without letting it pass to any considerable extent into the -surrounding tissues.<a id="FNanchor_70" href="#Footnote_70" class="fnanchor">[70]</a> Only after an interval of many hours does the -prosenchyma become stained in some places. Here, as before, an absence -of rapid exudation accompanies an absence of woody deposit; and both -these go along with the absence of intermittent strains. Take again the -fleshy roots. The Turnip, the Carrot, and the Beetroot, have vessels -that retain very persistently the coloured liquids they take up. And -differing in this, as these roots do, from ordinary roots, we see -that they also differ from them in not being woody, and in not being -appreciably subject<span class="pagenum" id="Page_579">[579]</span> to the usual mechanical actions. In these cases, -as in the others, parts that ordinarily become dense, deviate from -this typical character when they are not exposed to those forces which -produce dense tissue by increasing the extravasation of sap.</p> - -<p>To complete the proof that such a relation exists, let me add the -results of some experiments on equal and similarly-developed parts, -kept respectively at rest and in motion. I have tested the effects on -large petioles, on herbaceous shoots, and on woody shoots. If two such -petioles as those of Rhubarb, with their leaves attached, have their -cut ends inserted in bottles of dye, and the one be bent backwards -and forwards while the other remains motionless, there arises, after -the lapse of an hour, scarcely any difference in the states of their -vessels: a certain proportion of these are in both cases charged with -the dye, and little exudation has been produced by the motion. Here, -however, it is to be observed that the causes of exudation are scarcely -operative; the vascular bundles are distributed all through the mass -of the petiole, which is formed of soft watery tissue; and they are, -therefore, not so circumstanced as to be effectually compressed by the -bends. In herbaceous stems, such as those of the Jerusalem Artichoke -and of the Foxglove, an effect scarcely more decided is produced; and -here, too, when we seek a reason, we find it in the non-fulfilment of -the mechanical conditions; for the vascular bundles are not so seated -between a tough layer of bark and a solid core as to be compressed at -each bend. When, however, we come to experiment upon woody shoots, we -meet with conspicuous effects, though by no means uniformly. In some -cases oscillations produce immense amounts of exudation—parallel -transverse sections of the compared shoots showing that where, in the -one that has been at rest, there are spots of colour round but a few -pitted ducts, in the one that has been kept in motion the substance of -the wood is soaked almost uniformly through with dye. In other cases, -especially where there is much undifferentiated tissue remaining, the -exudation is not very marked. The difference appears to depend on -the quantity of liquid contained in the shoot. If its substance is -relatively dry, the exudation is great; but it is comparatively small -if all the tissues are fully charged with sap. This contrast of results -is one which contemplation of the mechanical actions will lead us to -expect.</p> - -<p>And now, with these facts to aid our interpretation, let us return to -ordinary stems. If the upper end of a growing shoot, the prosenchyma -of which is but little thickened, be allowed to imbibe the dye, the -vessels of its medullary sheath alone become charged; and from them -there takes place but a slow oozing. If a like experiment be tried -with a lower part of the shoot, where the wood in course of formation -has its inner boundary marked but not its outer boundary, we find -that the pitted ducts, and more especially the inner ones, come into -play. And then lower still, where the wood<span class="pagenum" id="Page_580">[580]</span> has its periphery defined -and its histological characters decided, the appearances show that -the tissue forming its outer surface begins to take a leading part -in the transmission of liquid. What now is the explanation of these -changes, mechanically considered? In the young soft part of the shoot, -as in all normal and abnormal growths that have not formed wood, the -channels for the passage of sap are the spiral, annular, fenestrated, -or reticulated vessels. These vessels, here included in the bundles -of the medullary sheath, are, in common with the tissues around -them, subject, by the bendings of the shoot, to slight intermittent -compressions, and, especially the outermost of them, are thus forced -to give the prosenchyma an extra supply of nutritive liquid. The -thickening of the prosenchyma, spreading laterally as well as outwards -from each bundle of the medullary sheath, goes on until it meets the -thickenings that spread from the other bundles; and there is so formed -an irregular cylinder of hardened tissue, surrounding the medulla and -the vascular bundles of its sheath. As soon as this happens, these -vascular bundles become, to a considerable extent, shielded from the -effects of transverse strains, since the tensions and compressions -chiefly fall on the developing wood outside of them. Clearly, too, the -greatest stress must be felt by the outer layer of the developing wood: -being further removed from the neutral axis, it must be subject to -severer strains at each bend; and lying between the bark and the layer -of wood first formed, it must be most exposed to lateral compressions. -Among the elongated cells of this outer layer, some unite to form the -pitted ducts. Being, as we see, better circumstanced mechanically, -they become greater carriers of sap than the original vessels, and, -in consequence of this, as well as in consequence of their relative -proximity, become the sources of nutrition to the still more external -layers of wood-cells. The same causes and the same effects hold with -each new indurated coat deposited round the previously indurated coats.</p> - -<p>This description may be thought to go far towards justifying the -current views respecting the course taken by the sap. But the -justification is more apparent than real. In the first place, the -implication here is that the sap-carrying function is at first -discharged entirely by the vessels of the medullary sheath, and -that they cease to discharge this function only as fast as they are -relatively incapacitated by their mechanical circumstances. And the -second implication is, that it is not the wood itself, but the more -or less continuous canals formed in it, which are the subsequent -sap-distributors. This, though readily made clear by microscopic -examination of the large pitted ducts in a partially lignified shoot -that has absorbed the dye, is less manifestly true of the peripheral -layer of sap-carrying tissue finally formed. But it is really true -here. For this layer, though nominally a layer of wood, is practically -a layer of inosculating<span class="pagenum" id="Page_581">[581]</span> vessels. It is formed out of irregular lines -and networks of elongated pitted cells, obliquely united by their -ends. Examination of them after absorption of a dye, shows that it is -only along the continuous channels they unite to form that the current -has passed. But the essentially vascular character of this outer and -latest-formed layer of the alburnum is best seen in the fact that -the vascular systems of new axes take their rise from it, and form -with it continuous canals. If a shoot of last year in which growth -is recommencing, be cut lengthways after it has imbibed a dye, clear -proof is obtained that the passage of the dye into a lateral bud takes -place from this outermost layer of pitted cells, and that the channels -taken by the dye through the new tissue are composed of cells that pass -through modified forms into the spiral vessels of the new medullary -sheath. This transition may be still more clearly traced in a terminal -bud that continues the line of last year’s shoot. A longitudinal -section of this shows that the vessels of the new medullary sheath do -not obtain their sap from the vessels of last year’s sheath (which, as -shown by the non-absorption of dye, have become inactive), but that -their supplies are obtained from those inosculating canals formed out -of last year’s outermost layer of prosenchyma, and that between the -component cells of this and those of the new vascular system there are -all gradations of structure.<a id="FNanchor_71" href="#Footnote_71" class="fnanchor">[71]</a></p> - -<p><span class="pagenum" id="Page_582">[582]</span></p> - -<p>It is not the aim of the foregoing reasoning to show that mechanical -actions are the sole causes of the formation of dense tissue in -plants. Dense tissue is in many cases formed where no such causes -have come into play—as, for example, in thorns and in the shells -of nuts. Here the natural selection of variations can alone have -operated. It is manifest, too, that even those supporting structures -the building up of which is above ascribed to intermittent strains, -may, in the individual plant of a species that ordinarily has them, be -developed to a great extent when intermittent strains are prevented. -We see this in trees that are artificially supported by nailing to -walls; and we also see a kindred fact in natural climbers. Though in -these cases the formation of wood is obviously less than it would be -were the stem and branches habitually moved about by the wind, it -nevertheless goes on. Clearly the tendency of the plant to repeat the -structure of its type (in the one case the structure of its species; -and in the other case that of the order from which it has diverged in -becoming a climber) is here almost the sole cause of wood formation. -But though in plants so circumstanced intermittent mechanical strains -have little or no direct share, it may still be true, and I believe -is true, that intermittent mechanical strains are the original cause; -for, as before hinted, the typical structure which the individual -thus repeats irrespective of its own conditions, is interpretable -as a typical structure that is itself the product of these actions -and reactions between the plant and its environment. Grant the -inheritance of functionally-produced modifications; grant that natural -selection will always co-operate in such way as to favour those -individuals and families in which functionally-produced modifications -have progressed most advantageously; and it will follow that this -mechanically-caused formation of dense substance, accumulating from -generation to generation by the survival of the fittest, will result -in an organic habit of forming dense tissue at the required places. -The deposit arising from exudation at the places of greatest strain, -recurring from generation to generation at the same places, will come -to be reproduced in anticipation of strain, and will continue to -be reproduced for a long time after a changed habit of the species -prevents the strain—eventually, however, decreasing, both through -functional inactivity and natural selection, to the point at which it -is in equilibrium with the requirement.</p> - -<p><span class="pagenum" id="Page_583">[583]</span></p> - -<p>Another side of the general question may now be considered. We have -seen how, by intermittent pressures on capillary vessels and ducts -and inosculating canals, there must be produced a draught of sap -towards the point of compression to replace the sap squeezed out. But -we have still to inquire what will be the effect on the distribution -of sap throughout the plant as a whole. It was concluded that out of -the compressed vessels the greater part of the liquid would escape -longitudinally—the longitudinal resistance to movement being least. -In every case the probabilities are infinity to one against the -resistances being equal upwards and downwards. Always, then, more sap -will be expelled in one direction than in the other. But in whichever -direction least sap is expelled, from that same direction most sap will -return when the vessels are relieved from pressure—the force which is -powerful in arresting the back current in that direction being the same -force which is powerful in producing a forward current. Ordinarily, the -more abundant supply of liquid being from below, there will result an -upward current. At each bend a portion of the contents will be squeezed -out through the sides of the vessels—a portion will be squeezed -downwards, reversing the current ascending from the roots, but soon -stopped by its resistance; while a larger portion will be squeezed -upwards towards the extremities of the vessels, where consumption and -loss are most rapid. At each recoil the vessels will be replenished, -chiefly by the repressed upward current; and at the next bend more of -it will be thrust onwards than backwards. Hence we have everywhere in -action a kind of rude force-pump, worked by the wind; and we see how -sap may thus be raised to a height far beyond that to which it could be -raised by capillary action, aided by osmose and evaporation.</p> - -<p>Thus far, however, the argument proceeds on the assumption that there -is liquid enough to replenish every time the vessels subject to -this process. But suppose the supply fails—suppose the roots have -exhausted the surrounding stock of moisture. Evidently the vessels thus -repeatedly having their contents squeezed out into the surrounding -tissue, cannot go on refilling themselves from other vessels without -tending to empty the vascular system. On the one hand, evaporation from -the leaves causing a draught on the capillary tubes that end in them, -continually generates a capillary tension upwards; while, on the other -hand, the vessels below, expanding after their sap has been squeezed -out, produce a tension both upwards and downwards towards the point -of loss. Were the limiting membranes of the vessels impermeable, the -movement of sap would, under these conditions, soon be arrested. But -these membranes are permeable; and the surrounding tissues readily -permit the passage of air. This state of tension, then, will cause an -entrance of air into the tubes; the columns of liquid they contain -will be interrupted by bubbles. It seems, indeed, not improbable that -this entrance of air may take<span class="pagenum" id="Page_584">[584]</span> place even when there is a good supply -of liquid, if the mechanical strains are so violent and the exudation -so rapid that the currents cannot refill the half-emptied vessels -with sufficient rapidity. And in this case the intruding air may -possibly play the same part as that contained in the air-chamber of a -force-pump—tending, by moderating the violence of the jets, and by -equalizing the strains, to prevent rupture of the apparatus. Of course -when the supply of liquid becomes adequate, and the strains not too -violent, these bubbles will be expelled as readily as they entered.</p> - -<p>Here, as before, let me add the conclusive proof furnished by a direct -experiment. To ascertain the amount of this propulsive action, I took -from the same tree, a Laurel, two equal shoots, and placing them in -the same dye, subjected them to conditions that were alike in all -respects save that of motion: while one remained at rest, the other -was bent backwards and forwards, now by switching and now by straining -with the fingers. After the lapse of an hour, I found that the dye had -ascended the oscillating shoot three times as far as it had ascended -the stationary shoot—this result being an average from several trials. -Similar trials brought out similar effects in other structures. The -various petioles and herbaceous shoots experimented upon for the -purpose of ascertaining the amount of exudation produced by transverse -strains, showed also the amount of longitudinal movement. It was -observable that the height ascended by the dye was in all cases greater -where there had been oscillation than where there had been rest—the -difference, however, being much less marked in succulent structures -than in woody ones.</p> - -<p>It need scarcely be said that this mechanical action is not here -assigned as the sole cause of circulation, but as a cause co-operating -with others, and helping others to produce effects that could not -otherwise be produced. Trees growing in conservatories afford us -abundant proof that sap is raised to considerable heights by other -forces. Though it is notorious that trees so circumstanced do not -thrive unless, through open sashes, they are frequently subject -to breezes sufficient to make their parts oscillate, yet there is -evidently a circulation that goes on without mechanical aid. The -<i>causes</i> of circulation are those actions only which disturb the -liquid equilibrium in a plant, by permanently abstracting water or -sap from some part of it; and of these the first is the absorption of -materials for the formation of new tissue in growing parts; the second -is the loss by evaporation, mainly through adult leaves; and the third -is the loss by extravasation, through compressed vessels. Only so far -as it produces this last, can mechanical strain be regarded as truly a -cause of circulation. All the other actions concerned must be classed -as <i>aids</i> to circulation—as facilitating that re-distribution -of liquid that continually restores the equilibrium continually -disturbed; and of these<span class="pagenum" id="Page_585">[585]</span> capillary action may be named as the first, -osmose as the second, and the propulsive effect of mechanical strains -as the third. The first two of these aids are doubtless capable by -themselves of producing a large part of the observed result—more of -the observed result than is at first sight manifest; for there is -an important indirect effect of osmotic action which appears to be -overlooked. Osmose does not aid circulation only by setting up, within -the plant, exchange currents between the more dense and the less dense -solutions in different parts of it; but it aids circulation much more -by producing distention of the plant as a whole. In consequence of the -average contrast in density between the water outside of the plant and -the sap inside of it, the constant tendency is for the plant to absorb -a quantity in excess of its capacity, and so to produce distention -and erection of its tissues. It is because of this that the drooping -plant raises itself when watered; for capillary action alone could only -refill its tissues without changing their attitudes. And it is because -of this that juicy plants with collapsible structures bleed so rapidly -when cut, not only from the cut surface of the rooted part, but from -the cut surface of the detached part—the elastic tissues tending to -press out the liquid which distends them. And manifestly if osmose -serves thus to maintain a state of distention throughout a plant, -it indirectly furthers circulation; since immediately evaporation -or growth at any part, by abstracting liquid from the neighbouring -tissues, begins to diminish the liquid pressure within such tissues, -the distended structures throughout the rest of the plant thrust -their liquid contents towards the place of diminished pressure. This, -indeed, may very possibly be the most efficient of the agencies at -work. Remembering how great is the distention producible by osmotic -absorption—great enough to burst a bladder—it is clear that the -force with which the distended tissues of a plant urge forward the sap -to places of consumption, is probably very great. We must therefore -regard the aid which mechanical strains give as being one of several. -Oscillations help directly to restore any disturbed liquid equilibrium; -and they also help indirectly, by facilitating the re-distribution -caused by capillary action and the process just described; but in the -absence of oscillations the equilibrium may still be restored, though -less rapidly and within narrower limits of distance.</p> - -<p>One half of the problem of the circulation, however, has been left out -of sight. Thus far our inquiry has been, how the ascending current -of sap is produced. There remains the rationale of the descending -current. What forces cause it, and through what tissues it takes place, -are questions to which no satisfactory answers have been given. That -the descent is due to gravitation, as some allege, is difficult to -conceive, since, as gravitation acts equally on all liquid columns -contained in the stem, it is not easy to see why it should produce -downward movements in some while permitting<span class="pagenum" id="Page_586">[586]</span> upward movements in -others—unless, indeed, there existed descending tubes too wide -to admit of much capillary action, which there do not. Moreover, -gravitation is clearly inadequate to cause currents towards the roots -out of branches that droop to the ground. Here the gravitation of the -contained liquid columns must nearly balance that of the connected -columns in the stem, leaving no appreciable force to cause motion. Nor -does there seem much probability in the assumption that the route of -the descending sap is through the cambium layer, since experiments on -the absorption of dyes prove that simple cellular tissue is a very bad -conductor of liquids: their movement through it does not take place -with one-fiftieth of the rapidity with which it takes place through -vessels.<a id="FNanchor_72" href="#Footnote_72" class="fnanchor">[72]</a></p> - -<p>Of course the defence for these hypotheses is, that there must be a -downward current, which must have a course and a cause; and the very -natural assumption has been that the course and the cause must be other -than those which produce the ascending current. Nevertheless there -is an alternative supposition to which the foregoing considerations -introduce us. It is quite possible for the same vascular system -to serve as a channel for movement in opposite directions at -different times. We have among animals well-known cases in which the -blood-vessels carry a current first in one direction and then, after -a brief pause, in the reverse direction. And there seems an <i>à -priori</i> probability that, lowly-organized as they are, plants are -more likely to have distributing appliances of this imperfect kind than -to have two sets of channels for two simultaneous currents. If, led -by this suspicion, we inquire whether among the forces which unite to -produce movements of sap, there are any variations or intermissions -capable of determining the currents in different directions, we quickly -discover that there are such, and that the hypothesis of an alternating -motion of the sap, now centrifugal and now centripetal, through the -same vessels, has good warrant. What are the several forces at work? -First may be set down that tendency existing in every part of a plant -to expand into its typical form, and to absorb nutritive liquids in -doing this. The resulting competition<span class="pagenum" id="Page_587">[587]</span> for sap will, other things being -equal, cause currents towards the most rapidly-growing parts—towards -unfolding shoots and leaves, but not towards adult leaves. Next we -have evaporation, acting more on the adult leaves than on those which -are in the bud, or but partially developed. This evaporation is both -regularly and irregularly intermittent. Depending chiefly on the -action of the sun, it is, in fine weather, greatly checked or wholly -arrested every evening; and in cloudy weather must be much retarded -during the day. Further, every hygrometric variation, as well as every -variation in the movement of the air, must vary the evaporation. -This chief action, therefore, which, by continually emptying the -ends of the capillary tubes, makes upward currents possible, is one -which intermits every night, and every day is strong or feeble as -circumstances determine. Then, in the third place, we have this rude -pumping process above described, going on with greater vigour when -the wind is violent, and with less vigour when it is gentle—drawing -liquid <i>towards</i> different parts according to their degrees of -oscillation, and <i>from</i> different parts according as they can most -readily furnish it. And now let us ask what must result under changing -conditions from these variously-conflicting and conspiring forces. When -a warm sunshine, causing rapid evaporation, is emptying the vessels of -the leaves, the osmotic and capillary actions that refill them will -be continually aided by the pumping action of the swaying petioles, -twigs, and branches, provided their oscillations are moderate. Under -these conditions the current of sap, moving in the direction of least -resistance, will set towards the leaves. But what will happen when the -sun sets? There is now nothing to determine currents either upwards -or downwards, except the relative rates of growth in the parts and -the relative demands set up by the oscillations; and the oscillations -acting alone, will draw sap to the oscillating parts as much from above -as from below. If the resistance to be overcome by a current setting -back from the leaves is less than the resistance to be overcome by a -current setting up from the roots, then a current will set back from -the leaves. Now it is, I think, tolerably manifest that in the swaying -twigs and minor branches, less force will be required to overcome the -inertia of the short columns of liquid between them and the leaves than -to overcome the inertia of the long columns between them and the roots. -Hence during the night, as also at other times when evaporation is not -going on, the sap will be drawn out of the leaves into the adjacent -supporting parts; and their nutrition will be increased. If the wind is -strong enough to produce a swaying of the thicker branches, the back -current will extend to them also; and a further strengthening will -result from their absorption of the elaborated sap. And when the great -branches and the stem are bent backwards and forwards by a<span class="pagenum" id="Page_588">[588]</span> gale, they -too will share in the nutrition. It may at first sight seem that these -parts, being nearer to the roots than to the leaves, will draw their -supplies from the roots only. But the quantity which the roots can -furnish is insufficient to meet so great a demand. Under the conditions -described, the exudation of sap from the vessels will be very great, -and the draught of liquid required to refill them, not satisfied by -that which the root-fibres can take in, will extend to the leaves. -Thus sap will flow to the several parts according to their respective -degrees of activity—to the leaves while light and heat enable them to -discharge their functions, and back to the twigs, branches, stem, and -roots when these become active and the leaves inactive, or when their -activity dominates over that of the leaves. And this distribution of -nutriment, varying with the varying activities of the parts, is just -such a distribution as we know must be required to keep up the organic -balance.</p> - -<p>To this explanation it may be objected that it does not account for -the downward current of sap in plants that are sheltered. The stem and -roots of a drawing-room Geranium display a thickening which implies -that nutritive matters have descended from the leaves, although there -are none of those oscillations by which the sap is said to be drawn -downwards as well as upwards. The reply is, that the stem and roots -tend to repeat their typical structures, and that the absorption of -sap for the formation of their respective dense tissues, is here the -force which determines the descent. Indeed it must be borne in mind -that the mechanical strains and the pumping process which they keep -up, as well as the distention caused by osmose, do not in themselves -produce a current either upwards or downwards: they simply help to move -the sap towards that place where there is the most rapid abstraction -of it—the place towards which its motion is least resisted. Whether -there is oscillation or whether there is not, the physiological demands -of the different parts of the plant determine the direction of the -current; and all which the oscillations and the distention do is to -facilitate the supply of these demands. Just as much, therefore, -in a plant at rest as in a plant in motion, the current will set -downwards when the function of the leaves is arrested, and when there -is nothing to resist that abstraction of sap caused by the tendency -of the stem- and root-tissues to assume their typical structures. To -which admission, however, it must be added that since this typical -structure assumed, though imperfectly assumed, by the hothouse plant, -is itself interpretable as the inherited effect of external mechanical -actions on its ancestors, we may still consider the current set up by -the assumption of the typical structure to be indirectly due to such -actions.</p> - -<p>Interesting evidence of another order here demands notice. In the -course of experiments on the absorption of dyes by leaves, it happened -that in making sections parallel to the plane of a leaf, with<span class="pagenum" id="Page_589">[589]</span> the -view of separating its middle layer containing the vessels, I came -upon some structures that were new to me. These structures, where they -are present, form the terminations of the vascular system. They are -masses of irregular and imperfectly united fibrous cells, such as those -out of which vessels are developed; and they are sometimes slender, -sometimes bulky—usually, however, being more or less club-shaped. In -transverse sections of leaves their distinctive characters are not -shown: they are taken for the smaller veins. It is only by carefully -slicing away the surface of a leaf until we come down to that part -which contains them, that we get any idea of their nature. Fig. 1 -represents a specimen taken from a leaf of <i>Euphorbia neriifolia</i>. -Occupying one of the interspaces of the ultimate venous network, it -consists of a spirally-lined duct or set of ducts, which connects with -the neighbouring vein a cluster of half-reticulated, half-scalariform -cells. These cells have projections, many of them tapering, that insert -themselves into the adjacent intercellular spaces, thus producing -an extensive surface of contact between the organ and the imbedding -tissues. A further trait is, that the ensheathing prosenchyma is -either but little developed or wholly absent; and consequently this -expanded vascular structure, especially at its end, comes immediately -in contact with the tissues concerned in assimilation. The leaf of -<i>Euphorbia neriifolia</i> is a very fleshy one; and in it these -organs are distributed through a compact, though watery, cellular mass. -But in any leaf of the ordinary type which possesses them, they lie in -the network-parenchyma composing its lower layer; and wherever they -occur in this layer its cells unite to enclose them. This arrangement -is shown in fig. 2, representing a sample from the Caoutchouc-leaf, as -seen with the upper part of its envelope removed; and it is shown still -more clearly in a sample from the leaf of <i>Panax Lessonii</i>, fig. -3. Figures 4 and 5 represent, without their sheaths, other such organs -from the leaves of <i>Panax Lessonii</i> and <i>Clusia flava</i>. Some -relation seems to exist between their forms and the thicknesses of the -layers in which they lie. Certain very thick leaves, such as those of -<i>Clusia flava</i>, have them less abundantly distributed than is -usual, but more massive. Where the parenchyma is developed not to so -great an extreme, though still largely, as in the leaves of Holly, -<i>Aucuba</i>, <i>Camellia</i>, they are not so bulky; and in thinner -leaves, like those of Privet, Elder, &c., they become longer and -less conspicuously club-shaped. Some adaptations to their respective -positions seem implied by these modifications; and we may naturally -expect that in many thin leaves these free ends, becoming still -narrower, lose the distinctive and suggestive characters possessed by -those shown in the diagrams. Relations of this kind are not regular, -however. In various other genera, members of which I have examined, -as <i>Rhus</i>, <i>Viburnum</i>, <i>Griselinia</i>, <i>Brexia</i>, -<i>Botryodendron</i>, <i>Pereskia</i>, the variations in the<span class="pagenum" id="Page_590">[590]</span> bulk -and form of these structures are not directly determined by the -spaces which the leaves allow: obviously there are other modifying -causes. It should be added that while these expanded free extremities -graduate into tapering free extremities, not differing from ordinary -vessels, they also pass insensibly into the ordinary inosculations. -Occasionally, along with numerous free endings, there occur loops; and -from such loops there are transitions to the ultimate meshes of the -veins.</p> - -<p>These organs are by no means common to all leaves. In many that -afford ample spaces for them they are not to be found. So far as I -have observed, they are absent from the thick leaves of plants which -form very little wood. In <i>Sempervivum</i>, in <i>Echeveria</i>, -in <i>Bryophyllum</i>, they do not appear to exist; and I have been -unable to discover them in <i>Kalanchoë rotundifolia</i>, in <i>Kleinia -ante-euphorbium</i> and <i>ficoides</i>, in the several species of -<i>Crassula</i>, and in other succulent plants. It may be added that -they are not absolutely confined to leaves, but occur in stems that -have assumed the functions of leaves. At least I have found, in the -green parenchyma of <i>Opuntia</i>, organs that are analogous though -much more rudely and irregularly formed. In other parts, too, that -have usurped the leaf-function, they occur, as in the phyllodes of -the Australian Acacias. These have them abundantly developed; and it -is interesting to observe that here, where the two vertically-placed -surfaces of the flattened-out petiole are equally adapted to the -assimilative function, there exist two layers of these expanded -vascular terminations, one applied to the inner surface of each layer -of parenchyma.</p> - -<p>Considering the structures and positions of these organs, as well as -the natures of the plants possessing them, may we not form a shrewd -suspicion respecting their function? Is it not probable that they -facilitate absorption of the juices carried back from the leaf for -the nutrition of the stem and roots? They are admirably adapted for -performing this office. Their component fibrous cells, having angles -insinuated between the cells of the parenchyma, are shaped just as they -should be for taking up its contents; and the absence of sheathing -tissue between them and the parenchyma facilitates the passage of the -elaborated liquids. Moreover there is the fact that they are allied to -organs which obviously have absorbent functions. I am indebted to Dr. -Hooker for pointing out the figures of two such organs in the “Icones -Anatomicæ” of Link. One of them is from the end of a dicotyledonous -root-fibre, and the other is from the prothallus of a young Fern. In -each case a cluster of fibrous cells, seated at a place from which -liquid has to be drawn, is connected by vessels with the parts to which -liquid has to be carried. There can scarcely be a doubt, then, that in -both cases absorption is effected through them. I have met with another -such organ, more elaborately constructed, but evidently adapted to the -same<span class="pagenum" id="Page_591">[591]</span> office, in the common Turnip-root. As shown by the end view and -longitudinal section in figs. 6 and 7, this organ consists of rings of -fenestrated cells, arranged with varying degrees of regularity into a -funnel, ordinarily having its apex directed towards the central mass -of the Turnip, with which it has, in some cases at least, a traceable -connexion by a canal. Presenting as it does an external porous surface -terminating one of the branches of the vascular system, each of these -organs is well fitted for taking up with rapidity the nutriment laid -by in the Turnip-root, and used by the plant when it sends up its -flower-stalk. Nor does even this exhaust the analogies. The cotyledons -of the young bean, experimented upon as before described, furnished -other examples of such structures, exactly in the places where, if -they are absorbents, we might expect to find them. Amid the branchings -and inosculations of the vascular layer running through the mass of -nutriment deposited in each cotyledon, there are conspicuous free -terminations that are club-shaped, and prove to be composed, like those -in leaves, of irregularly formed and clustered fibrous cells; and some -of them, diverging from the plane of the vascular layer, dip down into -the mass of starch and albumen which the young plant has to utilize, -and which these structures can have no other function but to take up.</p> - -<p>Besides being so well fitted for absorption, and besides being -similar to organs which we cannot doubt are absorbents, these -vascular terminations in leaves afford us yet another evidence of -their functions. They are seated in a tissue so arranged as specially -to facilitate the abstraction of liquid. The centripetal movement -of the sap must be set up by a force that is comparatively feeble, -since, the parietes of the ducts being porous, air will enter if the -tension on the contained columns becomes considerable. Hence it is -needful that the exit of sap from the leaves should meet with very -little resistance. Now were it not for an adjustment presently to -be described, it would meet with great resistance, notwithstanding -the peculiar fitness of these organs to take it in. Liquid cannot be -drawn out of any closed cavity without producing a collapse of the -cavity’s sides; and if its sides are not readily collapsible, there -must be a corresponding resistance to the abstraction of liquid from -it. Clearly the like must happen if the liquid is to be drawn out of -a tissue which cannot either diminish in bulk bodily or allow its -components individually to diminish in bulk. In an ordinary leaf, the -upper layer of parenchyma, formed as it is of closely-packed cells -that are without interspaces, and are everywhere held fast within -their framework of veins, can neither contract easily as a mass, nor -allow its separate cells to do so. Quite otherwise is it with the -network-parenchyma below. The long cells of this, united merely by -their ends and having their flexible sides surrounded by air, may -severally have their contents considerably increased and decreased -without offering<span class="pagenum" id="Page_592">[592]</span> appreciable resistances: and the network-tissue -which they form will, at the same time, be capable of undergoing -slight expansions and contractions of its thickness. In this layer -occur these organs that are so obviously fitted for absorption. Here -we find them in direct communication with its system of collapsible -cells. The probability appears to be, that when the current sets into -the leaf, it passes through the vessels and their sheaths chiefly into -the upper layer of cells (this upper layer having a larger surface -of contact with the veins than the lower layer, and being the seat -of more active processes); and that the juices of the upper layer, -enriched by the assimilated matters, pass into the network-parenchyma, -which serves as a reservoir from which they are from time to time -drawn for the nutrition of the rest of the plant, when the actions -determine the downward current. Should it be asked what happens where -the absorbents, instead of being inserted in a network-parenchyma, are, -as in the leaves of <i>Euphorbia neriifolia</i>, inserted in a solid -parenchyma, the reply is, that such a parenchyma, though not furnished -with systematically arranged air-chambers, nevertheless contains air -in its intercellular spaces; and that when there occurs a draught upon -its contents, the expansion of this air and the entrance of more from -without, quickly supply the place of the abstracted liquid.</p> - -<p>If then, returning to the general argument, we conclude that these -expanded terminations of the vascular system in leaves are absorbent -organs, we find a further confirmation of the views set forth -respecting the alternating movement of the sap along the same channels. -These spongioles of the leaves, like the spongioles of the roots, being -appliances by which liquid is taken up to be carried into the mass -of the plant, we are obliged to regard the vessels that end in these -spongioles of the leaves as being the channels of the down current -whenever it is produced. If the elaborated sap is abstracted from the -leaves by these absorbents, then we have no alternative but to suppose -that, having entered the vascular system, the elaborated sap descends -through it. And seeing how, by the help of these special terminations, -it becomes possible for the same vessels to carry back a quality of sap -unlike that which they bring up, we are enabled to understand tolerably -well how this rhythmical movement produces a downward transfer of -materials for growth.</p> - -<hr class="tb" /> - -<p>The several lines of argument may now be brought together; and along -with them may be woven up such evidences as remain. Let me first point -out the variety of questions to which the hypothesis supplies answers.</p> - -<p>It is required to account for the ascent of sap to a height beyond that -to which capillary action can raise it. This ascent is accounted for -by the propulsive action of transverse strains, joined with that of -osmotic distention. A cause has to be assigned for that rise of sap<span class="pagenum" id="Page_593">[593]</span> -which, in the spring, while yet there is no considerable evaporation to -aid it, goes on with a power which capillarity does not explain. The -co-operation of the same two agencies is assignable for this result -also.<a id="FNanchor_73" href="#Footnote_73" class="fnanchor">[73]</a> The circumstance that vessels and ducts here contain sap and -there contain air, and at the same place contain at different seasons -now air and now sap is a fact calling for explanation. An explanation -is furnished by these mechanical actions which involve the entrance -or expulsion of air according to the supply of liquid. That vessels -and ducts which were originally active sap-carriers go completely out -of use, and have their function discharged by other vessels or ducts, -is an anomaly that has to be solved. Again, we are supplied with a -solution: these deserted vessels and ducts are those which, by the -formation of dense tissue outside of them, become so circumstanced that -they cannot be compressed as they originally were. A channel has to be -found for the downward current of sap, which, on any other hypothesis -than the foregoing, must be a channel separate from that taken by the -upward current; and yet no good evidence of a separate channel has -been pointed out. Here, however, the difficulty disappears, since one -channel suffices for the current alternating upwards and downwards -according to the conditions. Moreover there has to be found a force -producing or facilitating the downward current, capable even of drawing -sap out of drooping branches; and no such force is forthcoming. The -hypothesis set forth dispenses with this necessity; under the recurring -change of conditions, the same distention and oscillation which before -raised the sap to the places of consumption, now bring it down to the -places of consumption. A physical process has to be pointed out by -which the material that forms dense tissue is deposited at the places -where it is wanted, rather than at other places. This physical process -the hypothesis indicates. It is requisite to find an explanation of the -fact that, when plants ordinarily swayed about by the wind are grown -indoors, the formation of wood is so much diminished that they become -abnormally slender. Of this an explanation is supplied. Yet a further<span class="pagenum" id="Page_594">[594]</span> -fact to be interpreted is, that in the same individual plant homologous -parts, which, according to the type of the plant, should be equally -woody, become much thicker one than another if subject to greater -mechanical stress. And of this too an interpretation is similarly -afforded.</p> - -<p>Now the sufficiency of the assigned actions to account for so many -phenomena not otherwise explained, would be strong evidence that the -rationale is the true one, even were it of a purely hypothetical -kind. How strong, then, becomes the reason for believing it the true -one when we remember that the actions alleged demonstrably go on in -the way asserted. They are ever operating before our eyes; and that -they produce the effects in question is a conclusion deducible from -mechanical principles, a conclusion established by induction, and a -conclusion verified by experiment. These three orders of proof may be -briefly summed up as follows.</p> - -<p>That plants which have to raise themselves above the earth’s surface, -and to withstand the actions of the wind, must have a power of -developing supporting structure, is an <i>à priori</i> conclusion which -may be safely drawn. It is an equally safe <i>à priori</i> conclusion, -that if the supporting structure, either as a whole or in any of -its parts, has to adapt itself to the particular strains which the -individual plant is subject to by its particular circumstances, there -must be at work some process by which the strength of the supporting -structure is everywhere brought into equilibrium with the forces it -has to bear. Though the typical distribution of supporting structure -in each kind of plant may be explained teleologically by those whom -teleological explanations satisfy; and though otherwise this typical -distribution may be ascribed to natural selection acting apart from any -directly adaptive process; yet it is manifest that those departures -from the typical distribution which fit the parts of each plant to -their special conditions are explicable neither teleologically nor by -natural selection. We are, therefore, compelled to admit that, if in -each plant there goes on a balancing of the particular strains by the -particular strengths, there must be a physical or physico-chemical -process by which the adjustments of the two are effected. Meanwhile we -are equally compelled to admit, <i>à priori</i>, that the mechanical -actions to be resisted, themselves affect the internal tissues in -such ways as to further the increase of that dense substance by which -they are resisted. It is demonstrable that bending the petioles, -shoots, and stems must compress the vessels beneath their surfaces, -and increase the exudation of nutritive matters from them, and must do -this actively in proportion as the bends are great and frequent; so -that while, on the one hand, it is a necessary deduction that, if the -parts of each plant are to be severally strengthened according to the -several strains, there must be some direct connexion between strains -and strengths, it is, on the other hand, a necessary deduction from<span class="pagenum" id="Page_595">[595]</span> -mechanical principles that the strains do act in such ways as to aid -the increase of the strengths. How a like correspondence between two -<i>à priori</i> arguments holds in the case of the circulation, needs -not to be shown in detail. It will suffice to remind the reader that -while the raising of sap to heights beyond the limit of capillarity -implies some force to effect it, we have in the osmotic distention -and the intermittent compressions caused by transverse strains, -forces which, under the conditions, cannot but tend to effect it; -and similarly with the requirement for a downward current, and the -production of a downward current.</p> - -<p>Among the inductive proofs we find a kindred agreement. Different -individuals of the same species, and different parts of the same -individual, do strengthen in different degrees; and there is a clearly -traceable connexion between their strengthenings and the intermittent -strains they are exposed to. This evidence, derived from contrasts -between growths on the same plant or on plants of the same type, is -enforced by evidence derived from contrasts between plants of different -types. The deficiency of woody tissue which we see in plants called -succulent, is accompanied by a bulkiness of the parts which prevents -any considerable oscillations; and this character is also habitually -accompanied by a dwarfed growth. When, leaving these relations as -displayed externally, we examine them internally, we find the facts -uniting to show, by their agreements and differences, that between -the compression of the sap-canals and the production of wood there -is a direct relation. We have the facts, that in each plant, and in -every new part of each plant, the formation of sap-canals precedes -the formation of wood; that the deposit of woody matter, when it -begins, takes place around these sap-canals, and afterwards around -the new sap-canals successively developed; that this formation of -wood around the sap-canals takes place where the coats of the canals -are demonstrably permeable, and that the amount of wood formation is -proportionate to the permeability. And then that the permeability and -extravasation of sap occur wherever, in the individual or in the type, -there are intermittent compressions, is proved alike by ordinary cases -and by exceptional cases. In the one class of cases we see that the -deposit of wood round the vessels begins to take place when they come -into positions that subject them to intermittent compressions, while it -ceases when they become shielded from compressions. And in the other -class of cases, where, from the beginning, the vessels are shielded -from compression by surrounding fleshy tissue, there is a permanent -absence of wood formation.</p> - -<p>To which complete agreement between the deductive and inductive -inferences has to be added the direct proof supplied by experiments. It -is put beyond doubt by experiment that the liquids absorbed by plants -are distributed to their different parts through their<span class="pagenum" id="Page_596">[596]</span> vessels—at -first by the spiral or allied vessels originally developed, and then by -the better-placed ducts formed later. By experiment it is demonstrated -that the intermittent compressions caused by oscillations urge the -sap along the vessels and ducts. And it is also experimentally proved -that the same intermittent compressions produce exudation of sap from -vessels and ducts into the surrounding tissue.</p> - -<p>That the processes here described, acting through all past time, have -sufficed of themselves to develope the supporting and distributing -structures of plants, is not alleged. What share the natural selection -of variations distinguished as spontaneous, has had in establishing -them, is a question which remains to be discussed. Whether acting -alone natural selection would have sufficed to evolve these vascular -and resisting tissues, I do not profess to say. That it has been a -co-operating cause, I take to be self-evident: it must all along -have furthered the action of any other cause, by preserving the -individuals on which such other cause had acted most favourably. -Seeing, however, the conclusive proof which we have that another cause -has been in action—certainly on individuals, and, in all probability, -by inheritance on races—we may most philosophically ascribe the -genesis of these internal structures to this cause, and regard natural -selection as having here played the part of an accelerator.</p> - - -<h4 class="smaller">EXPLANATION OF PLATE.</h4> - -<p>Fig. 1. Absorbent organ from the leaf of <i>Euphorbia neriifolia</i>. -The cluster of fibrous cells forming one of the terminations of the -vascular system is here imbedded in a solid parenchyma.</p> - -<p>Fig. 2. A structure of analogous kind from the leaf of <i>Ficus -elastica</i>. Here the expanded terminations of the vessels are -imbedded in the network-parenchyma, the cells of which unite to form -envelopes for them.</p> - -<p>Fig. 3. Shows on a larger scale one of these absorbents from the leaf -of <i>Panax Lessonii</i>. In this figure is clearly seen the way in -which the cells of the network-parenchyma unite into a closely-fitting -case for the spiral cells.</p> - -<p>Fig. 4. Represents a much more massive absorbent from the same leaf, -the surrounding tissues being omitted.</p> - -<p>Fig. 5. Similarly represents, without its sheath, an absorbent from the -leaf of <i>Clusia flava</i>.</p> - -<p>Fig. 6. End view of an absorbent organ from the root of a Turnip. It is -taken from the outermost layer of vessels. Its funnel-shaped interior -is drawn as it presents itself when looked at from the outside of this -layer, its narrow end being directed towards the centre of the Turnip.</p> - -<p>Fig. 7. A longitudinal section through the axis of another such organ, -showing its annuli of reticulated cells when cut through. The cellular -tissue which fills the interior is supposed to be removed.</p> - -<p><span class="pagenum" id="Page_597">[597]</span></p> - -<p>Fig. 8. A less developed absorbent, showing its approximate connexion -with a duct. In their simplest forms, these structures consist of only -two fenestrated cells, with their ends bent round so as to meet. Such -types occur in the central mass of the Turnip, where the vascular -system is relatively imperfect. Besides the comparatively regular forms -of these absorbents, there are forms composed of amorphous masses -of fenestrated cells. It should be added that both the regular and -irregular kinds are very variable in their numbers: in some turnips -they are abundant, and in others scarcely to be found. Possibly their -presence depends on<span class="pagenum" id="Page_598">[598]</span> the age of the Turnip. Judging from the period -during which my investigations were made, namely winter and early -spring, I suspect that they are developed only in preparation for -sending up the flower-stalk.</p> - - <div class="figcenter" id="i_597"> - <img - class="p2" - src="images/i_597.jpg" - alt="" /> - <p class="p0 center p-left">Figs.1–8.</p> - </div> - -<p class="p2">Let me add that experiments on circulation in plants made during the -state of inactivity, when it is to be presumed that the vessels and -tissues contain but little gap, are much more successful than those -made in the summer. It would seem that when the tissues are fully -charged with sap the taking up of dyes is comparatively slow and the -above-described effects are not so easily demonstrable.</p> - -<hr class="tb" /> - -<p>[An expert writes concerning this essay:—“I have not attempted to -annotate critically this paper. There is no doubt that many of your -conclusions are perfectly sound, particularly those relating to the -passage of crude sap through the <i>cavities</i> of the elements of the -wood, though the opinion that the actual passage was through the walls -very generally held till about 12 years ago.”]</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_599">[599]</span></p> - -<h3>APPENDIX D.<br /> -<span class="subhed1">ON THE ORIGIN OF THE VERTEBRATE TYPE.</span></h3></div> - - -<div class="blockquot"> - -<p>[<i>When studying the development of the vertebrate skeleton, -there occurred to me the following idea respecting the possible -origin of the notochord. I was eventually led to omit the few -pages of Appendix in which I had expressed this idea, because -it was unsupported by developmental evidence. The developmental -evidence recently discovered, however, has led Professor Haeckel -and others to analogous views respecting the affiliation -of the</i> Vertebrata <i>on the</i> Molluscoida. <i>Having -fortunately preserved a proof of the suppressed pages, I am able -now to add them. With the omission of a superfluous paragraph, -they are reprinted verbatim from this proof, which dates back to -the autumn of 1865, at which time the chapter on “The Shapes of -Vertebrate Skeletons” was written.</i>—December, 1869.]</p> -</div> - -<p>The general argument contained in Chap. XVI. of Part IV., I have -thought it undesirable to implicate with any conception more -speculative than those essential to it; and to avoid so implicating it, -I transfer to this place an hypothesis respecting the derivation of the -rudimentary vertebrate structure, which appears to me worth considering.</p> - -<p>Among those molluscoid animals with which the lowest vertebrate animal -has sundry traits in common, it very generally happens that while the -adult is stationary the larva is locomotive. The locomotion of the -larva is effected by the undulations of a tail. In shape and movement -one of these young Ascidians is not altogether unlike a Tadpole. And -as the tail of the Tadpole disappears when its function comes to be -fulfilled by limbs; so the Ascidian larva’s tail disappears when -fixation of the larva renders it useless. This disappearance of the -tail, however, is not without exception. The <i>Appendicularia</i> -is an Ascidian which retains its tail throughout life; and by its -aid continues throughout life to swim about. Now this tail of the -<i>Appendicularia</i> has a very suggestive structure. It is long, -tapering to a point, and flattened. From end to end there runs a -mid-rib, which appears to be an imbedded gelatinous rod, not unlike -a notochord. Extending along the two sides of<span class="pagenum" id="Page_600">[600]</span> this mid-rib, are -bundles of muscular fibres; and its top bears a gangliated nervous -thread, giving off, at intervals, branches to the muscular fibres. -In the <i>Appendicularia</i> this tail, which is inserted at the -lower part of the back, is bent forwards, so as not to be adapted for -propelling the body of the animal head foremost; but the homologous -tails of the larval Ascidians are directed backwards, so as to produce -forward movement. If we suppose a type like the <i>Appendicularia</i> -in the structure and insertion of its permanent tail, but resembling -the larval forms in the direction of its tail, it is, I think, not -difficult to see that functional adaptation joined with natural -selection, might readily produce a type approximating to that -whose origin we are considering. It is a fair assumption that an -habitually-locomotive creature would profit by increased power of -locomotion. This granted, it follows that such further development of -the tail-structures as might arise from enhanced function, and such -better distribution of them as spontaneous variation might from time -to time initiate, would be perpetuated. What must be the accompanying -changes? The more vigorous action of such an appendage implies a firmer -insertion into the body; and this would be effected by the prolongation -forwards of the central axis of the tail into the creature’s back. As -fast as there progressed this fusion of the increasingly-powerful tail -with the body, the body would begin to partake of its oscillations; and -at the same time that the resistant axis of the tail advanced along -the dorsal region, its accompanying muscular fibres would spread over -the sides of the body: gradually taking such modified directions and -insertions as their new conditions rendered most advantageous. Without -further explanation, those who examine drawings of the structures -described, will, I think, see that in such a way a tail homologous -with that of the <i>Appendicularia</i>, would be likely, in the course -of that development required for its greater efficiency, gradually to -encroach on the body, until its mid-rib became the dorsal axis, its -gangliated nerve-thread the spinal chord, and its muscular fibres the -myocommata. Such a development of an appendage into a dominant part of -the organism, though at first sight a startling supposition, is not -without plenty of parallels: instance the way in which the cerebral -ganglia, originally mere adjuncts of the spinal chord, eventually -become the great centres of the nervous system to which the spinal -chord is quite subordinate; or instance the way in which the limbs, -small and inconspicuous in fishes, become, in Man, masses which, taken -together, outweigh the trunk. It may be added that these familiar cases -have a further appropriateness; for they exhibit higher degrees of that -same increasing dominance of the organs of external relation, which the -hypothesis itself implies.</p> - -<p><span class="pagenum" id="Page_601">[601]</span></p> - -<p>Of course, if the rudimentary vertebrate apparatus thus grew into, -and spread over, a molluscoid visceral system, the formation of the -notochord under the action of alternating transverse strains, did not -take place as suggested in <a href="#sect255">§ 255</a>; but it does not therefore follow -that its differentiation from surrounding tissues was not mechanically -initiated in the way described. For what was said in that section -respecting the effects of lateral bendings of the body, equally -applies to lateral bendings of the tail; and as fast as the developing -tail encroached on the body, the body would become implicated in the -transverse strains, and the differentiation would advance forwards -under the influences originally alleged. Obviously, too, though the -lateral muscular masses would in this case have a different history; -yet the segmentation of them would be eventually determined by the -assigned causes. For as fast as the strata of contractile fibres, -developing somewhat in advance of the dorsal axis, spread along the -sides, they would come under the influence of the alternate flexions; -and while, by survival of the fittest, their parts became adjusted -in direction, their segmentation would, as before, accompany their -increasing massiveness. The actions and reactions due to lateral -undulations would still, therefore, be the causes of differentiation, -with which natural selection would co-operate.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_602">[602]</span></p> - -<h3>APPENDIX D 2.<br /> -<span class="subhed1">THE ANNULOSE TYPE.</span></h3></div> - - -<p>The production of a segmental structure by undulatory movements, -suggested in Appendix D, as also in B (first published in 1858) as -explaining the vertebral column, has been recently suggested by Prof. -Korschelt as the cause of that segmentation of the annulose type which -gives the name to it. He espouses a—</p> - -<div class="blockquot"> - -<p>“view which is based upon the assumption that at first an -unsegmented, elongated ancestral form was produced by terminal -growth, whereupon the entire body became separated at once into -a large number of segments by a re-arrangement of the individual -organs. This assumption is supported by the consideration that -with the lateral sinuous movement of the body, and with the -rigidity of the tissues caused by increasing differentiation, -the formation of alternating regions of greater and less -motility was of considerable advantage to the individual, and -rendered possible a further elongation of the body. The first -cause for the appearance of metameric segmentation would then be -sought in the manner of locomotion and in mechanical conditions. -However, this latter view is not supported in any way by -embryology.” (<i>Embryology of Invertebrates</i>, Part I, pp. -349–50.)</p> -</div> - -<p>I venture to think the confession that this view “is not supported in -any way by embryology” should be joined with the confession that it -is at variance with that abstract embryology which comprehends the -process of development in general. The assumption that there took -place “a re-arrangement of the individual organs” of “an unsegmented, -elongated ancestral form,” in such wise that the organs, previously -single, presently became multiple, so that instead of one organ of each -kind there were substituted many organs of each kind, is inconsistent -with the general law of evolution, organic and other—implies not -integration but disintegration. Everywhere the advance is from many -like parts performing like functions to relatively few unlike parts -performing unlike functions. The higher forms of the annulose type -itself show this. Compare a myriapod and a crab. In the one we have -not only a great number of similar segments bearing similar limbs, -but we have in each segment a dilatation of the main blood-vessel—a -rudimentary heart—a swollen portion of the nerve cord—a small -ganglion—and so on; whereas in the other,<span class="pagenum" id="Page_603">[603]</span> besides relatively few -segments and few limbs (sundry of them extremely unlike the rest) we -have a vascular system concentrated into a central heart with arteries -and a concentrated nervous system, such that the great ganglia in the -integrated carapace immensely subordinate the ganglia of the remaining -segments; and similarly with the other organs. Now unless it be denied -that these highest decapods have been evolved from low types akin to -myriapods in composition, it must be admitted that the progress has -been from a string of many like segments with similar sets of organs -to a group of relatively-few unlike segments with dissimilar sets of -organs. If so we cannot rationally deny that the progress has been -of this nature up from the lowest annelid, instead of having been, -as Prof. Korschelt’s hypothesis implies, of opposite nature at the -beginning.</p> - -<p>In a preceding passage a clear recognition of the normal course of -development occurs. In opposing the view set forth in <a href="#sect205">§§ 205–7</a> of this -work, Prof. Korschelt says:—</p> - -<div class="blockquot"> - -<p>“It seems scarcely favourable to this theory that the degree -of independence which the individual segments present is -comparatively slight. The most important organs (nervous system, -body musculature, blood-vascular system) show themselves to be -single fundaments of the entire body, and are also developed as -such even though they also exhibit evidences of metamerism. Even -the excretory canals may give up their segmental isolation and -become united to one another by means of longitudinal canals.” -(<i>Ib.</i> p. 348.)</p> -</div> - -<p>On turning back to <a href="#sect206">§ 206</a>, the reader will, I think, demur to the -assertion that the independence is “comparatively slight”; seeing -that, as in <i>Ctenodrilus</i>, a single segment sometimes becomes -separate and reproduces other segments to form a new series. Instead -of admitting that “the most important organs” “show themselves to be -single fundaments of the entire body,” it may be held, contrariwise, -that their original independence in each segment is masked only to -the degree involved by their co-operation as parts of a compound -organism. But chiefly I remark that when it is said that “the excretory -canals may give up their segmental isolation and become united” by -“longitudinal canals,” there is a clear confession that the isolation -of these organs was original and their union superinduced—an -implication that the course of evolution is as I have described it, and -at variance with the course of evolution assumed by Prof. Korschelt.</p> - -<p>Yet another incongruity is involved in his interpretation. He writes:—</p> - -<div class="blockquot"> - -<p>“Just as in the consideration of the tapeworm chain we were -induced by the comparison with unsegmented forms to refer the -entire chain to an unsegmented individual, and, on the other -hand, to see in the proglottis, not a complete individual, but -only the abstricted hinder portion of the body of the Cestode, -in the same manner, and with much more reason, we adhere to the -individuality of the Annelid body.” (P. 349.)</p> -</div> - -<p><span class="pagenum" id="Page_604">[604]</span></p> - -<p>And then on the preceding page, referring to the composition of the -Annelid body, he says:—“The most natural comparisons are those -with the tapeworm chain and with the strobila of the Scyphomedusæ.” -Now since it is here assumed that the tapeworm and the strobila are -analogous in composition, it is implied that the detached proglottis -and the detached medusa are analogous; and hence if we are to regard -the proglottis as “not a complete individual but only the abstricted -hinder portion of the body of the Cestode,” then we must similarly -regard the medusa as not a complete individual, but only the abstricted -hinder portion of the strobila. This commits us to the strange -conclusion that whereas individuality is ascribed to the original -simple polyp, and by and by to the partially-segmented strobila, though -these are without special senses and with only rudiments of muscular -and nervous systems, individuality is denied to the detached medusa, -which has organs of sense, a distinct nervo-muscular system and a -considerable power of locomotion, as well as a generative system: -traits which in other cases characterize developed individuals. Here -also, then, there seems to be an inversion of the ordinary conception.</p> - -<p>This conception of the proglottis and the medusa is, I see, accepted -by some as tenable. But if we accept it we must accept also an -analogous conception, which will I think be regarded as untenable. It -is that supplied by the <i>Aphides</i>. From an egg proceeds a series -of sexless and wingless females, and at the end of the series there -come winged males and females with resulting gamic reproduction. If -instead of forming a discrete series the imperfect females formed a -concrete series, the members of which could individually feed without -being detached from one another, as the segments of a tapeworm can, -the parallelism would be complete; and then, according to the view -in question, we should have to regard the perfect males and females -eventually arising, not as individuals but as terminal portions of -the series, containing generative products and having wings for the -dispersion of them—locomotive egg-bearing segments of the chain. -Whoever espouses this view must hold either that the first imperfect -female of the series was the individual or that the entire string -of them constituted the individual (in conformity with a view once -propounded by Prof. Huxley). But he must do more than this. Since the -<i>Aphides</i> have descended from some winged species of the order -<i>Hemiptera</i>, he must hold that among those remote ancestors each -particular fly, male or female, was an individual; but that when -abundant food and inert life led to the partheno-genetic habit, and to -chains of sexless forms, the males and females eventually produced at -the end of each chain, though, like their remote ancestors, possessed -of procreative organs and wings, are not individuals.</p> - -<p><span class="pagenum" id="Page_605">[605]</span></p> - -<p>[Some memoranda bearing on the question here discussed, mislaid at the -time when the chapter dealing with it was revised, have been discovered -in time for utilization in this appendix.]</p> - -<p>One of my critics says:—</p> - -<div class="blockquot"> - -<p>“You have overstated the case in your favour: the alimentary -canal does not, as you suggest, show a segmentation -corresponding to that of the other organs in Annelids. Either -it is a simple uniform tube, or else its differentiations -(pharynx, œsophagus, crop, intestine) are quite independent of -the repetition of the somites.”</p> -</div> - -<p>In presence of statements made in works of authority, this objection -greatly surprises me. I meet with the descriptive word “moniliform” -applied to the intestine in some Annelids, and then in the Text Book of -Claus, translated and edited by Sedgwick, it is said, concerning the -alimentary canal in the <i>Annelida</i>:—</p> - -<div class="blockquot"> - -<p>“This is followed by the gastric region of the gut, which -occupies the greatest portion of the length of the body, and -is either regularly constricted in correspondence with the -segments, or possesses lateral diverticula.” (P. 365.)</p> -</div> - -<p>And again on p. 369 it is said:—</p> - -<div class="blockquot"> - -<p>“The intestine usually preserves the same structure in its -entire length and is divided by regular constrictions into -a number of divisions or chambers, which correspond to the -segments and dilate again into lateral diverticula and cæca.”</p> -</div> - -<p>The alimentary canal thus presents the segmental character as clearly -as consists with fulfilment of its function. If the successive segments -are co-operating units of a compound animal having but one mouth, -then, necessarily, the gut cannot be completely cut into parts, each -answering to a segment, for there could be, in that case, no passage -for the food. If the portion of the intestine belonging to each segment -has a conspicuous dilatation, or has a cæcum on each side, it exhibits -the segmental character as much as the physical requirements permit. So -far from being at variance with the hypothesis, its structure exhibits -a verification of it.</p> - -<p>The next objection runs as follows:—</p> - -<div class="blockquot"> - -<p>“Then, again, the ovaries and testes do not exhibit a -corresponding segmentation. When it is allowable to speak of -ovary or testis at all as in <i>Lumbricus</i>, we find that in -the case of both organs we have at most two pairs.”</p> -</div> - -<p>It seems to me that the distribution of the generative organs in -a comparatively-developed member of the Annelid type, is not the -question. We have to ask what it is in undeveloped members of that -type. Among them the repetition of generative parts is in some cases -just what the theory implies. Thus in Claus I read:—“In the marine -<i>Chætopoda</i>, the ova or spermatozoa originate on the body-wall -from cells of the peritoneal membrane, either in<span class="pagenum" id="Page_606">[606]</span> the anterior segments -alone or along the whole length of the body.” So that in these last -cases there are, in all the segments, parts from which arise generative -products. The fact that these parts are not definite ovaries and testes -is irrelevant. Ovaries and testes are developed generative structures, -and in the order of evolution are preceded by undeveloped ones; and the -fact that these undeveloped ones are found in little-developed members -of the type conforms perfectly to the hypothesis. [I may remark in -passing that here is a good illustration of that process of evolution -which, in the above speculation of Prof. Korschelt, is supposed to be -inverted: many dispersed, similar, and indefinite parts, are integrated -into a few localized and definite parts.]</p> - -<p>In continuation the critic above quoted says:—“My position is that -the repetition of segments in an Annelid is a phenomenon of the same -nature as the repetition of hairs in a Mammal or of scutes in a -Reptile”, and he proceeds to give instances of repetitions of organs -in other types, as of the reproductive structures and excretory system -in the young Dog-fish or of the ovaries in <i>Amphioxus</i>. These -examples do not seem to me relevant. No parallelism exists between the -repetition of a particular organ in an animal, and the repetition of -an entire cluster of organs constituting a physiological whole. The -repetitions of the ovaries in <i>Amphioxus</i> and of the excretory -system in a young Dog-fish, occur without threatening to divide into -similar parts the entire organism. But the segmental repetitions in -an annulose creature implicate the structures at large, and would, if -pushed a little further, result in separate creatures. The segment -of a low Annelid contains alimentary, vascular, nervous, excretory, -reproductive, sensory and locomotive organs—all the organs required -for carrying on life, save certain organs of external relation which -its position excludes. When there is shown some vertebrate animal, or -proto-vertebrate animal, that is divisible into parts each of which is -in great measure physiologically independent, I shall feel obliged to -abandon my position.</p> - -<hr class="tb" /> - -<p>While this appendix is in hand I have received from another expert, -whose view is in general agreement with my own, a letter containing the -following passage:—</p> - -<div class="blockquot"> - -<p>“You will see that Dohrn’s theory was the antithesis of your -own view of vertebrate structure, namely that the vertebræ -were formed by the segmentation, from mechanical causes of a -body originally simple. This view of yours has been confirmed -by later researches, which have shown that the most primitive -forms allied to the Vertebrates, possessing the essential -organs, viz., gill-slits, notochord, and dorsal nerve cord, -are not segmented animals, like Annelids and <i>Crustacea</i>, -but simple animals, having at most three regions, not exactly -corresponding to segments. These primitive unsegmented forms -are Ascidian tadpoles, <i>Balanoglossus</i>, and certain other -primitive forms. The embryology of Vertebrates also proves -that they are<span class="pagenum" id="Page_607">[607]</span> originally simple and not segmented animals, -especially the fact that there is originally one pronephric duct -or primitive kidney.”</p> -</div> - -<p>Nevertheless there survives a leaning towards the notion of a segmental -origin of the <i>Vertebrata</i>. But the repetitions of organs named in -support of this notion have, I think, no more relation to the genesis -of the vertebrate type than the multiplication of vertebræ in a snake -has relation to the genesis of the vertebral column.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_608">[608]</span></p> - -<h3>APPENDIX E.<br /> -<span class="subhed1">THE SHAPES AND ARRANGEMENTS OF FLOWERS.</span></h3></div> - - -<p>In Part IV., Chapter X., under the title of “The Shapes of Flowers,” I -have, after describing their several kinds of symmetry, as habitually -related to their positions, made some remarks by way of interpretation. -The truth that flowers exhibit a radial symmetry when they are so -placed as to be equally affected all round by incident forces, having -been exemplified, and also the truth that they assume a bilateral -symmetry when they are so placed that their two sides are conditioned -in ways different from the ways in which their upper and lower -parts are conditioned; I have gone on to inquire (in <a href="#sect234">§ 234</a>) by what -causes such modifications of form are produced. I have stated that, -originally, I inclined to ascribe them entirely to differences in the -relations of the parts to physical forces—light, heat, gravitation, -etc.; but that I found sundry facts stood in the way of this -interpretation. And I have said that “Mr. Darwin’s investigations into -the fertilization of Orchids led me to take into account an unnoticed -agency.” Continuing to recognize the physical forces as factors having -some influence, I have concluded that the most important factor is -the action of insects; which, aiding most the fertilization of those -flowers which most facilitate their entrance, produce, in course of -generations, a form of flower specially adapted to the special position.</p> - -<p>Though still adhering to this interpretation, I have since found reason -to think that the original interpretation contains a larger portion -of truth than I supposed at the time when I was led thus to revise -it. While staying at Mürren, in Switzerland, in 1872, I observed -some modifications in a species of Gentian, which proved to me that -the action of incident physical forces on flowers is, in some cases, -very rapid and decided. The species furnishing this evidence was the -<i>Gentiana Asclepiadea</i>; which I found in a copse formed of bushes -that were here wide apart and there close together. In some places not -near to the bushes, the individuals of the species grew vertically; in -other places, partially shaded, their inclined shoots curved in such<span class="pagenum" id="Page_609">[609]</span> -directions as to get the most light; and in other cases their shoots -were led to take directions almost or quite horizontal. That, along -with these modifications in the directions of their shoots, there went -adjustments in the attitudes of their leaves, was a fact not specially -worthy of remark; for plants placed inside the windows of houses -habitually show us that leaves quickly bend themselves into attitudes -giving them the greatest amounts of light. But the fact which attracted -my attention was, that the flowers changed their attitudes in an -equally-marked manner. The radial distribution passed into a bilateral -distribution with the greatest readiness. Comparison of the annexed -figures will show the character of this change.</p> - -<p>Figure I. represents part of a vertically-growing shoot. This -belonged to an individual growing unimpeded by bushes, and getting -light on all sides. Here it is observable that the pairs of leaves, -placed alternately in directions transverse to one another—one pair -pointing, say, north and south, and the next pair pointing east and -west—maintain, taking them in the aggregate, a radial distribution; -and it is also observable that the alternate pairs of flowers are -similarly arranged.</p> - -<p>Figure II. is a sketch from a shoot which leaned towards one side, -and of which the higher part, as it bent more and more, got its upper -side more and more differently conditioned from its lower side. Here -we find that not only the leaves, but also the flowers, have adjusted -themselves to the changed conditions. The leaves of the lowest pair -hang out in the normal way, on the opposite sides of the axis, so that -a plane passing through their surfaces will cut the axis transversely; -and their two axillary flower-buds, <i>c</i> and <i>d</i>, are -similarly placed on opposite sides of the axis. But at the other part -of the shoot, we see both that the leaves have adjusted themselves so -that their planes, no longer cutting the axis transversely, keep a -fit adjustment with respect to the light; and also that the flowers, -no longer on opposite sides of the axis, have bent round to the upper -side, as at <i>a</i> and <i>b</i>.</p> - -<p>Figure III. shows us this re-arrangement carried still further. The -shoot it represents was growing in a direction nearly horizontal, and -therefore receiving the light only on one side. And here, besides -seeing that the leaves have so adjusted themselves that they all lie in -approximately the same plane, which is parallel to the axis instead of -transverse to it, we see that the two pairs of flower-buds have both -come round to the upper side of the axis. So that in this shoot, the -original radial symmetry in the arrangement of leaves and flowers, is -completely changed into a bilateral symmetry.</p> - - <div class="figcenter" id="i_610"> - <img - class="p2" - src="images/i_610.jpg" - alt="" /> - <p class="p0 center p-left">Figs. 1–3.</p> - </div> - -<p class="p2">These facts do not, it is true, prove any modification in the forms<span class="pagenum" id="Page_611">[611]</span> -of the flowers themselves: they only prove modification in the grouping -of the flowers. But beyond showing, as they do conclusively, how -readily a bilateral arrangement of flowers is producible out of an -arrangement that was not bilateral, by the action of light, etc.; they -give increased probability to the belief that changes in the shapes -of flowers are producible by the same agencies. Doubtless this change -in the attitudes of the flower-buds is due to the action of light on -their calyces and peduncles more than to its action on their unfolding -corollas. But along with an action so decided on the growth of these -sheathing and supporting organs containing chlorophyll, it is scarcely -probable that there is <i>no</i> action on the growth of the petals, -containing other colouring matter; considering that in both cases the -development of the colouring matter depends on the action of light, and -considering also the effect of light on petals, familiarly shown by -their opening and closing. And if even but a small effect is producible -on the growth of the corolla, then it is to be expected that light will -be an agent in changing the form of the corolla, when the attitude of -the flower causes its parts to be differently exposed. For a small -effect on the individual flower will become a great effect in the -flowers of remote descendants; provided the changed attitudes of the -flowers preserve considerable constancy throughout the succession of -individuals.</p> - -<p>Be this as it may, however, the facts I have here described, which -I doubt not other observers have seen paralleled in other plants, -are instructive, as showing how quickly certain metamorphoses are -produced, and as implying the easy establishment of such metamorphoses -as permanent characters in a species, if the modifying conditions -become permanent. The changes of arrangement I have pointed out, do not -become permanent in this species because its individuals are variously -affected by the modifying forces: on some they do not act at all, -on some a little, on some much; and even on the same individual the -different shoots are quite differently affected. But if the habit of -this plant were greatly changed—if, for instance, by spreading into -habitats yielding abundant nutriment, the plant became very luxuriant, -and, multiplying its branches, grew shrub-like; it is clear that, being -shaded by one another, these branches would be habitually circumstanced -in a way like that which we here see produces bilateralness in the -distribution of the flowers, if not in the flowers themselves; and -being thus permanently affected, would become permanently bilateral. -Accumulating by inheritance, what is here only an individual -peculiarity, would become a peculiarity of the species—a specific -character.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_612">[612]</span></p> - -<h3>APPENDIX F.<br /> -<span class="subhed1">PHYSIOLOGICAL (OR CONSTITUTIONAL) UNITS.</span></h3></div> - - -<p>There has recently come before me a fact which has a significant -bearing on the hypothesis of Constitutional units: serving, indeed, to -give an apparently conclusive proof of its truth. Before stating it, -however, I may with advantage re-state the several evidences already -assigned in support of it.</p> - -<hr class="tb" /> - -<p>1. First comes the <i>à priori</i> reason. These units in the germ -of an organism which cause development into a special structure, -cannot be <i>chemical</i> units—cannot be simply molecules of proteid -substance in one or other of its forms; since these are not special -to any type of creature but common to all creatures. Nor can they be -what we may call <i>morphological</i> units—the cells or protoplasts; -because in the early stages of development the cells of one organism -are indistinguishable from those of others, and because were cells -the units of composition there could be no interpretation of what are -called unicellular organisms—nothing to account for the innumerable -varieties of them. Hence, of necessity, the structural elements -of which each organism is built, being neither proteid molecules -nor cells, must be something between them: probably some complex -combination of different isomeric forms of proteids.</p> - -<hr class="tb" /> - -<p>2. That units of such natures are the essential components of each -species of organism, is shown by the fact that in low types of -creatures, little differentiated into special tissues, any considerable -portion of the body will, when separated, begin to assume the structure -proper to the species—a truth recently shown afresh by Prof. T. H. -Morgan’s experiments on the regeneration of <i>Planaria maculata</i> -(already referred to in <a href="#sect206">§ 206</a>) showing that various fragments cut out -develop into new individuals, and that when, being too small they die -before doing this, there is always an abortive attempt to assume the -specific structure.</p> - -<hr class="tb" /> - -<p>3. This truth that a portion of undifferentiated tissue, if adequate in -quantity, assumes the structure of the type, illustrating<span class="pagenum" id="Page_613">[613]</span> as it does -the proclivity of the constitutional units towards the structure of -the species, allies itself with the phenomena of both agamogenesis and -gamogenesis. The first of these shows us how a fissiparously-detached -portion of the parental tissue takes on the same form as the parent; -and the second shows how those small detached portions distinguished -as sperm-cell and germ-cell also, when united and supplied with the -needful materials, do the same thing.</p> - -<hr class="tb" /> - -<p>4. But the set of phenomena following the union of sperm-cell and -germ-cell differ in a certain way from those which follow when a -<i>gemma</i> or other unfertilized portion of parental tissue is -detached. The incomprehensibleness of this difference as otherwise -contemplated, and the partial comprehensibleness of it when joined with -the hypothesis of physiological units, furnish a further support for -the hypothesis.</p> - -<p>The familiar truth learnt by the tyro in algebra that an apparent -solution which contains the unknown quantity is no solution, is a -truth apt to be overlooked in other spheres than the algebraic. An -illustration is supplied by the answer once given in Parliament to the -question “What is an Archdeacon?”—“One who discharges archidiaconal -functions.” But science as well as daily life furnishes examples. -When it is said by Engelmann, Hensen, Hertwig, and Maupas that “the -essential end of sexuality is rejuvenescence, that is, the restoration -of growth-energy,” we have another instance of an explanation which -explains nothing. What is the phenomenon to be explained? That -unfolding of an organism from a germ which displays growth-energy. And -what is the explanation? The giving of fresh growth-energy. The unknown -quantity “growth-energy” is contained in the explanation proposed. -There exists no conception of “juvenescence” save that derived from -observing developing plants and animals; and if “re” be prefixed, no -interpretation is thereby given to the unexplained thing “juvenescence.”</p> - -<p>Coleridge somewhere comments on a source of fallacy which he calls the -“hypostasis of a relation”—the changing of a relation into a thing. -The plumber who tells you that water rises in a pump “by suction” -supplies an instance. Having assumed suction to be an agent, he -thinks that he understands how the piston does its work. Some of the -explanations given of fertilization supply further instances. When it -is said that sexual union has for its end “to give increased vigour -to all the vital processes,” it is tacitly implied that vigour is a -something—a something which can be given. But now, in the first place, -it is only by the hypostasis of a relation that we are led to think -of vigour as a thing. Vigour is a state—that state of a living body -which enables it to<span class="pagenum" id="Page_614">[614]</span> give out much motion. What enables it to do this? -The presence in it of abundant molecules containing much molecular -motion which can be transformed into molar motion: the transformation -being effected by the falling of these molecules into their simpler -and relatively-inert components, which are thereupon excreted. -Energy-containing matter is used up, and more energy or vigour can be -given only by supplying more such matter. How then can the union of -two nuclei—those of the sperm-cell and germ-cell—give vigour? Only -an infinitesimal portion of vigour in the sense above explained exists -in either, and the union of them leaves it still infinitesimal. And -then, even supposing the vigour to be an entity and to be appreciable -in quantity, how could it go on producing that immense combination -of physiological actions seen in the unfolding of the germ into an -organism? and how could it go on producing the physiological actions of -an adult organism during a whole century?</p> - -<p>May we not then say that these proposed explanations leave the question -where it was—are nominal solutions, not real solutions?</p> - -<hr class="tb" /> - -<p>5. But the hypothesis of constitutional units furnishes, if not a -satisfactory answer yet, something in the nature of an answer—a true -cause; that is to say, a cause actually known to us as operating in -other cases. In <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect92">§ 92</a> it was pointed out that in proportion as units -are similar, there may be built up from them an aggregate which is -relatively stable, and that along with increasing dissimilarity the -stability of the aggregate decreases. It was inferred that if a group -of constitutional units belonging to one individual which have become -moulded into relatively exact congruity with the organism and with -one another by long co-operation, are mingled with some belonging -to another individual which, differently circumstanced, has become -somewhat different in itself and in its units, then the mass formed by -the union of the two groups will be relatively unstable—relatively -modifiable by incident forces. Whereas in either organism, no longer -perpetually changed in the relations of its parts by growth, there is -an approach towards equilibrium between the whole and its components, -the components contributed by the two to form a germ, being slightly -unlike one another, will not form a group in a state of equilibrium. -The group they form will be capable of easy change by incident forces; -and they will so be rendered free to follow their proclivities towards -the typical form of the species. Inferring this we must also infer that -so long as these two sets of slightly different units are not exposed -to any constant forces tending to coerce them into the same form, there -will continue to exist in the nuclei of all descendant cells this same -relative instability and consequent plasticity.</p> - -<p><span class="pagenum" id="Page_615">[615]</span></p> - -<p>Such evidence as we have verifies this interpretation. There is -first the universal fact that development of the germ begins when -it is exposed to an incident force—heat—the undulations of which, -increasing the oscillations of the mixed units, give them greater -freedom to arrange themselves in conformity with their type. We see -this alike when spring warmth makes a seed germinate and when the -warmth of a sitting hen sets up organization in her eggs. Heat frees -the molecules of inorganic matter from local restraints and, as we see -in molten metal, lets them yield to other forces; and similarly in this -organic matter, the units are made free to follow their proclivities. -Then, secondly, there comes the evidence from comparisons between the -effects of mixing constitutional units differing in various degrees. -Let the cluster of mixed units be derived from animals that are -ordinally distinct. Nothing happens. The units each contributes tend to -arrange themselves after the parental type. Hence a conflict between -the tendencies towards two markedly unlike structures, and no structure -arises. Suppose the mixed units come from two kindred species—say -horse and ass. The structures which they respectively tend to form, -being in their main characters alike, there is such co-operation -as produces a working organism but an organism in certain respects -imperfect—a mule. Suppose, again, the units come from two varieties -of the same species. A perfect organism results, and, as shown by Mr. -Darwin when detailing the effects of crossing, an unusually vigorous -organism. The units being more unlike than those belonging to the same -variety, the instability of the germ-plasm is unusually great, and -the transformations which constitute development and action become -unusually active. When, as in ordinary cases, the units are supplied by -members of the same variety who have not been made very much alike by -their antecedents, there follows the usual amount of organic vigour. -Coming now to the results of breeding in-and-in—breeding between -individuals whose constitutions (<i>i.e.</i> constitutional units) have -for generations been growing more alike in the absence of crossing with -other stirps—we see that diminution of organic vigour is displayed: -there is a decrease in the rate of physiological change. Finally, on -coming to a closer relationship, as in marriages between cousins, in -whom the constitutional units are more than commonly alike, we see -there frequently follows either barrenness or the production of feeble -offspring.</p> - -<p>All these facts, then, are congruous with the hypothesis that the -use of fertilization is the mixing of unlike units, and consequent -production of plasticity. Leaving out cases in which the unlikenesses -are so great as wholly to prevent co-operation among the units, the -degree of vigour, that is, the activity of physiological<span class="pagenum" id="Page_616">[616]</span> change, is -great where the unlikeness is great and diminishes with the approach -towards likeness.</p> - -<hr class="tb" /> - -<p>6. The existence of constitutional units seems otherwise necessarily -implied. I refer to the fact that no organism is a homogeneous mean -between its parents but consists of a mixture of parts, some following -one parent and some the other. Among illustrations of this the most -conspicuous are those yielded by the variously-mixed colours of -hair or feathers. Horses, cattle, dogs, cats, hens, pigeons display -these mixtures: colours in one place like the mother and in another -place like the father. As the internal organs are invisible, and as -visible organs have indefinite shapes and graduate indefinitely into -adjacent ones, the mixture of traits is elsewhere less conspicuous; but -occasional marked cases (especially in malformations) leave no doubt -that it pervades the entire organism.</p> - -<p>This peculiarity of transmission seems necessarily to imply that there -are distinct units derived from the two parents, and that in the course -of development there is more or less segregation of them—those of -the one origin predominating so far in some places as to give special -likeness to one parent, and those derived from the other doing the like -in other places. All which interpretation is impossible unless the -hypothesis of constitutional units be admitted.</p> - -<hr class="tb" /> - -<p>7. I come at length to the special evidence referred to at the outset. -It is evidence of the same nature as that just assigned, but carried -to a higher stage. It is furnished not by the segregation of traits -derived from two parents of the same variety, but is furnished by the -segregation of traits derived from parents of different varieties. In -articles on “Bud Variations or Sports” (<i>Gardener’s Chronicle</i>, -1891) Dr. Masters gives various examples of the separation or unmixing -of ancestral constitutions. Mr. Noble formed a hybrid between -<i>Clematis Jackmani</i> and <i>C. patens</i>. One of these varieties -flowers in the autumn on new wood, while the other flowers in the -spring on old wood; and the result is that flowers of two kinds, quite -unlike, are produced at different parts of the year, and that by -pruning so as to cut away one or other set of shoots, the plant may be -made to produce exclusively for the time being one or other sort of -flower.</p> - -<div class="blockquot"> - -<p>“Another very interesting case of unmixing, or, if it be -preferred, of partial mixture, is afforded by Neubert’s -Berberis. This is a hybrid between the evergreen pinnate-leaved -Mahonia and the deciduous simple-leaved Berberis vulgaris, and -it bears leaves some of which are intermediate in appearance, -while others are much like those of one or other of its parents.</p> - -<p>“A not uncommon illustration of a similar kind, is the -production of a Peach and a Nectarine on the same branch, and we -have just learnt from<span class="pagenum" id="Page_617">[617]</span> Canon Ellacombe that some of the Berlin -Hellebores show evidence of their hybrid nature by occasionally -producing foliage [and flowers?] of the two parents separately -from the same root-stock.</p> - -<p>“In addition to the cases given above, we may here cite a few -more which have come under our notice, such as a Chrysanthemum, -half the florets of which are of one colour, half of another. -A hybrid Calanthe, showing a similar piebald variation, is -shown in Fig. 14. A very curious case was that of the Narcissus -received from Mr. Walker, and in which flowers of two distinct -varieties sprang from the same bulb. Grapes not uncommonly show -their crossed origin by presenting a striped appearance, one -stripe being of one colour, one of another, as may also be seen -in the Orange, Apple, Lemon, and Currant.”</p> -</div> - -<p>Thus, however the germ-plasm is constituted its essential components -cannot be all alike. Before there can be this dissociation of ancestral -characters, there must be in the germ-plasm different elements capable -of being dissociated. This single fact seems to compel us to assume -constitutional units.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_618">[618]</span></p> - -<h3>APPENDIX G.<br /> -<span class="subhed1">THE INHERITANCE OF FUNCTIONALLY-CAUSED MODIFICATIONS.</span></h3></div> - - -<p>In Part II, Chapter X<sup>A</sup>, I have confessed that the process by which -a structure changed by use or disuse affects the sperm-cells or -germ-cells whence arise descendants, is unimaginable: without, however, -inferring that therefore such a process does not exist. With others -it seems different. Some three years ago the following expression of -opinion came to me from a zoological expert:—</p> - -<div class="blockquot"> - -<p>“Many zoologists—most of us here at Cambridge—are intensely -opposed to the doctrine of the inheritability of acquired -variations. Even assuming that the developmental power of a -germ is determined by its molecular structure (and I for one -would question this—Driesch and his school when they find that -they can squeeze a developing egg into all sorts of shapes -without altering the final result, that one blastomere in an -egg which has divided into 8 is still able to reproduce a whole -embryo—question it also), we still fail to conceive any means -by which, for instance, a change in the development of a muscle -or nerve can effect a corresponding change in that part of the -germ which is destined to produce a corresponding part in the -descendant.”</p> -</div> - -<p>Here it will be observed that belief in the inheritance of structural -effects wrought by use and disuse, is rejected because of inability “to -conceive any means” by which the modifications produced in an organ can -effect a correlated modification in the germ of a descendant: failure -to conceive is the test. The implication is that some alternative -hypothesis is accepted because the correlating of a variation in an -organ with a corresponding germ-variation is effected by a means which -<i>is</i> conceivable. This is the hypothesis of Weismann. Concerning -its conceivability I have, in the chapter just named, already written -as follows:—</p> - -<div class="blockquot"> - -<p>“If we follow Prof. Weismann we are led into an astounding -supposition. He admits that every variable part must have a -special determinant, and that this results in the assumption of -over two hundred thousand for the four wings of a butterfly. -Let us ask what must happen in the case of a peacock’s feather. -On looking at the eye near its end, we see that the minute -processes on the edge of each lateral thread must have been in -some way exactly adjusted, in colour and position, so as to fall -into line with the processes on adjacent threads: otherwise the -symmetrical arrangement of coloured rings would be impossible. -Each of these processes, then, being an<span class="pagenum" id="Page_619">[619]</span> independent variable, -must have had its particular determinant. Now there are about -300 threads on the shaft of a large feather, and each of them -bears on the average 1,600 processes, making for the whole -feather 480,000 of these processes. For one feather alone there -must have been 480,000 determinants, and for the whole tail -many millions. And these, along with the determinants for the -detailed parts of all the other feathers, and for the variable -components of all organs forming the body at large, must have -been contained in the microscopic head of a spermatozoon!” [And -each of them must, throughout all the complex developmental -processes, have preserved the ability to find its way to the -exact place where it was wanted!]</p> -</div> - -<p>If my Cambridge correspondent is able to conceive this process implied -by the hypothesis of Weismann, I can only say that he has an enviable -power of imagination.</p> - -<hr class="tb" /> - -<p>But now comes the strange fact that an impossibility of thought -implied by Weismann’s hypothesis does not cause rejection of it, but -yet is urged as a reason for rejecting an alternative hypothesis -which does not imply it. One objector cannot conceive that “a change -in the development of a muscle or nerve can effect a corresponding -change in that part of the germ which is destined to <i>produce a -corresponding part</i> in the descendant”; and another objector says -it is “very hard to believe” that a functionally-changed organ will so -affect spermatozoa and ova that “<i>one particular part of them</i> -will be so altered that the organisms which grow up from them will -be able to present the same modification on the application of a -different stimulus.” It is tacitly assumed by both that, as in the -hypothesis of Weismann so in the counter-hypothesis, a particular -part of the germ-plasm gives origin to a particular part of the -developed organism. But nothing of the kind is implied. The nature -of the counter-hypothesis (at any rate as held by me) is entirely -misapprehended. Anyone who turns back to the chapters in the first -volume where the conception of physiological units (or constitutional -units) was set forth, or who re-reads the foregoing appendix, will -see that there is altogether excluded any idea of correlation between -certain parts of the germ and certain parts of the resulting organism. -The units are supposed to be all alike, and during the progressive -embryological changes local groups of them are supposed to take on -different forms and structures under the combined forces, general and -local, brought to bear on them. This conception is necessitated by all -the evidence. The fact disclosed by the experiments of Driesch, Wilson, -and Chabry, that from fractions of an ovum structures may be obtained -like that obtained from the whole ovum, only smaller, necessitates -it. The fact that any sufficiently large fragment of a polyp or -planarian, no matter from what part of the body taken, will develop -into a complete polyp or planarian necessitates it. The fact that from -an undifferentiated portion<span class="pagenum" id="Page_620">[620]</span> of a plant, even so small as a scale, -a complete plant may arise necessitates it. And it is necessitated -by the fact that among plants, roots are produced by imbedded shoots -and shoots by roots, as well as by the fact that low animals, such -as hydroids, if deprived of both head and root, will develop a head -from the root part and a root from the head part, if their respective -conditions are inverted. All this evidence shows conclusively that -the component units of each species, whether existing in the germ or -in the developed organism, are, when not yet differentiated by local -conditions, all alike, and that the notion of special parts of the -germ-plasm correlated with special parts of the resulting organism, is -entirely alien to the hypothesis.</p> - -<p>“But how do the units of a modified organ affect the units of the -germ in such wise that these produce an inherited modification of -the organ?” will be asked. This difficulty has been dealt with in <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect97">§§ 97<i>d</i>, 97<i>e</i></a>, - where the analogy between the social organism -and the individual organism has been brought in aid: serving, if not to -furnish a conception, yet to furnish an adumbration. Regarding citizens -as the units of an unfolding society, say a colony, it was pointed -out that the nature they inherit from a mother-society gives them a -proclivity towards a society of like structure, the traits of which -are progressively assumed as the colony grows sufficiently large to -make them possible. At the same time it was pointed out that while the -influence of the entire aggregate on the individuals is seen in this -forming of them into a society of the inherited type, the influences of -local circumstances, and of individuals on one another, in each group, -make them differentiate into appropriate social structures, taking on -fit occupations and industries: the implication being that in virtue -of their inherited natures they all have partial capacities for the -various activities they undertake; so that an immigrant clerk sets up a -tavern, a compositor takes to carpentering, and a university man rides -after cattle or is employed on a sheep farm. Evidence was given in that -place, as in the above paragraph, that the constitutional units of an -organism similarly have all of them potentialities for taking on this -or that structure and mode of action which local conditions determine. -It was further argued that as citizens are continually being remoulded -by their society into congruity with it, and, if circumstances change -them, tend to remould their society; so in the individual organism, -there is this reciprocal action of the whole on the units and of the -units on the whole. Hence it was inferred that the modified units in -any modified part tend to diffuse modifications like their own through -the units at large: being aided by the circulation of protoplasm, as -suggested in <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect54">§§ 54<i>d</i></a> and <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect97">97<i>f</i></a>. And it was urged that, -however inconceivably complex such a process may be, yet it seems not<span class="pagenum" id="Page_621">[621]</span> -incredible when we recognise the probability that an organism is more -or less permeable to undulations propagated by its molecules: Rontgen -rays giving warrant. If such units throughout the tissues may take in -and send out ethereal waves which bring it into rhythmical relations -with others of its kind and tend to produce congruity, it becomes, -if not conceivable still supposable, that throughout the circulating -protoplasm there goes on a continual harmonization of its components—a -moulding of each by all and of all by each. Should it be said that such -a process is too marvellous to be reasonably assumed, the reply is that -it is not more marvellous than heredity itself, which, were it not -familiar to us, would be thought incredible.</p> - -<hr class="tb" /> - -<p>But as I have said in the place referred to—“At last then we are -obliged to admit that the actual organizing process transcends -conception. It is not enough to say that we cannot know it; we must say -that we cannot even conceive it:” can only conceive the possibility of -a suggested interpretation.</p> - -<p>Hence we have to rely upon evidences of other kinds. Among these, some -which I think dispose absolutely of the fashionable hypothesis while -they harmonize with the opposed hypothesis, have now to be named. That -their implication should not have been generally recognized would have -seemed to me incomprehensible were it not that I have myself only now -observed this implication. The facts are these:—</p> - -<div class="blockquot"> - -<p>“Verlot mentions a gardener who could distinguish 150 kinds -of camellia, when not in flower; and it has been positively -asserted that the famous old Dutch florist Voorhelm, who -kept above 1,200 varieties of the hyacinth, was hardly ever -deceived in knowing each variety by the bulb alone. Hence we -must conclude that the bulbs of the hyacinth and the branches -and leaves of the camellia, though appearing to an unpractised -eye absolutely undistinguishable, yet really differ.” (Darwin, -<i>Variation of Animals and Plants, &c.</i>, vol. ii, p. 251.)</p> -</div> - -<p>More recently testimony to like effect has been given by Dr. Maxwell -Masters, and has already been quoted by me in a note to <a href="#sect286">§ 286</a> in -illustration of another truth. He says concerning such variations:—</p> - -<div class="blockquot"> - -<p>“To the untrained eye, the primordial differences noted are -often very slight; even the botanist, unless his attention -be specially directed to the matter, fails to see minute -differences which are perceptible enough to the raiser or his -workmen.... These apparently trifling morphological differences -are often associated with physiological variations which render -some varieties, say of wheat, much better enabled to resist -mildew and disease generally than others. Some, again, prove to -be better adapted for certain soils or for some climates than -others; some are less liable to injury from predatory birds than -others, and so on.”</p> -</div> - -<p>In his <i>Vegetable Teratology</i>, p. 493, Dr. Masters names another -fact having a like implication—the fact that among seedling<span class="pagenum" id="Page_622">[622]</span> stocks -which have not yet flowered, those which will produce double flowers -are distinguishable. He says:—</p> - -<div class="blockquot"> - -<p>“This separation of the single from the double-flowered plants, -M. Chatié tells us is not so difficult as might be supposed. The -single stocks, he explains, have deep green leaves (glabrous in -certain species), rounded at the top, the heart being in the -form of a shuttlecock, and the plant stout and thick-set in its -general aspect, while the plants yielding double flowers have -very long leaves of a light green colour, hairy and curled at -the edges, the heart consisting of whitish leaves, curved so -that they enclose it completely.”</p> -</div> - -<p>What is the general truth implied? Clearly that there exists no such -thing as an independent local variation. Some marked change in the form -or colour of a flower or a fruit draws attention; and, being a change -which interests the florist or gardener, pecuniarily or otherwise, -not only draws attention but usually monopolizes attention: the -natural impression produced being that this variation stands there by -itself—is without relation to variations elsewhere. But now it turns -out that there are concomitant variations all over the plant. Even in -underground bulbs certain appreciable differences go along with certain -conspicuous differences in the flowers. And if along with a striking -change in a flower which the florist contemplates, there go changes -all over the plant not obvious to careless observers but visible to -him, we must infer that there are everywhere minute differences which -even the florist cannot perceive: the whole constitution of the plant -has diverged in some measure from the constitutions of kindred plants. -Every local variation implies a change pervading the entire organism, -manifested in concomitant variations everywhere else.</p> - -<p>If so, what becomes of the hypothesis of determinants—the hypothesis -that there is a special element in the germ-plasm which results in a -special local modification in the adult organism? That there are no -facts supporting it has been all along manifest; but now it is manifest -that the facts directly contradict it.</p> - -<p>At the same time it may be remarked that while the facts are wholly -incongruous with the hypothesis of determinants and its accompanying -elaborate speculation, they are not incongruous with the alternative -hypothesis. Impossible though it may be to imagine the natures of -those ultimate units peculiar to each species, which have proclivities -towards the particular form of organization characterizing it, yet -that a change of structure arising in one part of the organism is -accompanied by multitudinous changes of structure in other parts of -the organism, is not only congruous with the belief that there exist -such constitutional units, but yields it distinct support. For if, as -above argued, a conspicuous local variation is not the result of any -modification of units special to the locality, but is the result of -a modification of<span class="pagenum" id="Page_623">[623]</span> the units at large, then it must happen that such -modification must have its effects on all other parts of the organism; -so that there cannot fail to result all those small concomitant -variations above indicated.</p> - -<p>May we not also say that it becomes less incomprehensible that -structural changes caused by use and disuse are inherited? If, as -we see, a local variation spontaneously arising is accompanied by -multitudinous other local variations, implying a necessary correlation -between each local variation and the general constitution of the -organism; then it may be argued that if a marked change of function in -an organ causes increase or decrease of it, this general correlation -implies that there must be a reciprocal reaction between the part and -the whole, tending to re-establish their congruity. The constitution -at large will in so far be changed, and along with its change will go -corresponding changes in the sperm-cells and germ-cells.</p> - -<hr class="tb" /> - -<p>Finally let me add, not another argument, but another fact of -observation, of the kind which opponents demand, but which, when they -are from time to time furnished, are severally pooh-poohed as not -enough. Each of them is spoken of as a solitary fact and slighted as -inadequate; and when by and by another is named, this is treated in -the same way; so that the facts which if brought together would be -recognized as sufficient are never brought together. That to which I -refer is set forth in a pamphlet by M. Leo Errera, Professor at the -University of Brussels, entitled “Hérédite d’un Caractère acquis chez -un Champignon pluricellulaire;” being an account of experiments of -Dr. Hunger, at the Botanical Institute in Brussels. First enumerating -various instances of adaptations to climate, as those of plants which, -fitted to northern regions, preserve their constitutional rapidity -of growth and seeding when brought south, and do this for several -generations, he goes on to detail the culture-experiments of M. Hunger, -and sums up the results of these in the following words:—</p> - -<div class="blockquot"> - -<p>“On déduit de là que:</p> - -<p>“1<sup>o</sup> Les conidies d’<i>Aspergillus niger</i> sont adaptées à la -concentration du milieu où a vécu l’individu qui les porte; cet -effet est encore plus marqué après deux générations passées dans -un milieu donné (Expér. I et II);</p> - -<p>“2<sup>o</sup> II s’agit d’une véritable adaptation et non pas simplement -d’un accroissement de vigueur chez les conidies provenant des -liquides concentrés, car ces mêmes conidies germent moins -rapidement et donnent des plantes moins vigoureuses que -les conidies normales lorsqu’on les sème de nouveau sur le -milieu-type: en s’adaptant aux liquides concentrés, elles se -sont <i>désadaptées</i> du liquide normal (Expér. III);</p> - -<p>“3<sup>o</sup> Une génération passée sur le liquide normal n’efface pas -l’influence d’une ou de deux générations antérieures passées sur -une liquide plus concentré (Expér. IV).</p> - -<p>“Tous ces résultats concordent: <i>ils montrent une légère, -mais incontestable transmission héréditaire de l’adaptation au -milieu</i>.”</p> -</div> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_625">[625]</span></p> - -<h2 class="smaller">SUBJECT-INDEX.</h2> -</div> - -<div class="blockquot"> - -<p>(For this Index as it appeared in previous editions the Author -is indebted to <span class="smcap">F. Howard Collins</span>, Esq., of Edgbaston, -Birmingham. It has now been adjusted to suit the present revised -and enlarged edition.)</p> -</div> - -<ul> - <li>Acacia, foliar organs, <b>II</b>, - <a href="#Page_41">41</a>, - <a href="#Page_264">264</a>.</li> - - <li><i>Acalephæ</i>: environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page105">105</a>;</li> - <li class="i1">water in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page173">173</a>.</li> - - <li><i>Acari</i>: special creation and effects of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page_428">428</a>;</li> - <li class="i1">direct transformations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page706">706</a>;</li> - <li class="i1">segmentation, <b>II</b>, - <a href="#Page_111">111</a>.</li> - - <li><i>Acorus calamus</i>, agamic propagation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page642">642</a>.</li> - - <li class="hangingindent" id="Acquired_characters">Acquired characters, inheritance of: functionally-produced modifications in plants and animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page307">307–13</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page318">318</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page526">526</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page541">541</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page562">562</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692–5</a>; <b>II</b>, - <a href="#Page_618">618–22</a>;</li> - <li class="hangingindent1">conceivability of, on the hypothesis of physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page368">368–71</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page695">695</a>; <b>II</b>, - <a href="#Page_618">618–22</a>;</li> - <li class="i1">diminution of jaw, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page541">541–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">current views on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page559">559–60</a>;</li> - <li class="i1">cessation of selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page560">560–3</a>;</li> - <li class="i1">Eimer’s theory of orthogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page560">560</a>;</li> - <li class="i1">species differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page573">573</a>;</li> - <li class="i1">location of mammalian testes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page573">573</a>;</li> - <li class="hangingindent1">tactual perceptiveness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page602">602–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page633">633</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page665">665</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page666">666</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page672">672–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="i1">blindness of cave-animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page647">647–9</a>;</li> - <li class="i1">co-adaptation of co-operative parts, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page621">621</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page663">663–5</a>;</li> - <li class="i1">transmission of disease, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page622">622–3</a>;</li> - <li class="hangingindent1">hypothesis supported by telegony, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page624">624–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page644">644–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page649">649–50</a>;</li> - <li class="hangingindent1">views of Darwin and neo-Darwinists, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page630">630</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page690">690</a>;</li> - <li class="i1">why facts in support are meagre, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page632">632</a>;</li> - <li class="i1">degradation of little toe, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page652">652–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page673">673</a>;</li> - <li class="hangingindent1">neuter forms of social insects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page658">658–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page663">663–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>;</li> - <li class="i1">degenerated instinct in ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660–2</a>;</li> - <li class="i1">rudimentary limbs of whale, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page669">669</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="i1">importance of question, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page672">672</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page690">690</a>;</li> - <li class="i1">monstrous development of honey-ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page683">683–4</a>;</li> - <li class="i1">osteology of Punjabis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>;</li> - <li class="i1">summary of evidences in support, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692–5</a>;</li> - <li class="i1">genesis of vertebrate skull, <b>II</b>, - <a href="#Page_227">227</a>;</li> - <li class="i1">false joints, <b>II</b>, - <a href="#Page_371">371</a>, - <a href="#Page_372">372</a>;</li> - <li class="i1">conceivability of rival hypotheses, <b>II</b>, - <a href="#Page_618">618–22</a>;</li> - <li class="i1">adaptation to environment in <i>Aspergillus</i>, <b>II</b>, - <a href="#Page_623">623</a>.</li> - - <li>Acrogens, the term, <b>II</b>, - <a href="#Page_55">55–6</a>.</li> - <li class="i1">(See <a href="#Archegoniateae"><i>Archegoniateæ</i></a>.)</li> - - <li><i>Actinophrys</i>: a primary aggregate, <b>II</b>, - <a href="#Page_76">76</a>;</li> - <li class="i1">genesis, <b>II</b>, - <a href="#Page_452">452</a>.</li> - - <li><i>Actinozoa</i>: multiaxial development, <b>I</b>, - <a href="#Page_166">166</a>;</li> - <li class="i1">waste and repair, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page213">213</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page219">219</a>;</li> - <li class="i1">differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page391">391</a>;</li> - <li class="i1">parasitism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page397">397</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_92">92</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_189">189</a>, - <a href="#Page_192">192</a>;</li> - <li class="i1">growth and genesis, <b>II</b>, - <a href="#Page_444">444</a>.</li> - - <li class="hangingindent">Activity: the principle of, the essential element in Life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page113">113</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page114">114</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page122">122</a>;</li> - <li class="i1">not inherent in living matter, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page120">120</a>;</li> - <li class="i1">nutrition and genesis, <i>résumé</i>, <b>II</b>, - <a href="#Page_497">497–9</a>;</li> - <li class="i1">and evolution, <b>II</b>, - <a href="#Page_501">501–4</a>.</li> - - <li>Adaptation: general truths, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page227">227–33</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page233">233–5</a>;</li> - <li class="i1">botanical, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page227">227</a>;</li> - <li class="i1">physiological, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page228">228–33</a>;</li> - <li class="i1">psychological, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page229">229</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page230">230–3</a>;</li> - <li class="hangingindent1">structural, functional, and interdependence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page235">235–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page240">240–1</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page318">318</a>;</li> - <li class="i1">social and organic stability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page240">240–2</a>;</li> - <li class="i1"><i>résumé</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page242">242–3</a>;</li> - <li class="i1">to varied media, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page479">479–81</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page489">489</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">multiplication of effects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page512">512–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page550">550</a>;</li> - <li class="i1">direct equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page522">522–3</a>;</li> - <li class="i1">natural selection and equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page530">530–5</a>;</li> - <li class="i1">non-adaptive specific characters, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page565">565</a>;</li> - <li class="i1">time required for effecting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page565">565–6</a>;</li> - <li class="i1">an obstacle to re-adaptation, <b>II</b>, - <a href="#Page_11">11</a>;</li> - <li class="i1">of skin and skeleton, <b>II</b>, - <a href="#Page_215">215</a>, - <a href="#Page_217">217</a>;</li> - <li class="i1">outer tissue, <b>II</b>, - <a href="#Page_312">312–4</a>, - <a href="#Page_387">387</a>;</li> - <li class="hangingindent1">skin and mucous membrane differentiation, <b>II</b>, - <a href="#Page_321">321–2</a>, - <a href="#Page_389">389</a>;</li> - <li class="i1">vascular system, <b>II</b>, - <a href="#Page_343">343–4</a>;</li> - <li class="i1">osseous, <b>II</b>, - <a href="#Page_352">352</a>;</li> - <li class="i1">muscular, <b>II</b>, - <a href="#Page_368">368–9</a>, - <a href="#Page_391">391</a>;</li> - <li class="i1">persistence of force and physiological, <b>II</b>, - <a href="#Page_394">394</a>;</li> - <li class="i1">of reproductive activity to conditions, <b>II</b>, - <a href="#Page_411">411–6</a>;</li> - <li class="i1">vertebræ development, <b>II</b>, - <a href="#Page_563">563–6</a>.</li> - <li class="i1">(<i>See also</i> <a href="#adaptation">Co-adaptation</a>.)</li> - - <li>Africa, effect of climate on inhabitants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page30">30</a>.</li> - - <li class="hangingindent" id="Agamogenesis">Agamogenesis: alternation with gamogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page266">266–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page272">272–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page284">284–94</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page336">336</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page592">592</a>; <b>II</b>, - <a href="#Page_415">415</a>;</li> - <li class="i1">parallelism in karyokinesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page267">267–8</a>;</li> - <li class="i1">a process of disintegration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page276">276–7</a>;</li> - <li class="hangingindent1">conditions determining its continuance, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page284">284–94</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page330">330</a>;</li> - <li class="i1">physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page351">351</a>; <b>II</b>, - <a href="#Page_613">613</a>;</li> - <li class="hangingindent1">spontaneous fission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page582">582</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page584">584–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page589">589–92</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page595">595–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page599">599</a>;</li> - <li class="hangingindent1">remarkable extent of, under favourable conditions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page591">591–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page640">640–1</a>;</li> - <li class="i1">in <i>Actinozoa</i>, <b>II</b>, - <a href="#Page_92">92</a>;</li> - <li class="i1">in <i>Hydrozoa</i>, <b>II</b>, - <a href="#Page_102">102</a>;</li> - <li class="i1">in <i>Annelida</i>, <b>II</b>, - <a href="#Page_103">103</a>;</li> - <li class="i1">innutrition, <b>II</b>, - <a href="#Page_179">179–80</a>.</li> - - <li><i>Agaricinæ</i>, <b>II</b>, - <a href="#Page_139">139</a>, - <a href="#Page_257">257</a>.</li> - - <li>Agassiz, L. J. R., zoological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page380">380</a>.</li> - - <li>Aggregates, Animal and Plant (<i>see</i> <a href="#Morphology">Morphology</a>).</li> - - <li>Agility, a vital attribute, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page578">578</a>.</li> - - <li>Agrimony, floral symmetry, <b>II</b>, - <a href="#Page_42">42</a>, - <a href="#Page_167">167</a>, - <a href="#Page_170">170</a>.</li> - - <li>Air, in vegetal tissues, <b>II</b>, - <a href="#Page_567">567–8</a>, - <a href="#Page_583">583</a>, - <a href="#Page_591">591</a>, - <a href="#Page_593">593</a>.</li> - - <li>“Air plants,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page208">208</a>.</li> - - <li>Albumen: properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page12">12</a>;</li> - <li class="i1">Lieberkühn’s formula, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page13">13</a>;</li> - <li class="i1">diffusibility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page19">19</a>;</li> - <li class="i1">in organic tissues, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page41">41</a>.</li> - - <li>Alcohols, properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page10">10–12</a>.</li> - - <li class="hangingindent" id="Algae"><i>Algæ</i>: reproduction, and the dynamic element in life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page118">118–9</a>;</li> - <li class="i1">multicentral development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page163">163</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page164">164</a>;</li> - <li class="i1">axial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>;</li> - <li class="i1">locomotive powers of minute forms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page196">196</a>;</li> - <li class="i1">uniform tissue and function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page200">200</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page586">586</a>;</li> - <li class="hangingindent1">gamogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page280">280</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page283">283</a>; <b>II</b>, - <a href="#Page_448">448</a>, - <a href="#Page_449">449</a>, - <a href="#Page_450">450</a>;</li> - <li class="i1">fertility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page582">582</a>; <b>II</b>, - <a href="#Page_440">440</a>, - <a href="#Page_441">441</a>;</li> - <li class="i1">fission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page584">584</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page585">585</a>;</li> - <li class="i1">unicellular forms, <b>II</b>, - <a href="#Page_22">22</a>;</li> - <li class="hangingindent1">integration in <i>Confervoideæ</i> and <i>Conjugateæ</i>, <b>II</b>, - <a href="#Page_25">25</a>;</li> - <li class="hangingindent1">pseudo-foliar and axial development, <b>II</b>, - <a href="#Page_28">28–33</a>, - <a href="#Page_57">57</a>;</li> - <li class="i1">foliar development, <b>II</b>, - <a href="#Page_76">76</a>, - <a href="#Page_91">91</a>;</li> - <li class="i1">branch symmetry, <b>II</b>, - <a href="#Page_145">145</a>;</li> - <li class="i1">cell metamorphoses, <b>II</b>, - <a href="#Page_176">176</a>;</li> - <li class="hangingindent1">tissue differentiation, <b>II</b>, - <a href="#Page_244">244</a>, - <a href="#Page_246">246</a>, - <a href="#Page_251">251</a>, - <a href="#Page_252">252</a>, - <a href="#Page_256">256</a>, - <a href="#Page_272">272</a>, - <a href="#Page_385">385–6</a>;</li> - <li class="hangingindent1">adaptation of reproductive activity to conditions, <b>II</b>, - <a href="#Page_289">289</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_292">292</a>;</li> - <li class="i1">indefiniteness, <b>II</b>, - <a href="#Page_295">295</a>;</li> - <li class="i1">genesis and development, <b>II</b>, - <a href="#Page_463">463</a>.</li> - - <li class="hangingindent" id="Alimentary_canal">Alimentary canal: metabolic processes and agents, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page68">68–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page74">74</a>;</li> - <li class="i1">structural traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page192">192</a>;</li> - <li class="i1">progressive development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page195">195</a>;</li> - <li class="i1">relation to environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page196">196</a>;</li> - <li class="i1">function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page205">205</a>;</li> - <li class="i1">segmentation in annelids, <b>II</b>, - <a href="#Page_125">125</a>;</li> - <li class="i1">differentiation, <b>II</b>, - <a href="#Page_301">301</a>, - <a href="#Page_302">302</a>, - <a href="#Page_321">321–2</a>, - <a href="#Page_323">323–5</a>, - <a href="#Page_389">389</a>;</li> - <li class="i1">specializations in birds, <b>II</b>, - <a href="#Page_325">325</a>;</li> - <li class="i1">in ruminants, <b>II</b>, - <a href="#Page_327">327–9</a>;</li> - <li class="i1">differentiation of liver, <b>II</b>, - <a href="#Page_329">329–33</a>;</li> - <li class="i1">muscularity, <b>II</b>, - <a href="#Page_364">364</a>.</li> - - <li>Allotropism: of organic constituents, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page4">4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>;</li> - <li class="i1">muscular action, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page59">59</a>.</li> - - <li>Alloys, melting point of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page339">339</a>.</li> - - <li class="hangingindent">Alternation of generations, misleading application of term, <b>II</b>, - <a href="#Page_84">84</a>.</li> - <li class="i1">(<i>See</i> <a href="#Agamogenesis">Agamogenesis</a> <i>and</i> <a href="#Gamogenesis">Gamogenesis</a>.)</li> - - <li>Amitosis, occurrence of, in morbid tissues, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page264">264</a>.</li> - - <li>Ammonia: properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page7">7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>;</li> - <li class="i1">nerve stimulation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page55">55</a>.</li> - - <li><i>Amœba</i>: central development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page163">163</a>;</li> - <li class="i1">a primary aggregate, <b>II</b>, - <a href="#Page_86">86</a>;</li> - <li class="i1">symmetry of encysted, <b>II</b>, - <a href="#Page_186">186</a>;</li> - <li class="i1">symbiosis, <b>II</b>, - <a href="#Page_400">400</a>.</li> - - <li id="Amphibia"><i>Amphibia</i>: classification of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page392">392</a>;</li> - <li class="i1">embryonic respiratory system, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page457">457</a>;</li> - <li class="i1">structure and media, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page483">483</a>;</li> - <li class="i1">limb locomotion, <b>II</b>, - <a href="#Page_15">15</a>;</li> - <li class="i1">segmentation, <b>II</b>, - <a href="#Page_122">122</a>, - <a href="#Page_225">225</a>;</li> - <li class="i1">outer tissues, <b>II</b>, - <a href="#Page_311">311</a>;</li> - <li class="i1">respiration, <b>II</b>, - <a href="#Page_334">334</a>, - <a href="#Page_338">338</a>;</li> - <li class="i1">Owen on skeleton, <b>II</b>, - <a href="#Page_552">552</a>, - <a href="#Page_557">557</a>, - <a href="#Page_558">558</a>.</li> - - <li class="hangingindent"><i>Amphioxus</i>: separation of segmentation spheres of egg, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page691">691</a>;</li> - <li class="i1">embryogeny, <b>II</b>, - <a href="#Page_121">121</a>;</li> - <li class="i1">local segmentation, <b>II</b>, - <a href="#Page_125">125–7</a>, - <a href="#Page_605">605</a>;</li> - <li class="hangingindent1">genesis of vertebrate axis, <b>II</b>, - <a href="#Page_213">213–6</a>, - <a href="#Page_218">218</a>, - <a href="#Page_222">222</a>;</li> - <li class="i1">development, <b>II</b>, - <a href="#Page_564">564</a>.</li> - - <li class="hangingindent"><i>Amphipnous cuchia</i>, vascular air-sacs, <b>II</b>, - <a href="#Page_337">337</a>.</li> - - <li class="hangingindent"><i>Anabas scandens</i>, the climbing fish, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page480">480</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page483">483</a>.</li> - - <li><i>Anacharis</i> (see <a href="#Eloidea"><i>Eloidea</i></a>).</li> - - <li>Anæsthetics, diverse effects of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page55">55</a>.</li> - - <li class="hangingindent"><i>Angræcum</i>, assimilative function of root, <b>II</b>, - <a href="#Page_255">255</a>.</li> - - <li>“Animal Spirits,” vitalism and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page115">115</a>.</li> - - <li class="hangingindent" id="Animals">Animals: nutrition and molecular re-arrangement, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page36">36–7</a>;</li> - <li class="i1">nitrogenous character, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page39">39–41</a>;</li> - <li class="i1">sensible motion, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page57">57</a>;</li> - <li class="i1">metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page62">62–77</a>;</li> - <li class="i1">multiplication of energies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page75">75</a>;</li> - <li class="i1">contrasted traits of plants and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page196">196</a>;</li> - <li class="i1">what is an individual? <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page246">246–7</a>;</li> - <li class="i1">solar influence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page500">500</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="hangingindent1">geologic changes affecting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page501">501–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page549">549</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page550">550</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="hangingindent1">interdependence with plants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page504">504–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page514">514</a>; <b>II</b>, - <a href="#Page_398">398–401</a>;</li> - <li class="i1">complexity of influences affecting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page506">506</a>;</li> - <li class="hangingindent1">geographical isolation and origin of species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page568">568–9</a>;</li> - <li class="i1">vital attributes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page577">577–9</a>;</li> - <li class="hangingindent1">distribution and antiquity of plant and animal types, <b>II</b>, - <a href="#Page_297">297</a>;</li> - <li class="hangingindent1">mutual dependence of organisms at large, <b>II</b>, - <a href="#Page_397">397–408</a>;</li> - <li class="i1">hypothetical plant-animal type, <b>II</b>, - <a href="#Page_397">397</a>;</li> - <li class="i1">progressive increase of size, <b>II</b>, - <a href="#Page_401">401</a>;</li> - <li class="i1">laws of multiplication, <b>II</b>, - <a href="#Page_411">411–6</a>;</li> - <li class="i1">rhythm in numbers, <b>II</b>, - <a href="#Page_419">419</a>;</li> - <li class="i1">law of weights and dimensions, <b>II</b>, - <a href="#Page_434">434</a>.</li> - - <li class="hangingindent">Animals, domesticated: variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page324">324</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page326">326</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page560">560</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page563">563</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">interbreeding, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page345">345–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page354">354</a>; <b>II</b>, - <a href="#Page_615">615</a>;</li> - <li class="i1">pure and mixed breeds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page354">354</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page625">625</a>.</li> - - <li id="Annelida"><i>Annelida</i>: phosphorescence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page50">50</a>;</li> - <li class="i1">axial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page166">166</a>;</li> - <li class="i1">integration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page363">363</a>;</li> - <li class="hangingindent1">larval forms and phylogeny, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page447">447</a>; <b>II</b>, - <a href="#Page_115">115</a>;</li> - <li class="i1">segmental fission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page588">588–9</a>;</li> - <li class="hangingindent1">segmentation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page98">98–101</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page103">103–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page602">602–5</a>; <b>II</b>, - <a href="#Page_107">107–9</a>, - <a href="#Page_125">125–7</a>;</li> - <li class="i1">lateral gemmation, <b>II</b>, - <a href="#Page_105">105</a>;</li> - <li class="i1">embryogeny, <b>II</b>, - <a href="#Page_119">119</a>;</li> - <li class="i1">bilateral symmetry, <b>II</b>, - <a href="#Page_197">197–200</a>;</li> - <li class="i1">genesis, <b>II</b>, - <a href="#Page_444">444</a>, - <a href="#Page_453">453</a>.</li> - - <li><i>Annulosa</i>: regeneration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page361">361–2</a>;</li> - <li class="i1">distinctive traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page392">392</a>;</li> - <li class="i1">origin of type, <b>II</b>, - <a href="#Page_98">98–110</a>, - <a href="#Page_602">602–6</a>;</li> - <li class="i1">unit of composition, <b>II</b>, - <a href="#Page_105">105</a>;</li> - <li class="i1">application of term, <b>II</b>, - <a href="#Page_111">111</a>;</li> - <li class="i1">vertebrate symmetry compared, <b>II</b>, - <a href="#Page_203">203–6</a>;</li> - <li class="i1">segmental differentiation, <b>II</b>, - <a href="#Page_207">207–9</a>;</li> - <li class="i1">unintegrated function in <i>Planaria</i>, <b>II</b>, - <a href="#Page_373">373</a>;</li> - <li class="i1">development and genesis, <b>II</b>, - <a href="#Page_464">464</a>;</li> - <li class="i1">nutrition and genesis, <b>II</b>, - <a href="#Page_490">490</a>.</li> - <li class="i1">(See also <a href="#Annelida"><i>Annelida</i></a> and <a href="#Arthropoda"><i>Arthropoda</i></a>.)</li> - - <li>Anthropomorphism, former prevalence of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page419">419</a>.</li> - - <li>Ants: utilization of aphids, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660–1</a>; <b>II</b>, - <a href="#Page_403">403</a>, - <a href="#Page_405">405</a>;</li> - <li class="i1">nest-mates, <b>II</b>, - <a href="#Page_405">405</a>;</li> - <li class="i1">castes in social species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page658">658–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>;</li> - <li class="hangingindent1">loss of self-feeding instinct in Amazons, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660–1</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page663">663–4</a>;</li> - <li class="i1">monstrous development of Honey-ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page683">683</a>;</li> - <li class="i1">bulk and fecundity, <b>II</b>, - <a href="#Page_492">492</a>.</li> - <li class="i1">(See also <a href="#Termites"><i>Termites</i></a>.)</li> - - <li><i>Aphis</i>: individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page249">249</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page250">250</a>; <b>II</b>, - <a href="#Page_603">603</a>;</li> - <li class="i1">parthenogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page274">274–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page289">289</a>;</li> - <li class="i1">fertility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page582">582</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page640">640–1</a>; <b>II</b>, - <a href="#Page_476">476</a>, - <a href="#Page_490">490</a>;</li> - <li class="i1">utilized by ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660–1</a>; <b>II</b>, - <a href="#Page_403">403</a>, - <a href="#Page_405">405</a>;</li> - <li class="hangingindent1">over-multiplication checked by lady-bird, <b>II</b>, - <a href="#Page_406">406</a>.</li> - - <li>Aquatic animals, large size attained by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page156">156</a>.</li> - - <li id="Arachnida"><i>Arachnida</i>: avoidance of danger, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page92">92</a>;</li> - <li class="i1">oviparous homogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>;</li> - <li class="i1">segmentation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page469">469</a>; <b>II</b>, - <a href="#Page_113">113</a>, - <a href="#Page_114">114</a>;</li> - <li class="i1">integration and homology, <b>II</b>, - <a href="#Page_111">111</a>, - <a href="#Page_121">121</a>;</li> - <li class="i1">bilateral symmetry, <b>II</b>, - <a href="#Page_198">198</a>.</li> - - <li><i>Arcella</i>: symmetry, <b>II</b>, - <a href="#Page_186">186</a>;</li> - <li class="i1">outer tissue differentiation, <b>II</b>, - <a href="#Page_309">309</a>.</li> - - <li id="Archegoniateae"><i>Archegoniateæ</i>: morphological composition, <b>II</b>, - <a href="#Page_32">32–5</a>;</li> - <li class="i1">growth and development, <b>II</b>, - <a href="#Page_50">50–6</a>;</li> - <li class="i1">tubular structure, <b>II</b>, - <a href="#Page_58">58</a>, - <a href="#Page_62">62</a>;</li> - <li class="i1">alternating generation not distinctive, <b>II</b>, - <a href="#Page_84">84</a>;</li> - <li class="i1">asymmetry and environment, <b>II</b>, - <a href="#Page_140">140</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_293">293</a>, - <a href="#Page_296">296</a>;</li> - <li class="i1">individuation and genesis, <b>II</b>, - <a href="#Page_441">441</a>, - <a href="#Page_451">451</a>, - <a href="#Page_463">463</a>.</li> - - <li>Archenteron: primitive externality, <b>II</b>, - <a href="#Page_301">301</a>;</li> - <li class="i1">formation of cœlom, <b>II</b>, - <a href="#Page_302">302</a>.</li> - - <li><i>Archiannelida</i>: segmentation, <b>II</b>, - <a href="#Page_125">125</a>.</li> - - <li><i>Arenicola marina</i>: polytrochal larvæ, <b>II</b>, - <a href="#Page_109">109</a>.</li> - - <li>Arm: embryogeny of human, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page169">169</a>;</li> - <li class="i1">vicarious use of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page209">209</a>.</li> - - <li>Army, morphological analogy, <b>II</b>, - <a href="#Page_6">6</a>.</li> - - <li>Arteries (<i>see</i> <a href="#Vascular_System">Vascular System</a>).</li> - - <li id="Arthropoda"><i>Arthropoda</i>: uniaxial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>;</li> - <li class="i1">protoplasmic continuity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page190">190</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page629">629</a>;</li> - <li class="i1">excursiveness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page481">481</a>;</li> - <li class="i1">limb locomotion, <b>II</b>, - <a href="#Page_15">15</a>;</li> - <li class="i1">integration and homology, <b>II</b>, - <a href="#Page_111">111–4</a>, - <a href="#Page_121">121</a>;</li> - <li class="i1">bilateral symmetry, <b>II</b>, - <a href="#Page_197">197–200</a>;</li> - <li class="i1">genesis, <b>II</b>, - <a href="#Page_445">445</a>, - <a href="#Page_453">453</a>.</li> - - <li>Ascidians: multiaxial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page166">166</a>;</li> - <li class="i1">functional differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page202">202</a>;</li> - <li class="i1">composite individuality of <i>Doliolum</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page247">247</a>;</li> - <li class="i1">self-fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page342">342</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_94">94</a>, - <a href="#Page_96">96</a>, - <a href="#Page_97">97</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_194">194</a>;</li> - <li class="i1">origin of vertebrate type, <b>II</b>, - <a href="#Page_194">194</a>, - <a href="#Page_598">598</a>, - <a href="#Page_605">605</a>.</li> - - <li><i>Ascomycetes</i>, reproduction, <b>II</b>, - <a href="#Page_450">450</a>.</li> - - <li>Assimilation: compared with reasoning, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page81">81–7</a>;</li> - <li class="i1">a trait of vitality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page577">577</a>.</li> - - <li id="Asteroidea"><i>Asteroidea</i>, radial symmetry, <b>II</b>, - <a href="#Page_196">196</a>.</li> - - <li>Astronomy: growth of celestial bodies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page135">135</a>;</li> - <li class="i1">Schleiden on individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page245">245</a>;</li> - <li class="i1">evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page432">432</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page435">435</a>;</li> - <li class="i1">classification of stars, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page444">444</a>;</li> - <li class="i1">rhythm of, and organic change, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page499">499–501</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">law of equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page519">519–20</a>;</li> - <li class="i1">co-operation of structure and function, <b>II</b>, - <a href="#Page_3">3</a>.</li> - - <li>Atavism: occurrence of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page305">305–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314</a>;</li> - <li class="i1">digital variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page321">321–3</a>.</li> - - <li>Atoms: use of term, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page6">6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page31">31</a>;</li> - <li class="i1">ethereal undulations and oscillations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page31">31–5</a>.</li> - - <li>Australia: settler’s usages, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364</a>;</li> - <li class="i1">ratio of jaw to skull in natives, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page541">541</a>.</li> - - <li>Axillary buds, origin and development, <b>II</b>, - <a href="#Page_65">65–8</a>.</li> - - <li>Axis: “neutral” of mechanics, <b>II</b>, - <a href="#Page_210">210</a>;</li> - <li class="i1">genesis of vertebrate, <b>II</b>, - <a href="#Page_212">212–6</a>, - <a href="#Page_224">224–7</a>.</li> -</ul> - -<ul> - <li><i>Bacteria</i>: fission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page270">270</a>;</li> - <li class="i1">non-nucleated, <b>II</b>, - <a href="#Page_20">20</a>;</li> - <li class="i1">rate of increase, <b>II</b>, - <a href="#Page_443">443</a>.</li> - - <li class="hangingindent">Baer, K. E. von: embryological formula, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page171">171</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page172">172</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page451">451</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page453">453</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page461">461</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page466">466</a>;</li> - <li class="i1">zoological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page383">383</a>;</li> - <li class="i1">on animal transitions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page480">480</a>.</li> - - <li><i>Balanophoræ</i>, inner tissue, <b>II</b>, - <a href="#Page_274">274</a>.</li> - - <li>Bark: varied development, <b>II</b>, - <a href="#Page_247">247–9</a>;</li> - <li class="hangingindent1">physiological differentiation, <b>II</b>, - <a href="#Page_249">249–50</a>, - <a href="#Page_258">258</a>, - <a href="#Page_386">386</a>.</li> - - <li><i>Basidiomycetes</i>, reproduction, <b>II</b>, - <a href="#Page_450">450</a>.</li> - - <li>Bat, infertility of, <b>II</b>, - <a href="#Page_473">473</a>.</li> - - <li class="hangingindent">Bates, H. W., protective mimicry of butterflies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page398">398</a>.</li> - - <li><i>Batrachia</i> (see <a href="#Amphibia"><i>Amphibia</i></a>).</li> - - <li>Bean, vascular system, <b>II</b>, - <a href="#Page_573">573</a>, - <a href="#Page_591">591</a>.</li> - - <li>Beaver, tail and co-adapted structures, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page616">616</a>.</li> - - <li>Bees (<i>see</i> <a href="#Insects">Insects</a>).</li> - - <li><i>Begoniaceæ</i>: multiplication <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page224">224</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page317">317</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page442">442</a>;</li> - <li class="i1">individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page251">251</a>;</li> - <li class="i1">development from scales, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page282">282</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_159">159</a>, - <a href="#Page_166">166</a>;</li> - <li class="i1">development, <b>II</b>, - <a href="#Page_271">271</a>.</li> - - <li class="hangingindent">Berkeley, M. J., indefiniteness of mosses and ferns, <b>II</b>, - <a href="#Page_296">296</a>.</li> - - <li>Bile, arrest of excretion, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page209">209</a>.</li> - - <li>Bilirubin and biliverdine, function of, <b>II</b>, - <a href="#Page_330">330</a>, - <a href="#Page_333">333</a>.</li> - - <li>Biology: definition and divisions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page124">124–5</a>;</li> - <li class="i1">organic structural phenomena, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page125">125–7</a>;</li> - <li class="i1">also functional, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page127">127–9</a>;</li> - <li class="hangingindent1">actions and reactions of function and structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page129">129–30</a>;</li> - <li class="i1">genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page130">130–1</a>;</li> - <li class="i1">limited knowledge of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page131">131</a>;</li> - <li class="i1">evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page432">432</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page434">434</a>;</li> - <li class="i1">sociological analogies (<i>see</i> <a href="#Sociology">Sociology</a>).</li> - - <li class="hangingindent">Biophors, Weismann’s germ-plasm units (<i>see</i> <a href="#Weismann">Weismann</a>).</li> - - <li class="hangingindent">Birds: flesh-eating and grain-eating contrasted, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page68">68</a>;</li> - <li class="i1">growth and expenditure of force, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page142">142</a>;</li> - <li class="i1">size of egg and adult, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page144">144</a>;</li> - <li class="i1">limitations on flight, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page155">155</a>;</li> - <li class="i1">self-mobility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page175">175</a>;</li> - <li class="i1">temperature, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page176">176</a>;</li> - <li class="hangingindent1">functional and structural differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page201">201</a>;</li> - <li class="i1">food of starving pigeon, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page215">215</a>;</li> - <li class="i1">viviparousness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>;</li> - <li class="i1">heredity and pigeon breeding, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page305">305</a>;</li> - <li class="i1">atavism in pigeon, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314</a>;</li> - <li class="i1">osseous variation in pigeon, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page321">321</a>;</li> - <li class="i1">classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page392">392</a>;</li> - <li class="hangingindent1">migrations and change of habits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page399">399</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page402">402</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page500">500</a>;</li> - <li class="i1">distribution in time, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page410">410</a>;</li> - <li class="i1">Darwin on petrels, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page455">455</a>;</li> - <li class="i1">rudimentary teeth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page457">457</a>;</li> - <li class="i1">vertebræ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page471">471</a>; <b>II</b>, - <a href="#Page_564">564</a>;</li> - <li class="i1">feather development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page473">473</a>;</li> - <li class="i1">habits of water ouzel, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page485">485</a>;</li> - <li class="i1">egg shells and direct equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page526">526</a>;</li> - <li class="i1">bones of waders and direct equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page527">527</a>;</li> - <li class="i1">fertility and nervous development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page598">598</a>;</li> - <li class="i1">cellular continuity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page629">629</a>;</li> - <li class="i1">adaptation of structure to environment, <b>II</b>, - <a href="#Page_12">12</a>;</li> - <li class="i1">sexual selection, <b>II</b>, - <a href="#Page_269">269</a>;</li> - <li class="i1">wing spurs, <b>II</b>, - <a href="#Page_313">313</a>;</li> - <li class="i1">outer tissue differentiation, <b>II</b>, - <a href="#Page_314">314–5</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">alimentary canal development, <b>II</b>, - <a href="#Page_325">325</a>, - <a href="#Page_327">327</a>;</li> - <li class="i1">muscular colour and activity, <b>II</b>, - <a href="#Page_365">365–9</a>;</li> - <li class="i1">nutrition, <b>II</b>, - <a href="#Page_433">433</a>;</li> - <li class="i1">cost of genesis, <b>II</b>, - <a href="#Page_436">436</a>;</li> - <li class="i1">growth and genesis, <b>II</b>, - <a href="#Page_454">454</a>, - <a href="#Page_458">458</a>;</li> - <li class="i1">heat expenditure and genesis, <b>II</b>, - <a href="#Page_468">468–9</a>, - <a href="#Page_474">474</a>;</li> - <li class="i1">activity and genesis, <b>II</b>, - <a href="#Page_470">470–2</a>, - <a href="#Page_474">474</a>;</li> - <li class="i1">contrasted mammalian fertility, <b>II</b>, - <a href="#Page_470">470</a>;</li> - <li class="i1">eggs of wild and tame, <b>II</b>, - <a href="#Page_478">478</a>;</li> - <li class="i1">fertility of blackbird and linnet compared, <b>II</b>, - <a href="#Page_503">503</a>;</li> - <li class="i1">Owen on skeleton of, <b>II</b>, - <a href="#Page_559">559</a>, - <a href="#Page_560">560</a>, - <a href="#Page_561">561</a>.</li> - - <li>Bischoff, embryogeny of human arm, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page169">169</a>.</li> - - <li class="hangingindent">Bison, modifications entailed by increased weight of head, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page512">512</a>.</li> - - <li class="hangingindent">Blackbird, contrasted with linnet in development, <b>II</b>, - <a href="#Page_503">503</a>.</li> - - <li>Blainville, de, definition of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page79">79</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page93">93</a>.</li> - - <li class="hangingindent">Blastosphere, independence of cells in Echinoderm larvæ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page185">185</a>.</li> - - <li class="hangingindent">Blastula, definition of life and formation of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page112">112</a>.</li> - - <li>Blood: similarity of iron peroxide, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page17">17</a>;</li> - <li class="i1">metabolic processes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>;</li> - <li class="i1">segregation of abnormal constituents, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page180">180</a>;</li> - <li class="i1">protozoon life of corpuscles, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page186">186–7</a>;</li> - <li class="i1">morbid changes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page221">221</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page701">701</a>;</li> - <li class="i1">assimilative power and organic repair, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page221">221–2</a>;</li> - <li class="i1">respiratory tissue differentiation, <b>II</b>, - <a href="#Page_310">310–1</a>;</li> - <li class="i1">pressure in mammals, <b>II</b>, - <a href="#Page_340">340</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Vascular_System">Vascular System</a>.)</li> - - <li class="hangingindent">Blow-fly, Weismann on nutrition and genesis in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page678">678–9</a>.</li> - - <li>Boers, Cape, habits and fertility, <b>II</b>, - <a href="#Page_508">508</a>.</li> - - <li>Boismont, A. B. de, on human fertility, <b>II</b>, - <a href="#Page_511">511</a>.</li> - - <li id="Bone">Bone: growth and function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page151">151</a>;</li> - <li class="i1">adaptability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page230">230</a>; <b>II</b>, - <a href="#Page_217">217–8</a>;</li> - <li class="i1">function and weight, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page308">308</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">mammalian cervical vertebræ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page394">394</a>;</li> - <li class="i1">evolution and vertebral column, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page470">470–1</a>;</li> - <li class="i1">partial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page473">473</a>;</li> - <li class="i1">size of head as influencing, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page512">512</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page536">536–9</a>;</li> - <li class="i1">direct equilibration and strength, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page527">527</a>;</li> - <li class="hangingindent1">natural selection and co-adaptations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page614">614–21</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page674">674</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page677">677</a>;</li> - <li class="i1">rudimentary limbs of whale, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page668">668</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="hangingindent1">inheritance of acquired modifications in Punjabis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>;</li> - <li class="i1">skull development, <b>II</b>, - <a href="#Page_222">222</a>;</li> - <li class="i1">theory of supernumerary, <b>II</b>, - <a href="#Page_223">223</a>;</li> - <li class="hangingindent1">Cope on origin of vertebrate osseous system, <b>II</b>, - <a href="#Page_225">225–7</a>;</li> - <li class="i1">differentiation, <b>II</b>, - <a href="#Page_344">344–56</a>;</li> - <li class="i1">false joints, <b>II</b>, - <a href="#Page_370">370–2</a>;</li> - <li class="i1">Owen’s theory of vertebrate skeleton, <b>II</b>, - <a href="#Page_548">548–66</a>.</li> - - <li>Book-worm, food of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page77">77</a>.</li> - - <li>Born, G., experiments on frog larvæ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page365">365</a>.</li> - - <li>Botany, biological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page124">124</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page125">125</a>.</li> - <li class="i1">(<i>See</i> <a href="#Plants">Plants</a>.)</li> - - <li><i>Bothriocephalus</i>, development, <b>II</b>, - <a href="#Page_490">490</a>.</li> - - <li><i>Botryllidæ</i>: development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page166">166</a>;</li> - <li class="i1">independence of components, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page247">247</a>;</li> - <li class="i1">agamogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page641">641</a>.</li> - - <li>Bower, Prof., on alternation of generations, <b>II</b>, - <a href="#Page_84">84</a>.</li> - - <li><i>Brachiopoda</i>, rude vascular system, <b>II</b>, - <a href="#Page_340">340</a>.</li> - - <li>Bradbury, J. B., on vaso-dilators, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page55">55</a>.</li> - - <li class="hangingindent">Brain: natural selection and mental evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>;</li> - <li class="i1">analysis of substance, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page596">596</a>;</li> - <li class="i1">weight in higher animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page598">598–9</a>;</li> - <li class="i1">size in civilized and uncivilized, <b>II</b>, - <a href="#Page_530">530</a>.</li> - - <li>Branches (<i>see</i> <a href="#Morphology">Morphology</a>).</li> - - <li><i>Branchiæ</i> (<i>see</i> <a href="#Respiratory_System">Respiratory System</a>).</li> - - <li>Brass, effect of antimony on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page121">121</a>.</li> - - <li>Bread, diamagnetism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page370">370</a>.</li> - - <li>Breeding: heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page304">304–5</a>;</li> - <li class="i1">in-and-in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page344">344–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page353">353</a>; <b>II</b>, - <a href="#Page_615">615</a>;</li> - <li class="i1">pure and mixed, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page354">354</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page625">625</a>.</li> - - <li>Bricks, changed equilibrium shown by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page38">38</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page42">42</a>.</li> - - <li>Brodie, T. G., cell chemistry, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page260">260</a>.</li> - - <li class="hangingindent">Brownell, Miss J. L., on birth-rate in United States, <b>II</b>, - <a href="#Page_520">520</a>.</li> - - <li>Brown-Séquard, on inherited epilepsy, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page312">312</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page624">624</a>.</li> - - <li><i>Bryophyllum</i>, peculiar proliferation, <b>II</b>, - <a href="#Page_295">295</a>.</li> - - <li><i>Bryophyta</i>, large size attained by some, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page138">138</a>.</li> - - <li><i>Bryozoa</i>, gemmation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page588">588</a>.</li> - - <li>Budding (<i>see</i> <a href="#Gemmation">Gemmation</a>).</li> - - <li>Buds: development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page167">167–8</a>;</li> - <li class="i1">theories of heredity and cauline, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page358">358–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page360">360</a>;</li> - <li class="i1">axillary, <b>II</b>, - <a href="#Page_65">65–9</a>;</li> - <li class="i1">effects of nutrition, <b>II</b>, - <a href="#Page_73">73–4</a>.</li> - - <li>Butterfly: protective mimicry, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page398">398</a>;</li> - <li class="i1">instance of tame, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page684">684</a>.</li> -</ul> - -<ul> - - <li>Cabbage, varieties of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page302">302</a>.</li> - - <li class="hangingindent"><i>Cactaceæ</i>: foliar and axial development, <b>II</b>, - <a href="#Page_47">47–9</a>;</li> - <li class="i1">differentiation in, <b>II</b>, - <a href="#Page_258">258</a>, - <a href="#Page_276">276</a>, - <a href="#Page_282">282</a>;</li> - <li class="i1">vascular system, <b>II</b>, - <a href="#Page_282">282</a>;</li> - <li class="i1">dye permeability and circulation, <b>II</b>, - <a href="#Page_571">571</a>, - <a href="#Page_572">572</a>;</li> - <li class="i1">wood formation, <b>II</b>, - <a href="#Page_575">575</a>, - <a href="#Page_577">577</a>, - <a href="#Page_578">578</a>, - <a href="#Page_580">580</a>.</li> - - <li>“Callus,” budding from, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page358">358</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page359">359</a>.</li> - - <li>Camel, natural selection and hump of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page534">534</a>.</li> - - <li>Canadians, French, fertility of, <b>II</b>, - <a href="#Page_509">509</a>.</li> - - <li>Cancer, the definition of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page111">111</a>;</li> - <li class="i1">œsophageal, <b>II</b>, - <a href="#Page_324">324</a>;</li> - <li class="i1">and vascular system, <b>II</b>, - <a href="#Page_343">343</a>.</li> - - <li>Caoutchouc, leaf-structure, <b>II</b>, - <a href="#Page_589">589</a>.</li> - - <li>Capillaries (<i>see</i> <a href="#Vascular_System">Vascular System</a>).</li> - - <li class="hangingindent">Capillarity, and vegetal vascular system, <b>II</b>, - <a href="#Page_279">279–80</a>, - <a href="#Page_286">286</a>, - <a href="#Page_568">568</a>, - <a href="#Page_570">570</a>, - <a href="#Page_585">585</a>, - <a href="#Page_587">587</a>, - <a href="#Page_592">592–6</a>.</li> - - <li>Carbohydrates: instability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page10">10</a>;</li> - <li class="i1">the term “hydro-carbon,” <i>ib.</i>;</li> - <li class="i1">molecular changes in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page42">42–3</a>;</li> - <li class="i1">organic transformation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page43">43</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page48">48</a>;</li> - <li class="i1">metabolic processes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page63">63–77</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page262">262–3</a>; <b>II</b>, - <a href="#Page_362">362</a>.</li> - - <li>Carbon: properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page3">3–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page20">20</a>;</li> - <li class="i1">compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page6">6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page7">7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page10">10–12</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page13">13</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page24">24–5</a>.</li> - - <li class="hangingindent">Carbonic acid (carbon dioxide): properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page6">6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page7">7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>;</li> - <li class="hangingindent1">in animal and plant functions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page62">62</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page214">214</a>; <b>II</b>, - <a href="#Page_398">398</a>;</li> - <li class="i1">diffusibility, <b>II</b>, - <a href="#Page_331">331</a>.</li> - - <li>Carbonic oxide, properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page6">6</a>.</li> - - <li>Carnivores: nitrogenous food, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page47">47</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page68">68</a>;</li> - <li class="i1">katabolic process, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page71">71</a>;</li> - <li class="i1">restricted environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page396">396</a>;</li> - <li class="hangingindent1">their beneficial effects on animal life, <b>II</b>, - <a href="#Page_405">405–6</a>.</li> - - <li class="hangingindent">Carpenter, W. B.: on functional specialization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page208">208</a>;</li> - <li class="i1">reproduction of seaweed, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page582">582</a>;</li> - <li class="i1">vegetal cell multiplication, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page585">585</a>;</li> - <li class="hangingindent1">structure and multiplication of compound organisms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page586">586–9</a>;</li> - <li class="i1">on fundamental traits of sex, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page595">595</a>;</li> - <li class="i1">nutritive system of invertebrates, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page595">595</a>;</li> - <li class="i1"><i>Macrocystis</i>, <b>II</b>, - <a href="#Page_450">450</a>;</li> - <li class="i1">nutrition and reproductive function, <b>II</b>, - <a href="#Page_460">460</a>.</li> - - <li>Cartilage (<i>see</i> <a href="#Bone">Bone</a>).</li> - - <li>Castration, effect of, on growth, <b>II</b>, - <a href="#Page_459">459</a>.</li> - - <li>“Castration parasitaire,” Julin on, <b>II</b>, - <a href="#Page_493">493–6</a>.</li> - - <li>Catalysis, and vital metamorphosis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page39">39</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page43">43</a>.</li> - - <li>Cattell, McKeen, on tactual perceptiveness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page666">666</a>.</li> - - <li class="hangingindent"><i>Caulerpa</i>, simulation of higher plant-forms, <b>II</b>, - <a href="#Page_22">22</a>.</li> - - <li class="hangingindent">Cave-animals, degeneration of eyes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page309">309</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page614">614</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page647">647–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>.</li> - - <li class="hangingindent" id="Cell">Cell, the: incomprehensibility of forces at work in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page118">118</a>;</li> - <li class="i1">protoplasts and their traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page181">181</a>;</li> - <li class="hangingindent1">the cell-theory, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page184">184</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page252">252</a>; <b>II</b>, - <a href="#Page_17">17–21</a>, - <a href="#Page_85">85</a>;</li> - <li class="i1">differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page188">188–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page194">194</a>;</li> - <li class="hangingindent1">the continuity of protoplasm, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page190">190–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page194">194</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page628">628–30</a>; <b>II</b>, - <a href="#Page_21">21</a>;</li> - <li class="i1">its structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page253">253–5</a>;</li> - <li class="i1">function of centrosome, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page254">254–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page257">257</a>;</li> - <li class="hangingindent1">structure and function of nucleus, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page255">255–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page258">258–9</a>;</li> - <li class="i1">karyokinesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page257">257–8</a>;</li> - <li class="i1">function of chromatin, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page259">259–65</a>;</li> - <li class="hangingindent1">fertilization and function of polar bodies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page266">266–8</a>;</li> - <li class="i1">theories of heredity based on theory, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page356">356</a>;</li> - <li class="hangingindent1">Weismann’s differentiation into reproductive and somatic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page622">622</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page628">628–30</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page633">633–44</a>;</li> - <li class="i1">nucleus absent or dispersed, <b>II</b>, - <a href="#Page_20">20</a>, - <a href="#Page_85">85</a>;</li> - <li class="i1">morphological differentiation, <b>II</b>, - <a href="#Page_175">175–7</a>;</li> - <li class="i1">animal morphology, <b>II</b>, - <a href="#Page_228">228–30</a>;</li> - <li class="i1">morphological summary, <b>II</b>, - <a href="#Page_233">233</a>;</li> - <li class="i1">vegetal tissue differentiation, <b>II</b>, - <a href="#Page_249">249–50</a>, - <a href="#Page_386">386</a>;</li> - <li class="i1">vascular development, <b>II</b>, - <a href="#Page_279">279–84</a>, - <a href="#Page_389">389</a>.</li> - - <li>Centipede, bilateral symmetry, <b>II</b>, - <a href="#Page_198">198–200</a>.</li> - - <li><i>Cephalopoda</i>: bilateral symmetry, <b>II</b>, - <a href="#Page_203">203</a>;</li> - <li class="i1">vascular system, <b>II</b>, - <a href="#Page_341">341</a>.</li> - - <li><i>Cercariæ</i> (see <a href="#Distoma"><i>Distoma</i></a>).</li> - - <li><i>Cereus</i>, tissue differentiation, <b>II</b>, - <a href="#Page_276">276</a>, - <a href="#Page_283">283</a>.</li> - - <li>Cesalpino, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page377">377</a>.</li> - - <li><i>Cestoda</i> (see <a href="#Entozoa"><i>Entozoa</i></a>).</li> - - <li><i>Chætopoda</i>, segmentation, <b>II</b>, - <a href="#Page_98">98</a>, - <a href="#Page_103">103</a>, - <a href="#Page_605">605</a>.</li> - - <li><i>Chaja</i>, wing spurs, <b>II</b>, - <a href="#Page_313">313</a>.</li> - - <li>Change, and definition of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page81">81–90</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page113">113</a>.</li> - - <li class="hangingindent">Charles, R. H., on inheritance of acquired modifications in leg-bones of Punjabis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>.</li> - - <li>Chatié, on single and double stocks, <b>II</b>, - <a href="#Page_622">622</a>.</li> - - <li class="hangingindent" id="Chemistry">Chemistry: properties of organic elements, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page3">3–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page20">20</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page22">22</a>;</li> - <li class="i1">of diatomic compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page7">7–10</a>;</li> - <li class="i1">tri-atomic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page10">10–12</a>;</li> - <li class="i1">poly-atomic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page12">12–13</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page25">25</a>;</li> - <li class="i1">traits of evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page23">23–4</a>;</li> - <li class="hangingindent1">ethereal undulations and atomic oscillation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page31">31–6</a>;</li> - <li class="hangingindent1">chemical affinity and organic change, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page36">36–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page38">38–43</a>;</li> - <li class="i1">oxidation and generation of heat, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page46">46–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page60">60</a>;</li> - <li class="i1">generation of nerve force, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page52">52</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page60">60</a>;</li> - <li class="i1">metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page62">62–77</a>;</li> - <li class="i1">physiology and organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page127">127</a>;</li> - <li class="i1">flesh constituents, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page154">154</a>;</li> - <li class="hangingindent1">composition of organisms and environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page173">173</a>;</li> - <li class="hangingindent1">organic development and differential assimilation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page179">179–80</a>;</li> - <li class="i1">chemical units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page225">225</a>; <b>II</b>, - <a href="#Page_612">612</a>;</li> - <li class="i1">primitive ideas of elements, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page417">417</a>;</li> - <li class="i1">evolution of organic compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page696">696–701</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page703">703</a>.</li> - - <li>Chestnut, leaf symmetry, <b>II</b>, - <a href="#Page_149">149</a>, - <a href="#Page_153">153</a>.</li> - - <li class="hangingindent"><i>Chiton</i>: simulation of segmentation, <b>II</b>, - <a href="#Page_116">116</a>, - <a href="#Page_118">118</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_202">202</a>.</li> - - <li>Chlorophyll: function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page65">65</a>; <b>II</b>, - <a href="#Page_263">263</a>;</li> - <li class="i1">nutrition and absence of, <b>II</b>, - <a href="#Page_74">74</a>;</li> - <li class="i1">constitution, <b>II</b>, - <a href="#Page_262">262</a>;</li> - <li class="i1">symbiotic presence in animals, <b>II</b>, - <a href="#Page_400">400</a>.</li> - - <li class="hangingindent"><i>Chondracanthus gibbosus</i>, enormous development of reproductive system, <b>II</b>, - <a href="#Page_487">487</a>.</li> - - <li><i>Chordata</i>, affinities, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page466">466</a>.</li> - - <li>Chromatin (<i>see</i> <a href="#Cell">Cell</a>).</li> - - <li>Circle, the, and evolution hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page433">433</a>.</li> - - <li>Circulation (<i>see</i> <a href="#Vascular_System">Vascular System</a>).</li> - - <li class="hangingindent"><i>Cirrhipedia</i>: Darwin on retrograde development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page458">458</a>;</li> - <li class="hangingindent1">remarkable transformation in <i>Sacculina</i>, <b>II</b>, - <a href="#Page_494">494–5</a>.</li> - - <li class="hangingindent">Civilization, human evolution and genesis, <b>II</b>, - <a href="#Page_529">529–31</a>.</li> - - <li><i>Cladophora</i>: integration, <b>II</b>, - <a href="#Page_25">25</a>;</li> - <li class="i1">axial development, <b>II</b>, - <a href="#Page_28">28</a>.</li> - - <li>Classification: subjective conception, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page78">78</a>;</li> - <li class="i1">two purposes of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page374">374</a>;</li> - <li class="i1">a gradual process, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page375">375</a>;</li> - <li class="i1">botanical, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page377">377–80</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page389">389–90</a>;</li> - <li class="i1">zoological, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page380">380–9</a>;</li> - <li class="hangingindent1">incomplete equivalence of groups, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page389">389</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page445">445–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page448">448</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page555">555</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page572">572</a>;</li> - <li class="i1">group attributes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page390">390–3</a>;</li> - <li class="i1">the truths interpreted, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page393">393–4</a>;</li> - <li class="i1">ethnologic and linguistic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page441">441–6</a>;</li> - <li class="i1">organic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page443">443</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page447">447</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page555">555</a>;</li> - <li class="i1">differences in kind and degree, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page444">444–6</a>;</li> - <li class="i1">antecedent structural similarity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page447">447</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page448">448–9</a>;</li> - <li class="i1">Von Baer’s formula, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page451">451–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page555">555</a>;</li> - <li class="i1">organic, not uniserial, <b>II</b>, - <a href="#Page_115">115</a>.</li> - - <li class="hangingindent"><i>Classification of the Sciences, The</i>, and evolution and dissolution, <b>II</b>, - <a href="#Page_5">5</a>.</li> - - <li class="hangingindent">Claus, C, on segmentation in Annelids and Chætopods, <b>II</b>, - <a href="#Page_605">605</a>.</li> - - <li>Clover: flower and axial development, <b>II</b>, - <a href="#Page_45">45</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_152">152</a>.</li> - - <li class="hangingindent" id="adaptation">Co-adaptation of co-operative parts: principles underlying, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page234">234–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page511">511–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page514">514–5</a>;</li> - <li class="i1">slow operation of the process, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page236">236</a>;</li> - <li class="i1">sociological analogy, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page237">237–40</a>;</li> - <li class="i1">reversion under original conditions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page240">240</a>;</li> - <li class="i1">the analogy continued, <i>ib.</i>;</li> - <li class="i1">the case of bison’s head, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page512">512</a>;</li> - <li class="hangingindent1">natural selection an inadequate explanation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page535">535</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page614">614–21</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="hangingindent1">Romanes on “cessation of selection” as effecting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page560">560</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page561">561–2</a>;</li> - <li class="hangingindent1">Weismann’s theories, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page560">560–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page663">663–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page674">674–5</a>;</li> - <li class="i1">natural selection and economy of growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page562">562</a>;</li> - <li class="i1">physiological processes involved, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page566">566–7</a>;</li> - <li class="hangingindent1">Wallace’s argument from artificial selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page615">615</a>;</li> - <li class="i1">what are co-operative parts? <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page616">616–7</a>;</li> - <li class="i1">“intra-selection” examined, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676–8</a>.</li> - - <li>Coal, social effects of supply, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page238">238–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page241">241</a>.</li> - - <li>Cocoa-nut, growth and fertility, <b>II</b>, - <a href="#Page_457">457</a>.</li> - - <li class="hangingindent">Coccospheres: vital problem presented by protective structures, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page119">119</a>;</li> - <li class="i1">imbricated plates, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page182">182</a>.</li> - - <li>Cockroach, ousting of European species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page399">399</a>.</li> - - <li>Cod: ova of, <b>II</b>, - <a href="#Page_435">435</a>;</li> - <li class="i1">growth and fertility, <b>II</b>, - <a href="#Page_454">454</a>.</li> - - <li><i>Codium</i>: symmetry, <b>II</b>, - <a href="#Page_136">136</a>;</li> - <li class="i1">tissue differentiation, <b>II</b>, - <a href="#Page_246">246</a>.</li> - - <li class="hangingindent" id="Coelenterata"><i>Cœlenterata</i>: rudimentary contractile organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page58">58</a>;</li> - <li class="i1">vital changes in polyp, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page95">95</a>;</li> - <li class="i1">axial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page166">166</a>;</li> - <li class="i1">environment and structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page173">173</a>;</li> - <li class="i1">self-mobility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page175">175</a>; <b>II</b>, - <a href="#Page_14">14</a>, - <a href="#Page_15">15</a>;</li> - <li class="i1">functional differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page201">201</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page391">391</a>;</li> - <li class="i1">inactivity and waste, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page213">213</a>;</li> - <li class="i1">reparative power, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page219">219</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page224">224</a>;</li> - <li class="i1">individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page246">246</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page247">247</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page250">250</a>;</li> - <li class="i1">heterogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page273">273</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page277">277</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page296">296</a>;</li> - <li class="hangingindent1">negative disintegration in <i>Hydrozoa</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page276">276</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page587">587</a>;</li> - <li class="i1">reproductive tissue, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page281">281</a>;</li> - <li class="i1">differentiation in <i>Hydrozoa</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page391">391</a>;</li> - <li class="i1">classificatory value, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page446">446</a>;</li> - <li class="i1">regeneration of fragments, <b>II</b>, - <a href="#Page_90">90</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_90">90</a>, - <a href="#Page_102">102</a>, - <a href="#Page_105">105</a>, - <a href="#Page_124">124</a>;</li> - <li class="i1">gemmation, <b>II</b>, - <a href="#Page_91">91</a>;</li> - <li class="i1">tertiary aggregation, <b>II</b>, - <a href="#Page_92">92</a>, - <a href="#Page_95">95</a>, - <a href="#Page_124">124</a>;</li> - <li class="i1">molluscan affinities, <b>II</b>, - <a href="#Page_115">115</a>;</li> - <li class="i1">radial symmetry, <b>II</b>, - <a href="#Page_188">188</a>;</li> - <li class="i1">symmetry of compound, <b>II</b>, - <a href="#Page_192">192–3</a>;</li> - <li class="i1">segmental differentiation, <b>II</b>, - <a href="#Page_207">207</a>;</li> - <li class="hangingindent1">physiological differentiation in <i>Hydra</i> and analogy, <b>II</b>, - <a href="#Page_300">300</a>;</li> - <li class="i1">ciliation of blastula, <b>II</b>, - <a href="#Page_301">301</a>;</li> - <li class="i1">tissue reduplication, <b>II</b>, - <a href="#Page_301">301–2</a>, - <a href="#Page_389">389</a>;</li> - <li class="i1">outer tissue differentiation, <b>II</b>, - <a href="#Page_309">309</a>;</li> - <li class="i1">osmosis in <i>Hydra</i>, <b>II</b>, - <a href="#Page_339">339</a>;</li> - <li class="i1">vascular system in <i>Hydra</i>, <b>II</b>, - <a href="#Page_340">340</a>, - <a href="#Page_376">376</a>;</li> - <li class="i1">functional co-ordination, <b>II</b>, - <a href="#Page_376">376</a>;</li> - <li class="i1">symbiosis, <b>II</b>, - <a href="#Page_400">400</a>;</li> - <li class="i1">asexual genesis, <b>II</b>, - <a href="#Page_443">443–4</a>;</li> - <li class="i1">growth and sexual genesis, <b>II</b>, - <a href="#Page_452">452</a>;</li> - <li class="i1">development and genesis, <b>II</b>, - <a href="#Page_462">462</a>;</li> - <li class="i1">nutrition and genesis, <b>II</b>, - <a href="#Page_476">476</a>.</li> - - <li>Cœlom, origin and function, <b>II</b>, - <a href="#Page_302">302–3</a>.</li> - - <li class="hangingindent">Collins, F. Howard, jaws and teeth of savages and civilized, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page541">541</a>.</li> - - <li>Colloids: T. Graham on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page15">15–8</a>;</li> - <li class="i1">diffusibility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page18">18–21</a>;</li> - <li class="i1">organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page21">21</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page25">25</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page26">26</a>;</li> - <li class="i1">pliability and elasticity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page27">27</a>;</li> - <li class="i1">capillary affinity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page28">28</a>;</li> - <li class="i1">isomerism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page59">59</a>;</li> - <li class="i1">instability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page350">350</a>;</li> - <li class="i1">molecular mobility and diffusibility, <b>II</b>, - <a href="#Page_331">331</a>;</li> - <li class="hangingindent1">instability of, and nerve differentiation, <b>II</b>, - <a href="#Page_356">356–61</a>;</li> - <li class="i1">and muscular tissue, <b>II</b>, - <a href="#Page_361">361–4</a>.</li> - - <li class="hangingindent">Colonies, autogenous development and parallel in heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page366">366–8</a>; <b>II</b>, - <a href="#Page_620">620</a>.</li> - - <li>Colour: sensation of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page54">54</a>;</li> - <li class="i1">phœnogamic, <b>II</b>, - <a href="#Page_75">75</a>, - <a href="#Page_265">265–6</a>;</li> - <li class="i1">light and vegetal, <b>II</b>, - <a href="#Page_261">261–2</a>;</li> - <li class="i1">floral fertilization, <b>II</b>, - <a href="#Page_267">267–9</a>;</li> - <li class="i1">sexual selection, <b>II</b>, - <a href="#Page_269">269</a>;</li> - <li class="i1">activity and muscular, <b>II</b>, - <a href="#Page_365">365–9</a>;</li> - <li class="hangingindent1">physiological units and mixture of, in offspring, <b>II</b>, - <a href="#Page_616">616</a>, - <a href="#Page_617">617</a>.</li> - - <li class="hangingindent">Commensalism, organic Integration as displayed in, <b>II</b>, - <a href="#Page_402">402–4</a>.</li> - - <li><i>Compositæ</i>: floral symmetry, <b>II</b>, - <a href="#Page_173">173</a>.</li> - - <li>Condor, weight of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page155">155</a>.</li> - - <li><i>Confervoideæ</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page280">280</a>; <b>II</b>, - <a href="#Page_25">25</a>, - <a href="#Page_28">28</a>, - <a href="#Page_449">449</a>.</li> - <li class="i1">(See <a href="#Algae"><i>Algæ</i></a>.)</li> - - <li><i>Conjugateæ</i>, <b>II</b>, - <a href="#Page_449">449</a>.</li> - <li class="i1">(See <a href="#Algae"><i>Algæ</i></a>.)</li> - - <li>Conjugation, in <i>Algæ</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279</a>;</li> - <li class="i1">in <i>Protozoa</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page280">280</a>; <b>II</b>, - <a href="#Page_452">452</a>;</li> - <li class="i1">can fission persist without? <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page637">637</a>;</li> - <li class="i1">relation to growth, <b>II</b>, - <a href="#Page_449">449</a>.</li> - - <li>Connective tissue, Hertwig’s classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page189">189</a>.</li> - - <li>Constitutional units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page369">369</a>.</li> - <li class="i1">(<i>See</i> <a href="#Physiological_Units">Physiological Units</a>.)</li> - - <li>Consumption, hereditary transmission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page307">307</a>.</li> - - <li>Co-ordination of actions (<i>see</i> <a href="#Life">Life</a>).</li> - - <li class="hangingindent">Cope, E. D., on origin of vertebrate structure, <b>II</b>, - <a href="#Page_225">225–7</a>.</li> - - <li class="hangingindent"><i>Cormophyta</i>: slight internal differentiation, <b>II</b>, - <a href="#Page_273">273</a>;</li> - <li class="i1">vascular system, <b>II</b>, - <a href="#Page_280">280</a>.</li> - - <li><i>Corpuscula tactus</i>, their function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page75">75</a>.</li> - - <li>Correspondence, use of word, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page97">97</a>.</li> - <li class="i1">(<i>See</i> <a href="#Life">Life</a>.)</li> - - <li>Cousin-marriages, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page345">345</a>; <b>II</b>, - <a href="#Page_615">615</a>.</li> - - <li>Cow: what prompts her to mumble a bone? <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page120">120</a>.</li> - - <li>Cow-parsnip (see <i>Heracleum</i>).</li> - - <li>Crab (see <a href="#Crustacea"><i>Crustacea</i></a>).</li> - - <li>Creation (<i>see</i> <a href="#Special_creation">Special creation</a>).</li> - - <li><i>Crinoidea</i>, symmetry, <b>II</b>, - <a href="#Page_195">195–6</a>.</li> - - <li>Crocodile, continuous growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page154">154</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page292">292</a>.</li> - - <li class="hangingindent">Crookes, Sir W., hypothetical chemical unit “protyle,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page22">22</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page23">23</a>.</li> - - <li><i>Cruciferæ</i>, floral symmetry, <b>II</b>, - <a href="#Page_164">164</a>, - <a href="#Page_171">171</a>.</li> - - <li id="Crustacea"><i>Crustacea</i>: locomotion of lobster, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page175">175</a>;</li> - <li class="i1">regeneration of limbs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page224">224</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page360">360</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page589">589</a>; <b>II</b>, - <a href="#Page_76">76</a>;</li> - <li class="i1">homogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>;</li> - <li class="hangingindent1">genesis and nutrition in <i>Daphnidæ</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page290">290–1</a>;</li> - <li class="i1">growth and genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page292">292</a>;</li> - <li class="hangingindent1">degeneration of eye in cave-inhabiting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page309">309</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page614">614</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page648">648</a>;</li> - <li class="i1">hermit-crab parasite, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page397">397</a>;</li> - <li class="i1">changes of media, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page401">401</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page481">481–2</a>;</li> - <li class="i1">retrograde development in cirripedes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page458">458</a>;</li> - <li class="i1">segmentation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page468">468–9</a>; <b>II</b>, - <a href="#Page_114">114</a>;</li> - <li class="i1">Darwin on jaws and legs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page471">471</a>;</li> - <li class="i1">survival of cirripedes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page517">517</a>;</li> - <li class="i1">integration and homology, <b>II</b>, - <a href="#Page_111">111–4</a>, - <a href="#Page_121">121</a>, - <a href="#Page_603">603</a>;</li> - <li class="i1">bilateral symmetry, <b>II</b>, - <a href="#Page_198">198–201</a>;</li> - <li class="i1">eyes, <b>II</b>, - <a href="#Page_318">318</a>;</li> - <li class="i1">dermal structure of hermit-crab, <b>II</b>, - <a href="#Page_322">322</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">fertility, <b>II</b>, - <a href="#Page_453">453</a>;</li> - <li class="hangingindent1">nutrition and genesis in parasitic species, <b>II</b>, - <a href="#Page_487">487</a>;</li> - <li class="i1">“castration parasitaire,” <b>II</b>, - <a href="#Page_493">493–6</a>.</li> - - <li>Crystalloids: Prof. Graham on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page15">15–8</a>;</li> - <li class="i1">diffusibility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page18">18–21</a>;</li> - <li class="i1">organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page21">21–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page26">26</a>.</li> - - <li class="hangingindent">Crystals: simulation of life in “storm glass,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page96">96</a>;</li> - <li class="i1">growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page135">135–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page577">577</a>;</li> - <li class="i1">segregation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page179">179</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page221">221</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page223">223</a>;</li> - <li class="i1">equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page337">337</a>;</li> - <li class="i1">physiological units and polarity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page701">701–6</a>;</li> - <li class="i1">time and formation, <b>II</b>, - <a href="#Page_77">77</a>.</li> - - <li class="hangingindent"><i>Ctenodrilus</i>, segmental individuality, <b>II</b>, - <a href="#Page_103">103</a>, - <a href="#Page_603">603</a>, - <a href="#Page_604">604</a>.</li> - - <li>Cube, bilateral symmetry, <b>II</b>, - <a href="#Page_132">132</a>.</li> - - <li>Cunningham, J. T., <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#pagevi">vi</a>; <b>II</b>, - <a href="#Page_vi">vi</a>;</li> - <li class="i1">on non-adaptive specific characters, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page565">565</a>;</li> - <li class="i1">food of blow-fly larvæ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page678">678</a>;</li> - <li class="i1">arthropod segmentation, <b>II</b>, - <a href="#Page_114">114</a>;</li> - <li class="i1">egg-production of Conger, <b>II</b>, - <a href="#Page_425">425</a>.</li> - - <li>Cuttle-fish, Individuality of <i>Hectocotylus</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page250">250</a>.</li> - - <li>Cuvier, zoological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page381">381</a>.</li> - - <li>Cyanogen, properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page7">7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>.</li> - - <li><i>Cyclichthys</i>, dermal structure, <b>II</b>, - <a href="#Page_306">306</a>.</li> -</ul> - -<ul> - <li>Dalyell, Sir J., regeneration in <i>Dasychone</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page361">361</a>;</li> - <li class="i1">propagation of <i>Hydra</i>, <b>II</b>, - <a href="#Page_476">476</a>.</li> - - <li><i>Daphnidæ</i>, heterogenesis and nutrition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page290">290–1</a>.</li> - - <li>Darwin, C: <i>Origin of Species</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page129">129</a>; <b>II</b>, - <a href="#Page_528">528</a>;</li> - <li class="i1">natural selection and function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page308">308–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">atavism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314</a>;</li> - <li class="i1">osseous variations in pigeons, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page321">321</a>;</li> - <li class="i1">plant variation and domestication, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page325">325</a>;</li> - <li class="i1">“spontaneous variation,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page328">328</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page697">697</a>;</li> - <li class="hangingindent1">floral fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page340">340</a>; <b>II</b>, - <a href="#Page_168">168</a>, - <a href="#Page_267">267</a>, - <a href="#Page_407">407</a>, - <a href="#Page_608">608</a>;</li> - <li class="hangingindent1">intercrossing and self-fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page344">344</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page345">345</a>;</li> - <li class="i1">intercrossing <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page347">347</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page611">611</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page669">669</a>;</li> - <li class="hangingindent1">his theory of pangenesis examined, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page356">356–62</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page370">370</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page372">372</a>;</li> - <li class="i1">plant-fertilization and distribution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page397">397</a>;</li> - <li class="i1">habits of birds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page400">400</a>;</li> - <li class="i1">distribution and natural barriers, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page402">402</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page476">476</a>;</li> - <li class="hangingindent1">disappearance and non-reappearance of species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page406">406</a>;</li> - <li class="i1">distribution in time and space, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page410">410</a>;</li> - <li class="i1">linguistic classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page442">442</a>;</li> - <li class="i1">classification of organisms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page443">443</a>;</li> - <li class="i1">classification and descent, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page448">448</a>;</li> - <li class="i1">on petrels, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page455">455</a>;</li> - <li class="i1">suppression of organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page457">457</a>;</li> - <li class="i1">development of <i>Cirrhipedia</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page438">438</a>;</li> - <li class="i1">jaws and legs of <i>Crustacea</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page471">471</a>;</li> - <li class="i1">aborted organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page474">474</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page563">563</a>;</li> - <li class="hangingindent1">relations of species in Galapagos archipelago, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page478">478</a>;</li> - <li class="i1">opinions of E. Darwin and Lamarck, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page491">491</a>;</li> - <li class="i1">the term “survival of the fittest,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page530">530</a>;</li> - <li class="hangingindent1">Indirect equilibration by natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page530">530–5</a>;</li> - <li class="hangingindent1">inheritance of acquired characters, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page535">535–42</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page560">560</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page630">630</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page690">690</a>;</li> - <li class="i1">Wallace on natural selection in man, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>;</li> - <li class="hangingindent1">misleading connotations of term “natural selection,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page609">609</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page695">695</a>;</li> - <li class="i1">caste gradations and jaws of driver ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page658">658</a>;</li> - <li class="i1">attachment of climbing plants, <b>II</b>, - <a href="#Page_276">276–7</a>;</li> - <li class="i1">vegetal fructification, <b>II</b>, - <a href="#Page_294">294</a>;</li> - <li class="i1">earth-worm, <b>II</b>, - <a href="#Page_402">402</a>;</li> - <li class="hangingindent1">animal sterility and domestication, <b>II</b>, - <a href="#Page_480">480</a>, - <a href="#Page_483">483</a>;</li> - <li class="i1">variation in hyacinth and camellia, <b>II</b>, - <a href="#Page_621">621</a>.</li> - - <li class="hangingindent">Darwin, Dr. E., modifiability of organisms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page490">490</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page492">492–7</a>.</li> - - <li>Death: an arrest of vital correspondence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page102">102</a>;</li> - <li class="i1">only limit to vegetal growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page153">153</a>;</li> - <li class="hangingindent1">cessation of co-ordination of actions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page578">578</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page579">579</a>;</li> - <li class="i1">Weismann’s hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page636">636–8</a>;</li> - <li class="i1">physiological integration, <b>II</b>, - <a href="#Page_374">374</a>, - <a href="#Page_392">392</a>;</li> - <li class="i1">cause of natural, <b>II</b>, - <a href="#Page_413">413</a>;</li> - <li class="i1">relation to births, <b>II</b>, - <a href="#Page_417">417</a>.</li> - - <li class="hangingindent">Definiteness: of vital change, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page87">87–90</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page106">106</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page109">109</a>;</li> - <li class="i1">developmental, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page178">178</a>;</li> - <li class="i1">functional, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page212">212</a>;</li> - <li class="i1">segregation of evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page514">514–6</a>.</li> - - <li>Definition, difficulties of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page78">78</a>; <b>II</b>, - <a href="#Page_17">17</a>.</li> - - <li class="hangingindent">Degeneracy, morphological obscurations due to, <b>II</b>, - <a href="#Page_12">12</a>, - <a href="#Page_13">13</a>.</li> - - <li><i>Dendrobium</i> (<i>see</i> <a href="#Orchids">Orchids</a>).</li> - - <li><i>Desmidiaceæ</i>: unicellular, <b>II</b>, - <a href="#Page_21">21</a>;</li> - <li class="i1">linear and central aggregation, <b>II</b>, - <a href="#Page_23">23</a>;</li> - <li class="i1">natural selection and symmetry, <b>II</b>, - <a href="#Page_134">134</a>, - <a href="#Page_133">133</a>;</li> - <li class="i1">morphological differentiation, <b>II</b>, - <a href="#Page_177">177</a>;</li> - <li class="i1">tissue, <b>II</b>, - <a href="#Page_244">244</a>;</li> - <li class="i1">genesis, <b>II</b>, - <a href="#Page_440">440</a>, - <a href="#Page_449">449</a>.</li> - - <li class="hangingindent">Determinants, Weismann’s germ-plasm units (<i>see</i> <a href="#Germ_plasm">Germ-plasm</a>).</li> - - <li class="hangingindent">Development: an increase of structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page162">162</a>; <b>II</b>, - <a href="#Page_461">461</a>;</li> - <li class="i1">primarily central, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page162">162</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page166">166</a>;</li> - <li class="i1">uni- and multicentral, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page163">163–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page166">166–7</a>;</li> - <li class="i1">axial, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page164">164</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page167">167</a>;</li> - <li class="i1">uni- and multiaxial, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165–6</a>;</li> - <li class="hangingindent1">a change to coherent definite heterogeneity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page167">167–70</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page179">179</a>;</li> - <li class="i1">Von Baer’s formula, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page171">171–2</a>;</li> - <li class="hangingindent1">individual differentiation from environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page172">172–8</a>;</li> - <li class="i1">cell-formation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page225">225</a>;</li> - <li class="i1">discontinuous, and agamogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page275">275</a>;</li> - <li class="i1">Prof. Huxley’s classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page276">276</a>;</li> - <li class="hangingindent1">sociological parallel to autogenous, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364–8</a>; <b>II</b>, - <a href="#Page_620">620</a>;</li> - <li class="i1">retrograde, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page457">457–8</a>;</li> - <li class="i1">inequalities among co-operative parts, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page617">617</a>;</li> - <li class="i1">“heterochrony,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page655">655</a>;</li> - <li class="i1">continuous and discontinuous vegetal, <b>II</b>, - <a href="#Page_52">52</a>;</li> - <li class="i1">summary of physiological, <b>II</b>, - <a href="#Page_384">384–90</a>;</li> - <li class="i1">nutrition and genesis, <i>résumé</i>, <b>II</b>, - <a href="#Page_497">497–9</a>;</li> - <li class="i1">evolution, <b>II</b>, - <a href="#Page_501">501–5</a>;</li> - <li class="i1">commencement of genesis, <b>II</b>, - <a href="#Page_506">506</a>;</li> - <li class="i1">of vertebrate limbs, <b>II</b>, - <a href="#Page_553">553</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Multiplication">Multiplication</a>.)</li> - - <li><i>Development Hypothesis, The</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page417">417</a>.</li> - - <li>Dialects (<i>see</i> <a href="#Language">Language</a>).</li> - - <li>Dialysis, and diffusibillty. <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page19">19</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page20">20</a>.</li> - - <li>Diastase, decomposition of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page38">38</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page40">40</a>.</li> - - <li><i>Diatomaceæ</i>: tissue, <b>II</b>, - <a href="#Page_244">244</a>;</li> - <li class="i1">genesis, <b>II</b>, - <a href="#Page_440">440</a>, - <a href="#Page_448">448</a>.</li> - - <li>Diatomic compounds (<i>see</i> <a href="#Chemistry">Chemistry</a>).</li> - - <li class="hangingindent" id="Dicotyledons">Dicotyledons: growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page139">139</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page143">143</a>; <b>II</b>, - <a href="#Page_63">63–4</a>, - <a href="#Page_69">69–72</a>, - <a href="#Page_78">78</a>, - <a href="#Page_82">82–3</a>;</li> - <li class="i1">uniaxial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>;</li> - <li class="i1">stem and leaf functions, <b>II</b>, - <a href="#Page_257">257</a>;</li> - <li class="i1">mechanical stress and wood formation, <b>II</b>, - <a href="#Page_277">277</a>;</li> - <li class="i1">growth and genesis, <b>II</b>, - <a href="#Page_451">451</a>.</li> - - <li>Differentiation (<i>see</i> <a href="#Morphology">Morphology</a> <i>and</i> <a href="#Physiology">Physiology</a>).</li> - - <li><i>Difflugia</i>: primary aggregate, <b>II</b>, - <a href="#Page_86">86–7</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_186">186</a>;</li> - <li class="i1">outer tissue differentiation, <b>II</b>, - <a href="#Page_309">309</a>.</li> - - <li class="hangingindent">Diffusion, of colloids and crystalloids, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page18">18–20</a>; <b>II</b>, - <a href="#Page_331">331</a>.</li> - - <li>Digestion: action of nitrogenous compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>;</li> - <li class="i1">obesity, <b>II</b>, - <a href="#Page_480">480–4</a>;</li> - <li class="i1">fertility, <b>II</b>, - <a href="#Page_514">514</a>.</li> - - <li>Dimorphism: floral, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page534">534</a>;</li> - <li class="i1">sexual, in parasites, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page315">315</a>;</li> - <li class="i1">social insects (<i>see</i> <a href="#Insects">Insects</a>).</li> - - <li>Dinosaurs, size of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page139">139</a>.</li> - - <li><i>Diphyes</i>: individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page246">246</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_192">192</a>.</li> - - <li id="Disease">Disease: segregation of blood constituents, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page179">179</a>;</li> - <li class="i1">changes in blood from, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page221">221</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page701">701</a>;</li> - <li class="i1">heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page306">306–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page312">312–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page622">622–3</a>;</li> - <li class="i1">belief in supernatural origin, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page419">419</a>;</li> - <li class="i1">parasitism and special creation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page427">427</a>;</li> - <li class="i1">morbid products as specific characters, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page567">567</a>;</li> - <li class="i1">telegony, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646</a>;</li> - <li class="i1">dermal structure, <b>II</b>, - <a href="#Page_306">306</a>;</li> - <li class="i1">intestinal muscular hypertrophy, <b>II</b>, - <a href="#Page_325">325</a>;</li> - <li class="hangingindent1">indigestion and alimentary canal development, <b>II</b>, - <a href="#Page_328">328</a>;</li> - <li class="i1">jaundice and bilirubin, <b>II</b>, - <a href="#Page_330">330</a>;</li> - <li class="i1">localization of excretion, <b>II</b>, - <a href="#Page_331">331</a>;</li> - <li class="i1">membranes in inflammatory, <b>II</b>, - <a href="#Page_343">343</a>;</li> - <li class="i1">osseous differentiation in rickets, <b>II</b>, - <a href="#Page_352">352</a>;</li> - <li class="i1">fatty degeneration, <b>II</b>, - <a href="#Page_482">482</a>.</li> - - <li>Disintegration, physiological (<i>see</i> <a href="#Physiology">Physiology</a>).</li> - - <li id="Distoma"><i>Distoma</i>: metagenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page273">273–4</a>;</li> - <li class="i1">disintegration of genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page276">276</a>;</li> - <li class="i1">cycle of generations, <b>II</b>, - <a href="#Page_489">489</a>.</li> - - <li>Distribution: physical limits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page396">396</a>;</li> - <li class="i1">organic environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page396">396–8</a>;</li> - <li class="i1">parasitic conditions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page397">397–8</a>;</li> - <li class="i1">simultaneity of agencies affecting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page398">398</a>;</li> - <li class="hangingindent1">mutual encroachments of species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page398">398–401</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page477">477</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page489">489</a>;</li> - <li class="hangingindent1">facts disproving pre-adaptation to habitats, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page401">401–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page411">411–2</a>;</li> - <li class="i1">of animals and plants in time, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page404">404–11</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page412">412</a>;</li> - <li class="hangingindent1">ousting of native species in New Zealand, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page477">477</a>;</li> - <li class="i1">local influences, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page477">477–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page489">489</a>;</li> - <li class="i1">through varied media, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page479">479–85</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page489">489</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">past and present organic forms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page485">485–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">complex organization and, <b>II</b>, - <a href="#Page_296">296–7</a>.</li> - - <li>Division of labour, physiological (<i>see</i> <a href="#Labour">Labour</a>).</li> - - <li>Dog: contrasted lives of tortoise and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page103">103</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page104">104</a>;</li> - <li class="i1">inherited habits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page309">309</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page573">573</a>;</li> - <li class="i1">abnormal digits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page324">324</a>;</li> - <li class="i1">interbreeding of divergent varieties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page565">565</a>;</li> - <li class="i1">decrease of jaw, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page615">615</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">telegony, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page645">645</a>;</li> - <li class="i1">conditions affecting fertility, <b>II</b>, - <a href="#Page_474">474</a>, - <a href="#Page_479">479</a>.</li> - - <li>Dohrn, theory of vertebrate structure, <b>II</b>, - <a href="#Page_606">606</a>.</li> - - <li class="hangingindent"><i>Doliolum</i>, combination of individualities, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page247">247</a>.</li> - - <li>Domestication (<i>see</i> <a href="#Animals">Animals</a>).</li> - - <li>Doubleday, E., on nutrition of genesis, <b>II</b>, - <a href="#Page_510">510–2</a>.</li> - - <li class="hangingindent">Driesch, separation of segmentation spheres of <i>Echinus</i> ovum, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page691">691</a>; <b>II</b>, - <a href="#Page_618">618</a>.</li> - - <li>Dropsy (<i>see</i> <a href="#Disease">Disease</a>).</li> - - <li><i>Drosera</i>: individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page251">251</a>;</li> - <li class="i1">proliferous growth, <b>II</b>, - <a href="#Page_75">75</a>.</li> - - <li class="hangingindent">Du Bois-Reymond, E. H., electricity from muscles and nerves, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page50">50</a>.</li> - - <li>Dumas, antithesis of animals and plants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page62">62</a>.</li> - - <li>Dwarfs, Hindu family of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page316">316</a>.</li> -</ul> - -<ul> - <li>Ear, development of vertebrate, <b>II</b>, - <a href="#Page_318">318</a>, - <a href="#Page_320">320</a>.</li> - - <li class="hangingindent">Earth, climatic rhythm and organic change, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page499">499–501</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>.</li> - - <li>Earth-worm: bilateral symmetry, <b>II</b>, - <a href="#Page_199">199</a>, - <a href="#Page_200">200</a>;</li> - <li class="i1">mould production, <b>II</b>, - <a href="#Page_402">402</a>.</li> - - <li><i>Echinococcus</i> (see <a href="#Entozoa"><i>Entozoa</i></a>).</li> - - <li class="hangingindent"><i>Echinodermata</i>: independence of blastosphere cells, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page185">185</a>;</li> - <li class="i1">protoplasmic continuity in embryos, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page190">190</a>;</li> - <li class="hangingindent1">separation of segmentation spheres of ovum, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page691">691</a>; <b>II</b>, - <a href="#Page_618">618</a>;</li> - <li class="i1">symmetry, <b>II</b>, 191, - <a href="#Page_195">195–6</a>.</li> - - <li class="hangingindent">Economy: of growth in natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page536">536</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page562">562</a>;</li> - <li class="i1">a trait of organic evolution, <b>II</b>, - <a href="#Page_501">501</a>, - <a href="#Page_504">504</a>.</li> - - <li>Ectoderm: functional differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page202">202</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page203">203</a>;</li> - <li class="i1">functional vicariousness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page209">209</a>;</li> - <li class="i1">reproductive function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page281">281</a>.</li> - - <li class="hangingindent">Effects, Multiplication of: variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page329">329–30</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page333">333</a>;</li> - <li class="hangingindent1">organic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page511">511–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page515">515</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page517">517</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page549">549</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>; <b>II</b>, - <a href="#Page_405">405–6</a>;</li> - <li class="i1">morphological development, <b>II</b>, - <a href="#Page_7">7–9</a>, - <a href="#Page_234">234</a>;</li> - <li class="i1">physiological differentiation, <b>II</b>, - <a href="#Page_390">390–1</a>, - <a href="#Page_392">392</a>.</li> - - <li id="Egg">Eggs (<i>see</i> <a href="#Embryology">Embryology</a>).</li> - - <li>Eimer, T., theory of orthogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page563">563–4</a>.</li> - - <li class="hangingindent"><i>Elasmobranchii</i>: protoplasmic continuity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page629">629</a>;</li> - <li class="i1">segmentation, <b>II</b>, - <a href="#Page_126">126</a>.</li> - - <li>Electricity: genesis in organic matter, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page50">50–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page60">60</a>;</li> - <li class="i1">muscular action, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page59">59</a>;</li> - <li class="i1">incomprehensibility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page121">121</a>.</li> - - <li class="hangingindent">Elephant: fertility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page583">583</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page599">599</a>; <b>II</b>, - <a href="#Page_459">459</a>, - <a href="#Page_506">506</a>;</li> - <li class="i1">cerebro-spinal system, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page598">598</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page599">599</a>.</li> - - <li>Elk, Irish, horns and correlated parts, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page537">537</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page674">674</a>.</li> - - <li id="Eloidea"><i>Eloidea canadensis</i>: individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page248">248</a>;</li> - <li class="i1">enormous agamic multiplication, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page642">642</a>.</li> - - <li>Elongation, and locomotion in animals, <b>II</b>, - <a href="#Page_15">15</a>.</li> - - <li id="Embryology">Embryology: as aiding biology, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page125">125–6</a>;</li> - <li class="i1">simulated growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page136">136</a>;</li> - <li class="hangingindent1">initial and final organic bulks, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page143">143</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page158">158</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page161">161</a>;</li> - <li class="i1">fœtal flesh constituents, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page154">154</a>;</li> - <li class="i1">human arm development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page169">169</a>;</li> - <li class="i1">Von Baer’s formula, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page170">170–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page451">451–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page466">466</a>;</li> - <li class="i1">embryonic heat, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page177">177</a>;</li> - <li class="i1">spherical organic form, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page177">177</a>;</li> - <li class="i1">unit-life in multicellular organisms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page185">185–6</a>;</li> - <li class="i1">functional differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page203">203</a>;</li> - <li class="i1">individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page246">246–7</a>;</li> - <li class="i1">unspecialized reproductive tissue, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279–83</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page317">317</a>;</li> - <li class="i1">changes following impregnation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page283">283–4</a>;</li> - <li class="i1">nutrition and vegetal growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page285">285–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295–7</a>;</li> - <li class="i1">and animal growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page289">289–94</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295–7</a>;</li> - <li class="i1">physiological units and heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page317">317–9</a>;</li> - <li class="hangingindent1">variation and parental functional condition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page324">324</a>;</li> - <li class="i1">uterine environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page327">327–8</a>;</li> - <li class="hangingindent1">physiological units and variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page330">330–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page458">458</a>;</li> - <li class="i1">fertilized and unfertilized ova, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page340">340–1</a>;</li> - <li class="i1">hermaphrodism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page341">341–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page344">344</a>;</li> - <li class="i1">sociological parallel, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page366">366–8</a>;</li> - <li class="hangingindent1">evolution hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page434">434</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page436">436</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page453">453</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page454">454</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page555">555</a>;</li> - <li class="i1">petrel development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page455">455</a>;</li> - <li class="hangingindent1">substitution and suppression of organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page456">456–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page466">466</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page472">472–3</a>;</li> - <li class="hangingindent1">structural proclivities of physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page458">458</a>;</li> - <li class="i1">abridgment of stages, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page458">458–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page464">464</a>;</li> - <li class="hangingindent1">disappearance of intermediate forms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page459">459–60</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page463">463</a>;</li> - <li class="i1">pre-adaptation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page461">461–3</a>;</li> - <li class="hangingindent1">discrimination of species in early stages, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page461">461</a>;</li> - <li class="hangingindent1">anomalous persistence of ancestral traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page463">463–5</a>;</li> - <li class="i1">phylogeny, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page486">486</a>;</li> - <li class="i1">egg-shell function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page527">527</a>;</li> - <li class="hangingindent1">genesis of grades in social insects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page654">654–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page658">658–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page679">679–80</a>;</li> - <li class="i1">determination of sex, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page657">657</a>;</li> - <li class="i1">order of development qualified by needs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page679">679</a>;</li> - <li class="i1">osteology of Punjabis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>;</li> - <li class="hangingindent1">direct transformations and physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page706">706</a>;</li> - <li class="i1">transformation of blastema, <b>II</b>, - <a href="#Page_20">20</a>;</li> - <li class="i1">arrest of growth and innutrition, <b>II</b>, - <a href="#Page_73">73</a>;</li> - <li class="hangingindent1">development of segmented animals, <b>II</b>, - <a href="#Page_100">100–2</a>, - <a href="#Page_602">602</a>;</li> - <li class="hangingindent1">adaptive vertebrate segmentation, <b>II</b>, - <a href="#Page_118">118–23</a>, - <a href="#Page_124">124</a>, - <a href="#Page_223">223–4</a>, - <a href="#Page_605">605–6</a>;</li> - <li class="i1">animal cell morphology, <b>II</b>, - <a href="#Page_228">228</a>;</li> - <li class="hangingindent1">primary differentiations of germinal layers, <b>II</b>, - <a href="#Page_300">300–2</a>;</li> - <li class="i1">lung development, <b>II</b>, - <a href="#Page_333">333–4</a>;</li> - <li class="i1">mammalian ova-maturation, <b>II</b>, - <a href="#Page_342">342–3</a>;</li> - <li class="i1">movements of ova, <b>II</b>, - <a href="#Page_356">356</a>, - <a href="#Page_363">363</a>;</li> - <li class="i1">modifications in mole, <b>II</b>, - <a href="#Page_391">391</a>;</li> - <li class="i1">genesis and nutrition, <b>II</b>, - <a href="#Page_424">424</a>, - <a href="#Page_425">425</a>;</li> - <li class="i1">fish ova, <b>II</b>, - <a href="#Page_435">435</a>, - <a href="#Page_454">454</a>;</li> - <li class="i1">cost of genesis, <b>II</b>, - <a href="#Page_435">435–6</a>;</li> - <li class="i1">number of birds’ eggs, <b>II</b>, - <a href="#Page_454">454–6</a>, - <a href="#Page_478">478</a>;</li> - <li class="i1">heat and genesis, <b>II</b>, - <a href="#Page_468">468</a>, - <a href="#Page_474">474</a>;</li> - <li class="i1">activity and genesis in birds, <b>II</b>, - <a href="#Page_470">470–2</a>, - <a href="#Page_474">474</a>;</li> - <li class="i1">vertebrate limb development, <b>II</b>, - <a href="#Page_553">553</a>;</li> - <li class="i1">ossification in vertebrates, <b>II</b>, - <a href="#Page_556">556</a>;</li> - <li class="i1">Owen’s vertebrate theory, <b>II</b>, - <a href="#Page_563">563</a>;</li> - <li class="i1">development of vertebræ, <b>II</b>, - <a href="#Page_564">564</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Multiplication">Multiplication</a>.)</li> - - <li>Embryology of conceptions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page451">451</a>.</li> - - <li class="hangingindent">Emigrants, type of organization among, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364</a>; <b>II</b>, - <a href="#Page_620">620</a>.</li> - - <li>Endoderm: functional differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page202">202</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page203">203</a>;</li> - <li class="i1">functional vicariousness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page209">209</a>.</li> - - <li>Endogen, application of term, <b>II</b>, - <a href="#Page_62">62</a>, - <a href="#Page_78">78</a>, - <a href="#Page_82">82</a>.</li> - <li class="i1">(<i>See</i> <a href="#Monocotyledons">Monocotyledons</a>.)</li> - - <li id="Energy">Energy: evolution of, in animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page71">71–7</a>;</li> - <li class="i1">organic growth and expenditure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page141">141</a>;</li> - <li class="i1">functional transfer, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page201">201–6</a>;</li> - <li class="hangingindent1">chromatin as the source of, in karyokinesis, <b>II</b>, - <a href="#Page_261">261–5</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Force">Force</a>.)</li> - - <li id="Entozoa"><i>Entozoa</i>: metagenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page273">273</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page641">641</a>;</li> - <li class="i1">self-fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page342">342</a>;</li> - <li class="i1">distribution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page398">398</a>;</li> - <li class="i1">and special creation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page428">428</a>;</li> - <li class="i1">fission in simple types, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page584">584</a>;</li> - <li class="i1">nutrition and genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page641">641</a>; <b>II</b>, - <a href="#Page_488">488</a>;</li> - <li class="i1">direct transformation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page706">706</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_102">102</a>;</li> - <li class="i1">segmentation, <b>II</b>, - <a href="#Page_107">107</a>, - <a href="#Page_108">108</a>;</li> - <li class="hangingindent1">interdependence and organic integration, <b>II</b>, - <a href="#Page_404">404</a>.</li> - - <li class="hangingindent">Environment: degree of life and complexity of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page104">104–7</a>;</li> - <li class="hangingindent1">relation to organic structure and function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page172">172–8</a>; <b>II</b>, - <a href="#Page_12">12–5</a>;</li> - <li class="hangingindent1">adaptation to varied media an evidence of evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page479">479–81</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">influence of solar system, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page500">500</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">inherited adaptation to, <b>II</b>, - <a href="#Page_623">623</a>.</li> - - <li><i>Eolis</i>, branchiæ, <b>II</b>, - <a href="#Page_118">118</a>.</li> - - <li>Epidermis (<i>see</i> <a href="#Skin">Skin</a>).</li> - - <li class="hangingindent">Epilepsy: definition of life and movements in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page112">112</a>;</li> - <li class="i1">heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page312">312</a>.</li> - - <li>Epithelium: ciliated, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page187">187</a>;</li> - <li class="i1">Hertwig’s classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page189">189</a>;</li> - <li class="i1">reproductive function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page280">280</a>;</li> - <li class="i1">“pavement” and “cylinder,” <b>II</b>, - <a href="#Page_229">229</a>.</li> - - <li><i>Epizoa</i>: distribution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page398">398</a>;</li> - <li class="i1">special creation and effects of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page428">428</a>;</li> - <li class="hangingindent1">interdependence and organic integration, <b>II</b>, - <a href="#Page_404">404</a>;</li> - <li class="i1">nutrition and genesis, <b>II</b>, - <a href="#Page_487">487</a>.</li> - - <li>Equilibration: variation and law of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page326">326</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page334">334</a>;</li> - <li class="i1">molecular arrangement, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page337">337–45</a>;</li> - <li class="i1">of organic change, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page348">348</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page347">347</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">direct and indirect, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page519">519–22</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page573">573</a>;</li> - <li class="i1">adaptation by direct, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page522">522–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page551">551</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="hangingindent1">nutrition, defence, and fertilization of plants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page523">523–5</a>;</li> - <li class="i1">direct of animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page525">525–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page551">551</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="hangingindent1">natural selection and indirect, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page530">530–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page552">552</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">of natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page543">543–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page552">552–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">increasing importance of direct, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>;</li> - <li class="hangingindent1">of forces acting on species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page571">571–2</a>; <b>II</b>, - <a href="#Page_417">417–20</a>;</li> - <li class="i1">phenomena not accounted for by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page573">573</a>;</li> - <li class="i1">tissue differentiation, <b>II</b>, - <a href="#Page_245">245</a>;</li> - <li class="i1">genesis of nervous system, <b>II</b>, - <a href="#Page_307">307–8</a>;</li> - <li class="i1">functional, <b>II</b>, - <a href="#Page_391">391–4</a>;</li> - <li class="i1">laws of multiplication, <b>II</b>, - <a href="#Page_411">411–6</a>;</li> - <li class="i1">in human and social evolution, <b>II</b>, - <a href="#Page_537">537</a>.</li> - <li class="hangingindent1">(<i>See also</i> <a href="#Acquired_characters">Acquired characters</a> <i>and</i> <a href="#Natural_selection">Natural selection</a>.)</li> - - <li class="hangingindent">Errera, L., on inherited adaptation to environment in Aspergillus, <b>II</b>, - <a href="#Page_623">623</a>.</li> - - <li>Ethnology: heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page303">303–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page310">310</a>;</li> - <li class="i1">plasticity of mixed races, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page354">354</a>;</li> - <li class="i1">primitive ideas, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page417">417</a>;</li> - <li class="i1">evolution and classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page441">441–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page446">446</a>;</li> - <li class="i1">natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>.</li> - - <li class="hangingindent"><i>Euphorbiaceæ</i>: foliar and axial development, <b>II</b>, - <a href="#Page_47">47–8</a>;</li> - <li class="i1">physiological differentiation, <b>II</b>, - <a href="#Page_258">258</a>;</li> - <li class="i1">dye permeability and circulation, <b>II</b>, - <a href="#Page_571">571</a>;</li> - <li class="i1">wood formation, <b>II</b>, - <a href="#Page_575">575</a>, - <a href="#Page_577">577</a>, - <a href="#Page_578">578</a>;</li> - <li class="i1">foliar vascular system, <b>II</b>, - <a href="#Page_589">589–92</a>, - <a href="#Page_596">596</a>.</li> - - <li>Evaporation: organic change, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page28">28</a>;</li> - <li class="i1">vegetal circulation, <b>II</b>, - <a href="#Page_587">587</a>.</li> - - <li class="hangingindent" id="Evolution">Evolution: chemical elements and compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page22">22–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page67">67</a>;</li> - <li class="hangingindent1">primordial form of living matter, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page63">63–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page181">181</a>; <b>II</b>, - <a href="#Page_21">21–2</a>;</li> - <li class="i1">definitions of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page107">107–10</a>;</li> - <li class="i1">growth the primary trait of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page135">135</a>;</li> - <li class="i1">comprehends growth and development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page162">162</a>;</li> - <li class="i1">illustrations in development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page167">167–70</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page178">178–9</a>;</li> - <li class="hangingindent1">progressive structural differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page181">181–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page192">192–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page211">211–2</a>;</li> - <li class="i1">life before organization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page210">210</a>;</li> - <li class="i1">heterogeneity of function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page211">211</a>;</li> - <li class="i1">stability of species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page242">242</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page515">515</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page518">518</a>;</li> - <li class="i1">individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page247">247</a>;</li> - <li class="i1">cell-organization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page262">262</a>;</li> - <li class="hangingindent1">genesis, heredity, and variation resulting from, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page354">354–5</a>;</li> - <li class="i1">period required for organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page407">407</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page565">565–6</a>;</li> - <li class="hangingindent1">contrasted with special creation hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page415">415</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page431">431–40</a>;</li> - <li class="i1">derivation of hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page431">431</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page439">439</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page554">554</a>;</li> - <li class="i1">increasing belief in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page431">431–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page439">439</a>;</li> - <li class="hangingindent1">experiences supporting conceivability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page433">433–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page439">439</a>;</li> - <li class="i1">direct evidence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page435">435–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page439">439</a>;</li> - <li class="i1">malevolence not implied by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page437">437–9</a>;</li> - <li class="hangingindent1">evidence from classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page443">443</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page444">444</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page449">449</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page466">466</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page555">555</a>;</li> - <li class="i1">embryology, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page451">451–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page466">466</a>;</li> - <li class="hangingindent1">substitution and suppression of organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page456">456–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page466">466</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page472">472–3</a>;</li> - <li class="i1">insect segmentation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page468">468–9</a>;</li> - <li class="i1">vertebral column development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page470">470–2</a>;</li> - <li class="i1">rudimentary organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page472">472–5</a>;</li> - <li class="i1">adaptation to varied media, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page479">479–85</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">growth of the theory of organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page490">490–8</a>;</li> - <li class="hangingindent1">instability of the homogeneous, a cause, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page509">509–11</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page516">516</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page550">550</a>;</li> - <li class="hangingindent1">multiplication of effects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page511">511–14</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page517">517–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page550">550</a>; <b>II</b>, - <a href="#Page_405">405</a>;</li> - <li class="hangingindent1">segregation, and heterogeneity and definiteness of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page514">514–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page550">550</a>;</li> - <li class="hangingindent1">natural selection and general doctrine of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page543">543–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">factors tabulated, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page551">551</a>;</li> - <li class="i1">inductive evidences summarized, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page555">555–6</a>;</li> - <li class="i1">surviving disbelief in France, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page559">559</a>;</li> - <li class="i1">current theories of organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page559">559–74</a>;</li> - <li class="i1">Eimer’s theory of orthogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page563">563–4</a>;</li> - <li class="i1">Gulick on monotypic and polytypic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page569">569</a>;</li> - <li class="i1">phenomena unexplained by theories, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page573">573–4</a>;</li> - <li class="hangingindent1">inorganic and the <i>System of Philosophy</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page696">696</a>;</li> - <li class="i1">“spontaneous generation,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page696">696–701</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page702">702</a>;</li> - <li class="i1">dissolution and problems of morphology, <b>II</b>, - <a href="#Page_4">4–6</a>;</li> - <li class="i1">morphology and formula, <b>II</b>, - <a href="#Page_7">7–9</a>, - <a href="#Page_231">231–5</a>;</li> - <li class="i1">difficulties of definition, <b>II</b>, - <a href="#Page_17">17</a>;</li> - <li class="i1">cell-doctrine, <b>II</b>, - <a href="#Page_17">17–21</a>, - <a href="#Page_85">85</a>;</li> - <li class="i1">unicellular origin of plants, <b>II</b>, - <a href="#Page_21">21–2</a>;</li> - <li class="i1"><i>résumé</i> of plant-morphology, <b>II</b>, - <a href="#Page_78">78–80</a>;</li> - <li class="hangingindent1">origin and differentiation of phænogamic type, <b>II</b>, - <a href="#Page_83">83</a>;</li> - <li class="i1">physiological problems, <b>II</b>, - <a href="#Page_239">239–43</a>;</li> - <li class="i1">tissue differentiation, <b>II</b>, - <a href="#Page_244">244–6</a>, - <a href="#Page_385">385</a>;</li> - <li class="i1">integration of organic world, <b>II</b>, - <a href="#Page_396">396</a>, - <a href="#Page_406">406</a>;</li> - <li class="i1">race and individual multiplication, <b>II</b>, - <a href="#Page_428">428–30</a>;</li> - <li class="i1">declining fertility and human, <b>II</b>, - <a href="#Page_431">431</a>, - <a href="#Page_529">529–30</a>;</li> - <li class="i1">individuation, genesis, and, <b>II</b>, - <a href="#Page_501">501–5</a>;</li> - <li class="i1">human life, prospective, <b>II</b>, - <a href="#Page_522">522–5</a>;</li> - <li class="i1">forces influencing human, <b>II</b>, - <a href="#Page_525">525–8</a>;</li> - <li class="i1">future of population, <b>II</b>, - <a href="#Page_532">532–7</a>;</li> - <li class="i1">self-sufficingness of, <b>II</b>, - <a href="#Page_537">537</a>;</li> - <li class="i1">vertebral, <b>II</b>, - <a href="#Page_563">563–6</a>.</li> - - <li>Excretion: genesis of organs of, <b>II</b>, - <a href="#Page_303">303</a>;</li> - <li class="i1">localization of, <b>II</b>, - <a href="#Page_331">331–3</a>.</li> - - <li>Exogen, application of term, <b>II</b>, - <a href="#Page_82">82</a>.</li> - <li class="i1">(<i>See</i> <a href="#Dicotyledons">Dicotyledons</a>.)</li> - - <li>Expenditure (<i>see</i> <a href="#Multiplication">Multiplication</a>).</li> - - <li class="hangingindent">Eye, the: molecular transformations in visual process, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page75">75–6</a>;</li> - <li class="hangingindent1">progressive development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page195">195</a>; <b>II</b>, - <a href="#Page_317">317–9</a>;</li> - <li class="i1">waste and repair, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page218">218</a>;</li> - <li class="i1">transmitted defects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page306">306</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page311">311</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page694">694</a>;</li> - <li class="hangingindent1">degeneration in cave-animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page309">309</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page614">614</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page647">647–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">late development in insects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page658">658</a>;</li> - <li class="i1">migration in flat fishes, <b>II</b>, - <a href="#Page_205">205</a>.</li> -</ul> - -<ul> - <li class="hangingindent">Fabre, J. H., nutrition and sex in <i>Osmia tricornis</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page657">657</a>.</li> - - <li>False joints, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page230">230</a>;</li> - <li class="hangingindent1">theories of heredity and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page362">362</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364</a>; <b>II</b>, - <a href="#Page_371">371–2</a>.</li> - - <li class="hangingindent">Fats, the: physical and chemical properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page10">10–12</a>;</li> - <li class="i1">non-nitrogenous, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page41">41</a>;</li> - <li class="i1">action of bile, <b>II</b>, - <a href="#Page_330">330</a>.</li> - - <li>Fatty degeneration, and failing vitality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page41">41</a>.</li> - - <li>Feathers, development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page474">474</a>; <b>II</b>, - <a href="#Page_314">314–6</a>.</li> - - <li>Feet, heredity and size, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page311">311</a>.</li> - - <li class="hangingindent">Ferments, changes and nitrogenous character of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page38">38</a>.</li> - - <li>Ferns: foliar development and nutrition, <b>II</b>, - <a href="#Page_76">76</a>;</li> - <li class="i1">inner tissue differentiation, <b>II</b>, - <a href="#Page_273">273</a>;</li> - <li class="i1">indefiniteness, <b>II</b>, - <a href="#Page_296">296</a>;</li> - <li class="i1">genesis, <b>II</b>, - <a href="#Page_441">441</a>, - <a href="#Page_463">463</a>.</li> - - <li>Fertility, the General Law of Animal, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page577">577–601</a>.</li> - <li class="i1">(<i>See</i> <a href="#Multiplication">Multiplication</a>.)</li> - - <li class="hangingindent" id="Fertilization">Fertilization: unit-life of generative elements, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page185">185–6</a>;</li> - <li class="i1">the function of chromatin, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page260">260</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page263">263–5</a>;</li> - <li class="i1">extrusion of polar bodies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page266">266–8</a>;</li> - <li class="hangingindent1">nature and functions of generative elements, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279–83</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page317">317</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page334">334</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page342">342</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page593">593–7</a>;</li> - <li class="hangingindent1">differentiation and variation effected by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page330">330–2</a>;</li> - <li class="hangingindent1">the essential object of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page340">340–1</a>; <b>II</b>, - <a href="#Page_614">614–6</a>;</li> - <li class="i1">hermaphrodism and self-, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page341">341–2</a>;</li> - <li class="i1">crossing and its effects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page343">343–7</a>;</li> - <li class="i1">isolation of species in respect of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page570">570</a>;</li> - <li class="i1">floral (<i>see</i> <a href="#Flowers">Flowers</a>).</li> - - <li><i>Ficus</i>, foliar structure, <b>II</b>, - <a href="#Page_589">589</a>, - <a href="#Page_596">596</a>.</li> - - <li>Fingers: embryogeny of human, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page169">169</a>;</li> - <li class="i1">heredity and abnormal, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page305">305</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page321">321–3</a>;</li> - <li class="i1">autogenous development of supernumerary, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page363">363</a>;</li> - <li class="i1">rudimentary, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page473">473</a>.</li> - - <li>Fishes: sizes of ova and adult, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page143">143–4</a>;</li> - <li class="i1">growth of pike, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page154">154</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page292">292</a>;</li> - <li class="i1">size and environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page156">156</a>;</li> - <li class="i1">temperature, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page174">174</a>;</li> - <li class="i1">self-mobility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page175">175</a>;</li> - <li class="i1">continuity of blastomeres, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page214">214</a>; <b>II</b>, - <a href="#Page_327">327</a>;</li> - <li class="i1">genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>; <b>II</b>, - <a href="#Page_435">435</a>, - <a href="#Page_436">436</a>;</li> - <li class="hangingindent1">conditions affecting genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page292">292–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page583">583</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page598">598</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page599">599</a>; <b>II</b>, - <a href="#Page_454">454</a>;</li> - <li class="i1">classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page392">392</a>;</li> - <li class="i1">change of media, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page401">401</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page480">480</a>;</li> - <li class="i1">distribution in time, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page408">408–9</a>;</li> - <li class="i1">climbing species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page480">480</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page482">482</a>;</li> - <li class="i1">migrations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page500">500</a>;</li> - <li class="i1">dermal structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page526">526</a>; <b>II</b>, - <a href="#Page_305">305–6</a>, - <a href="#Page_315">315</a>, - <a href="#Page_387">387</a>;</li> - <li class="hangingindent1">Cunningham on non-adaptive specific characters, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page565">565</a>;</li> - <li class="i1">elongation and locomotion, <b>II</b>, - <a href="#Page_15">15</a>;</li> - <li class="i1">segmentation, <b>II</b>, - <a href="#Page_122">122</a>, - <a href="#Page_225">225</a>;</li> - <li class="i1">bilateral symmetry, <b>II</b>, - <a href="#Page_203">203–5</a>;</li> - <li class="i1">eyes of <i>Pleuronectidæ</i>, <b>II</b>, - <a href="#Page_205">205</a>;</li> - <li class="hangingindent1">genesis of vertebrate axis, <b>II</b>, - <a href="#Page_212">212–6</a>, - <a href="#Page_218">218–21</a>, - <a href="#Page_225">225</a>;</li> - <li class="i1">ossification of paleozoic, <b>II</b>, - <a href="#Page_218">218</a>;</li> - <li class="i1">respiratory organs, <b>II</b>, - <a href="#Page_334">334–8</a>;</li> - <li class="i1">activity and muscular colour, <b>II</b>, - <a href="#Page_365">365–9</a>;</li> - <li class="hangingindent1">Owen on skeleton, <b>II</b>, - <a href="#Page_552">552</a>, - <a href="#Page_557">557</a>, - <a href="#Page_558">558–60</a>, - <a href="#Page_562">562</a>, - <a href="#Page_564">564</a>.</li> - - <li>Fission (<i>see</i> <a href="#Agamogenesis">Agamogenesis</a>).</li> - - <li>Flint, Austin, on telegony, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page644">644</a>.</li> - - <li>Flounder, symmetry and eyes, <b>II</b>, - <a href="#Page_205">205</a>.</li> - - <li>Flower, Sir W., on ferret, <b>II</b>, - <a href="#Page_480">480</a>.</li> - - <li id="Flowers">Flowers: pollen propulsion in orchids, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page57">57</a>;</li> - <li class="i1">nature of reproductive elements, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page283">283</a>;</li> - <li class="hangingindent1">insect fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page340">340</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page525">525</a>; <b>II</b>, - <a href="#Page_168">168</a>, - <a href="#Page_174">174</a>, - <a href="#Page_267">267</a>, - <a href="#Page_407">407</a>;</li> - <li class="i1">self- and mutual fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page342">342–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page570">570</a>;</li> - <li class="i1">Darwin on homologies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page472">472</a>;</li> - <li class="hangingindent1">direct equilibration and fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page525">524–5</a>;</li> - <li class="i1">dimorphism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page534">534</a>;</li> - <li class="i1">foliar homology of petals, <b>II</b>, - <a href="#Page_43">43–6</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_132">132</a>, - <a href="#Page_161">161</a>, - <a href="#Page_162">162–4</a>, - <a href="#Page_170">170</a>, - <a href="#Page_174">174</a>, - <a href="#Page_608">608</a>;</li> - <li class="i1">fertilization and symmetry, <b>II</b>, - <a href="#Page_164">164–70</a>;</li> - <li class="i1">clusters and components, <b>II</b>, - <a href="#Page_170">170–4</a>;</li> - <li class="hangingindent1">nutrition and inflorescence, <b>II</b>, - <a href="#Page_179">179–80</a>, - <a href="#Page_541">541–2</a>, - <a href="#Page_546">546–7</a>;</li> - <li class="i1">tissue differentiation, <b>II</b>, - <a href="#Page_265">265–9</a>;</li> - <li class="hangingindent1">separation of ancestral traits in hybrids, <b>II</b>, - <a href="#Page_616">616–7</a>.</li> - - <li>Fly, beneficial parasitism, <b>II</b>, - <a href="#Page_406">406</a>.</li> - - <li>Food (<i>see</i> <a href="#Nutrition">Nutrition</a>).</li> - - <li class="hangingindent">Food-cavity, genesis and development of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page188">188</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page195">195</a>.</li> - - <li><i>Foraminifera</i>: form, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page173">173</a>;</li> - <li class="i1">primary aggregate, <b>II</b>, - <a href="#Page_87">87</a>, - <a href="#Page_124">124</a>;</li> - <li class="i1">progressing integration, <b>II</b>, - <a href="#Page_89">89–90</a>, - <a href="#Page_124">124</a>.</li> - - <li id="Force">Force: action on like and unlike units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page5">5</a>;</li> - <li class="i1">expenditure and organic growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page149">149–54</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page161">161</a>;</li> - <li class="hangingindent1">functional accumulation, transfer, and expenditure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page198">198–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page201">201–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page391">391</a>;</li> - <li class="i1">waste and expenditure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page214">214–5</a>;</li> - <li class="i1">distribution during strain, <b>II</b>, - <a href="#Page_209">209–12</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Energy">Energy</a>, <i>and</i> <a href="#Persistence_of_force">Persistence of Force</a>.)</li> - - <li>Fossils (<i>see</i> <a href="#Palaeontology">Palæontology</a>).</li> - - <li>Foster, Sir M., on storage of glycogen, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page70">70</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page74">74</a>;</li> - <li class="hangingindent1">Increase of weight in hybernating dormouse, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page214">214</a>.</li> - - <li>Fowls (see <a href="#Gallinaceae"><i>Gallinaceæ</i></a>).</li> - - <li class="hangingindent">Foxglove: abnormal development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page287">287</a>; <b>II</b>, - <a href="#Page_46">46</a>;</li> - <li class="i1">floral distribution, <b>II</b>, - <a href="#Page_141">141</a>;</li> - <li class="i1">nutrition and growth, <b>II</b>, - <a href="#Page_179">179</a>.</li> - - <li class="hangingindent">France: surviving disbelief in organic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page559">559</a>;</li> - <li class="i1">rate of multiplication, <b>II</b>, - <a href="#Page_509">509</a>, - <a href="#Page_512">512</a>.</li> - - <li>Frankland, Sir E., on isomerism of protein, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page700">700</a>.</li> - - <li class="hangingindent">Fraser, Col. A. T., on family of Hindu dwarfs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page316">316</a>.</li> - - <li class="hangingindent">Fries, E., multiplication of <i>Reticularia</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page582">582</a>; <b>II</b>, - <a href="#Page_450">450</a>.</li> - - <li>Frog: vitality of detached heart, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page111">111</a>;</li> - <li class="i1">of larval fragments, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page365">365</a>.</li> - - <li>Fry, Sir E., on alternation of generations, <b>II</b>, - <a href="#Page_84">84</a>.</li> - - <li><i>Fuci</i>: cell multiplication, <b>II</b>, - <a href="#Page_27">27</a>;</li> - <li class="i1">undifferentiated outer tissue, <b>II</b>, - <a href="#Page_256">256</a>.</li> - - <li class="hangingindent" id="Function">Function: as a basis of classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page124">124–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page129">129–31</a>;</li> - <li class="hangingindent1">simultaneous progress of structure and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page197">197</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page211">211</a>;</li> - <li class="i1">divisions of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page198">198–200</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page391">391</a>;</li> - <li class="hangingindent1">correlative complexity of structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page200">200</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page210">210–1</a>;</li> - <li class="i1">progressive differentiations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page201">201–4</a>;</li> - <li class="i1">concomitant integration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page205">205–8</a>;</li> - <li class="i1">specialization and vicariousness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page208">208–10</a>;</li> - <li class="i1">formula of evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page211">211</a>;</li> - <li class="i1">diminished ability and overwork, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page215">215–6</a>;</li> - <li class="i1">growth and increased, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page228">228–33</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page234">234–5</a>;</li> - <li class="hangingindent1">interdependence of social and organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page237">237–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page240">240–2</a>;</li> - <li class="hangingindent1">structure and heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page306">306–13</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page318">318–9</a> - (<i>see</i> <a href="#Acquired_characters">Acquired Characters</a>);</li> - <li class="i1">aids natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page308">308</a>;</li> - <li class="i1">organic interdependence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page318">318–9</a>;</li> - <li class="i1">parental condition and variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page324">324</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page326">326</a>;</li> - <li class="i1">variation and altered, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page325">325–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page333">333–4</a>;</li> - <li class="i1">as causing variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page334">334–5</a>;</li> - <li class="hangingindent1">effect on physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page353">353–4</a>; <b>II</b>, - <a href="#Page_620">620</a>;</li> - <li class="i1">zoological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page391">391–3</a>;</li> - <li class="i1">multiplication of effects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page512">512</a>;</li> - <li class="i1">law of equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page519">519–22</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">correlation of changes in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page529">529</a>;</li> - <li class="i1">structural effects of changing, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page541">541–2</a>;</li> - <li class="i1">structural co-operation, <b>II</b>, - <a href="#Page_3">3</a>, - <a href="#Page_217">217</a>;</li> - <li class="i1">vicarious vegetal, <b>II</b>, - <a href="#Page_270">270</a>;</li> - <li class="i1">vicariousness and specialization, <b>II</b>, - <a href="#Page_293">293</a>;</li> - <li class="i1">epidermic structure, <b>II</b>, - <a href="#Page_312">312–4</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">structure and muscular, <b>II</b>, - <a href="#Page_369">369</a>, - <a href="#Page_391">391</a>;</li> - <li class="i1">adaptive bone-structures, <b>II</b>, - <a href="#Page_370">370–1</a>;</li> - <li class="i1">equilibration and adaptation, <b>II</b>, - <a href="#Page_392">392</a>;</li> - <li class="i1">persistence of force and adaptation, <b>II</b>, - <a href="#Page_394">394</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Physiology">Physiology</a>.)</li> - - <li><i>Fungi</i>: nitrogenous character, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page40">40</a>;</li> - <li class="i1">development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page163">163</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page164">164</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>;</li> - <li class="i1">conjugation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279</a>; <b>II</b>, - <a href="#Page_449">449</a>;</li> - <li class="i1">fission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page584">584</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page585">585</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_24">24–5</a>, - <a href="#Page_293">293</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_137">137–40</a>, - <a href="#Page_146">146</a>;</li> - <li class="i1">puff-ball tissue, <b>II</b>, - <a href="#Page_246">246</a>, - <a href="#Page_252">252</a>, - <a href="#Page_386">386</a>;</li> - <li class="i1">tissue differentiation, <b>II</b>, - <a href="#Page_256">256</a>;</li> - <li class="i1">inner tissue, <b>II</b>, - <a href="#Page_279">279</a>;</li> - <li class="i1">indefiniteness, <b>II</b>, - <a href="#Page_295">295</a>;</li> - <li class="i1">growth and genesis, <b>II</b>, - <a href="#Page_459">459</a>;</li> - <li class="i1">nutrition and genesis, <b>II</b>, - <a href="#Page_487">487</a>.</li> -</ul> - -<ul> - <li class="hangingindent" id="Gallinaceae"><i>Gallinaceæ</i>: conditions affecting fertility, <b>II</b>, - <a href="#Page_454">454–5</a>, - <a href="#Page_469">469</a>, - <a href="#Page_471">471</a>;</li> - <li class="i1">masculine traits of old hens, <b>II</b>, - <a href="#Page_495">495</a>.</li> - - <li>Galls: definition of life and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page111">111</a>;</li> - <li class="i1">Hertwig on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page690">690</a>.</li> - - <li>Galton, F., on variation outside the mean, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page669">669</a>.</li> - - <li id="Gamogenesis">Gamogenesis: homogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page270">270</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page336">336</a>;</li> - <li class="i1">heterogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page270">270</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page336">336</a>;</li> - <li class="i1">independence of offspring, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page278">278</a>;</li> - <li class="i1">reproductive tissue, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279–84</a>;</li> - <li class="i1">vegetal nutrition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page285">285–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page293">293</a>; <b>II</b>, - <a href="#Page_39">39</a>;</li> - <li class="i1">animal nutrition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page289">289–94</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page297">297</a>;</li> - <li class="i1">when and why does it recur? <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page294">294–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page336">336–40</a>;</li> - <li class="i1">effect on species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page347">347–9</a>;</li> - <li class="i1">leaf formation, <b>II</b>, - <a href="#Page_39">39</a>;</li> - <li class="i1">alternating generation in liverworts, <b>II</b>, - <a href="#Page_80">80–4</a>;</li> - <li class="i1">molluscan homogenesis, <b>II</b>, - <a href="#Page_116">116</a>, - <a href="#Page_117">117–8</a>;</li> - <li class="i1">vertebrate, <b>II</b>, - <a href="#Page_118">118</a>;</li> - <li class="i1">growth, <b>II</b>, - <a href="#Page_266">266</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Fertilization">Fertilization</a>, <i>and</i> <a href="#Multiplication">Multiplication</a>.)</li> - - <li><i>Gasteropoda</i> (see <a href="#Mollusca"><i>Mollusca</i></a>).</li> - - <li class="hangingindent">Geddes and Thompson, on the determination of sex, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page657">657</a>.</li> - - <li>Gelatine, nutritive value of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page77">77</a>.</li> - - <li id="Gemmation">Gemmation: and genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page272">272–6</a>;</li> - <li class="i1">theories of heredity and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page361">361</a>;</li> - <li class="i1">annulose, <b>II</b>, - <a href="#Page_100">100–5</a>, - <a href="#Page_106">106</a>.</li> - - <li>Generalization, impossibility of perfect, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page450">450</a>.</li> - - <li>Generation, and genesis: the words, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page269">269</a>.</li> - - <li>Genesis (<i>see</i> <a href="#Multiplication">Multiplication</a>).</li> - - <li><i>Gentiana</i>: floral arrangement, <b>II</b>, - <a href="#Page_608">608–11</a>.</li> - - <li>Genus: indefinite value, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page389">389</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page446">446</a>;</li> - <li class="hangingindent1">instability of homogeneous and heterogeneity of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page509">509–11</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page515">515</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page517">517–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page550">550</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>.</li> - - <li>Geology: growth displayed in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page135">135</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page136">136</a>;</li> - <li class="i1">distribution in time, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page404">404–11</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page412">412</a>;</li> - <li class="i1">special creation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page419">419</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page426">426</a>;</li> - <li class="i1">evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page432">432</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page437">437</a>;</li> - <li class="i1">record congruous with evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page485">485–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="hangingindent1">organic influence of changes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page501">501–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page549">549</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page550">550</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">climatic influence of changes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page503">503</a>;</li> - <li class="i1">time required for organic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page555">565–6</a>;</li> - <li class="i1">rise of insect and plant relations, <b>II</b>, - <a href="#Page_407">407</a>;</li> - <li class="i1">human evolution and changes, <b>II</b>, - <a href="#Page_534">534</a>.</li> - - <li>Geometry, evolution illustrated by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page433">433–4</a>.</li> - - <li>Germ-cell: unspecialized nature, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279–83</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page317">317</a>;</li> - <li class="i1">dissimilarity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page330">330</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page332">332</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page334">334</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page342">342</a>;</li> - <li class="i1">equilibrium, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page340">340</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Fertilization">Fertilization</a>.)</li> - - <li id="Germ_plasm">Germ-plasm, Weismann’s theory of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page357">357–8</a>;</li> - <li class="i1">inconsistent with plant embryogeny, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page359">359</a>;</li> - <li class="i1">regeneration of lost limbs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page362">362</a>;</li> - <li class="hangingindent1">variations in peacock’s tail feather, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page372">372</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page695">695</a>; <b>II</b>, - <a href="#Page_618">618–9</a>;</li> - <li class="hangingindent1">alleged differentiation of reproductive and somatic cells, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page622">622</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page628">628–30</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page633">633–44</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646</a>;</li> - <li class="hangingindent1">origin of variations in neuter insects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page659">659</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page663">663–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page671">671</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>;</li> - <li class="i1">correlated variations in stag, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page677">677</a>;</li> - <li class="i1">insuperable difficulties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page682">682</a>;</li> - <li class="hangingindent1">conceivability of hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page695">695</a>; <b>II</b>, - <a href="#Page_619">619</a>;</li> - <li class="hangingindent1">correlated variations in cultivated plants, <b>II</b>, - <a href="#Page_621">621–2</a>.</li> - - <li>Ghost-theory, Vitalism and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page114">114</a>.</li> - - <li>Giraffe, co-adaptation of structures, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page615">615</a>.</li> - - <li>Gizzard, development of birds, <b>II</b>, - <a href="#Page_320">320</a>.</li> - - <li>Glass, molecular re-arrangement, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page337">337</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page352">352</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page704">704</a>.</li> - - <li>Glove, strain analogy, <b>II</b>, - <a href="#Page_575">575</a>.</li> - - <li>Glycogen, In animal metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page70">70</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page72">72</a>.</li> - - <li class="hangingindent">Goethe, J. W. von: foliar homology, <b>II</b>, - <a href="#Page_43">43–4</a>, - <a href="#Page_543">543</a>, - <a href="#Page_544">544</a>;</li> - <li class="i1">archetypal hypothesis, <b>II</b>, - <a href="#Page_122">122</a>;</li> - <li class="i1">vegetal fructification and nutrition, <b>II</b>, - <a href="#Page_180">180</a>;</li> - <li class="i1">theory of supernumerary bones, <b>II</b>, - <a href="#Page_223">223</a>;</li> - <li class="i1">on the skull, <b>II</b>, - <a href="#Page_561">561</a>.</li> - - <li>Gold, effect of bismuth on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page121">121</a>.</li> - - <li>Gorilla, callosities, <b>II</b>, - <a href="#Page_312">312</a>.</li> - - <li>Gould, J., <i>Birds of Australia</i>, <b>II</b>, - <a href="#Page_469">469</a>.</li> - - <li>Gout (<i>see</i> <a href="#Disease">Disease</a>).</li> - - <li class="hangingindent">Grafting, Born’s experiments with frog larvæ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page365">365</a>.</li> - - <li class="hangingindent">Graham, T., properties of water, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>; <b>II</b>, - <a href="#Page_359">359</a>;</li> - <li class="hangingindent1">colloids and crystalloids, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page15">15–8</a>; <b>II</b>, - <a href="#Page_356">356</a>;</li> - <li class="i1">their diffusibility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page18">18–20</a>;</li> - <li class="i1">sapid and insipid substances, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page53">53</a>.</li> - - <li><i>Graminæ</i>: foliar surfaces, <b>II</b>, - <a href="#Page_61">61</a>, - <a href="#Page_263">263</a>;</li> - <li class="i1">floral symmetry, <b>II</b>, - <a href="#Page_165">165</a>;</li> - <li class="i1">physiological differentiation, <b>II</b>, - <a href="#Page_257">257</a>.</li> - - <li class="hangingindent">Graminivores, food contrasted with that of carnivores, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page68">68</a>.</li> - - <li>Grassi, on food habits of <i>Termites</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page686">686</a>.</li> - - <li>Gravity: its ultimate incomprehensibility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page121">121</a>;</li> - <li class="i1">vegetal circulation, <b>II</b>, - <a href="#Page_586">586</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Specific_Gravity">Specific Gravity</a>.)</li> - - <li><i>Gregarina</i>: central development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page163">163</a>;</li> - <li class="i1">primary aggregate, <b>II</b>, - <a href="#Page_87">87</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_186">186</a>.</li> - - <li>Grimaux, on artificial proteids, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page39">39</a>.</li> - - <li id="Growth">Growth: organic and inorganic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page135">135–7</a>;</li> - <li class="i1">simulation of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page136">136</a>;</li> - <li class="i1">limits to, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page137">137</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page155">155–7</a>;</li> - <li class="i1">structural complexity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page138">138–40</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page145">145–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page161">161</a>;</li> - <li class="i1">nutrition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page140">140</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page147">147–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page161">161</a>;</li> - <li class="i1">expenditure of energy, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page141">141–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page161">161</a>;</li> - <li class="i1">initial and final bulks, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page143">143–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page157">157–60</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page161">161</a>;</li> - <li class="i1">final arrest of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page149">149–55</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page639">639</a>;</li> - <li class="i1">where unceasing, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page154">154</a>;</li> - <li class="i1"><i>résumé</i> with generalizations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page161">161</a>;</li> - <li class="i1">defined, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page162">162</a>; <b>II</b>, - <a href="#Page_461">461</a>;</li> - <li class="i1">increased function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page228">228–33</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page234">234–5</a>;</li> - <li class="i1">functional interdependence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page235">235–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page240">240</a>;</li> - <li class="hangingindent1">nutrition and vegetal, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page293">293</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page294">294–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page336">336</a>; <b>II</b>, - <a href="#Page_39">39</a>;</li> - <li class="hangingindent1">heterogenesis and animal nutrition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page289">289–93</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page296">296</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page336">336</a>;</li> - <li class="hangingindent1">homo- and heterogenesis and natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page294">294–8</a>;</li> - <li class="i1">of acrogens, <b>II</b>, - <a href="#Page_56">56</a>;</li> - <li class="i1">cylindrical form of vegetal, <b>II</b>, - <a href="#Page_56">56–64</a>;</li> - <li class="i1">endogenous, <b>II</b>, - <a href="#Page_60">60–2</a>, - <a href="#Page_78">78</a>;</li> - <li class="i1">exogenous, <b>II</b>, - <a href="#Page_63">63–4</a>, - <a href="#Page_78">78</a>;</li> - <li class="i1">plant differentiation, <b>II</b>, - <a href="#Page_129">129–131</a>;</li> - <li class="i1">tissue differentiation, <b>II</b>, - <a href="#Page_370">370</a>;</li> - <li class="hangingindent1">formation of adaptive bone-structures, <b>II</b>, - <a href="#Page_370">370–2</a>;</li> - <li class="hangingindent1">progressive increase of size with evolution, <b>II</b>, - <a href="#Page_401">401–2</a>;</li> - <li class="i1">vegetal, and asexual genesis, <b>II</b>, - <a href="#Page_439">439–42</a>;</li> - <li class="i1">animal, and asexual genesis, <b>II</b>, - <a href="#Page_442">442–5</a>;</li> - <li class="i1">antagonistic to asexual genesis, <b>II</b>, - <a href="#Page_446">446</a>;</li> - <li class="i1">vegetal and sexual genesis, <b>II</b>, - <a href="#Page_448">448–51</a>;</li> - <li class="i1">animal and sexual genesis, <b>II</b>, - <a href="#Page_452">452–6</a>, - <a href="#Page_495">495</a>;</li> - <li class="i1">antagonistic to sexual genesis, <b>II</b>, - <a href="#Page_457">457–8</a>;</li> - <li class="i1">nutrition and genesis, <i>résumé</i>, <b>II</b>, - <a href="#Page_497">497–9</a>;</li> - <li class="i1">evolution and, <b>II</b>, - <a href="#Page_501">501–5</a>;</li> - <li class="i1">commencement of genesis, <b>II</b>, - <a href="#Page_506">506</a>;</li> - <li class="hangingindent1">fertilization and restoration of growth-energy, <b>II</b>, - <a href="#Page_613">613</a>.</li> - - <li class="hangingindent">Gulick, T.: on monotypic and polytypic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page569">569</a>;</li> - <li class="i1">physiological selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page569">569–71</a>.</li> - - <li>Gunpowder, nitrogenous instability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page8">8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page43">43</a>.</li> - - <li><i>Gymnotus</i>, electricity of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page51">51</a>.</li> - - <li class="hangingindent"><i>Gyrodactylus elegans</i>, rapid succession of generations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page641">641</a>; <b>II</b>, - <a href="#Page_488">488</a>.</li> -</ul> - -<ul> - <li>Habit, change of, in plants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page308">308</a>.</li> - - <li>Hæmal, term applied to female element, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page594">594–5</a>.</li> - - <li>Hairs: non-conductors of heat, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page526">526</a>;</li> - <li class="i1">vegetal, and natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page532">532</a>;</li> - <li class="i1">development, <b>II</b>, - <a href="#Page_314">314–6</a>;</li> - <li class="i1">tactual organs, <b>II</b>, - <a href="#Page_317">317</a>.</li> - - <li>Hand: embryogeny, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page169">169</a>;</li> - <li class="i1">heredity and size of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page311">311</a>;</li> - <li class="i1">distribution of veins, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364</a>.</li> - - <li>Hardy, W. B., <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#pagevii">vii</a>; <b>II</b>, - <a href="#Page_vi">vi</a>.</li> - - <li>Hare: activity and muscular colour, <b>II</b>, - <a href="#Page_365">365</a>;</li> - <li class="i1">expenditure and genesis, <b>II</b>, - <a href="#Page_472">472</a>.</li> - - <li>Hart, J. A., on “Parasol” ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page687">687–8</a>.</li> - - <li>Havilland, G. D., collection of Termites, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page687">687</a>.</li> - - <li>Haystack, chemical action in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page74">74</a>.</li> - - <li>Head, structural influence of size, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page512">512</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page537">537</a>.</li> - - <li>Hearing: the sense of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page54">54</a>;</li> - <li class="i1">multiplying agencies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page75">75</a>.</li> - - <li>Heart (<i>see</i> <a href="#Vascular_System">Vascular System</a>).</li> - - <li class="hangingindent" id="Heat">Heat: action on di- and tri-atomic compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page7">7–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page10">10–12</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page23">23</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page24">24</a>;</li> - <li class="i1">on colloids and crystalloids, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page26">26</a>;</li> - <li class="i1">organic changes from evaporation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page29">29</a>;</li> - <li class="i1">chemical decomposition by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page33">33</a>;</li> - <li class="i1">organic oxidation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page46">46–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page60">60</a>;</li> - <li class="i1">growth and organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page152">152–3</a>;</li> - <li class="i1">animal, vegetal, and environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page174">174–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page177">177</a>;</li> - <li class="i1">alloy melting points, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page339">339</a>;</li> - <li class="hangingindent1">organic effects of rhythm in terrestrial, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page498">498</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">effect on physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page705">705</a>;</li> - <li class="i1">respiration in fishes, <b>II</b>, - <a href="#Page_337">337</a>;</li> - <li class="i1">animal preservation, <b>II</b>, - <a href="#Page_434">434</a>;</li> - <li class="hangingindent1">vertebrate expenditure and genesis, <b>II</b>, - <a href="#Page_468">468–9</a>, - <a href="#Page_474">474</a>;</li> - <li class="i1">insect genesis, <b>II</b>, - <a href="#Page_476">476</a>;</li> - <li class="i1">seasonal variations and genesis, <b>II</b>, - <a href="#Page_484">484–5</a>;</li> - <li class="i1">in germination, <b>II</b>, - <a href="#Page_615">615</a>.</li> - - <li>Hebrew idea of creation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page421">421</a>.</li> - - <li><i>Hectocotylus</i>, individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page250">250</a>.</li> - - <li>Hellin, D., on multiparity and twin-births, <b>II</b>, - <a href="#Page_457">457</a>.</li> - - <li class="hangingindent">Hen, what prompts her to pick up egg-shell fragments? <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page120">120</a>.</li> - - <li class="hangingindent">Henslow, Rev. G., inheritance of functionally-produced changes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page560">560</a>.</li> - - <li id="Hepaticae"><i>Hepaticæ</i>: Schleiden on, <b>II</b>, - <a href="#Page_51">51</a>, - <a href="#Page_52">52</a>;</li> - <li class="i1">continuous and discontinuous development, <b>II</b>, - <a href="#Page_52">52</a>;</li> - <li class="i1">phyletic homologies, <b>II</b>, - <a href="#Page_80">80–4</a>;</li> - <li class="hangingindent1">meaning of so-called alternating generation, <b>II</b>, - <a href="#Page_84">84</a>;</li> - <li class="i1">vascular system, <b>II</b>, - <a href="#Page_280">280</a>;</li> - <li class="i1">genesis and development, <b>II</b>, - <a href="#Page_463">463</a>.</li> - - <li>Heredity: structural modification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page232">232</a>;</li> - <li class="i1">function of cell-nucleus in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page258">258–59</a>;</li> - <li class="i1">general truths, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page301">301–4</a>;</li> - <li class="hangingindent1">transmission of congenital peculiarities, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page304">304–7</a>;</li> - <li class="hangingindent1">structure and altered function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page307">307–13</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page318">318–9</a> - (<i>see also</i> <a href="#Acquired_characters">Acquired Characters</a>);</li> - <li class="hangingindent1">atavism, or recurrence of ancestral traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314</a>;</li> - <li class="i1">sex limitation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314–6</a>;</li> - <li class="hangingindent1">physiological units, <i>résumé</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page350">350–5</a>; <b>II</b>, - <a href="#Page_612">612–6</a>;</li> - <li class="hangingindent1">Darwin’s and Weismann’s theories examined, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page356">356</a> <i>et seq.</i>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page559">559–61</a>; <b>II</b>, - <a href="#Page_622">622</a>;</li> - <li class="i1">true theory must include plants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page358">358</a>;</li> - <li class="hangingindent1">inadequacy of theory of physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page360">360–1</a>;</li> - <li class="i1">sociological parallel, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page366">366–8</a>;</li> - <li class="i1">natural selection (<i>q. v.</i>), <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page545">545–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">ethnology and natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>;</li> - <li class="i1">unsolved problems, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page573">573–4</a>;</li> - <li class="i1">mutilations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page631">631</a>;</li> - <li class="i1">ultimate process incomprehensible, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page695">695</a>;</li> - <li class="i1">cell-doctrine, <b>II</b>, - <a href="#Page_19">19</a>;</li> - <li class="i1">physiological development, <b>II</b>, - <a href="#Page_242">242</a>;</li> - <li class="i1">wood formation, <b>II</b>, - <a href="#Page_287">287</a>;</li> - <li class="i1">tissue differentiation, <b>II</b>, - <a href="#Page_304">304</a>, - <a href="#Page_312">312–4</a>;</li> - <li class="i1">respiratory system, <b>II</b>, - <a href="#Page_311">311</a>;</li> - <li class="i1">osseous differentiation, <b>II</b>, - <a href="#Page_351">351</a>;</li> - <li class="i1">muscular adaptation, <b>II</b>, - <a href="#Page_367">367</a>;</li> - <li class="hangingindent1">persistence of force and physiological adaptation, <b>II</b>, - <a href="#Page_394">394</a>;</li> - <li class="i1">vegetal vascular system, <b>II</b>, - <a href="#Page_574">574</a>, - <a href="#Page_582">582</a>, - <a href="#Page_588">588</a>, - <a href="#Page_596">596</a>.</li> - - <li>Hermaphrodism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page340">340–3</a>.</li> - - <li class="hangingindent">Hertwig, O.: on Weismann’s germ-plasm theory, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page690">690</a>;</li> - <li class="i1">cell characters, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page691">691</a>;</li> - <li class="i1">meaning of fertilization, <b>II</b>, - <a href="#Page_613">613</a>.</li> - - <li>Hertwig, R., classification of tissues, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page189">189</a>.</li> - - <li>Heterochrony of development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page655">655</a>.</li> - - <li>Heterogeneity: in chemical evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page23">23–4</a>;</li> - <li class="i1">of vital changes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page84">84–90</a>;</li> - <li class="i1">of development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page170">170</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page178">178</a>;</li> - <li class="i1">functional, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page204">204–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page211">211–2</a>;</li> - <li class="i1">of organic matter, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page350">350–5</a>;</li> - <li class="hangingindent1">organic and instability of homogeneous, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page509">509–11</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page517">517</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page549">549</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">segregation accompanying, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page514">514–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page517">517–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page550">550</a>.</li> - - <li>Heterogenesis: occurrence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page270">270</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page272">272–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page336">336</a>;</li> - <li class="i1">animal nutrition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page289">289–91</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295–7</a>;</li> - <li class="i1">natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295–8</a>;</li> - <li class="i1">heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page301">301</a>.</li> - - <li>Hindus: food, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page68">68</a>;</li> - <li class="i1">dwarf family, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page316">316</a>.</li> - - <li>Histology (<i>see</i> <a href="#Physiology">Physiology</a>).</li> - - <li class="hangingindent">Hofmeister, sporophytic generation of Archegoniates, <b>II</b>, - <a href="#Page_80">80</a>.</li> - - <li>Hollyhock, floral symmetry, <b>II</b>, - <a href="#Page_167">167</a>, - <a href="#Page_169">169</a>, - <a href="#Page_170">170</a>.</li> - - <li class="hangingindent">Homogeneous, instability of the: variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page330">330</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page334">334</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page342">342</a>;</li> - <li class="i1">evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page509">509–11</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page517">517</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page549">549</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">morphological development, <b>II</b>, - <a href="#Page_7">7–9</a>, - <a href="#Page_234">234</a>;</li> - <li class="i1">direction of vegetal growth, <b>II</b>, - <a href="#Page_181">181</a>;</li> - <li class="i1">radial symmetry, <b>II</b>, - <a href="#Page_190">190</a>;</li> - <li class="i1">physiological differentiation, <b>II</b>, - <a href="#Page_384">384</a>, - <a href="#Page_392">392</a>.</li> - - <li>Homogenesis (<i>see</i> <a href="#Gamogenesis">Gamogenesis</a>).</li> - - <li>Homology, simulation of, by analogy, <b>II</b>, - <a href="#Page_14">14</a>.</li> - - <li>Hooker, Sir J. D., <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#pageix">ix</a>;</li> - <li class="i1">European plants in New Zealand, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page477">477</a>;</li> - <li class="i1">plant distribution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page479">479</a>;</li> - <li class="i1">adaptation of plants to varied media, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page484">484</a>;</li> - <li class="i1">plant growth, <b>II</b>, - <a href="#Page_56">56</a>;</li> - <li class="i1"><i>Balanophoræ</i> and <i>Raffiesiaceæ</i>, <b>II</b>, - <a href="#Page_274">274</a>;</li> - <li class="i1">structural complexity, <b>II</b>, - <a href="#Page_295">295</a>, - <a href="#Page_297">297</a>;</li> - <li class="hangingindent1">relative antiquity and distribution of plants and animals, <b>II</b>, - <a href="#Page_297">297</a>;</li> - <li class="i1">bean vascular system, <b>II</b>, - <a href="#Page_574">574</a>.</li> - - <li class="hangingindent">Hooker, Sir W., on fructification in <i>Jungermanniaceæ</i>, <b>II</b>, - <a href="#Page_52">52</a>.</li> - - <li class="hangingindent">Horns, natural selection and correlated variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page537">537</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page567">567</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page674">674</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page677">677</a>.</li> - - <li>Horse: ancestral types, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page409">409</a>;</li> - <li class="i1">fertility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page598">598</a>;</li> - <li class="i1">weight of brain, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page599">599</a>;</li> - <li class="i1">quagga markings, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page624">624</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page627">627</a>.</li> - - <li>Husbandry, co-ordination of actions in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page96">96</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page579">579</a>.</li> - - <li>Hutchinson, Sir J., hereditary syphilis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page623">623</a>.</li> - - <li>Huxley, T. H., <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#pageix">ix</a>;</li> - <li class="hangingindent1">“continuous” and “discontinuous” development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page164">164</a>;</li> - <li class="i1">classification of development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page276">276</a>;</li> - <li class="i1">hermaphrodism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page344">344</a>;</li> - <li class="i1">zoological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page383">383</a>;</li> - <li class="i1">on “Persistent Types,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page408">408–9</a>;</li> - <li class="i1">ancestral equine types, <i>ib.</i>;</li> - <li class="hangingindent1">segmentation of articulates, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page468">468–9</a>; <b>II</b>, - <a href="#Page_113">113</a>;</li> - <li class="hangingindent1">agamic multiplication of <i>Aphis</i> and <i>Entozoa</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page640">640–1</a>; <b>II</b>, - <a href="#Page_476">476</a>;</li> - <li class="i1">cell-doctrine, <b>II</b>, - <a href="#Page_21">21</a>;</li> - <li class="i1">vertebrate embryo, <b>II</b>, - <a href="#Page_119">119</a>, - <a href="#Page_120">120</a>;</li> - <li class="i1">molluscan symmetry, <b>II</b>, - <a href="#Page_202">202</a>;</li> - <li class="i1">tegumentary organs, <b>II</b>, - <a href="#Page_314">314</a>, - <a href="#Page_315">315</a>;</li> - <li class="i1">vertebrate sensory organs, <b>II</b>, - <a href="#Page_318">318</a>, - <a href="#Page_319">319</a>;</li> - <li class="i1"><i>Chondracanthus</i>, <b>II</b>, - <a href="#Page_487">487</a>;</li> - <li class="i1">Owen’s vertebrate theory, <b>II</b>, - <a href="#Page_563">563</a>.</li> - - <li>Hyacinth: lateral spike, <b>II</b>, - <a href="#Page_42">42</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_141">141</a>, - <a href="#Page_162">162</a>.</li> - - <li>Hybernation, waste and repair in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page214">214–5</a>.</li> - - <li class="hangingindent">Hybrids, separation of ancestral traits in, <b>II</b>, - <a href="#Page_616">616–7</a>.</li> - - <li>Hydro-carbons: properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page6">6–9</a>;</li> - <li class="i1">the term carbo-hydrates (<i>q. v.</i>), <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page10">10</a>.</li> - - <li>Hydrochloric acid, in gastric juice, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>.</li> - - <li>Hydrogen: chemical and physical properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page3">3–5</a>;</li> - <li class="i1">compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page6">6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page8">8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page10">10–12</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page12">12–13</a>.</li> - - <li><i>Hydrozoa</i> (see <a href="#Coelenterata"><i>Cœlenterata</i></a>).</li> - - <li><i>Hymenoptera</i> (<i>see</i> <a href="#Insects">Insects</a>).</li> - - <li>Hypertrophy (<i>see</i> <a href="#Disease">Disease</a>).</li> - - <li>Hypospadias, telegonic transmission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646</a>.</li> - - <li class="hangingindent">Hypostasis of a relation, exemplified in explanations of fertilization, <b>II</b>, - <a href="#Page_613">613</a>.</li> -</ul> - -<ul> - <li>Ideas (<i>see</i> <a href="#Psychology">Psychology</a>).</li> - - <li>Individuality: the botanical, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page244">244–6</a>;</li> - <li class="i1">the zoological, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page246">246–7</a>;</li> - <li class="i1">the fertilized germ product, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page248">248–9</a>;</li> - <li class="i1">definition of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page250">250</a>.</li> - - <li class="hangingindent">Individuation: and genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page583">583–4</a>; <b>II</b>, - <a href="#Page_428">428–30</a>, - <a href="#Page_499">499</a>;</li> - <li class="i1">total cost, <b>II</b>, - <a href="#Page_435">435–7</a>;</li> - <li class="i1">genesis and evolution, <b>II</b>, - <a href="#Page_501">501–5</a>, - <a href="#Page_529">529</a>, - <a href="#Page_530">530</a>.</li> - - <li><i>Infusoria</i>: functional specialization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page391">391</a>;</li> - <li class="i1">primary aggregate, <b>II</b>, - <a href="#Page_87">87</a>;</li> - <li class="i1">asymmetry, <b>II</b>, - <a href="#Page_187">187</a>, - <a href="#Page_188">188</a>;</li> - <li class="i1">differentiation, <b>II</b>, - <a href="#Page_299">299</a>, - <a href="#Page_385">385</a>;</li> - <li class="i1">genesis, <b>II</b>, - <a href="#Page_442">442</a>, - <a href="#Page_446">446</a>, - <a href="#Page_452">452</a>.</li> - - <li class="hangingindent">Injuries, repair of animal, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page219">219</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page222">222–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page316">316</a>; <b>II</b>, - <a href="#Page_102">102</a>, - <a href="#Page_611">611</a>.</li> - - <li>Insanity, inherited, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314</a>.</li> - - <li id="Insects">Insects: temperature, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page47">47</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page174">174</a>;</li> - <li class="i1">phosphorescence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page49">49</a>;</li> - <li class="i1">self-mobility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page175">175</a>;</li> - <li class="i1">parthenogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page274">274–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page277">277</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page294">294</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page592">592</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page640">640</a>;</li> - <li class="i1">growth and reproduction, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page292">292</a>;</li> - <li class="hangingindent1">species distribution determined by presence of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page396">396–7</a>;</li> - <li class="hangingindent1">eyes of cave-inhabiting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page309">309</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page614">614</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page647">647–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">persistent types, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page408">408</a>;</li> - <li class="i1">retrograde development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page458">458</a>;</li> - <li class="i1">segmentation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page468">468–9</a>; <b>II</b>, - <a href="#Page_114">114</a>;</li> - <li class="i1">aborted organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page474">474</a>;</li> - <li class="i1">East Indian distribution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page478">478</a>;</li> - <li class="hangingindent1">floral fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page525">525</a>; <b>II</b>, - <a href="#Page_168">168–9</a>, - <a href="#Page_406">406–7</a>, - <a href="#Page_608">608</a>;</li> - <li class="i1">appliances for cleaning antennæ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page651">651</a>;</li> - <li class="i1">eyes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page658">658</a>; <b>II</b>, - <a href="#Page_318">318</a>;</li> - <li class="i1">integration and homology, <b>II</b>, - <a href="#Page_111">111–3</a>, - <a href="#Page_121">121</a>;</li> - <li class="i1">bilateral symmetry, <b>II</b>, - <a href="#Page_198">198</a>;</li> - <li class="i1">sexual selection, <b>II</b>, - <a href="#Page_269">269</a>;</li> - <li class="i1">eyes, <b>II</b>, - <a href="#Page_318">318</a>;</li> - <li class="i1">environment, <b>II</b>, - <a href="#Page_433">433</a>;</li> - <li class="i1">cost of genesis, <b>II</b>, - <a href="#Page_436">436</a>, - <a href="#Page_437">437</a>;</li> - <li class="i1">development and genesis, <b>II</b>, - <a href="#Page_461">461</a>;</li> - <li class="i1">nutrition and genesis, <b>II</b>, - <a href="#Page_476">476</a>, - <a href="#Page_490">490–2</a>.</li> - - <li class="hangingindent">Insects, Social, origin of caste gradations in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page654">654–65</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page674">674</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page678">678–84</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page686">686–8</a>.</li> - - <li>Instability of the homogeneous (<i>see</i> Homogeneous).</li> - - <li class="hangingindent">Instinct: organic evolution and co-ordination of, in mason-wasp, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page574">574</a>;</li> - <li class="i1">a vital attribute, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page578">578</a>;</li> - <li class="hangingindent1">loss of self-feeding, in Amazon ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660–1</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page663">663–4</a>.</li> - - <li>Integration: in chemical evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page23">23</a>;</li> - <li class="i1">morphological composition, <b>II</b>, - <a href="#Page_4">4–6</a>;</li> - <li class="i1">arthropod, <b>II</b>, - <a href="#Page_111">111–4</a>, - <a href="#Page_121">121</a>;</li> - <li class="i1">physiological, in plants, <b>II</b>, - <a href="#Page_292">292–5</a>, - <a href="#Page_295">295–8</a>, - <a href="#Page_390">390</a>;</li> - <li class="i1">of organic world, <b>II</b>, - <a href="#Page_396">396–408</a>;</li> - <li class="i1">genesis, <b>II</b>, - <a href="#Page_424">424</a>, - <a href="#Page_426">426–9</a>.</li> - - <li>Intelligence, a vital attribute, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page579">579</a>.</li> - - <li>Internodes: varied development, <b>II</b>, - <a href="#Page_45">45</a>;</li> - <li class="i1">nutrition and length, <b>II</b>, - <a href="#Page_178">178–9</a>.</li> - - <li>Intestine (<i>see</i> <a href="#Alimentary_canal">Alimentary Canal</a>).</li> - - <li>Intra-selection, Roux’s theory of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page562">562</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676–8</a>.</li> - - <li>Irish, nutrition and genesis, <b>II</b>, - <a href="#Page_510">510</a>.</li> - - <li>Iron: colloidal form of peroxide, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page17">17</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page20">20</a>;</li> - <li class="i1">molecular re-arrangement, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page337">337</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page704">704</a>;</li> - <li class="i1">vegetal absorption, <b>II</b>, - <a href="#Page_573">573</a>.</li> - - <li class="hangingindent">Iron industry, interdependence of social function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page237">237–41</a>.</li> - - <li>Isolation, and species differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page568">568–9</a>.</li> - - <li>Isomerism: of organic constituents, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page4">4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page25">25</a>;</li> - <li class="i1">tri- and poly-atomic compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page11">11</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page13">13</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page25">25</a>;</li> - <li class="i1">muscular action, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page59">59</a>;</li> - <li class="i1">organic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page700">700</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page703">703</a>;</li> - <li class="i1">differentiation of nerve tissue, <b>II</b>, - <a href="#Page_356">356–60</a>, - <a href="#Page_361">361</a>;</li> - <li class="i1">of muscular tissue, <b>II</b>, - <a href="#Page_361">361–4</a>.</li> -</ul> - -<ul> - <li class="hangingindent">Jackson, J. Hughlings, on inheritance of nervous peculiarities, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page313">313</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page694">694</a>.</li> - - <li>Jaundice (<i>see</i> <a href="#Disease">Disease</a>).</li> - - <li>Jaws, of uncivilized and civilized, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page541">541–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>.</li> - - <li>Johnson, G. Lindsey, on inherited myopia, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page694">694</a>.</li> - - <li>Jones, T. Rymer, on fission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page585">585</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page590">590</a>.</li> - - <li class="hangingindent">Julin, C., on “castration parasitaire” in Crustaceans, <b>II</b>, - <a href="#Page_493">493–6</a>.</li> - - <li><i>Jungermanniaceæ</i>: morphology, <b>II</b>, - <a href="#Page_33">33–4</a>;</li> - <li class="i1">relations of high and low types, <b>II</b>, - <a href="#Page_35">35</a>, - <a href="#Page_55">55</a>;</li> - <li class="hangingindent1">continuous and discontinuous development, <b>II</b>, - <a href="#Page_52">52–5</a>, - <a href="#Page_92">92</a>;</li> - <li class="i1">tubular structure, <b>II</b>, - <a href="#Page_58">58</a>, - <a href="#Page_62">62</a>;</li> - <li class="i1">proliferous growth, <b>II</b>, - <a href="#Page_67">67</a>, - <a href="#Page_91">91</a>;</li> - <li class="i1">colour, <b>II</b>, - <a href="#Page_75">75</a>, - <a href="#Page_265">265</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_140">140</a>;</li> - <li class="i1">fertility and growth, <b>II</b>, - <a href="#Page_441">441</a>.</li> - - <li>Jussieu, A. de, plant classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page378">378</a>.</li> -</ul> - -<ul> - <li id="Karyokinesis">Karyokinesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page257">257</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page259">259</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page263">263–5</a>.</li> - - <li>Kerner, A., on cauline buds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page358">358</a>;</li> - <li class="hangingindent1">plant classification in <i>Natural History of Plants</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page378">378–9</a>.</li> - - <li>Kidd, Benj., his acceptance of Weismannism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page690">690</a>.</li> - - <li>Kitto, Dr., his visual memory and deafness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page230">230</a>.</li> - - <li>Klebs, on <i>Hydrodictyon</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page288">288</a>;</li> - <li class="i1"><i>Vaucheria</i>, <b>II</b>, - <a href="#Page_84">84</a>.</li> - - <li class="hangingindent">Klein, E., multiplication of <i>Bacteria</i>, <b>II</b>, - <a href="#Page_443">443</a>.</li> - - <li class="hangingindent">Korschelt, E., annulose segmentation, <b>II</b>, - <a href="#Page_103">103</a>, - <a href="#Page_601">601–3</a>, - <a href="#Page_605">605</a>;</li> - <li class="i1"><i>Arenicola</i> larvæ, <b>II</b>, - <a href="#Page_109">109</a>.</li> -</ul> - -<ul> - <li class="hangingindent" id="Labour">Labour, physiological division of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page204">204</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page207">207</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page591">591</a>; <b>II</b>, - <a href="#Page_373">373</a>;</li> - <li class="hangingindent1">its meaning and Weismann’s fallacious interpretation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page634">634–5</a>.</li> - - <li class="hangingindent">Lacaze-Duthiers, on origin of annulose type, <b>II</b>, - <a href="#Page_110">110</a>.</li> - - <li>Lamarck: zoological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page382">382</a>;</li> - <li class="i1">opinions of E. Darwin and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page491">491</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page493">493–7</a>;</li> - <li class="i1">neo-Darwinists and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page630">630–1</a>.</li> - - <li class="hangingindent"><i>Laminariaceæ</i>: pseudo-foliar and axial development, <b>II</b>, - <a href="#Page_30">30</a>;</li> - <li class="i1">tissue, <b>II</b>, - <a href="#Page_247">247</a>, - <a href="#Page_256">256</a>, - <a href="#Page_272">272</a>.</li> - - <li id="Language">Language: and evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page442">442</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page444">444</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page446">446</a>;</li> - <li class="i1">perceptiveness of tongue-tip, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page607">607</a>.</li> - - <li class="hangingindent">Lankester, Sir E. Ray, absence of nucleus in <i>Archerina</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page183">183</a>;</li> - <li class="i1">diversity of <i>Protozoa</i>, <i>ib.</i>;</li> - <li class="i1">zoological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page387">387</a>;</li> - <li class="i1">blindness of cave-animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page647">647–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page649">649</a>.</li> - - <li>Laugh, definition of life and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page112">112</a>.</li> - - <li>Laurel, leaves of, <b>II</b>, - <a href="#Page_149">149</a>, - <a href="#Page_249">249</a>.</li> - - <li>Leaves: growth of shoot, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page168">168</a>;</li> - <li class="i1">development and aggregation, <b>II</b>, - <a href="#Page_37">37–42</a>, - <a href="#Page_76">76</a>;</li> - <li class="i1">stem-like stalks, <b>II</b>, - <a href="#Page_41">41</a>;</li> - <li class="i1">homologies, <b>II</b>, - <a href="#Page_42">42</a>, - <a href="#Page_75">75–7</a>, - <a href="#Page_83">83</a>;</li> - <li class="i1">nutrition and compound, <b>II</b>, - <a href="#Page_42">42</a>;</li> - <li class="i1">foliar and axial development, <b>II</b>, - <a href="#Page_46">46–50</a>, - <a href="#Page_541">541–7</a>;</li> - <li class="i1">“adnate,” <b>II</b>, - <a href="#Page_58">58</a>;</li> - <li class="i1">proliferous growth, <b>II</b>, - <a href="#Page_67">67</a>, - <a href="#Page_91">91</a>;</li> - <li class="i1">nutrition and development, <b>II</b>, - <a href="#Page_76">76–8</a>;</li> - <li class="i1">symmetry, and of branches, <b>II</b>, - <a href="#Page_148">148–50</a>, - <a href="#Page_151">151</a>;</li> - <li class="i1">size and distribution of leaflets, <b>II</b>, - <a href="#Page_152">152–5</a>;</li> - <li class="i1">transition from compound to simple, <b>II</b>, - <a href="#Page_155">155–8</a>;</li> - <li class="i1">unsymmetrical form, <b>II</b>, - <a href="#Page_158">158–9</a>;</li> - <li class="i1">natural selection and distribution, <b>II</b>, - <a href="#Page_179">179</a>;</li> - <li class="i1">morphological summary, <b>II</b>, - <a href="#Page_234">234–5</a>;</li> - <li class="i1">tissue differentiation, <b>II</b>, - <a href="#Page_247">247</a>;</li> - <li class="i1">distribution, <b>II</b>, - <a href="#Page_249">249</a>;</li> - <li class="i1">outer tissues of stem and, <b>II</b>, - <a href="#Page_256">256–9</a>, - <a href="#Page_270">270</a>, - <a href="#Page_386">386</a>;</li> - <li class="i1">distribution of stomata, <b>II</b>, - <a href="#Page_260">260–1</a>;</li> - <li class="i1">wax deposit on, <b>II</b>, - <a href="#Page_260">260</a>, - <a href="#Page_261">261</a>;</li> - <li class="i1">light and colour, <b>II</b>, - <a href="#Page_261">261–2</a>;</li> - <li class="i1">superficial differentiation, <b>II</b>, - <a href="#Page_263">263–5</a>, - <a href="#Page_270">270</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">abortive in parasitic plants, <b>II</b>, - <a href="#Page_274">274</a>;</li> - <li class="i1">submerged, in aquatic plants, <b>II</b>, - <a href="#Page_274">274–5</a>;</li> - <li class="i1">inner tissue differentiation, <b>II</b>, - <a href="#Page_278">278</a>, - <a href="#Page_388">388</a>;</li> - <li class="i1">vascular tissue differentiation, <b>II</b>, - <a href="#Page_286">286</a>, - <a href="#Page_288">288</a>, - <a href="#Page_388">388</a>;</li> - <li class="i1">dye absorption and circulation, <b>II</b>, - <a href="#Page_570">570–4</a>, - <a href="#Page_577">577</a>;</li> - <li class="i1">vascular system, <b>II</b>, - <a href="#Page_588">588–92</a>, - <a href="#Page_596">596</a>;</li> - <li class="i1">arrangement, <b>II</b>, - <a href="#Page_608">608–11</a>.</li> - - <li><i>Lepidoptera</i> (<i>see</i> <a href="#Insects">Insects</a>).</li> - - <li><i>Lepidosiren</i>: ossification, <b>II</b>, - <a href="#Page_218">218</a>;</li> - <li class="i1">respiration, <b>II</b>, - <a href="#Page_338">338</a>;</li> - <li class="i1">skeleton, <b>II</b>, - <a href="#Page_553">553</a>, - <a href="#Page_555">555</a>, - <a href="#Page_560">560</a>.</li> - - <li><i>Lepidosteus</i>: armour, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page526">526</a>;</li> - <li class="i1">air-bladder, <b>II</b>, - <a href="#Page_334">334</a>.</li> - - <li class="hangingindent">Leroy-Beaulieu, Pierre, on Australian miners’ usages, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364</a>.</li> - - <li><i>Lessonia</i>: Hooker on growth, <b>II</b>, - <a href="#Page_56">56</a>;</li> - <li class="i1">branch symmetry, <b>II</b>, - <a href="#Page_146">146</a>.</li> - - <li>Lewes, G. H., definition of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page80">80</a>.</li> - - <li>Lichens: tissue, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page586">586</a>;</li> - <li class="i1">cell multiplication, <b>II</b>, - <a href="#Page_27">27</a>;</li> - <li class="i1">Hooker on growth, <b>II</b>, - <a href="#Page_56">56</a>;</li> - <li class="i1">tubular structure, <b>II</b>, - <a href="#Page_57">57</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_293">293</a>;</li> - <li class="i1">dual nature, <b>II</b>, - <a href="#Page_399">399</a>;</li> - <li class="i1">reproduction, <b>II</b>, - <a href="#Page_450">450</a>.</li> - - <li>Liebig, Baron, nitrogenous food stuffs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page47">47–8</a>.</li> - - <li id="Life">Life: co-ordination of actions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page79">79</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page89">89</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page577">577–80</a>;</li> - <li class="i1">defined by Schelling, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page78">78</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page178">178</a>;</li> - <li class="i1">Richeraud, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page79">79</a>;</li> - <li class="i1">De Blainville, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page79">79</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page93">93</a>;</li> - <li class="i1">Lewes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page80">80</a>;</li> - <li class="hangingindent1">definition yielded by contrasting most unlike kinds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page81">81–8</a>;</li> - <li class="i1">changes showing, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page91">91</a>;</li> - <li class="i1">vital actions and environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page92">92–3</a>;</li> - <li class="i1">resulting addition to conception, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page93">93</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page326">326</a>;</li> - <li class="i1">Comte’s definition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page93">93</a>;</li> - <li class="hangingindent1">correspondence of external and internal relations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page93">93–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page100">100</a>; <b>II</b>, - <a href="#Page_523">523</a>;</li> - <li class="i1">continuous adjustment of such relations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page99">99</a>;</li> - <li class="hangingindent1">completeness proportionate to correspondence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page101">101–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page109">109</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page349">349</a>;</li> - <li class="i1">length and complexity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page103">103</a>;</li> - <li class="hangingindent1">complexity of environment and degree of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page104">104–6</a>;</li> - <li class="i1">definitions of evolution and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page107">107–10</a>;</li> - <li class="i1">deficiencies of formula, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page112">112–3</a>;</li> - <li class="i1">activity the essential element, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page113">113</a>;</li> - <li class="hangingindent1">hypothesis of independent vital principle examined, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page114">114–7</a>;</li> - <li class="hangingindent1">difficulties of physico-chemical theory, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page117">117–20</a>;</li> - <li class="i1">ultimate incomprehensibility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page120">120–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page373">373</a>;</li> - <li class="i1">validity of conclusions reached, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page123">123</a>;</li> - <li class="i1">is organization produced by? <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page197">197</a>;</li> - <li class="i1">precedes organization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page210">210</a>;</li> - <li class="i1">definitions of individuality and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page250">250</a>;</li> - <li class="i1">effect of incident forces on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page348">348–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page355">355</a>;</li> - <li class="i1">length in individuals and species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page422">422</a>;</li> - <li class="i1">equilibration of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page547">547</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">final formulation of definition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page580">580</a>;</li> - <li class="hangingindent1">co-ordination of actions and sexual differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page593">593</a>;</li> - <li class="i1">“absolute” commencement of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page699">699</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page702">702</a>;</li> - <li class="i1">integration and augmentation, <b>II</b>, - <a href="#Page_426">426</a>;</li> - <li class="i1">prospective human, <b>II</b>, - <a href="#Page_522">522–5</a>.</li> - - <li class="hangingindent" id="Light">Light: influence on organisms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page30">30–6</a>; <b>II</b>, - <a href="#Page_433">433</a>;</li> - <li class="i1">nitrogenous plants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page40">40</a>;</li> - <li class="i1">organic phosphorescence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page49">49</a>;</li> - <li class="i1">heliotropism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page92">92</a>; <b>II</b>, - <a href="#Page_160">160</a>;</li> - <li class="i1">effects on organic matter, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page149">149</a>;</li> - <li class="i1">plant adaptation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page227">227</a>;</li> - <li class="hangingindent1">rhythmical variation of, and organic life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page499">499</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">vegetal influences, <b>II</b>, - <a href="#Page_130">130</a>, - <a href="#Page_131">131</a>, - <a href="#Page_147">147</a>, - <a href="#Page_149">149</a>, - <a href="#Page_158">158</a>;</li> - <li class="i1">influence on flowers, <b>II</b>, - <a href="#Page_167">167–8</a>, - <a href="#Page_608">608–11</a>;</li> - <li class="i1">vegetal tissue differentiation, <b>II</b>, - <a href="#Page_253">253–5</a>, - <a href="#Page_258">258</a>, - <a href="#Page_259">259</a>;</li> - <li class="i1">action on leaves, <b>II</b>, - <a href="#Page_260">260–4</a>;</li> - <li class="i1">on plant vascular system, <b>II</b>, - <a href="#Page_288">288</a>, - <a href="#Page_297">297</a>, - <a href="#Page_586">586</a>;</li> - <li class="i1">development of sensory organs, <b>II</b>, - <a href="#Page_320">320</a>.</li> - - <li><i>Liliaceæ</i>, floral symmetry, <b>II</b>, - <a href="#Page_170">170</a>.</li> - - <li>Lime, leaf forms, <b>II</b>, - <a href="#Page_158">158</a>, - <a href="#Page_159">159</a>.</li> - - <li>Lindley, J., plant classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page377">377</a>.</li> - - <li>Linnæus, C., classificatory system, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page377">377</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page380">380</a>.</li> - - <li class="hangingindent">Linnet, contrasted with blackbird in development, <b>II</b>, - <a href="#Page_503">503</a>.</li> - - <li>Liver: metabolic processes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page70">70</a>;</li> - <li class="i1">vitality of excised, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page111">111</a>;</li> - <li class="i1">development, <b>II</b>, - <a href="#Page_329">329–33</a>.</li> - - <li>Liver-fluke (see <a href="#Distoma"><i>Distoma</i></a>).</li> - - <li>Liverworts (see <a href="#Hepaticae"><i>Hepaticæ</i></a>).</li> - - <li>Lizard, regeneration of lost tail, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page360">360</a>.</li> - - <li>Locomotion (<i>see</i> <a href="#Motion">Motion</a>).</li> - - <li>Logic, reasoning and definition of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page81">81–6</a>.</li> - - <li>Logwood, vegetal staining, <b>II</b>, - <a href="#Page_569">569–74</a>, - <a href="#Page_577">577–81</a>, - <a href="#Page_584">584</a>.</li> - - <li>Longevity, and complexity of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page102">102–3</a>.</li> - - <li class="hangingindent">Lubbock, Sir J.: on growth and genesis in insects and crustaceans, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page292">292</a>;</li> - <li class="i1">aquatic flies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page400">400</a>.</li> - - <li>Lungs (<i>see</i> <a href="#Respiratory_System">Respiratory System</a>).</li> - - <li>Lymphatic system: amœboid cells, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page187">187</a>;</li> - <li class="i1">structural traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page192">192</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page193">193</a>.</li> -</ul> - -<ul> - <li>MacBride, E. W., <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#pagevi">vi</a>; <b>II</b>, - <a href="#Page_vi">vi</a>;</li> - <li class="i1">zoological phyla, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page396">386–7</a>;</li> - <li class="i1">arthropod segmentation, <b>II</b>, - <a href="#Page_114">114</a>;</li> - <li class="i1">ctenidia of slug, <b>II</b>, - <a href="#Page_117">117</a>;</li> - <li class="i1">conjugation of <i>Paramæcium</i>, <b>II</b>, - <a href="#Page_452">452</a>.</li> - - <li class="hangingindent"><i>Macrocystis pyrifera</i>, gigantic seaweed, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page121">121</a>.</li> - - <li>Magenta, vegetal staining, <b>II</b>, - <a href="#Page_569">569–74</a>, - <a href="#Page_577">577–81</a>, - <a href="#Page_584">584</a>.</li> - - <li>Magnetism: muscular action, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page59">59</a>;</li> - <li>incomprehensibility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page121">121</a>.</li> - - <li class="hangingindent">Maillet, B. de, modifiability of organisms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page490">490</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page496">496</a>.</li> - - <li class="hangingindent"><i>Mammalia</i>: temperature and molecular change, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page30">30</a>;</li> - <li class="i1">nutrition and growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page141">141</a>;</li> - <li class="i1">expenditure of force, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page142">142</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page156">156</a>;</li> - <li class="i1">flesh constituents, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page154">154</a>;</li> - <li class="i1">temperature, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page174">174</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page177">177</a>;</li> - <li class="i1">self-mobility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page175">175</a>;</li> - <li class="hangingindent1">functional and structural differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page201">201</a>;</li> - <li class="i1">heart-function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page206">206</a>;</li> - <li class="i1">viviparous homogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>;</li> - <li class="i1">variation and uterine environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page327">327</a>;</li> - <li class="i1">classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page392">392</a>;</li> - <li class="i1">cervical vertebræ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page394">394</a>; <b>II</b>, - <a href="#Page_564">564</a>;</li> - <li class="i1">aquatic types, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page400">400</a>;</li> - <li class="i1">fossil remains and rate of evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page407">407</a>;</li> - <li class="i1">ancient and modern forms contrasted, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page408">408–10</a>;</li> - <li class="i1">embryonic respiratory system, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page456">456</a>;</li> - <li class="i1">suppression of teeth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page457">457</a>;</li> - <li class="i1">arrested development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page473">473–4</a>;</li> - <li class="i1">simulated homologies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page485">485</a>;</li> - <li class="i1">natural selection and inactive parts, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page534">534</a>;</li> - <li class="i1">re-development of rudimentary organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page563">563</a>;</li> - <li class="i1">location of testes and current theories, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page573">573</a>;</li> - <li class="i1">fertility and development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page583">583</a>; <b>II</b>, - <a href="#Page_465">465</a>;</li> - <li class="i1">fertility and nervous development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page598">598–9</a>;</li> - <li class="i1">locomotion and elongated form, <b>II</b>, - <a href="#Page_15">15</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_204">204</a>;</li> - <li class="i1">tegumentary structure, <b>II</b>, - <a href="#Page_314">314</a>;</li> - <li class="i1">circulation, <b>II</b>, - <a href="#Page_340">340</a>;</li> - <li class="i1">vascularity and ova-maturation, <b>II</b>, - <a href="#Page_342">342–3</a>;</li> - <li class="i1">activity and muscular colour, <b>II</b>, - <a href="#Page_365">365–9</a>;</li> - <li class="i1">functional integration, <b>II</b>, - <a href="#Page_375">375</a>;</li> - <li class="i1">outer tissue differentiation, <b>II</b>, - <a href="#Page_387">387</a>;</li> - <li class="i1">growth and genesis, <b>II</b>, - <a href="#Page_456">456</a>, - <a href="#Page_459">459</a>;</li> - <li class="i1">comparative fertility, <b>II</b>, - <a href="#Page_465">465</a>, - <a href="#Page_470">470</a>;</li> - <li class="i1">heat expenditure and genesis, <b>II</b>, - <a href="#Page_467">467–9</a>;</li> - <li class="i1">activity and fertility, <b>II</b>, - <a href="#Page_472">472</a>;</li> - <li class="i1">nutrition and genesis, <b>II</b>, - <a href="#Page_479">479–80</a>.</li> - - <li id="Man">Man: effect of climate on vigour, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page30">30</a>;</li> - <li class="i1">flesh and grain eaters compared, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page68">68</a>;</li> - <li class="i1">longevity and life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page103">103</a>;</li> - <li class="i1">complex environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page105">105</a>;</li> - <li class="i1">embryogeny of arm, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page169">169</a>;</li> - <li class="hangingindent1">fertility and conditions affecting it, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page300">300</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page570">570</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page583">583</a>; <b>II</b>, - <a href="#Page_484">484</a>, - <a href="#Page_506">506–21</a>;</li> - <li class="hangingindent1">inheritance of functionally-produced changes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page310">310–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page541">541</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page605">605</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page608">608</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page652">652</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page673">673</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693–4</a>;</li> - <li class="i1">heredity and sex, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page315">315–6</a>;</li> - <li class="i1">function of bilirubin, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page330">330</a>;</li> - <li class="i1">cousin-marriages, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page346">346</a>; <b>II</b>, - <a href="#Page_615">615</a>;</li> - <li class="i1">primitive notions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page417">417–9</a>;</li> - <li class="i1">inutility of <i>Appendix vermiformis</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page474">474</a>;</li> - <li class="i1">diminution of jaw, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page541">541</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">co-ordination of actions greatest in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page579">579</a>;</li> - <li class="i1">fundamental traits of sex, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page594">594–7</a>;</li> - <li class="i1">obesity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page594">594</a>;</li> - <li class="i1">substance and weight of brain, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page596">596</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page599">599</a>;</li> - <li class="hangingindent1">distribution of tactual perceptiveness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page602">602–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page665">665–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page672">672–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="i1">telegony, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page625">625</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page644">644–5</a>;</li> - <li class="i1">degradation of little toe, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page652">652</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page673">673</a>;</li> - <li class="hangingindent1">transmitted osteological peculiarities of Punjabis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>;</li> - <li class="i1">traits of twin-bearing women, <b>II</b>, - <a href="#Page_457">457</a>;</li> - <li class="i1">comparative mammalian fertility, <b>II</b>, - <a href="#Page_465">465</a>;</li> - <li class="i1">future evolution, <b>II</b>, - <a href="#Page_522">522–37</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Language">Language</a> <i>and</i> <a href="#Sociology">Sociology</a>.)</li> - - <li>Manatee, nailless paddles, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page473">473</a>.</li> - - <li>Manx cats, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page303">303</a>.</li> - - <li><i>Marchantiaceæ</i>: symmetry, <b>II</b>, - <a href="#Page_140">140</a>;</li> - <li class="i1">outer tissue differentiation, <b>II</b>, - <a href="#Page_252">252</a>.</li> - - <li>Marmot, hybernation and waste, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page214">214–5</a>.</li> - - <li>Marriage (<i>see</i> <a href="#Multiplication">Multiplication</a>).</li> - - <li>Marsh, O. C., on telegony, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page644">644</a>.</li> - - <li>Masters, M. T., on foliar homology, <b>II</b>, - <a href="#Page_46">46–7</a>;</li> - <li class="hangingindent1">selection of inconspicuous variations in plants, <b>II</b>, - <a href="#Page_298">298</a>, - <a href="#Page_621">621</a>;</li> - <li class="hangingindent1">separation of ancestral constitutions in plant hybrids, <b>II</b>, - <a href="#Page_616">616</a>;</li> - <li class="i1">single and double stocks, <b>II</b>, - <a href="#Page_622">622</a>.</li> - - <li class="hangingindent">Matter, incomprehensibility of interactions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page121">121–2</a>.</li> - - <li>Mechanics: transverse strains, <b>II</b>, - <a href="#Page_209">209–12</a>;</li> - <li class="hangingindent1">genesis of vertebrate axis, <b>II</b>, - <a href="#Page_212">212–6</a>, - <a href="#Page_216">216–8</a>, - <a href="#Page_224">224</a>, - <a href="#Page_225">225–7</a>;</li> - <li class="i1">osseous differentiation, <b>II</b>, - <a href="#Page_345">345–51</a>;</li> - <li class="i1">disintegrated motion, <b>II</b>, - <a href="#Page_375">375</a>;</li> - <li class="i1">analogy from locomotive, <b>II</b>, - <a href="#Page_517">517–9</a>;</li> - <li class="i1">future human evolution, <b>II</b>, - <a href="#Page_524">524</a>;</li> - <li class="i1">strain and vegetal structure, <b>II</b>, - <a href="#Page_574">574–88</a>, - <a href="#Page_592">592–6</a>.</li> - - <li><i>Medusæ</i>: contractile functions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page58">58</a>; <b>II</b>, - <a href="#Page_374">374</a>;</li> - <li class="i1">individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page248">248</a>;</li> - <li class="i1">heterogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page273">273</a>;</li> - <li class="i1">fertility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page582">582</a>;</li> - <li class="i1">strobilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page592">592</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_188">188–91</a>.</li> - - <li class="hangingindent">Mehnert, E., on feet of pentadactyle vertebrates, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page461">461</a>.</li> - - <li>Mensel’s salt, temperature and isomerism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page77">77</a>.</li> - - <li class="hangingindent">Metabolism: antithesis between plants and animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page62">62–3</a>;</li> - <li class="i1">evolution hypothesis and primordial, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page63">63–4</a>;</li> - <li class="i1">in plants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page64">64–7</a>;</li> - <li class="i1">animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page67">67–77</a>;</li> - <li class="i1">nervo-muscular activities, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page71">71–7</a>;</li> - <li class="i1">summary, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page77">77</a>;</li> - <li class="i1">cell processes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page261">261</a>.</li> - - <li>Metals: remarkable interactions of some, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page121">121</a>;</li> - <li class="i1">melting of alloys, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page339">339</a>;</li> - <li class="i1">atomic re-arrangement, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page352">352</a>.</li> - - <li>Metamerism (<i>see</i> <a href="#Segmentation">Segmentation</a>).</li> - - <li class="hangingindent"><i>Metazoa</i>: cellular structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page184">184</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page194">194</a>; <b>II</b>, - <a href="#Page_21">21</a>;</li> - <li class="i1">subordination of units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page185">185–7</a>;</li> - <li class="i1">general characters of tissues, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page188">188–9</a>;</li> - <li class="i1">protoplasmic continuity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page190">190–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page194">194</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page628">628</a>;</li> - <li class="i1">genesis of food-cavity and visual organ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page195">195</a>;</li> - <li class="i1">Weismann’s differentiation theory, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page637">637–43</a>.</li> - - <li>Meteorology: non-vital changes shown in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page82">82</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page84">84</a>;</li> - <li class="i1">crystallization of “storm glass,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page96">96</a>;</li> - <li class="i1">special creation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page419">419</a>;</li> - <li class="i1">rhythm in, and organic change, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page499">499–501</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">variations due to geologic change, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page503">503</a>.</li> - - <li><i>Microstomida</i>, segmental reproduction, <b>II</b>, - <a href="#Page_102">102</a>.</li> - - <li>Migration: of animal species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page396">396–401</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page411">411</a>;</li> - <li class="i1">solar influences, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page500">500</a>;</li> - <li class="i1">part played by, in organic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page568">568</a>;</li> - <li class="i1">causes of, <b>II</b>, - <a href="#Page_533">533–4</a>.</li> - - <li>Milk, heat and supply of, <b>II</b>, - <a href="#Page_468">468</a>.</li> - - <li class="hangingindent">Milne-Edwards, H., “physiological division of labour,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page204">204</a>;</li> - <li class="i1">Weismann’s erroneous application of it, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page634">634</a>;</li> - <li class="i1">on ocular structure, <b>II</b>, - <a href="#Page_318">318</a>.</li> - - <li>Mind (<i>see</i> <a href="#Psychology">Psychology</a>).</li> - - <li>Mitosis (<i>see</i> <a href="#Karyokinesis">Karyokinesis</a>).</li> - - <li>Mobility, molar and molecular, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page14">14</a>;</li> - <li class="i1">environment and self-mobility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page177">177</a>.</li> - - <li>Mohl, on phænogamic growth, <b>II</b>, - <a href="#Page_82">82</a>.</li> - - <li>Mole, modifications due to habits, <b>II</b>, - <a href="#Page_391">391</a>.</li> - - <li>Molecules: mechanically considered, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page14">14</a>;</li> - <li class="i1">stability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page337">337–40</a>;</li> - <li class="i1">nerve differentiation, <b>II</b>, - <a href="#Page_355">355–61</a>, - <a href="#Page_379">379–82</a>.</li> - - <li id="Mollusca"><i>Mollusca</i>: axial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>;</li> - <li class="i1">genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>; <b>II</b>, - <a href="#Page_444">444</a>;</li> - <li class="i1">hermaphrodism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page341">341</a>;</li> - <li class="i1">classificatory traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page392">392</a>;</li> - <li class="i1">distribution in time, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page405">405</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page408">408</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page410">410</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page446">446–7</a>;</li> - <li class="hangingindent1">trochophore and its relationships, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page447">447</a>; <b>II</b>, - <a href="#Page_108">108</a>, - <a href="#Page_109">109</a>, - <a href="#Page_115">115</a>;</li> - <li class="i1">development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page460">460</a>;</li> - <li class="i1">amphibious and terrestrial, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page481">481</a>;</li> - <li class="i1">indirect equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page534">534</a>;</li> - <li class="i1">secondary aggregation, <b>II</b>, - <a href="#Page_115">115–7</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_201">201–3</a>;</li> - <li class="i1">outer tissue, <b>II</b>, - <a href="#Page_310">310</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">alimentary system, <b>II</b>, - <a href="#Page_325">325</a>;</li> - <li class="i1">vascular system, <b>II</b>, - <a href="#Page_340">340–1</a>.</li> - - <li><i>Molluscoida</i>, <b>II</b>, - <a href="#Page_598">598</a>.</li> - <li class="i1">(See <a href="#Polyzoa"><i>Polyzoa</i></a> and <a href="#Tunicata"><i>Tunicata</i></a>.)</li> - - <li id="Monocotyledons">Monocotyledons: growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page138">138</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page139">139</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page143">143</a>;</li> - <li class="i1">uniaxial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>;</li> - <li class="hangingindent1">cotyledonous germination and endogenous growth, <b>II</b>, - <a href="#Page_59">59–62</a>, - <a href="#Page_69">69–72</a>, - <a href="#Page_82">82–3</a>, - <a href="#Page_181">181–2</a>;</li> - <li class="hangingindent1">absence of helical phyllotaxy in <i>Ravenala</i>, <b>II</b>, - <a href="#Page_182">182</a>;</li> - <li class="i1">surface contrasts, <b>II</b>, - <a href="#Page_257">257</a>;</li> - <li class="i1">outer leaf tissue, <b>II</b>, - <a href="#Page_263">263</a>;</li> - <li class="i1">wood formation, <b>II</b>, - <a href="#Page_278">278</a>;</li> - <li class="i1">growth and genesis, <b>II</b>, - <a href="#Page_451">451</a>.</li> - - <li>Monstrosities, in plants, <b>II</b>, - <a href="#Page_78">78</a>, - <a href="#Page_541">541</a>, - <a href="#Page_546">546</a>;</li> - <li class="i1">vertebrate, <b>II</b>, - <a href="#Page_118">118</a>.</li> - - <li class="hangingindent">Morgan, T. H., on regeneration of <i>Planaria</i>, <b>II</b>, - <a href="#Page_102">102</a>, - <a href="#Page_611">611</a>.</li> - - <li id="Morphology">Morphology: facts comprised in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page125">125–6</a>;</li> - <li class="i1">morphological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page190">190–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page225">225</a>;</li> - <li class="i1">rudimentary organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page472">472–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">structural and functional co-operation, <b>II</b>, - <a href="#Page_3">3</a>, - <a href="#Page_239">239</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_4">4–6</a>, - <a href="#Page_181">181–96</a>;</li> - <li class="i1">change of shape, <b>II</b>, - <a href="#Page_6">6</a>;</li> - <li class="i1">formula of evolution, <b>II</b>, - <a href="#Page_7">7–9</a>;</li> - <li class="i1">as interpreted by phylogeny, <b>II</b>, - <a href="#Page_10">10–6</a>;</li> - <li class="i1">evolution and cell-doctrine, <b>II</b>, - <a href="#Page_17">17–21</a>.</li> - - <li class="hangingindent">Morphology, Animal: evolution and segmentation of <i>Articulata</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page468">468–9</a>;</li> - <li class="i1">vertebral column development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page470">470</a>;</li> - <li class="i1">simulated homologies, <b>II</b>, - <a href="#Page_14">14–5</a>;</li> - <li class="i1">primary aggregates, <b>II</b>, - <a href="#Page_85">85–8</a>, - <a href="#Page_123">123–4</a>;</li> - <li class="i1">secondary, <b>II</b>, - <a href="#Page_88">88–91</a>, - <a href="#Page_124">124</a>;</li> - <li class="i1">tertiary, <b>II</b>, - <a href="#Page_91">91–3</a>;</li> - <li class="hangingindent1">integration and independence of individuality, <b>II</b>, - <a href="#Page_93">93–9</a>, - <a href="#Page_124">124</a>;</li> - <li class="hangingindent1">annulose segmentation, <b>II</b>, - <a href="#Page_98">98–101</a>, - <a href="#Page_106">106–10</a>, - <a href="#Page_125">125–7</a>, - <a href="#Page_602">602–7</a>;</li> - <li class="hangingindent1">progressive annulose integration, <b>II</b>, - <a href="#Page_100">100–5</a>, - <a href="#Page_111">111–5</a>, - <a href="#Page_121">121</a>, - <a href="#Page_124">124</a>, - <a href="#Page_223">223</a>;</li> - <li class="i1">unintegrated molluscan form, <b>II</b>, - <a href="#Page_115">115–7</a>;</li> - <li class="hangingindent1">vertebrate segmentation and integration, <b>II</b>, - <a href="#Page_117">117–23</a>, - <a href="#Page_124">124–7</a>, - <a href="#Page_223">223–4</a>, - <a href="#Page_602">602</a>, - <a href="#Page_606">606–7</a>;</li> - <li class="i1">motion and symmetry, <b>II</b>, - <a href="#Page_183">183–5</a>;</li> - <li class="hangingindent1">symmetry of primary and secondary aggregates, <b>II</b>, - <a href="#Page_186">186</a>, - <a href="#Page_187">187–91</a>;</li> - <li class="i1">of compound <i>Cœlenterata</i>, <b>II</b>, - <a href="#Page_192">192–4</a>;</li> - <li class="i1">simulation of plant shapes, <b>II</b>, - <a href="#Page_192">192</a>;</li> - <li class="hangingindent1">symmetry of <i>Polyzoa</i> and <i>Tunicata</i>, <b>II</b>, - <a href="#Page_194">194</a>;</li> - <li class="hangingindent1">of <i>Platyhelminthes</i> and <i>Echinoderms</i>, <b>II</b>, - <a href="#Page_195">195–7</a>;</li> - <li class="i1">of <i>Annulosa</i>, <b>II</b>, - <a href="#Page_197">197–201</a>;</li> - <li class="i1">of molluscs, <b>II</b>, - <a href="#Page_201">201–3</a>;</li> - <li class="i1">of vertebrates, <b>II</b>, - <a href="#Page_203">203–6</a>, - <a href="#Page_208">208</a>;</li> - <li class="i1">similarity of animal and plant, <b>II</b>, - <a href="#Page_206">206</a>;</li> - <li class="i1">cell-shapes, <b>II</b>, - <a href="#Page_228">228–30</a>;</li> - <li class="hangingindent1">evolution and generalizations summarized, <b>II</b>, - <a href="#Page_231">231–5</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Structure">Structure</a>.)</li> - - <li class="hangingindent">Morphology, Vegetal: simulated homologies, <b>II</b>, - <a href="#Page_13">13–4</a>;</li> - <li class="i1">unicellular plants, <b>II</b>, - <a href="#Page_21">21</a>;</li> - <li class="i1">aggregation and integration, <b>II</b>, - <a href="#Page_22">22–6</a>, - <a href="#Page_78">78–9</a>;</li> - <li class="i1">pseudo-foliar development, <b>II</b>, - <a href="#Page_26">26–8</a>;</li> - <li class="i1">pseudo-axial, <b>II</b>, - <a href="#Page_28">28–9</a>;</li> - <li class="i1">pseudo-foliar and axial, <b>II</b>, - <a href="#Page_30">30–2</a>;</li> - <li class="i1">composition of Archegoniates, <b>II</b>, - <a href="#Page_33">33–5</a>;</li> - <li class="hangingindent1">leaf development and aggregation, <b>II</b>, - <a href="#Page_37">37–42</a>, - <a href="#Page_75">75–8</a>;</li> - <li class="i1">foliar homologies, <b>II</b>, - <a href="#Page_42">42–6</a>, - <a href="#Page_75">75–8</a>;</li> - <li class="i1">foliar and axial development, <b>II</b>, - <a href="#Page_46">46–50</a>, - <a href="#Page_541">541–7</a>;</li> - <li class="hangingindent1">growth and development of Archegoniates, <b>II</b>, - <a href="#Page_50">50–6</a>;</li> - <li class="i1">of Phænogams, <b>II</b>, - <a href="#Page_56">56–64</a>, - <a href="#Page_78">78–80</a>;</li> - <li class="i1">axillary bud development, <b>II</b>, - <a href="#Page_65">65–9</a>;</li> - <li class="i1">phænogamic modes of growth, <b>II</b>, - <a href="#Page_69">69–72</a>;</li> - <li class="i1">homologies, <b>II</b>, - <a href="#Page_73">73–5</a>, - <a href="#Page_80">80–4</a>;</li> - <li class="hangingindent1">development of foliar into axial organs, <b>II</b>, - <a href="#Page_75">75–8</a>;</li> - <li class="i1"><i>résumé</i>, <b>II</b>, - <a href="#Page_78">78–80</a>;</li> - <li class="i1">criticisms and replies, <b>II</b>, - <a href="#Page_80">80–4</a>;</li> - <li class="i1">can plant shapes be formulated? <b>II</b>, - <a href="#Page_128">128</a>;</li> - <li class="i1">growth and differentiation, <b>II</b>, - <a href="#Page_129">129–31</a>;</li> - <li class="i1">kinds of symmetry, <b>II</b>, - <a href="#Page_131">131–3</a>;</li> - <li class="i1">symmetry of primary aggregates, <b>II</b>, - <a href="#Page_134">134–7</a>;</li> - <li class="i1">of secondary, <b>II</b>, - <a href="#Page_137">137–40</a>;</li> - <li class="i1">tertiary, <b>II</b>, - <a href="#Page_140">140–3</a>;</li> - <li class="i1">symmetry and environing influences, <b>II</b>, - <a href="#Page_143">143–4</a>;</li> - <li class="i1">symmetry of branches, <b>II</b>, - <a href="#Page_145">145–8</a>;</li> - <li class="i1">leaf and branch symmetry, <b>II</b>, - <a href="#Page_148">148–50</a>;</li> - <li class="i1">phænogamic unit homology, <b>II</b>, - <a href="#Page_151">151</a>;</li> - <li class="i1">size and distribution of leaflets, <b>II</b>, - <a href="#Page_152">152–5</a>;</li> - <li class="hangingindent1">transition from compound to simple leaves, <b>II</b>, - <a href="#Page_155">155–8</a>;</li> - <li class="i1">unsymmetrical leaf development, <b>II</b>, - <a href="#Page_158">158–9</a>;</li> - <li class="i1">differentiation of homologous units, <b>II</b>, - <a href="#Page_159">159–60</a>;</li> - <li class="i1">floral symmetry, <b>II</b>, - <a href="#Page_161">161–74</a>;</li> - <li class="hangingindent1">cell-differentiation and metamorphosis, <b>II</b>, - <a href="#Page_175">175–7</a>;</li> - <li class="i1">nutrition and differentiation, <b>II</b>, - <a href="#Page_178">178</a>;</li> - <li class="i1">and inflorescence, <b>II</b>, - <a href="#Page_179">179</a>;</li> - <li class="i1">helical growth of phænogams, <b>II</b>, - <a href="#Page_180">180–1</a>;</li> - <li class="i1">summary of symmetry, <b>II</b>, - <a href="#Page_234">234</a>;</li> - <li class="i1">stress and structure, <b>II</b>, - <a href="#Page_275">275–9</a>, - <a href="#Page_388">388</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Structure">Structure</a>.)</li> - - <li>Morton, Lord, quagga-marked foal, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page624">624</a>.</li> - - <li class="hangingindent">Moser, impressions produced by light on metals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page352">352</a>.</li> - - <li>Mosses: varied development, <b>II</b>, - <a href="#Page_501">501</a>, - <a href="#Page_52">52</a>;</li> - <li class="i1">homologies, <b>II</b>, - <a href="#Page_80">80</a>, - <a href="#Page_81">81</a>;</li> - <li class="i1">indefiniteness, <b>II</b>, - <a href="#Page_296">296</a>;</li> - <li class="i1">multiplication, <b>II</b>, - <a href="#Page_441">441</a>.</li> - - <li>Moth, clothes, food of larva, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page77">77</a>.</li> - - <li class="hangingindent" id="Motion">Motion: organic, and environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page75">75–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page175">175–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page196">196</a>;</li> - <li class="i1">of animals and waste, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page214">214</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page220">220</a>;</li> - <li class="i1">simulation of locomotive structures, <b>II</b>, - <a href="#Page_15">15</a>.</li> - - <li>Motor organs, differentiation of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page262">262</a>.</li> - - <li>Mountains: climatic effects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page504">504</a>;</li> - <li class="i1">growth of trees on, <b>II</b>, - <a href="#Page_142">142</a>.</li> - - <li>Mouse: fertility of, <b>II</b>, - <a href="#Page_421">421</a>, - <a href="#Page_473">473</a>;</li> - <li class="i1">tapeworm parasitism, <b>II</b>, - <a href="#Page_490">490</a>;</li> - <li class="i1">compared with rat, <b>II</b>, - <a href="#Page_503">503–4</a>.</li> - - <li><i>Mucor</i>, <b>II</b>, - <a href="#Page_22">22</a>, - <a href="#Page_123">123</a>.</li> - - <li>Mucous membrane, differentiation, <b>II</b>, - <a href="#Page_321">321–2</a>, - <a href="#Page_389">389</a>.</li> - - <li class="hangingindent" id="Multiplication">Multiplication: decline of fertility with evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page103">103</a>; <b>II</b>, - <a href="#Page_431">431</a>;</li> - <li class="i1">vitalism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page116">116</a>;</li> - <li class="i1">phenomena classified, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page130">130</a>;</li> - <li class="i1">the term “genesis,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page269">269</a>;</li> - <li class="i1">processes classified, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page270">270–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page336">336</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page583">583</a>;</li> - <li class="i1">a process of disintegration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page276">276</a>;</li> - <li class="i1">reproductive tissue in gamogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page278">278–84</a>;</li> - <li class="i1">nutrition and growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page285">285–94</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page299">299</a>;</li> - <li class="i1">natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295–8</a>;</li> - <li class="i1">hermaphrodism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page340">340–4</a>;</li> - <li class="i1">in-and-in breeding, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page344">344–7</a>;</li> - <li class="i1">physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page350">350–5</a>;</li> - <li class="hangingindent1">law of race-maintenance, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page581">581</a>; <b>II</b>, - <a href="#Page_420">420–3</a>, - <a href="#Page_430">430</a>;</li> - <li class="hangingindent1">effect of mental application, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page597">597</a>; <b>II</b>, - <a href="#Page_511">511–4</a>, - <a href="#Page_516">516–9</a>, - <a href="#Page_530">530</a>;</li> - <li class="hangingindent1">individuation antagonistic to, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page598">598–600</a>; <b>II</b>, - <a href="#Page_428">428–30</a>, - <a href="#Page_435">435–7</a>, - <a href="#Page_499">499</a>, - <a href="#Page_501">501–5</a>;</li> - <li class="i1">checks put by carnivores on, <b>II</b>, - <a href="#Page_405">405</a>;</li> - <li class="i1">four factors in rate of, <b>II</b>, - <a href="#Page_416">416</a>, - <a href="#Page_435">435</a>;</li> - <li class="i1">destructive and preservative forces, <b>II</b>, - <a href="#Page_417">417–20</a>;</li> - <li class="i1">rhythm of species, <b>II</b>, - <a href="#Page_419">419</a>;</li> - <li class="hangingindent1">nutrition and disintegration of, <b>II</b>, - <a href="#Page_424">424</a>, - <a href="#Page_425">425</a>, - <a href="#Page_430">430</a>;</li> - <li class="i1">integration and genesis, <b>II</b>, - <a href="#Page_426">426–8</a>;</li> - <li class="i1">influence of environment, <b>II</b>, - <a href="#Page_432">432–3</a>;</li> - <li class="i1">and variations of expenditure, <b>II</b>, - <a href="#Page_433">433–5</a>;</li> - <li class="i1">growth and asexual genesis, <b>II</b>, - <a href="#Page_439">439–46</a>;</li> - <li class="i1">asexual and sexual distinguished, <b>II</b>, - <a href="#Page_448">448</a>;</li> - <li class="i1">sexual genesis and growth, <b>II</b>, - <a href="#Page_448">448–58</a>, - <a href="#Page_495">495</a>;</li> - <li class="i1">and development, <b>II</b>, - <a href="#Page_461">461–5</a>;</li> - <li class="i1">plant expenditure, <b>II</b>, - <a href="#Page_467">467</a>;</li> - <li class="i1">animal expenditure, <b>II</b>, - <a href="#Page_468">468–72</a>;</li> - <li class="i1">nutrition in plants, <b>II</b>, - <a href="#Page_475">475</a>, - <a href="#Page_511">511</a>;</li> - <li class="i1">in animals, <b>II</b>, - <a href="#Page_476">476–84</a>, - <a href="#Page_511">511</a>;</li> - <li class="i1">seasonal variations, <b>II</b>, - <a href="#Page_484">484–5</a>;</li> - <li class="i1">nutrition, <i>résumé</i>, <b>II</b>, - <a href="#Page_486">486</a>, - <a href="#Page_497">497–9</a>;</li> - <li class="i1">nutrition and parasitic, <b>II</b>, - <a href="#Page_486">486–90</a>;</li> - <li class="i1">reversion to agamogenesis, <b>II</b>, - <a href="#Page_490">490–2</a>;</li> - <li class="i1">human fertility, <b>II</b>, - <a href="#Page_506">506–10</a>;</li> - <li class="i1">Doubleday on, <b>II</b>, - <a href="#Page_510">510–2</a>;</li> - <li class="i1">civilized and uncivilized, <b>II</b>, - <a href="#Page_514">514–6</a>;</li> - <li class="i1">human evolution and decline in, <b>II</b>, - <a href="#Page_529">529–31</a>;</li> - <li class="i1">the future of population, <b>II</b>, - <a href="#Page_532">532–7</a>;</li> - <li class="i1">equilibration and evolution, <b>II</b>, - <a href="#Page_537">537</a>.</li> - - <li>Muscle: electrical contrasts, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page50">50</a>;</li> - <li class="i1">action of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page59">59</a>;</li> - <li class="i1">metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page70">70</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page71">71–4</a>;</li> - <li class="i1">definition of life and actions of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page112">112–3</a>;</li> - <li class="i1">growth and function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page151">151</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page155">155</a>;</li> - <li class="i1">development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page170">170</a>;</li> - <li class="i1">Hertwig’s classification of tissues, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page189">189</a>;</li> - <li class="i1">functional differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page203">203–4</a>;</li> - <li class="i1">waste and repair, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page215">215–7</a>;</li> - <li class="hangingindent1">modifiability and adaptability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page228">228–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page230">230</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page232">232</a>;</li> - <li class="hangingindent1">correlated variations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page536">536–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page614">614–21</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">resistance to strains, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page639">639</a>;</li> - <li class="i1">action on bones in Punjabis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>;</li> - <li class="i1">differentiation, <b>II</b>, - <a href="#Page_361">361–9</a>;</li> - <li class="i1">activity and colour, <b>II</b>, - <a href="#Page_365">365–9</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_376">376</a>, - <a href="#Page_382">382</a>;</li> - <li class="i1">equilibration in action, <b>II</b>, - <a href="#Page_393">393</a>;</li> - <li class="i1">activity and fertility in birds, <b>II</b>, - <a href="#Page_470">470–2</a>;</li> - <li class="i1">future human evolution, <b>II</b>, - <a href="#Page_523">523</a>;</li> - <li class="i1">origin of vertebrate type, <b>II</b>, - <a href="#Page_598">598–600</a>.</li> - - <li>Music: limited adaptability of voice and ear, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page231">231</a>;</li> - <li class="i1">inheritance of faculty, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page311">311–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page694">694</a>.</li> - - <li class="hangingindent">Mutilations, the question of their inheritance, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page631">631</a>.</li> - - <li><i>Mycetozoa</i>, growth and reproduction, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page298">298–9</a>.</li> - - <li class="hangingindent">Myocommata (myotomes), and vertebrate skeleton, <b>II</b>, - <a href="#Page_216">216</a>, - <a href="#Page_217">217–8</a>, - <a href="#Page_222">222</a>.</li> - - <li>Myopia, inheritance of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page306">306</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page694">694</a>.</li> - - <li><i>Myrianida fasciata</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page361">361</a>; <b>II</b>, - <a href="#Page_445">445</a>.</li> - - <li><i>Myriapoda</i>: gemmation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page589">589</a>;</li> - <li class="i1">segmentation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page590">590</a>; <b>II</b>, - <a href="#Page_113">113</a>, - <a href="#Page_114">114</a>, - <a href="#Page_601">601</a>;</li> - <li class="i1">degenerated eyes of cave-inhabiting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page649">649</a>;</li> - <li class="i1">integration and homology, <b>II</b>, - <a href="#Page_111">111–4</a>;</li> - <li class="i1">genesis, <b>II</b>, - <a href="#Page_445">445</a>.</li> - - <li><i>Myxothallophyta</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page378">378</a>.</li> -</ul> - -<ul> - <li>Nails, mammalian, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page473">473</a>.</li> - - <li class="hangingindent"><i>Nais</i>: regeneration of detached parts, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page219">219</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page361">361</a>.</li> - - <li class="hangingindent">Narcissus, separation of ancestral traits in hybrids, <b>II</b>, - <a href="#Page_617">617</a>.</li> - - <li id="Natural_selection">Natural selection: structural modification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page211">211</a>;</li> - <li class="i1">in cell processes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page263">263–4</a>;</li> - <li class="i1">multiplication, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295–8</a>;</li> - <li class="i1">aided by function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page308">308–10</a>;</li> - <li class="i1">special creation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page426">426–7</a>;</li> - <li class="i1">the term “survival of the fittest,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page530">530</a>;</li> - <li class="hangingindent1">indirect equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page530">530–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page552">552–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page571">571</a>;</li> - <li class="hangingindent1">changes unexplained by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page535">535–42</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page571">571</a>; <b>II</b>, - <a href="#Page_371">371</a>;</li> - <li class="i1">tendency to economy, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page536">536</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page562">562</a>;</li> - <li class="i1">decrease of jaw, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page541">541</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">general doctrine of evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page543">543–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">unceasing operation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page552">552</a>;</li> - <li class="i1">human races, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>;</li> - <li class="i1">current views, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page559">559–60</a>;</li> - <li class="i1">panmixia and cessation of selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page560">560–3</a>;</li> - <li class="i1">intra-selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page562">562</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676–8</a>;</li> - <li class="i1">Eimer’s theory of orthogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page564">564</a>;</li> - <li class="i1">Mr. Cunningham’s criticism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page565">565–6</a>;</li> - <li class="i1">location of mammalian testes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page573">573</a>;</li> - <li class="i1">co-ordinated instincts of mason-wasp, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page574">574</a>;</li> - <li class="hangingindent1">tactual perceptiveness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page603">603–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page633">633</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page665">665</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page671">671</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page672">672</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="hangingindent1">erroneously identified with artificial selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page609">609</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page695">695</a>;</li> - <li class="i1">reversed selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page611">611</a>;</li> - <li class="hangingindent1">blindness of cave-animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page613">613</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page614">614</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page647">647–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="hangingindent1">co-adaptation of co-operative parts, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page614">614</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page621">621</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page663">663–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page674">674</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="i1">where operative, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page632">632</a>;</li> - <li class="i1">Weismann on conceivability of process, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page651">651</a>;</li> - <li class="i1">degeneration of little toe, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page652">652–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page673">673</a>;</li> - <li class="hangingindent1">genesis of caste gradations In social insects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page654">654–60</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page663">663</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page684">684</a>;</li> - <li class="i1">self-feeding instinct in ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>;</li> - <li class="i1">rudimentary organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page667">667–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page671">671</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="i1">horns of stag, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="i1">musical faculty, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page694">694</a>;</li> - <li class="i1">the neo-Darwinian position reviewed, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page694">694–5</a>;</li> - <li class="i1">vegetal nutrition, <b>II</b>, - <a href="#Page_51">51–2</a>;</li> - <li class="i1">upright vegetal growth, <b>II</b>, - <a href="#Page_56">56–7</a>;</li> - <li class="i1">endogenous growth, <b>II</b>, - <a href="#Page_57">57–8</a>;</li> - <li class="i1">exogenous, <b>II</b>, - <a href="#Page_64">64</a>;</li> - <li class="i1"><i>Navicula</i> symmetry, <b>II</b>, - <a href="#Page_135">135</a>;</li> - <li class="i1">foliar, <b>II</b>, - <a href="#Page_158">158</a>;</li> - <li class="i1">foliar distribution, <b>II</b>, - <a href="#Page_167">167</a>, - <a href="#Page_179">179</a>;</li> - <li class="hangingindent1">floral fertilization and symmetry, <b>II</b>, - <a href="#Page_168">168–70</a>, - <a href="#Page_608">608–11</a>;</li> - <li class="i1">helical phænogamic growth, <b>II</b>, - <a href="#Page_181">181</a>;</li> - <li class="hangingindent1"><i>Echinodermata</i> and bilateral symmetry, <b>II</b>, - <a href="#Page_197">197</a>;</li> - <li class="i1">vertebrate structure, <b>II</b>, - <a href="#Page_214">214–20</a>, - <a href="#Page_227">227</a>;</li> - <li class="i1">phænogamic tissue differentiation, <b>II</b>, - <a href="#Page_248">248</a>;</li> - <li class="i1">physiological differentiation, <b>II</b>, - <a href="#Page_252">252</a>, - <a href="#Page_256">256</a>;</li> - <li class="i1">rootlets of ivy, <b>II</b>, - <a href="#Page_254">254</a>;</li> - <li class="i1">stomata and foliar surfaces, <b>II</b>, - <a href="#Page_261">261</a>, - <a href="#Page_262">262</a>;</li> - <li class="i1">floral fertilization, <b>II</b>, - <a href="#Page_268">268–9</a>;</li> - <li class="i1">sexual selection, <b>II</b>, - <a href="#Page_269">269</a>;</li> - <li class="i1">vegetal tissue differentiation, <b>II</b>, - <a href="#Page_279">279</a>;</li> - <li class="i1">wood formation, <b>II</b>, - <a href="#Page_287">287–8</a>, - <a href="#Page_290">290</a>;</li> - <li class="i1">animal tissue differentiation, <b>II</b>, - <a href="#Page_304">304–8</a>;</li> - <li class="i1">evolution of nervous system, <b>II</b>, - <a href="#Page_307">307–8</a>;</li> - <li class="i1">respiratory system, <b>II</b>, - <a href="#Page_311">311</a>;</li> - <li class="i1">dermal callosities, <b>II</b>, - <a href="#Page_312">312–4</a>;</li> - <li class="i1">sensory organ complexities, <b>II</b>, - <a href="#Page_321">321</a>;</li> - <li class="hangingindent1">skin and mucous membrane differentiation, <b>II</b>, - <a href="#Page_322">322</a>;</li> - <li class="i1">localization of excretion, <b>II</b>, - <a href="#Page_333">333</a>;</li> - <li class="i1">respiratory organs of fishes, <b>II</b>, - <a href="#Page_335">335–8</a>;</li> - <li class="i1">heart and vascular system, <b>II</b>, - <a href="#Page_341">341</a>, - <a href="#Page_344">344</a>;</li> - <li class="i1">osseous differentiation, <b>II</b>, - <a href="#Page_355">355</a>;</li> - <li class="i1">also muscular, <b>II</b>, - <a href="#Page_363">363</a>, - <a href="#Page_368">368–9</a>;</li> - <li class="i1">“false joints,” <b>II</b>, - <a href="#Page_371">371</a>;</li> - <li class="i1">insect nutrition and genesis, <b>II</b>, - <a href="#Page_499">499</a>;</li> - <li class="i1">economics of evolution, <b>II</b>, - <a href="#Page_501">501–5</a>;</li> - <li class="hangingindent1">author’s enunciation of survival of the fittest in 1852, <b>II</b>, - <a href="#Page_528">528–9</a>;</li> - <li class="i1">evils of interference with, in man, <b>II</b>, - <a href="#Page_532">532–3</a>;</li> - <li class="i1">vegetal tissue formation, <b>II</b>, - <a href="#Page_582">582</a>, - <a href="#Page_594">594–6</a>;</li> - <li class="i1">origin of vertebrate type, <b>II</b>, - <a href="#Page_599">599</a>.</li> - - <li>Nature, more complex than supposed, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page252">252</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page450">450</a>.</li> - - <li><i>Navicula</i>, symmetry, <b>II</b>, - <a href="#Page_134">134–5</a>.</li> - - <li>“Nebular Hypothesis,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page23">23</a>.</li> - - <li class="hangingindent">Negation, inconceivability of, the ultimate test of truth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>.</li> - - <li>Negroes, telegony In United States, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page644">644–5</a>.</li> - - <li class="hangingindent"><i>Nemertidæ</i>: continuing vitality of pilidium, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page250">250</a>;</li> - <li class="i1">bilateral symmetry, <b>II</b>, - <a href="#Page_195">195</a>.</li> - - <li>Neo-Darwinists, and Lamarck, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page630">630</a>;</li> - <li class="i1">their position reviewed, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page694">694–5</a>.</li> - - <li>Nerves: electrical phenomena, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page51">51</a>;</li> - <li class="i1">generation of nerve force, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page52">52–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page60">60</a>;</li> - <li class="i1"><i>corpuscula tactus</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page75">75</a>;</li> - <li class="i1">Hertwig’s classification of tissues, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page189">189</a>;</li> - <li class="i1">structural traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page192">192</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page193">193</a>;</li> - <li class="i1">environment and structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page196">196</a>;</li> - <li class="i1">differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page203">203</a>; <b>II</b>, - <a href="#Page_355">355–61</a>;</li> - <li class="i1">vasomotor system, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page206">206</a>;</li> - <li class="i1">vicarious function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page209">209</a>;</li> - <li class="i1">activity and waste, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page216">216</a>;</li> - <li class="i1">adaptability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page229">229</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page232">232</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page236">236</a>;</li> - <li class="i1">parallelism in cell processes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page260">260–2</a>;</li> - <li class="i1">heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page313">313</a>;</li> - <li class="i1">effects of severance, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page349">349</a>;</li> - <li class="i1">relative development in men and women, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page594">594</a>;</li> - <li class="i1">analysis of brain substance, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page596">596</a>;</li> - <li class="hangingindent1">individuation and development of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page598">598</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page599">599</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page600">600</a>;</li> - <li class="hangingindent1">distribution of tactual perceptiveness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page603">603–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page633">633</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page665">665–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page671">671</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page672">672</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="i1">alleged costliness of tissue, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page662">662</a>;</li> - <li class="i1">instinct degeneration in ants, <i>ib.</i>;</li> - <li class="i1">“sensation areas,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page666">666</a>;</li> - <li class="i1">segmentation in Annelids, <b>II</b>, - <a href="#Page_125">125</a>;</li> - <li class="i1">ectodermal derivation, <b>II</b>, - <a href="#Page_303">303–4</a>;</li> - <li class="i1">co-operating factors in evolution of, <b>II</b>, - <a href="#Page_307">307–8</a>;</li> - <li class="i1">differentiation from muscle, <b>II</b>, - <a href="#Page_363">363</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Psychology">Psychology</a>.)</li> - - <li>Nervousness, hereditary transmission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page307">307</a>.</li> - - <li>Neurine, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page594">594</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page597">597</a>.</li> - - <li>Neuter insects (<i>see</i> <a href="#Insects">Insects</a>).</li> - - <li>New Zealand: invasion of alien species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page477">477</a>;</li> - <li class="i1">kinship of past and present forms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page489">489</a>.</li> - - <li>Nitrogen: properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page3">3–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page20">20</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page24">24</a>;</li> - <li class="hangingindent1">compounds and their properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page6">6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page8">8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page12">12–14</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page25">25–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page39">39</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page41">41</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page42">42–3</a>; <b>II</b>, - <a href="#Page_250">250</a>;</li> - <li class="i1">organic importance, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page42">42–3</a>;</li> - <li class="i1">evolution of heat and oxidation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page47">47</a>;</li> - <li class="i1">violent organic effects of compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page54">54–5</a>;</li> - <li class="i1">function in metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page63">63–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page66">66</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page68">68–76</a>;</li> - <li class="i1">presence in protoplasm, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page66">66</a>;</li> - <li class="i1">action in digestion, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>;</li> - <li class="i1">fat accumulation and fertility, <b>II</b>, - <a href="#Page_483">483</a>.</li> - - <li>Nitro-glycerine, violent effects of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page55">55</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page122">122</a>.</li> - - <li>Notochord: segmentation, <b>II</b>, - <a href="#Page_125">125</a>, - <a href="#Page_218">218–22</a>;</li> - <li class="i1">formation, <b>II</b>, - <a href="#Page_217">217–8</a>, - <a href="#Page_600">600</a>;</li> - <li class="i1">in Permian vertebrates, <b>II</b>, - <a href="#Page_225">225</a>.</li> - - <li>Noumenon, life not manifested as, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page580">580</a>.</li> - - <li>Nuclein, <b>II</b>, - <a href="#Page_21">21</a>.</li> - - <li>Nucleus: central development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page163">163</a>;</li> - <li class="i1">in simple organisms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page183">183</a>;</li> - <li class="i1">phenomena exhibited by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page255">255–8</a>;</li> - <li class="i1">current hypotheses of function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page258">258–9</a>;</li> - <li class="i1">properties and function of chromatin, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page259">259–65</a>;</li> - <li class="i1">fusion in fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page283">283–4</a>;</li> - <li class="i1">function in unicellular reproduction, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page595">595–6</a>;</li> - <li class="i1">absence of, <b>II</b>, - <a href="#Page_20">20–1</a>;</li> - <li class="i1">diffused form, <b>II</b>, - <a href="#Page_85">85</a>;</li> - <li class="i1">macro- and micronucleus in conjugation, <b>II</b>, - <a href="#Page_452">452</a>.</li> - - <li id="Nutrition">Nutrition: organic molecular re-arrangement, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page36">36</a>;</li> - <li class="hangingindent1">nitrogenous and non-nitrogenous, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page47">47–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page68">68</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page71">71–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page77">77</a>; <b>II</b>, - <a href="#Page_362">362</a>;</li> - <li class="i1">food assimilation and reasoning, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page81">81</a>;</li> - <li class="i1">needful for vital change, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page94">94</a>;</li> - <li class="hangingindent1">relation to growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page140">140</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page143">143</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page144">144</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page147">147–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page150">150</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page157">157</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page161">161</a>;</li> - <li class="i1">expenditure of energy, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page157">157</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page391">391</a>;</li> - <li class="i1">fluid, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page208">208</a>;</li> - <li class="i1">vegetal fructification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page267">267</a>; <b>II</b>, - <a href="#Page_266">266</a>;</li> - <li class="i1">vegetal growth and genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page293">293</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page294">294–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page336">336</a>;</li> - <li class="i1">animal growth and genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page289">289–93</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page336">336</a>;</li> - <li class="hangingindent1">conditions qualifying antagonism of growth and genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page299">299</a>;</li> - <li class="hangingindent1">competition among parts of an organism for, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page562">562</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page566">566</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676</a>;</li> - <li class="i1">sex differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page594">594–5</a>;</li> - <li class="i1">cell multiplication, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page638">638</a>;</li> - <li class="hangingindent1">differentiation of neuter insects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page655">655–60</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page674">674</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page686">686–8</a>;</li> - <li class="i1">monstrous ant forms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page683">683–4</a>;</li> - <li class="i1">leaf development, <b>II</b>, - <a href="#Page_39">39</a>, - <a href="#Page_42">42</a>, - <a href="#Page_73">73–8</a>;</li> - <li class="i1">vegetal development, <b>II</b>, - <a href="#Page_51">51–2</a>, - <a href="#Page_178">178</a>, - <a href="#Page_276">276</a>;</li> - <li class="i1">axillary buds, <b>II</b>, - <a href="#Page_65">65–9</a>, - <a href="#Page_73">73–4</a>;</li> - <li class="i1">effect on animal aggregation, <b>II</b>, - <a href="#Page_93">93</a>;</li> - <li class="i1">internodes and inflorescence, <b>II</b>, - <a href="#Page_178">178–80</a>;</li> - <li class="i1">helical phænogamic growth, <b>II</b>, - <a href="#Page_181">181</a>;</li> - <li class="i1">action of bile, <b>II</b>, - <a href="#Page_330">330</a>;</li> - <li class="i1">osseous development, <b>II</b>, - <a href="#Page_349">349</a>, - <a href="#Page_353">353</a>;</li> - <li class="i1">genesis, <b>II</b>, - <a href="#Page_419">419</a>, - <a href="#Page_422">422</a>, - <a href="#Page_427">427</a>, - <a href="#Page_435">435–7</a>, - <a href="#Page_452">452</a>;</li> - <li class="i1">parental loss in feeding young, <b>II</b>, - <a href="#Page_424">424</a>, - <a href="#Page_429">429</a>;</li> - <li class="i1">diverse sources, <b>II</b>, - <a href="#Page_433">433</a>;</li> - <li class="i1">Carpenter on reproduction and, <b>II</b>, - <a href="#Page_460">460</a>;</li> - <li class="i1">animal development and genesis, <b>II</b>, - <a href="#Page_465">465</a>;</li> - <li class="i1">expenditure and genesis, <b>II</b>, - <a href="#Page_468">468</a>;</li> - <li class="i1">variations of genesis, <b>II</b>, - <a href="#Page_475">475–80</a>, - <a href="#Page_511">511</a>;</li> - <li class="i1">obesity and genesis, <b>II</b>, - <a href="#Page_480">480–4</a>, - <a href="#Page_511">511</a>;</li> - <li class="i1">general doctrine of genesis, <b>II</b>, - <a href="#Page_486">486</a>;</li> - <li class="i1">genesis and vegetal parasitism, <b>II</b>, - <a href="#Page_486">486</a>;</li> - <li class="i1">also animal, <b>II</b>, - <a href="#Page_487">487–90</a>, - <a href="#Page_495">495</a>;</li> - <li class="i1">insect genesis, <b>II</b>, - <a href="#Page_490">490–2</a>;</li> - <li class="i1">genesis, <i>résumé</i>, <b>II</b>, - <a href="#Page_497">497–9</a>;</li> - <li class="i1">and evolution, <b>II</b>, - <a href="#Page_501">501–4</a>;</li> - <li class="i1">of blackbird and linnet, <b>II</b>, - <a href="#Page_503">503</a>;</li> - <li class="i1">genesis in human race, <b>II</b>, - <a href="#Page_508">508–10</a>, - <a href="#Page_514">514–6</a>;</li> - <li class="i1">Doubleday on, <b>II</b>, - <a href="#Page_510">510–2</a>;</li> - <li class="i1">future human evolution, <b>II</b>, - <a href="#Page_526">526</a>, - <a href="#Page_531">531</a>;</li> - <li class="i1">floral monstrosities, <b>II</b>, - <a href="#Page_542">542</a>, - <a href="#Page_546">546</a>, - <a href="#Page_547">547</a>.</li> -</ul> - -<ul> - <li>Obesity, nutrition and genesis, <b>II</b>, - <a href="#Page_480">480–4</a>, - <a href="#Page_511">511</a>.</li> - - <li>Odoriferous glands, natural selection and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page534">534</a>.</li> - - <li>Odours: floral fertilization, <b>II</b>, - <a href="#Page_268">268–9</a>;</li> - <li class="i1">animal protection, <b>II</b>, - <a href="#Page_434">434</a>.</li> - - <li class="hangingindent">Offspring: parental loss entailed by nurture, <b>II</b>, - <a href="#Page_424">424</a>, - <a href="#Page_429">429</a>;</li> - <li class="i1">influence of age on, <b>II</b>, - <a href="#Page_507">507</a>.</li> - - <li>Oken, L., archetypal hypothesis, <b>II</b>, - <a href="#Page_122">122</a>;</li> - <li class="i1">theory of supernumerary bones, <b>II</b>, - <a href="#Page_223">223</a>;</li> - <li class="i1">on the skull, <b>II</b>, - <a href="#Page_561">561</a>.</li> - - <li>Oliver, F. W., classification of plants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page378">378–9</a>.</li> - - <li class="hangingindent"><i>Ophryotrocha puerilis</i>, ciliation of segments, <b>II</b>, - <a href="#Page_109">109</a>.</li> - - <li id="Orchids">Orchids: pollen propulsion, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page57">57</a>;</li> - <li class="i1">leaf formation in <i>Dendrobium</i>, <b>II</b>, - <a href="#Page_60">60–1</a>;</li> - <li class="hangingindent1">aërial roots and physiological differentiation, <b>II</b>, - <a href="#Page_255">255</a>, - <a href="#Page_257">257</a>;</li> - <li class="i1">foliar surface, <b>II</b>, - <a href="#Page_264">264</a>.</li> - - <li>Organic matter: properties of elements, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page3">3–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page22">22</a>;</li> - <li class="i1">of compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page5">5–13</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page25">25</a>;</li> - <li class="i1">molar and molecular mobility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page12">12–14</a>;</li> - <li class="i1">colloid and crystalloid form, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page15">15–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page25">25</a>;</li> - <li class="i1">their diffusibility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page18">18–21</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page26">26</a>;</li> - <li class="i1">extreme complexity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page21">21</a>;</li> - <li class="i1">laws of evolution and genesis of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page22">22–4</a>;</li> - <li class="i1">modifiability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page27">27</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page44">44</a>;</li> - <li class="i1">capillarity and osmosis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page28">28</a>;</li> - <li class="i1">effects of heat, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page29">29</a>;</li> - <li class="i1">of light, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page30">30–4</a>;</li> - <li class="i1">nitrogenous, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page39">39–43</a>;</li> - <li class="i1">oxidation and evolution of heat, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page46">46</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page60">60</a>;</li> - <li class="i1">genesis of electricity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page50">50–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page60">60</a>;</li> - <li class="i1">sensible motions in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page59">59</a>;</li> - <li class="i1">transformations and persistence of force, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page61">61</a>;</li> - <li class="i1">metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page62">62–77</a>;</li> - <li class="i1">artificial production of compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page64">64</a>;</li> - <li class="i1">contrasted with inorganic matter, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page107">107–8</a>;</li> - <li class="i1">incomprehensibility of vital changes in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page122">122</a>;</li> - <li class="i1">instability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page149">149</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page508">508</a>;</li> - <li class="i1">phosphorus in cell-organization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page260">260–1</a>;</li> - <li class="i1">heterogeneity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page350">350–5</a>;</li> - <li class="hangingindent1">“spontaneous generation” and evolution of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page696">696–701</a>;</li> - <li class="i1">cell-doctrine and evolution of, <b>II</b>, - <a href="#Page_17">17–21</a>.</li> - - <li>Organization (<i>see</i> <a href="#Structure">Structure</a>).</li> - - <li>Ormerod, Dr., on sex and nutrition in wasps, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page656">656</a>.</li> - - <li>Orthogenesis, Eimer’s theory of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page563">563–4</a>.</li> - - <li>Osmosis: organic effects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page28">28</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page29">29</a>;</li> - <li class="i1">in animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page58">58</a>;</li> - <li class="i1">in vascular system, <b>II</b>, - <a href="#Page_339">339</a>;</li> - <li class="i1">in vegetal tissue, <b>II</b>, - <a href="#Page_568">568</a>, - <a href="#Page_575">575</a>, - <a href="#Page_577">577</a>, - <a href="#Page_585">585</a>, - <a href="#Page_592">592–6</a>.</li> - - <li>Osteology (<i>see</i> <a href="#Bone">Bone</a>).</li> - - <li>Ovum (<i>see</i> <a href="#Egg">Egg</a> <i>and</i> <a href="#Fertilization">Fertilization</a>).</li> - - <li class="hangingindent">Owen, Sir R.: metagenesis and parthenogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page273">273–4</a>;</li> - <li class="i1">fossil mammals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page410">410</a>;</li> - <li class="i1">human parasites, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page427">427</a>;</li> - <li class="i1">continuous operation of creative power, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page492">492</a>;</li> - <li class="i1">fission in <i>Infusoria</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page584">584</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page585">585</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page595">595–6</a>;</li> - <li class="i1">parthenogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page592">592</a>;</li> - <li class="i1">theory of vertebrate skeleton, <b>II</b>, - <a href="#Page_123">123</a>, - <a href="#Page_548">548–66</a>;</li> - <li class="i1">theory of supernumerary bones, <b>II</b>, - <a href="#Page_223">223</a>;</li> - <li class="i1">Eschricht on <i>Ascaris</i>, <b>II</b>, - <a href="#Page_488">488</a>.</li> - - <li><i>Oxalis</i>: radial symmetry, <b>II</b>, - <a href="#Page_152">152</a>;</li> - <li class="i1">foliar surface, <b>II</b>, - <a href="#Page_264">264</a>.</li> - - <li>Oxen: comparison with sheep, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page158">158</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page160">160</a>;</li> - <li class="i1">cerebro-spinal system, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page508">508</a>.</li> - - <li>Oxidation (<i>see</i> <a href="#Oxygen">Oxygen</a>).</li> - - <li id="Oxygen">Oxygen: properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page3">3–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page20">20</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page22">22</a>;</li> - <li class="i1">compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page6">6–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page10">10–13</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page22">22</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page24">24–5</a>;</li> - <li class="i1">a crystalloid, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page21">21</a>;</li> - <li class="i1">combining power and atomic weight, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page33">33</a>;</li> - <li class="i1">organic change from, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page37">37</a>;</li> - <li class="i1">heat generation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page46">46–9</a>;</li> - <li class="i1">phosphorescence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page49">49</a>;</li> - <li class="i1">nerve force dependent on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page53">53</a>;</li> - <li class="i1">animal metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page72">72</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page73">73</a>;</li> - <li class="i1">necessary to animal life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page94">94–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page577">577</a>;</li> - <li class="i1">activity and amount inhaled, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page214">214</a>.</li> -</ul> - -<ul> - <li class="hangingindent">Packard, A. S., on eyes of cave-animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page648">648–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>.</li> - - <li class="hangingindent">Paget, Sir J., blood changes in small-pox and scarlatina, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page221">221</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page701">701</a>.</li> - - <li id="Palaeontology">Palæontology: distribution in time, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page404">404–11</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page412">412</a>;</li> - <li class="i1">special creation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page425">425</a>;</li> - <li class="i1">congruity with evolution hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page485">485–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">relations of present to extinct species, <b>II</b>, - <a href="#Page_10">10–11</a>;</li> - <li class="i1">scarcity of remains, <b>II</b>, - <a href="#Page_34">34–5</a>;</li> - <li class="i1">secondary thickening in plants, <b>II</b>, - <a href="#Page_56">56</a>;</li> - <li class="hangingindent1">Cope on osteology of Permian Vertebrates, <b>II</b>, - <a href="#Page_225">225–6</a>.</li> - - <li class="hangingindent">Pangenesis, Darwin’s theory of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page356">356</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page357">357</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page359">359</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page360">360</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page362">362</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page372">372</a>.</li> - - <li class="hangingindent">Panmixia, Weismann’s hypothesis of: Its relation to Romanes’ “cessation of selection,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page560">560</a>;</li> - <li class="hangingindent1">alleged selective process denied, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page561">561–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page667">667</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>;</li> - <li class="i1">distribution of tactual perceptiveness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page608">608</a>;</li> - <li class="i1">rudimentary eyes of cave fauna, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page647">647</a>;</li> - <li class="i1">Romanes on process, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page649">649</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page667">667</a>;</li> - <li class="hangingindent1">degeneration of self-feeding instinct In Amazon ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>;</li> - <li class="i1">rudimentary limbs of whale, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page668">668–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>;</li> - <li class="i1">a pure speculation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page671">671</a>;</li> - <li class="i1">markings on leg-bones of Punjabis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>.</li> - - <li><i>Paramœcium</i>: parasite infesting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page427">427</a>;</li> - <li class="i1">reproduction, <b>II</b>, - <a href="#Page_443">443</a>, - <a href="#Page_452">452</a>.</li> - - <li>Parasites: sexual dimorphism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page315">315</a>;</li> - <li class="i1">limits to distribution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page397">397</a>;</li> - <li class="i1">special creation and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page427">427–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page438">438</a>;</li> - <li class="i1">retrograde development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page457">457</a>; <b>II</b>, - <a href="#Page_12">12</a>;</li> - <li class="i1">aphis and ant, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660–1</a>; <b>II</b>, - <a href="#Page_403">403</a>, - <a href="#Page_405">405</a>;</li> - <li class="i1">as an integrating agency, <b>II</b>, - <a href="#Page_402">402–4</a>;</li> - <li class="i1">its comparative recency, <b>II</b>, - <a href="#Page_404">404</a>;</li> - <li class="i1">nutrition and genesis in vegetal, <b>II</b>, - <a href="#Page_486">486</a>;</li> - <li class="i1">in animal, <b>II</b>, - <a href="#Page_487">487–90</a>, - <a href="#Page_493">493</a>;</li> - <li class="hangingindent1">“castration parasitaire” in crustaceans, <b>II</b>, - <a href="#Page_493">493–6</a>.</li> - - <li>Parasol Ants, origin of classes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page687">687–8</a>.</li> - - <li>Parthenogenesis: occurrence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page274">274–5</a>;</li> - <li class="i1">alternating with gamogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page289">289–91</a>;</li> - <li class="i1">Owen on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page592">592</a>;</li> - <li class="i1">laws of multiplication, <b>II</b>, - <a href="#Page_415">415</a>;</li> - <li class="i1">in articulate animals, <b>II</b>, - <a href="#Page_445">445</a>.</li> - - <li>Pasteur, L., silkworm diseases, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page622">622–3</a>.</li> - - <li class="hangingindent">Peacock: theories of heredity and structure of tail feather, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page372">372–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page695">695</a>; <b>II</b>, - <a href="#Page_618">618–9</a>.</li> - - <li>Pear, foreright shoots, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page287">287</a>.</li> - - <li>Peloria: in <i>gloxinia</i>, <b>II</b>, - <a href="#Page_166">166</a>;</li> - <li class="i1">phænogams, <b>II</b>, - <a href="#Page_180">180</a>.</li> - - <li>Penguin, dermal structure, <b>II</b>, - <a href="#Page_314">314</a>.</li> - - <li>Pepsin, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>.</li> - - <li>Pericyclic fibres of monocotyledons, <b>II</b>, - <a href="#Page_278">278</a>.</li> - - <li class="hangingindent"><i>Peripatus capensis</i>, protoplasmic continuity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page629">629</a>.</li> - - <li class="hangingindent">Peri-visceral sac, function and differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page391">391</a>.</li> - - <li>Perkin, W. H., <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#pagevi">vi</a>.</li> - - <li class="hangingindent" id="Persistence_of_force">Persistence of force, corollaries from: properties of compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page3">3</a>;</li> - <li class="i1">organic transformation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page60">60</a>;</li> - <li class="i1">growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page150">150</a>;</li> - <li class="i1">organic energy, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page220">220</a>;</li> - <li class="i1">variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page335">335</a>;</li> - <li class="i1">genesis, heredity, and variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page354">354–5</a>;</li> - <li class="i1">morphological summary, <b>II</b>, - <a href="#Page_235">235</a>;</li> - <li class="i1">vegetal tissue differentiation, <b>II</b>, - <a href="#Page_245">245</a>;</li> - <li class="i1">physiological development, <b>II</b>, - <a href="#Page_394">394</a>.</li> - - <li>Petals: foliar homology, <b>II</b>, - <a href="#Page_43">43–6</a>;</li> - <li class="i1">“adnate,” <b>II</b>, - <a href="#Page_58">58</a>.</li> - - <li>Petrels, Darwin on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page455">455</a>.</li> - - <li>Phænogams: production of spermatozoids, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page186">186</a>;</li> - <li class="i1">morphological composition, <b>II</b>, - <a href="#Page_37">37–79</a>;</li> - <li class="i1">leaf transitions, <b>II</b>, - <a href="#Page_37">37–42</a>;</li> - <li class="i1">foliar homologies, <b>II</b>, - <a href="#Page_42">42–9</a>;</li> - <li class="i1">origin of type, <b>II</b>, - <a href="#Page_49">49–84</a>;</li> - <li class="i1">vertical growth, <b>II</b>, - <a href="#Page_56">56–64</a>;</li> - <li class="i1">axillary buds, <b>II</b>, - <a href="#Page_66">66</a>;</li> - <li class="hangingindent1">cotyledonous germination and endogenous growth, <b>II</b>, - <a href="#Page_69">69–72</a>;</li> - <li class="i1">axial homologies, <b>II</b>, - <a href="#Page_73">73–5</a>;</li> - <li class="i1">irregular development, <b>II</b>, - <a href="#Page_75">75–8</a>;</li> - <li class="i1">degree of composition, <b>II</b>, - <a href="#Page_78">78</a>;</li> - <li class="i1">reproductive homology, <b>II</b>, - <a href="#Page_80">80–4</a>;</li> - <li class="i1">uni- and multiaxial symmetry, <b>II</b>, - <a href="#Page_141">141–3</a>;</li> - <li class="i1">unit of composition, <b>II</b>, - <a href="#Page_151">151</a>;</li> - <li class="i1">helical growth, <b>II</b>, - <a href="#Page_181">181</a>;</li> - <li class="i1">secondary thickening, <b>II</b>, - <a href="#Page_247">247</a>;</li> - <li class="hangingindent1">tissue and leaf differentiation, <b>II</b>, - <a href="#Page_247">247–9</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">also bark and cambium, <b>II</b>, - <a href="#Page_249">249–50</a>, - <a href="#Page_386">386</a>;</li> - <li class="i1">also outer tissue, <b>II</b>, - <a href="#Page_252">252</a>, - <a href="#Page_256">256–9</a>, - <a href="#Page_270">270</a>, - <a href="#Page_386">386–7</a>;</li> - <li class="i1">wax deposit on leaves, <b>II</b>, - <a href="#Page_260">260–2</a>;</li> - <li class="hangingindent1">differentiation of inner tissues, <b>II</b>, - <a href="#Page_273">273–5</a>, - <a href="#Page_388">388</a>;</li> - <li class="i1">vascular system development, <b>II</b>, - <a href="#Page_280">280–4</a>, - <a href="#Page_388">388</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_293">293–5</a>, - <a href="#Page_296">296</a>, - <a href="#Page_390">390</a>;</li> - <li class="i1">insect fertilization, <b>II</b>, - <a href="#Page_407">407</a>;</li> - <li class="i1">multiplication, <b>II</b>, - <a href="#Page_441">441</a>, - <a href="#Page_442">442</a>;</li> - <li class="i1">genesis and growth, <b>II</b>, - <a href="#Page_451">451</a>, - <a href="#Page_457">457</a>;</li> - <li class="i1">and development, <b>II</b>, - <a href="#Page_464">464</a>;</li> - <li class="i1">and nutrition, <b>II</b>, - <a href="#Page_476">476</a>, - <a href="#Page_477">477</a>, - <a href="#Page_511">511</a>;</li> - <li class="hangingindent1">substitution of axial for foliar organs, <b>II</b>, - <a href="#Page_541">541–7</a>.</li> - - <li>Phenomenon, life manifested as, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page580">580</a>.</li> - - <li>Philology (<i>see</i> <a href="#Language">Language</a>).</li> - - <li><i>Phoronis</i>, individuality, <b>II</b>, - <a href="#Page_444">444</a>.</li> - - <li>Phosphorescence, organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page49">49</a>.</li> - - <li>Phosphorus: allotropic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page4">4</a>;</li> - <li class="i1">in cell physiology, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page259">259–62</a>;</li> - <li class="i1">cerebral activity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page596">596–7</a>;</li> - <li class="i1">organic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page703">703</a>.</li> - - <li>Photogenes, visibility of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page218">218</a>.</li> - - <li>Phylogeny: as interpreting morphology, <b>II</b>, - <a href="#Page_10">10–12</a>;</li> - <li class="i1">difficulties of affiliation, <b>II</b>, - <a href="#Page_34">34–5</a>.</li> - <li class="i1">(<i>See</i> <a href="#Embryology">Embryology</a> <i>and</i> <a href="#Evolution">Evolution</a>.)</li> - - <li id="Physiological_Units">Physiological Units: definition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page226">226</a>;</li> - <li class="i1">genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page280">280–1</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page316">316</a>;</li> - <li class="i1">heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page315">315–9</a>;</li> - <li class="i1">variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page330">330</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page331">331–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page333">333</a>; <b>II</b>, - <a href="#Page_619">619</a>;</li> - <li class="i1">stability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page340">340</a>; <b>II</b>, - <a href="#Page_614">614</a>;</li> - <li class="i1">self-fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page342">342–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page353">353</a>;</li> - <li class="i1">interbreeding, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page345">345</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page353">353</a>; <b>II</b>, - <a href="#Page_615">615</a>;</li> - <li class="hangingindent1">recapitulation of hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page350">350–5</a>; <b>II</b>, - <a href="#Page_612">612–7</a>;</li> - <li class="hangingindent1">structural proclivities, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page362">362</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page369">369–71</a>; <b>II</b>, - <a href="#Page_613">613</a>, - <a href="#Page_622">622</a>;</li> - <li class="i1">sociological analogy, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364</a>; <b>II</b>, - <a href="#Page_620">620</a>;</li> - <li class="i1">complexity in organized types, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page368">368–70</a>;</li> - <li class="i1">re-named “constitutional units,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page369">369</a>;</li> - <li class="i1">telegony, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page650">650</a>;</li> - <li class="i1">“mechanical theory,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page701">701–6</a>;</li> - <li class="i1">morphological development, <b>II</b>, - <a href="#Page_7">7–9</a>;</li> - <li class="i1">cell-doctrine, <b>II</b>, - <a href="#Page_17">17–21</a>;</li> - <li class="i1">development, <b>II</b>, - <a href="#Page_76">76</a>;</li> - <li class="i1">“false joints,” <b>II</b>, - <a href="#Page_371">371–2</a>;</li> - <li class="hangingindent1">dissociation of ancestral traits in hybrids, <b>II</b>, - <a href="#Page_616">616–7</a>;</li> - <li class="i1">inheritance of acquired characters, <b>II</b>, - <a href="#Page_618">618–23</a>.</li> - - <li>Physiological division of labour (<i>see</i> <a href="#Labour">Labour</a>).</li> - - <li>Physiological Selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page569">569–71</a>.</li> - - <li id="Physiology">Physiology: and psychology, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page127">127</a>;</li> - <li class="i1">subdivisions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page128">128</a>;</li> - <li class="i1">vicarious function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page208">208</a>;</li> - <li class="i1">primitive interpretations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page417">417</a>;</li> - <li class="hangingindent1">multiplication of effects exemplified, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page512">512</a>; <b>II</b>, - <a href="#Page_390">390</a>;</li> - <li class="i1">relations to morphology, <b>II</b>, - <a href="#Page_3">3</a>, - <a href="#Page_239">239–41</a>;</li> - <li class="hangingindent1">evolutionary interpretation of phenomena, <b>II</b>, - <a href="#Page_241">241–5</a>, - <a href="#Page_384">384–95</a>;</li> - <li class="i1">ultimate inconceivability of processes, <b>II</b>, - <a href="#Page_372">372</a>;</li> - <li class="hangingindent1">correlated integration and differentiation, <b>II</b>, - <a href="#Page_373">373</a>.</li> - - <li>Physiology, Animal: metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page67">67–77</a>;</li> - <li class="i1">vertebrate internal symmetry, <b>II</b>, - <a href="#Page_108">108</a>;</li> - <li class="hangingindent1">tissue differentiation in <i>Protozoa</i>, <b>II</b>, - <a href="#Page_299">299</a>, - <a href="#Page_385">385</a>;</li> - <li class="hangingindent1">primary tissue differentiation, <b>II</b>, - <a href="#Page_300">300–2</a>, - <a href="#Page_382">382</a>, - <a href="#Page_389">389</a>;</li> - <li class="hangingindent1">natural selection and tissue differentiation, <b>II</b>, - <a href="#Page_304">304–8</a>;</li> - <li class="i1">outer tissue in <i>Cœlenterata</i>, <b>II</b>, - <a href="#Page_309">309–10</a>;</li> - <li class="i1">respiratory organs, <b>II</b>, - <a href="#Page_310">310–1</a>, - <a href="#Page_333">333–8</a>;</li> - <li class="hangingindent1">differentiation of animal epidermic tissue, <b>II</b>, - <a href="#Page_312">312–4</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">development of tegumentary organs, <b>II</b>, - <a href="#Page_314">314–6</a>;</li> - <li class="i1">of sensory, <b>II</b>, - <a href="#Page_317">317–20</a>;</li> - <li class="hangingindent1">inner and outer tissue transition, <b>II</b>, - <a href="#Page_321">321–2</a>, - <a href="#Page_389">389</a>;</li> - <li class="i1">alimentary canal differentiation, <b>II</b>, - <a href="#Page_323">323–5</a>;</li> - <li class="i1">gizzard development in birds, <b>II</b>, - <a href="#Page_325">325</a>;</li> - <li class="i1">alimentary canal of ruminants, <b>II</b>, - <a href="#Page_327">327–9</a>;</li> - <li class="i1">differentiation of liver, <b>II</b>, - <a href="#Page_329">329–33</a>;</li> - <li class="i1">of animal vascular system, <b>II</b>, - <a href="#Page_339">339–44</a>;</li> - <li class="i1">of osseous system, <b>II</b>, - <a href="#Page_344">344–55</a>;</li> - <li class="i1">of nerve tissue, <b>II</b>, - <a href="#Page_355">355–61</a>;</li> - <li class="i1">of muscle, <b>II</b>, - <a href="#Page_361">361–9</a>;</li> - <li class="i1">differentiation and integration, <b>II</b>, - <a href="#Page_373">373–6</a>;</li> - <li class="i1">in vascular system, <b>II</b>, - <a href="#Page_376">376–9</a>, - <a href="#Page_383">383</a>;</li> - <li class="i1">in nerves, <b>II</b>, - <a href="#Page_379">379–82</a>;</li> - <li class="i1">origin of development, <b>II</b>, - <a href="#Page_384">384</a>;</li> - <li class="hangingindent1">differentiation and instability of homogeneous, <b>II</b>, - <a href="#Page_384">384–9</a>, - <a href="#Page_392">392</a>;</li> - <li class="i1">summary of development, <b>II</b>, - <a href="#Page_384">384–94</a>;</li> - <li class="i1">multiplication of effects, <b>II</b>, - <a href="#Page_390">390–1</a>, - <a href="#Page_392">392</a>;</li> - <li class="i1">equilibration, <b>II</b>, - <a href="#Page_391">391–4</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Function">Function</a>.)</li> - - <li>Physiology, Plant: metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page62">62–7</a>;</li> - <li class="hangingindent1">tissue differentiation in secondary aggregates, <b>II</b>, - <a href="#Page_246">246</a>, - <a href="#Page_385">385</a>;</li> - <li class="i1">in phænogams, <b>II</b>, - <a href="#Page_247">247–9</a>, - <a href="#Page_386">386</a>;</li> - <li class="i1">in bark and cambium, <b>II</b>, - <a href="#Page_249">249–50</a>, - <a href="#Page_386">386</a>;</li> - <li class="i1">in free and fixed surfaces, <b>II</b>, - <a href="#Page_251">251–6</a>, - <a href="#Page_270">270</a>, - <a href="#Page_386">386</a>;</li> - <li class="i1">outer stem and leaf tissue, <b>II</b>, - <a href="#Page_256">256–9</a>, - <a href="#Page_270">270</a>, - <a href="#Page_386">386</a>;</li> - <li class="hangingindent1">superficial differentiation in leaves, <b>II</b>, - <a href="#Page_260">260–4</a>, - <a href="#Page_270">270</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">floral tissue differentiation, <b>II</b>, - <a href="#Page_265">265–9</a>;</li> - <li class="i1">outer tissue, <i>résumé</i>, <b>II</b>, - <a href="#Page_270">270</a>;</li> - <li class="i1">inner tissue differentiation, <b>II</b>, - <a href="#Page_273">273–5</a>, - <a href="#Page_388">388</a>;</li> - <li class="i1">supporting tissue, <b>II</b>, - <a href="#Page_275">275–9</a>, - <a href="#Page_285">285–8</a>, - <a href="#Page_388">388</a>;</li> - <li class="hangingindent1">vascular system development, <b>II</b>, - <a href="#Page_273">273–5</a>, - <a href="#Page_279">279–84</a>, - <a href="#Page_285">285–8</a>, - <a href="#Page_388">388</a>;</li> - <li class="i1">inner tissue, summary, <b>II</b>, - <a href="#Page_288">288–91</a>, - <a href="#Page_388">388</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_292">292–8</a>;</li> - <li class="hangingindent1">differentiation and instability of homogeneous, <b>II</b>, - <a href="#Page_384">384–9</a>, - <a href="#Page_392">392</a>;</li> - <li class="i1">multiplication of effects, <b>II</b>, - <a href="#Page_390">390–1</a>, - <a href="#Page_392">392</a>;</li> - <li class="i1">equilibration, <b>II</b>, - <a href="#Page_391">391–4</a>;</li> - <li class="i1">circulation and wood formation, <b>II</b>, - <a href="#Page_564">564–97</a>;</li> - <li class="i1">dye permeability, <b>II</b>, - <a href="#Page_569">569–74</a>, - <a href="#Page_577">577–81</a>, - <a href="#Page_584">584</a>, - <a href="#Page_586">586</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Function">Function</a>.)</li> - - <li>Pickering, J. W., on artificial proteids, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page39">39</a>.</li> - - <li>Pig: colour of muscles, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page365">365–6</a>;</li> - <li class="i1">telegony, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page627">627</a>;</li> - <li class="i1">fertility of domestic and wild sow, <b>II</b>, - <a href="#Page_479">479–80</a>.</li> - - <li>Pigeons: food of starving, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page215">215</a>;</li> - <li class="i1">heredity and variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page305">305</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page321">321</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page615">615</a>;</li> - <li class="i1">atavism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314</a>;</li> - <li class="i1">fertility, <b>II</b>, - <a href="#Page_471">471–2</a>, - <a href="#Page_478">478</a>.</li> - - <li>Pike, unceasing growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page154">154</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page292">292</a>.</li> - - <li class="hangingindent">Pique-gouffe, commensal relations with buffalo, <b>II</b>, - <a href="#Page_403">403</a>.</li> - - <li><i>Plagiochila</i>, evolution of stem, <b>II</b>, - <a href="#Page_62">62</a>.</li> - - <li><i>Planaria</i>: integration, <b>II</b>, - <a href="#Page_101">101–2</a>;</li> - <li class="i1">Morgan on regeneration, <b>II</b>, - <a href="#Page_102">102</a>, - <a href="#Page_611">611</a>;</li> - <li class="i1">segmentation, <b>II</b>, - <a href="#Page_107">107</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_195">195</a>;</li> - <li class="i1">unintegrated function, <b>II</b>, - <a href="#Page_373">373</a>.</li> - - <li id="Plants">Plants: influence of heat, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page29">29</a>;</li> - <li class="i1">effect of solar rays, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page31">31–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page500">500</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">chemical composition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page40">40–1</a>;</li> - <li class="i1">heat generation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page47">47</a>;</li> - <li class="i1">phosphorescence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page49">49</a>;</li> - <li class="i1">electricity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page51">51</a>;</li> - <li class="i1">sensible motion, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page56">56–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page58">58</a>;</li> - <li class="i1">metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page62">62–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page70">70</a>;</li> - <li class="i1">vital changes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page86">86</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page87">87</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page91">91</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page94">94</a>;</li> - <li class="i1">simulation by crystals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page96">96</a>;</li> - <li class="i1">vital adjustments, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page102">102</a>;</li> - <li class="i1">length and complexity of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page103">103–4</a>;</li> - <li class="i1">biological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page125">125</a>;</li> - <li class="hangingindent1">growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page136">136</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page138">138</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page140">140</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page143">143</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page145">145–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page153">153</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page160">160–1</a>; <b>II</b>, - <a href="#Page_401">401–2</a>;</li> - <li class="i1">development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page163">163–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page167">167–70</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page272">272</a>;</li> - <li class="i1">weight, temperature, and self-mobility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page174">174</a>;</li> - <li class="i1">function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page174">174–8</a>;</li> - <li class="i1">structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page194">194–6</a>; <b>II</b>, - <a href="#Page_21">21</a>;</li> - <li class="i1">animal structure contrasted, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page196">196</a>;</li> - <li class="i1">function and structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page200">200</a>;</li> - <li class="i1">vicarious function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page208">208–9</a>;</li> - <li class="i1">waste and repair, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page213">213</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page220">220</a>;</li> - <li class="i1">physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page225">225–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page317">317</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page360">360</a>;</li> - <li class="i1">adaptation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page227">227</a>;</li> - <li class="i1">what is an individual? <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page244">244–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page250">250–1</a>;</li> - <li class="i1">genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page270">270</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page272">272–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page274">274</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page276">276–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279–85</a>;</li> - <li class="hangingindent1">relation of nutrition to growth and genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page284">284–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page294">294</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295–300</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page642">642</a>; <b>II</b>, - <a href="#Page_39">39</a>;</li> - <li class="i1">ovule homologues, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page288">288</a>;</li> - <li class="hangingindent1">natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page294">294–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page532">532</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page533">533</a>; <b>II</b>, - <a href="#Page_51">51</a>;</li> - <li class="i1">heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page301">301–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page308">308</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page358">358–60</a>;</li> - <li class="i1">variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page320">320</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page323">323–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page325">325–6</a>;</li> - <li class="i1">fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page340">340–5</a>;</li> - <li class="i1">classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page377">377–80</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page389">389–90</a>;</li> - <li class="hangingindent1">distribution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page396">396–400</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page401">401–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page404">404–12</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page478">478–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">special creation and parasitism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page428">428</a>;</li> - <li class="i1">evolution hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page434">434</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page443">443</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page449">449–50</a>;</li> - <li class="i1">rudimentary organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page474">474</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page475">475</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">varied media, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page484">484</a>; <b>II</b>, - <a href="#Page_32">32</a>;</li> - <li class="i1">alien and native species in New Zealand, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page477">477</a>;</li> - <li class="i1">E. Darwin and Lamarck on evolution of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page490">490–8</a>;</li> - <li class="i1">geologic changes affecting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page501">501–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="hangingindent1">interdependence of animals and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page504">504–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page514">514</a>; <b>II</b>, - <a href="#Page_398">398</a>;</li> - <li class="i1">complexity of influences affecting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page506">506</a>;</li> - <li class="i1">direct equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page523">523–5</a>;</li> - <li class="i1">indirect, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page532">532</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page533">533</a>;</li> - <li class="i1">seed distribution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page546">546</a>;</li> - <li class="i1">wood development, <b>II</b>, - <a href="#Page_285">285–7</a>, - <a href="#Page_289">289</a>, - <a href="#Page_567">567–97</a>;</li> - <li class="i1">interdependence, <b>II</b>, - <a href="#Page_402">402–3</a>, - <a href="#Page_404">404</a>;</li> - <li class="i1">insect relations, <b>II</b>, - <a href="#Page_406">406–7</a>;</li> - <li class="i1">adaptation and multiplication, <b>II</b>, - <a href="#Page_411">411–6</a>;</li> - <li class="i1">rhythm in numbers, <b>II</b>, - <a href="#Page_419">419</a>;</li> - <li class="i1">growth and asexual genesis, <b>II</b>, - <a href="#Page_439">439–42</a>;</li> - <li class="i1">growth and sexual genesis, <b>II</b>, - <a href="#Page_448">448–51</a>;</li> - <li class="i1">expenditure, <b>II</b>, - <a href="#Page_467">467</a>;</li> - <li class="i1">horticulture, nutrition, and genesis, <b>II</b>, - <a href="#Page_477">477</a>;</li> - <li class="i1">tree development, <b>II</b>, - <a href="#Page_553">553</a>;</li> - <li class="i1">circulation and wood formation, <b>II</b>, - <a href="#Page_567">567–92</a>;</li> - <li class="hangingindent1">dye permeability and circulation, <b>II</b>, - <a href="#Page_569">569–74</a>, - <a href="#Page_577">577–81</a>, - <a href="#Page_584">584</a>, - <a href="#Page_586">586</a>;</li> - <li class="hangingindent1"><i>résumé</i> on circulation and wood formation, <b>II</b>, - <a href="#Page_592">592–7</a>.</li> - <li class="hangingindent1">(<i>See also</i> <a href="#Multiplication">Multiplication</a>, <a href="#Morphology">Morphology</a>, <i>and</i> <a href="#Physiology">Physiology</a>.)</li> - - <li>Plasmodium, dissolution of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page185">185</a>.</li> - - <li>Plato, ἰδέα of, <b>II</b>, - <a href="#Page_550">550</a>.</li> - - <li><i>Platyhelminthes</i>: transverse fission, <b>II</b>, - <a href="#Page_101">101</a>;</li> - <li class="i1">segmented and non-segmented types, <b>II</b>, - <a href="#Page_102">102</a>, - <a href="#Page_107">107</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_195">195</a>, - <a href="#Page_197">197</a>;</li> - <li class="i1">multiplication and growth, <b>II</b>, - <a href="#Page_488">488–9</a>.</li> - - <li>Plethora, fertility and, <b>II</b>, - <a href="#Page_480">480–4</a>, - <a href="#Page_511">511</a>.</li> - - <li><i>Pleurococcaceæ</i>, unicellular form, <b>II</b>, - <a href="#Page_21">21</a>, - <a href="#Page_134">134</a>.</li> - - <li class="hangingindent"><i>Pleuronectidæ</i>: symmetry and location of eyes, <b>II</b>, - <a href="#Page_205">205</a>;</li> - <li class="i1">outer tissue, <b>II</b>, - <a href="#Page_387">387</a>.</li> - - <li><i>Plumatella</i>: metagenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page277">277</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_195">195</a>.</li> - - <li class="hangingindent"><i>Podostemaceæ</i>, undeveloped circulatory system, <b>II</b>, - <a href="#Page_274">274</a>.</li> - - <li class="hangingindent">Polar bodies, hypothesis concerning extrusion of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page266">266–8</a>.</li> - - <li class="hangingindent">Polarity, organic, of physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page226">226</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page315">315</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page317">317</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page332">332</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page350">350–1</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page701">701–6</a>.</li> - - <li>Polyatomic compounds (<i>see</i> <a href="#Chemistry">Chemistry</a>).</li> - - <li class="hangingindent"><i>Polychætæ</i>, anomalous development in <i>Myrianida</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page361">361</a>.</li> - - <li><i>Polycytharia</i>, integration, <b>II</b>, - <a href="#Page_90">90</a>, - <a href="#Page_124">124</a>.</li> - - <li><i>Polygastrica</i>, aggregation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page586">586</a>.</li> - - <li>Polymerism: of compounds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page11">11</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page25">25</a>;</li> - <li class="i1">nerve tissue, <b>II</b>, - <a href="#Page_356">356</a>.</li> - - <li><i>Polypori</i>, symmetry and environment, <b>II</b>, - <a href="#Page_139">139</a>.</li> - - <li>Polyps (see <a href="#Coelenterata"><i>Cœlenterata</i></a>).</li> - - <li id="Polyzoa"><i>Polyzoa</i>: size, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page140">140</a>;</li> - <li class="i1">multiaxial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>;</li> - <li class="i1">structural indefiniteness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page173">173</a>;</li> - <li class="i1">functional differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page202">202</a>;</li> - <li class="i1">trochophoral kinship, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page447">447</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_93">93–4</a>, - <a href="#Page_96">96</a>, - <a href="#Page_124">124</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_194">194</a>, - <a href="#Page_207">207</a>;</li> - <li class="i1">vascular system, <b>II</b>, - <a href="#Page_340">340</a>;</li> - <li class="i1">gemmation, <b>II</b>, - <a href="#Page_444">444</a>.</li> - - <li>Poor Laws, and natural selection, <b>II</b>, - <a href="#Page_532">532</a>.</li> - - <li class="hangingindent"><i>Population, A Theory of</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page265">265</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page577">577–601</a>; <b>II</b>, - <a href="#Page_411">411</a>.</li> - - <li>Potato: simulated growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page136">136</a>;</li> - <li class="hangingindent1">vicarious function of tuber, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page209">209</a>; <b>II</b>, - <a href="#Page_255">255</a>;</li> - <li class="i1">sub-species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page302">302</a>;</li> - <li class="i1">dye absorption, <b>II</b>, - <a href="#Page_279">279</a>.</li> - - <li class="hangingindent">Preservation: fertility and self-, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page581">581</a>; <b>II</b>, - <a href="#Page_423">423</a>, - <a href="#Page_430">430</a>;</li> - <li class="i1">nutrition, <b>II</b>, - <a href="#Page_493">493</a>.</li> - - <li class="hangingindent">“Progress; its Law and Cause,” theory of species differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page568">568</a>.</li> - - <li>Projectiles, factors in flight of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page450">450–1</a>.</li> - - <li>Proteids: metabolic function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page67">67</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page68">68</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page72">72</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page76">76</a>;</li> - <li class="i1">complexity of molecule, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page122">122</a>.</li> - - <li>Protein: evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page23">23</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page24">24</a>;</li> - <li class="i1">isomerism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page700">700</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page703">703</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page704">704</a>.</li> - - <li><i>Proteus</i>, degeneration of eye, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page613">613</a>.</li> - - <li><i>Protodrilus</i>, intestine segmentation, <b>II</b>, - <a href="#Page_125">125</a>.</li> - - <li><i>Protophyta</i>: internal movements, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page56">56</a>;</li> - <li class="i1">limit of growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page138">138</a>;</li> - <li class="i1">development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page164">164</a>;</li> - <li class="i1">structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page173">173</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page181">181–3</a>;</li> - <li class="i1">self-mobility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page175">175</a>;</li> - <li class="i1">individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page245">245</a>;</li> - <li class="hangingindent1">multiplication, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page270">270</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page276">276</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page581">581</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page584">584–5</a>; <b>II</b>, - <a href="#Page_439">439</a>, - <a href="#Page_462">462</a>;</li> - <li class="i1">genesis and nutrition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295</a>;</li> - <li class="i1">unicellular, <b>II</b>, - <a href="#Page_21">21</a>;</li> - <li class="i1">central aggregation, <b>II</b>, - <a href="#Page_24">24</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_134">134</a>;</li> - <li class="i1">tissues, <b>II</b>, - <a href="#Page_244">244</a>, - <a href="#Page_249">249</a>;</li> - <li class="i1">primary differentiation, <b>II</b>, - <a href="#Page_385">385</a>;</li> - <li class="i1">primordial type, <b>II</b>, - <a href="#Page_398">398</a>;</li> - <li class="i1">symbiosis, <b>II</b>, - <a href="#Page_400">400</a>.</li> - - <li class="hangingindent">Protoplasm: self-increasing function of primordial, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page63">63–4</a>;</li> - <li class="i1">plant metabolism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page65">65–7</a>;</li> - <li class="i1">complexity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page122">122</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page253">253–5</a>;</li> - <li class="i1">differentiation in simple organisms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page182">182–3</a>;</li> - <li class="hangingindent1">continuity and inter-circulation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page190">190–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page371">371</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page629">629</a>; <b>II</b>, - <a href="#Page_21">21</a>, - <a href="#Page_620">620</a>;</li> - <li class="i1">“streaming,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page253">253</a>;</li> - <li class="i1">structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page253">253–5</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Cell">Cell</a>.)</li> - - <li><i>Protozoa</i>: inorganic components, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page17">17</a>;</li> - <li class="i1">locomotion, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page58">58</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page175">175</a>; <b>II</b>, - <a href="#Page_14">14</a>;</li> - <li class="i1">vital changes shown by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page94">94</a>;</li> - <li class="i1">limitation of growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page138">138</a>;</li> - <li class="i1">development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page164">164</a>;</li> - <li class="i1">structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page173">173</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page181">181–3</a>;</li> - <li class="hangingindent1">incipient differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page198">198</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page391">391</a>; <b>II</b>, - <a href="#Page_299">299</a>, - <a href="#Page_309">309</a>;</li> - <li class="hangingindent1">multiplication, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page270">270</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page276">276</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page280">280</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page582">582</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page584">584</a>; <b>II</b>, - <a href="#Page_442">442</a>, - <a href="#Page_451">451–2</a>;</li> - <li class="i1">genesis and nutrition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page295">295</a>;</li> - <li class="i1">distribution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page396">396</a>;</li> - <li class="i1">parasites infesting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page427">427</a>;</li> - <li class="i1">Weismann’s hypothesis of immortality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page637">637</a>;</li> - <li class="i1">“spontaneous generation,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page697">697–701</a>;</li> - <li class="i1">non-nucleated, <b>II</b>, - <a href="#Page_20">20</a>;</li> - <li class="i1">primary aggregate, <b>II</b>, - <a href="#Page_86">86–7</a>, - <a href="#Page_124">124</a>;</li> - <li class="i1">progressing integration, <b>II</b>, - <a href="#Page_89">89–91</a>, - <a href="#Page_124">124</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_186">186</a>;</li> - <li class="i1">primordial plant-animal type, <b>II</b>, - <a href="#Page_397">397–8</a>;</li> - <li class="i1">symbiosis, <b>II</b>, - <a href="#Page_400">400</a>.</li> - - <li>Protyle, hypothetical chemical unit, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page22">22</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page23">23</a>.</li> - - <li>Pseud-axial development, vegetal, <b>II</b>, - <a href="#Page_28">28–9</a>, - <a href="#Page_30">30</a>.</li> - - <li class="hangingindent">Pseudo-foliar development, vegetal, <b>II</b>, - <a href="#Page_26">26–8</a>, - <a href="#Page_30">30</a>.</li> - - <li><i>Psychidæ</i>: parthenogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page275">275</a>;</li> - <li class="i1">sexual dimorphism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page683">683</a>.</li> - - <li class="hangingindent" id="Psychology">Psychology: reasoning and definition of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page81">81–8</a>;</li> - <li class="hangingindent1">correspondence shown by <i>recognition</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page95">95</a>;</li> - <li class="i1">contrasted with physiology, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page127">127</a>;</li> - <li class="i1">departments of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page127">127–8</a>;</li> - <li class="i1">vicarious function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page209">209</a>;</li> - <li class="i1">waste and repair in sensory organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page217">217</a>;</li> - <li class="i1">sensory adaptability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page229">229</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page231">231</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page232">232</a>;</li> - <li class="i1">inheritance of sensory defects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page306">306</a>;</li> - <li class="i1">musical talent, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page311">311–2</a>;</li> - <li class="hangingindent1">intellectual progress and special creation hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page417">417</a>;</li> - <li class="hangingindent1">special creation a pseud-idea, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page420">420</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page429">429</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page433">433</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page554">554</a>;</li> - <li class="hangingindent1">legitimacy of evolution hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page433">433–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page439">439</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page554">554</a>;</li> - <li class="i1">embryology of ideas, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page450">450</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page457">457</a>;</li> - <li class="hangingindent1">persistent formative power unrepresentable, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page492">492</a>;</li> - <li class="hangingindent1">E. Darwin’s and Lamarck’s theory of desires, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page494">494</a>;</li> - <li class="i1">natural selection and brain evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>;</li> - <li class="hangingindent1">genesis and cerebral activity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page594">594</a>; <b>II</b>, - <a href="#Page_512">512–4</a>, - <a href="#Page_516">516–9</a>, - <a href="#Page_530">530</a>;</li> - <li class="hangingindent1">heredity and distribution of tactual perceptiveness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page602">602–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page665">665–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page672">672</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="i1">inconceivability of the negation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>;</li> - <li class="i1">vitiation of evidence, <b>II</b>, - <a href="#Page_88">88</a>;</li> - <li class="i1">repetition and perception, <b>II</b>, - <a href="#Page_143">143</a>;</li> - <li class="i1">differentiation of sensory organs, <b>II</b>, - <a href="#Page_317">317–20</a>;</li> - <li class="i1">differentiation of nerve tissue, <b>II</b>, - <a href="#Page_355">355–61</a>;</li> - <li class="i1">functional integration, <b>II</b>, - <a href="#Page_376">376</a>;</li> - <li class="i1">also integration, <b>II</b>, - <a href="#Page_380">380–2</a>;</li> - <li class="i1">equilibration of nerve discharge, <b>II</b>, - <a href="#Page_393">393</a>;</li> - <li class="hangingindent1">human fertility and nerve development, <b>II</b>, - <a href="#Page_466">466</a>, - <a href="#Page_532">532</a>;</li> - <li class="i1">future human evolution, <b>II</b>, - <a href="#Page_523">523–5</a>, - <a href="#Page_527">527</a>;</li> - <li class="i1">human evolution and genesis, <b>II</b>, - <a href="#Page_529">529–31</a>;</li> - <li class="i1">future mental development, <b>II</b>, - <a href="#Page_535">535</a>;</li> - <li class="i1">origin of vertebrate type, <b>II</b>, - <a href="#Page_598">598–600</a>.</li> - - <li><i>Pteridophyta</i>: size attained by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page138">138</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page139">139</a>;</li> - <li class="i1">homologies, <b>II</b>, - <a href="#Page_80">80–1</a>, - <a href="#Page_82">82</a>;</li> - <li class="i1">frond surface differentiation, <b>II</b>, - <a href="#Page_260">260</a>.</li> - - <li><i>Pteropoda</i>: bilateral symmetry, <b>II</b>, - <a href="#Page_201">201</a>;</li> - <li class="i1">dermal respiration, <b>II</b>, - <a href="#Page_310">310</a>.</li> - - <li>Ptyaline, metabolic function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>.</li> - - <li class="hangingindent">Punjabis, inheritance of acquired osteological peculiarities, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>.</li> - - <li><i>Pyrosomidæ</i>: phosphorescence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page47">47</a>;</li> - <li class="i1">integration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page588">588</a>; <b>II</b>, - <a href="#Page_97">97</a>.</li> -</ul> - -<ul> - <li class="hangingindent">Quagga, telegonic transmission of markings to offspring of mare, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page624">624</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page627">627</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646</a>.</li> - - <li>Quills, development, <b>II</b>, - <a href="#Page_314">314–6</a>.</li> -</ul> - -<ul> - <li>Rabbit: activity and muscle colour, <b>II</b>, - <a href="#Page_365">365</a>;</li> - <li class="i1">over-running checked by weasels, <b>II</b>, - <a href="#Page_405">405</a>;</li> - <li class="i1">expenditure and genesis, <b>II</b>, - <a href="#Page_472">472</a>.</li> - - <li>Radial, definition, <b>II</b>, - <a href="#Page_148">148</a>.</li> - - <li><i>Radiolaria</i>: unicentral development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page163">163</a>;</li> - <li class="i1">secondary aggregation, <b>II</b>, - <a href="#Page_88">88</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_187">187</a>.</li> - - <li class="hangingindent"><i>Radula</i>, development of roots from leaflets, <b>II</b>, - <a href="#Page_34">34</a>.</li> - - <li><i>Rafflesiaceæ</i>: homogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page272">272</a>;</li> - <li class="i1">tissue differentiation, <b>II</b>, - <a href="#Page_274">274</a>;</li> - <li class="i1">nutrition and genesis, <b>II</b>, - <a href="#Page_486">486</a>.</li> - - <li>Rat (see <a href="#Rodentia"><i>Rodentia</i></a>).</li> - - <li>Rathke, H., on vertebrate embryo, <b>II</b>, - <a href="#Page_119">119</a>.</li> - - <li>Ray, J., plant classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page378">378</a>.</li> - - <li>Reasoning, compared with assimilation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page81">81–7</a>.</li> - - <li>Recapitulation, embryological, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page453">453</a>.</li> - - <li>Regeneration (<i>see</i> <a href="#Repair">Repair</a>).</li> - - <li class="hangingindent">Rejuvenescence, and sexual fertilization, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page637">637</a>; <b>II</b>, - <a href="#Page_613">613</a>.</li> - - <li>Remak, R., vertebrate embryo, <b>II</b>, - <a href="#Page_120">120</a>.</li> - - <li id="Repair">Repair: continuity of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page216">216–9</a>;</li> - <li class="hangingindent1">animal injuries, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page219">219</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page222">222–4</a>; <b>II</b>, - <a href="#Page_102">102</a>, - <a href="#Page_611">611</a>;</li> - <li class="i1">deductive interpretation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page221">221–2</a>;</li> - <li class="hangingindent1">theories of heredity and regenerative phenomena, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page360">360–1</a>.</li> - - <li>Repetition of like parts, <b>II</b>, - <a href="#Page_126">126</a>.</li> - - <li>Reproduction (<i>see</i> <a href="#Multiplication">Multiplication</a>).</li> - - <li id="Reptilia"><i>Reptilia</i>: growth and expenditure of force, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page142">142</a>;</li> - <li class="i1">sizes of ova and adult, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page144">144</a>;</li> - <li class="i1">longevity of crocodile, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page154">154</a>;</li> - <li class="i1">temperature, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page174">174</a>;</li> - <li class="i1">waste, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page214">214</a>;</li> - <li class="i1">distinctive characters, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page392">392</a>;</li> - <li class="i1">distribution in time, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page409">409</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page412">412</a>;</li> - <li class="i1">vertebral segmentation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page470">470</a>;</li> - <li class="i1">rudimentary limbs of snakes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page473">473</a>;</li> - <li class="i1">fertility and development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page583">583</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page598">598</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page599">599</a>;</li> - <li class="i1">regeneration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page589">589</a>;</li> - <li class="i1">elongated form, <b>II</b>, - <a href="#Page_15">15</a>;</li> - <li class="i1">supernumerary vertebræ, <b>II</b>, - <a href="#Page_123">123</a>, - <a href="#Page_564">564</a>;</li> - <li class="i1">bilateral symmetry, <b>II</b>, - <a href="#Page_203">203</a>, - <a href="#Page_204">204</a>;</li> - <li class="i1">Cope on segmentation in extinct, <b>II</b>, - <a href="#Page_225">225</a>, - <a href="#Page_226">226</a>;</li> - <li class="i1">activity and muscular colour, <b>II</b>, - <a href="#Page_365">365</a>;</li> - <li class="i1">functional integration, <b>II</b>, - <a href="#Page_375">375</a>;</li> - <li class="i1">outer tissue differentiation, <b>II</b>, - <a href="#Page_387">387</a>;</li> - <li class="i1">Owen on skeleton, <b>II</b>, - <a href="#Page_560">560</a>.</li> - - <li>Resistance of media to locomotion, <b>II</b>, - <a href="#Page_15">15</a>.</li> - - <li id="Respiratory_System">Respiratory System: effect of light, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page31">31</a>;</li> - <li class="i1">organic re-arrangement, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page37">37</a>;</li> - <li class="i1">cutaneous, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page209">209</a>;</li> - <li class="i1">air-cells of lungs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page254">254</a>;</li> - <li class="i1">embryonic branchiæ of salamander, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page457">457</a>;</li> - <li class="i1">differentiation, <b>II</b>, - <a href="#Page_310">310–1</a>, - <a href="#Page_333">333–8</a>;</li> - <li class="i1">physiological integration, <b>II</b>, - <a href="#Page_374">374–5</a>, - <a href="#Page_382">382</a>;</li> - <li class="hangingindent1">vascular differentiation and integration, <b>II</b>, - <a href="#Page_377">377</a>.</li> - - <li>Retrograde metamorphoses, in animals, <b>II</b>, - <a href="#Page_12">12</a>.</li> - - <li>Retzius, G., superficial nerve-endings, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page666">666</a>.</li> - - <li>Reversed Selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page611">611</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612</a>.</li> - - <li class="hangingindent">Rhabdospheres, calcareous armour and dynamic element in life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page119">119</a>.</li> - - <li>Rhizoids, foliar expansions, <b>II</b>, - <a href="#Page_50">50</a>.</li> - - <li><i>Rhizopoda</i>: structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page173">173</a>;</li> - <li class="i1">undifferentiated function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page200">200</a>;</li> - <li class="i1">a primary aggregate, <b>II</b>, - <a href="#Page_86">86</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_186">186</a>;</li> - <li class="i1">tissue differentiated, <b>II</b>, - <a href="#Page_299">299</a>, - <a href="#Page_385">385</a>;</li> - <li class="i1">motion of sarcode, <b>II</b>, - <a href="#Page_356">356</a>;</li> - <li class="i1">symbiosis, <b>II</b>, - <a href="#Page_400">400</a>.</li> - - <li>Rhythm: astronomic and organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page499">499</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">law of equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page520">520–1</a>;</li> - <li class="i1">in multiplication, <b>II</b>, - <a href="#Page_419">419</a>.</li> - - <li>Richeraud, Baron A., definition of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page79">79</a>.</li> - - <li>Riley, C. V., on telegony, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page645">645</a>;</li> - <li class="i1"><i>Termites</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page680">680</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page681">681</a>;</li> - <li class="i1">pouch of Honey-ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page684">684</a>.</li> - - <li id="Rodentia"><i>Rodentia</i>: incursions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page399">399</a>;</li> - <li class="i1">American types, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page403">403</a>;</li> - <li class="i1">fertility and development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page583">583</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page599">599</a>.</li> - - <li>Rivinus, plant classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page377">377</a>.</li> - - <li>Rokitansky, on false joints, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page230">230</a>.</li> - - <li class="hangingindent">Romanes, G. J.: on “cessation of selection,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page560">560–2</a>;</li> - <li class="i1">isolation and species differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page569">569</a>;</li> - <li class="i1">“physiological selection,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page569">569–71</a>;</li> - <li class="i1">panmixia, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page649">649</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page667">667</a>;</li> - <li class="i1">influence of a previous sire on progeny, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page649">649</a>.</li> - - <li>Röntgen rays, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page121">121</a>; <b>II</b>, - <a href="#Page_621">621</a>.</li> - - <li>Roots: developed from leaflets, <b>II</b>, - <a href="#Page_34">34</a>;</li> - <li class="i1">physiological differentiation, <b>II</b>, - <a href="#Page_253">253–5</a>, - <a href="#Page_270">270</a>;</li> - <li class="i1">nutrition from leaves, <b>II</b>, - <a href="#Page_274">274</a>;</li> - <li class="i1">size and function, <b>II</b>, - <a href="#Page_276">276</a>.</li> - - <li><i>Rotiferæ</i>: latent vitality of desiccated, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page117">117</a>;</li> - <li class="i1">trochopore, <b>II</b>, - <a href="#Page_108">108</a>, - <a href="#Page_109">109</a>;</li> - <li class="i1">molluscan relationship, <b>II</b>, - <a href="#Page_115">115</a>;</li> - <li class="i1">fertility and size, <b>II</b>, - <a href="#Page_453">453</a>, - <a href="#Page_459">459</a>.</li> - - <li>Roux, W.: “intra-selection,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676</a>;</li> - <li class="i1">functional adaptation, <b>II</b>, - <a href="#Page_354">354</a>.</li> - - <li class="hangingindent">Rudimentary organs: the definition of life and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page112">112</a>;</li> - <li class="hangingindent1">natural selection and eyes of cave fauna, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page309">309</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page647">647–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">evolution hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page472">472–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page556">556</a>;</li> - <li class="i1">limbs of whale, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page668">668–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>.</li> - - <li>Ruminants, alimentary canal development, <b>II</b>, - <a href="#Page_327">327–9</a>.</li> -</ul> - -<ul> - <li>Salamander, embryonic branchiæ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page457">457</a>.</li> - - <li class="hangingindent"><i>Salmonidæ</i>, reproduction and growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page291">291–3</a>; <b>II</b>, - <a href="#Page_454">454</a>.</li> - - <li><i>Salpidæ</i>: heterogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page272">272</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page277">277</a>;</li> - <li class="i1">integration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page588">588</a>; <b>II</b>, - <a href="#Page_97">97</a>.</li> - - <li>Sap (<i>see</i> <a href="#Vascular_System">Vascular system</a>).</li> - - <li><i>Sarcina</i>: central aggregation, <b>II</b>, - <a href="#Page_24">24</a>;</li> - <li class="i1">fertility, <b>II</b>, - <a href="#Page_440">440</a>.</li> - - <li>Savage, Dr., on “Heredity and Neurosis,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page313">313</a>.</li> - - <li><i>Scenedesmus</i>, individuation, <b>II</b>, - <a href="#Page_24">24</a>.</li> - - <li>Scent: natural selection and keenness of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page610">610</a>;</li> - <li class="i1">floral fertilization, <b>II</b>, - <a href="#Page_268">268–9</a>;</li> - <li class="i1">animal protection, <b>II</b>, - <a href="#Page_434">434</a>.</li> - - <li class="hangingindent">Schelling, E. W. J. von, definition of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page78">78</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page178">178</a>.</li> - - <li>Schleiden, J. M., on individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page245">245</a>;</li> - <li class="i1">on liverworts, <b>II</b>, - <a href="#Page_50">50</a>, - <a href="#Page_52">52</a>;</li> - <li class="i1">algal indefiniteness, <b>II</b>, - <a href="#Page_296">296</a>.</li> - - <li>Science, complex revelations of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page252">252</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page369">369</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page450">450</a>.</li> - - <li><i>Scyphomedusæ</i>, strobilization, <b>II</b>, - <a href="#Page_108">108</a>.</li> - - <li id="Sea">Sea: changes and movements in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page83">83</a>;</li> - <li class="i1">life in, lower than terrestrial, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page104">104</a>;</li> - <li class="i1">distribution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page396">396</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page517">517</a>;</li> - <li class="i1">change of media caused by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page481">481</a>;</li> - <li class="i1">geologic influence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page502">502</a>.</li> - - <li>Seals: nail-bearing toes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page473">473</a>;</li> - <li class="i1"><i>vibrissæ</i>, <b>II</b>, - <a href="#Page_317">317</a>.</li> - - <li>Seasons: reproductive periodicity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page299">299</a>;</li> - <li class="i1">variations of genesis with, <b>II</b>, - <a href="#Page_484">484–5</a>.</li> - - <li class="hangingindent">Sedgwick, Adam: on continuity of protoplasm in animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page190">190</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page629">629</a>; <b>II</b>, - <a href="#Page_21">21</a>;</li> - <li class="i1">zoological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page387">387</a>;</li> - <li class="hangingindent1">discrimination of species in embryonic stages, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page461">461</a>;</li> - <li class="i1">persistence of ancestral traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page463">463–4</a>;</li> - <li class="i1">Archiannelidan segmentation, <b>II</b>, - <a href="#Page_109">109</a>.</li> - - <li>Sedgwick, Wm.: heredity and sex, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page305">305</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314</a>;</li> - <li class="i1">telegonic transmission of hypospadias, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646</a>.</li> - - <li>Seeds: nitrogenous, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page40">40</a>;</li> - <li class="hangingindent1">temperature of germinating, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page47">47</a>; <b>II</b>, - <a href="#Page_615">615</a>;</li> - <li class="i1">vitalism and latent vitality of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page116">116–7</a>;</li> - <li class="i1">variation in environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page327">327</a>;</li> - <li class="i1">natural selection among, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page532">532</a>.</li> - - <li class="hangingindent" id="Segmentation">Segmentation (metameric): special creation hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page468">468–9</a>;</li> - <li class="hangingindent1">Huxley on number of somites in higher articulates, <i>ib.</i>;</li> - <li class="i1">in annulose animals, <b>II</b>, - <a href="#Page_98">98–110</a>, - <a href="#Page_111">111–5</a>, - <a href="#Page_601">601–5</a>;</li> - <li class="i1">simulated molluscan, <b>II</b>, - <a href="#Page_116">116</a>;</li> - <li class="i1">in vertebrates, <b>II</b>, - <a href="#Page_125">125–7</a>, - <a href="#Page_225">225–7</a>, - <a href="#Page_606">606–7</a>;</li> - <li class="i1">in elasmobranchs, <b>II</b>, - <a href="#Page_126">126</a>.</li> - - <li>Segregation: of growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page136">136</a>;</li> - <li class="i1">of like units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page179">179</a>;</li> - <li class="i1">organic repair, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page221">221</a>;</li> - <li class="i1">variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page331">331</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page334">334</a>;</li> - <li class="hangingindent1">heterogeneity, and definiteness of evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page514">514–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page517">517–8</a>;</li> - <li class="i1">morphological development, <b>II</b>, - <a href="#Page_7">7–9</a>;</li> - <li class="i1">physiological units, <b>II</b>, - <a href="#Page_616">616</a>.</li> - - <li class="hangingindent">Self-fertilization, animal and vegetal, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page341">341–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page353">353</a>.</li> - - <li>Senses, the (<i>see</i> <a href="#Psychology">Psychology</a>).</li> - - <li>Sex: in Ascidian colonies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page247">247</a>;</li> - <li class="i1">limitation of heredity by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314–6</a>;</li> - <li class="i1">correlated traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page371">371–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page513">513</a>;</li> - <li class="hangingindent1">nutrition and determination of, in social insects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page655">655–60</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page678">678–84</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page686">686–9</a>;</li> - <li class="i1">neural and hæmal traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page683">683</a>;</li> - <li class="i1">differentiation of organs, <b>II</b>, - <a href="#Page_303">303</a>;</li> - <li class="i1">castration and growth, <b>II</b>, - <a href="#Page_459">459</a>;</li> - <li class="hangingindent1">Julin on “castration parasitaire” in crustaceans, <b>II</b>, - <a href="#Page_493">493–6</a>;</li> - <li class="i1">the object of fertilization, <b>II</b>, - <a href="#Page_613">613</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Fertilization">Fertilization</a>.)</li> - - <li>Sexual Selection (<i>see</i> <a href="#Natural_selection">Natural Selection</a>).</li> - - <li>Sharp, D.: on insect somites, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page469">469</a>;</li> - <li class="i1">food habits of <i>Termites</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page686">686–7</a>.</li> - - <li>Sheep: contrasted with oxen, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page158">158</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page160">160</a>;</li> - <li class="i1">crossing of English and French breeds, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page625">625</a>;</li> - <li class="i1">nutrition and genesis, <b>II</b>, - <a href="#Page_480">480</a>.</li> - - <li class="hangingindent">Sherrington, Prof., on effects of nerve severance, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page349">349</a>.</li> - - <li class="hangingindent">Ship-building, interdependence of social functions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page237">237–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page241">241</a>.</li> - - <li class="hangingindent">Shipley, A. E.: segmentation of <i>Microstomida</i>, <b>II</b>, - <a href="#Page_102">102</a>;</li> - <li class="i1"><i>Protodrilus</i>, <b>II</b>, - <a href="#Page_125">125</a>.</li> - - <li>Silica, colloid and crystalloid, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page16">16</a>.</li> - - <li>Silicic acid: properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page16">16</a>;</li> - <li class="i1">isomerism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page59">59</a>.</li> - - <li>Silicon, allotropic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page4">4</a>.</li> - - <li>Silkworm disease, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page622">622–3</a>.</li> - - <li>Simulation: of homology by analogy, <b>II</b>, - <a href="#Page_14">14</a>, - <a href="#Page_485">485</a>;</li> - <li class="i1">of segmented structure by molluscs, <b>II</b>, - <a href="#Page_116">116</a>.</li> - - <li class="hangingindent"><i>Siphonophora</i>, specialization of component polyps, <b>II</b>, - <a href="#Page_95">95</a>.</li> - - <li><i>Sirenia</i>, simulated fish form, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page485">485</a>.</li> - - <li>Size (<i>see</i> <a href="#Growth">Growth</a>).</li> - - <li>Skeleton, vertebrate (see <a href="#Vertebrata"><i>Vertebrata</i></a>).</li> - - <li id="Skin">Skin: respiratory function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page209">209</a>;</li> - <li class="i1">adaptability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page228">228</a>; <b>II</b>, - <a href="#Page_312">312–4</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">transmitted peculiarities, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page306">306</a>;</li> - <li class="hangingindent1">Wallace on distribution of sensitiveness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646–7</a>;</li> - <li class="i1">differentiation, <b>II</b>, - <a href="#Page_215">215</a>, - <a href="#Page_217">217</a>, - <a href="#Page_304">304–7</a>;</li> - <li class="i1">tegumentary development, <b>II</b>, - <a href="#Page_314">314–6</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">differentiation of sensory organs, <b>II</b>, - <a href="#Page_317">317–20</a>;</li> - <li class="i1">and mucous membrane, <b>II</b>, - <a href="#Page_303">303–4</a>, - <a href="#Page_321">321–2</a>, - <a href="#Page_389">389</a>.</li> - - <li class="hangingindent">“Skin friction,” and locomotion of aquatic animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page156">156</a>.</li> - - <li>Skull (see <a href="#Vertebrata"><i>Vertebrata</i></a>).</li> - - <li>Sleep, repair favoured by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page216">216</a>.</li> - - <li>Small-pox, blood changes from, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page221">221</a>.</li> - - <li class="hangingindent">Smith, Prof. W., on fertility of <i>diatomaceæ</i>, <b>II</b>, - <a href="#Page_440">440</a>.</li> - - <li class="hangingindent">Smith, W. P., on telegony in calves and foals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page645">645</a>.</li> - - <li>Smith, W. W., on habits of Tetramorium, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660</a>.</li> - - <li>Snakes (see <a href="#Reptilia"><i>Reptilia</i></a>).</li> - - <li>“Social organism,” author’s essay on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page363">363</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676</a>.</li> - - <li id="Sociology">Sociology: environment and degree of life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page105">105–6</a>;</li> - <li class="i1">functional differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page204">204</a>;</li> - <li class="i1">division of labour, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page207">207</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page363">363–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page367">367</a>;</li> - <li class="i1">functional interdependence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page237">237–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page240">240–2</a>;</li> - <li class="hangingindent1">autogenous development of units in colonies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page367">367–8</a>; <b>II</b>, - <a href="#Page_620">620</a>;</li> - <li class="i1">belief in social evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page432">432</a>;</li> - <li class="i1">natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>; <b>II</b>, - <a href="#Page_532">532</a>;</li> - <li class="i1">integration and differentiation, <b>II</b>, - <a href="#Page_378">378–9</a>;</li> - <li class="i1">effects of population, <b>II</b>, - <a href="#Page_535">535–6</a>;</li> - <li class="i1">equilibration, <b>II</b>, - <a href="#Page_537">537</a>.</li> - - <li>Soil, dependence of plant evolution on, <b>II</b>, - <a href="#Page_402">402</a>.</li> - - <li class="hangingindent"><i>Solanum jasminoides</i>, organs of attachment, <b>II</b>, - <a href="#Page_276">276</a>.</li> - - <li class="hangingindent">Solar system, autogenous development illustrated by distribution of forces in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page366">366</a>.</li> - - <li>Sole, symmetry and location of eyes, <b>II</b>, - <a href="#Page_205">205</a>.</li> - - <li class="hangingindent">Soma-plasm, Weismann’s theory of differentiation from germ-plasm, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page357">357</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page622">622</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page628">628–30</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page633">633–44</a>.</li> - - <li>Somites (<i>see</i> <a href="#Segmentation">Segmentation</a>).</li> - - <li id="Special_creation">Special creation: and evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page412">412</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page415">415</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page431">431</a>;</li> - <li class="i1">improbabilities, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page418">418–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page430">430</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page439">439</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page554">554</a>;</li> - <li class="i1">inconceivability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page420">420</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page429">429</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page431">431</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page554">554</a>;</li> - <li class="i1">of individuals and species, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page421">421–4</a>;</li> - <li class="i1">the implication of beneficence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page425">425–9</a>;</li> - <li class="i1">summary, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page429">429</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page554">554</a>;</li> - <li class="i1">Von Baer’s formula, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page451">451–6</a>;</li> - <li class="i1">vertebrate skeleton, <b>II</b>, - <a href="#Page_551">551</a>, - <a href="#Page_556">556</a>, - <a href="#Page_565">565</a>.</li> - - <li>Species: adaptation and stability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page242">242</a>;</li> - <li class="i1">hereditary transmission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page301">301–4</a>;</li> - <li class="hangingindent1">variation in wild and cultivated, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page323">323–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page326">326</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="i1">gamogenesis and life of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page347">347–9</a>;</li> - <li class="hangingindent1">physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page362">362</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page369">369–71</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page458">458</a>; <b>II</b>, - <a href="#Page_613">613</a>;</li> - <li class="i1">indefiniteness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page389">389</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page445">445</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page572">572</a>;</li> - <li class="i1">special creation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page422">422–4</a>;</li> - <li class="hangingindent1">instability of homogeneous, and differentiation of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page509">509–11</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page515">515</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page517">517–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page550">550</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">persistence of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page516">516</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page518">518</a>; <b>II</b>, - <a href="#Page_10">10–11</a>;</li> - <li class="hangingindent1">natural selection and equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page543">543–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="i1">non-adaptive characters, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page565">565</a>;</li> - <li class="i1">morbid products as marks of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page567">567</a>;</li> - <li class="hangingindent1">migration and isolation as causes of differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page568">568–9</a>;</li> - <li class="i1">increasing multiformity of aggregate, <b>II</b>, - <a href="#Page_396">396</a>.</li> - - <li class="hangingindent" id="Specific_Gravity">Specific gravity, of organisms and environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page174">174</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page177">177</a>.</li> - - <li>Spermatozoa |</li> - <li>Sperm-cell | (<i>see</i> <a href="#Fertilization">Fertilization</a>).</li> - - <li>Sphere: tendency of units to form, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page15">15</a>;</li> - <li class="i1">the embryonic form, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page177">177</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_131">131</a>.</li> - - <li>Spheroid, symmetry, <b>II</b>, - <a href="#Page_132">132</a>.</li> - - <li>Spiders (see <a href="#Arachnida"><i>Arachnida</i></a>).</li> - - <li>Spine (see <a href="#Vertebrata"><i>Vertebrata</i></a>).</li> - - <li class="hangingindent">Sponge: structure and dynamic element in life, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page119">119</a>;</li> - <li class="i1">multicentral development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page164">164</a>;</li> - <li class="i1">units and aggregate, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page185">185</a>;</li> - <li class="i1">reproductive tissue, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page283">283</a>;</li> - <li class="i1">integration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page586">586</a>; <b>II</b>, - <a href="#Page_90">90</a>, - <a href="#Page_383">383</a>;</li> - <li class="i1">physiological differentiation, <b>II</b>, - <a href="#Page_300">300</a>, - <a href="#Page_386">386</a>;</li> - <li class="i1">development and genesis, <b>II</b>, - <a href="#Page_463">463</a>;</li> - <li class="i1">analogy from, <b>II</b>, - <a href="#Page_576">576</a>.</li> - - <li>Spontaneous generation: and heterogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page270">270</a>;</li> - <li class="i1">and evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page696">696–701</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page703">703</a>.</li> - - <li class="hangingindent">Stag, horns and correlated structures, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page567">567</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>.</li> - - <li>Stamens, and foliar homology, <b>II</b>, - <a href="#Page_44">44</a>.</li> - - <li>Starches: properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page11">11</a>;</li> - <li class="hangingindent1">transformations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page66">66</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page68">68</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page70">70</a>; <b>II</b>, - <a href="#Page_593">593</a>.</li> - - <li>Star-fishes (see <a href="#Asteroidea"><i>Asteroidea</i></a>).</li> - - <li>Statoblasts, of <i>Plumatella</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page277">277</a>.</li> - - <li>Steenstrup, on “Alternate Generation,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page592">592</a>.</li> - - <li>Sterility (<i>see</i> <a href="#Multiplication">Multiplication</a>).</li> - - <li>Stickleback: ova, <b>II</b>, - <a href="#Page_454">454</a>;</li> - <li class="i1"><i>bothriocephalus</i> in, <b>II</b>, - <a href="#Page_490">490</a>.</li> - - <li>Stomach (<i>see</i> <a href="#Alimentary_canal">Alimentary Canal</a>).</li> - - <li>Stomata, distribution, <b>II</b>, - <a href="#Page_260">260–1</a>.</li> - - <li>Straight line, and evolution hypothesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page433">433</a>.</li> - - <li class="hangingindent" id="Strain">Strain: compression and tension of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page151">151</a>; <b>II</b>, - <a href="#Page_209">209–12</a>;</li> - <li class="i1">relation to mass, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page155">155–7</a>;</li> - <li class="i1">vegetal structure, <b>II</b>, - <a href="#Page_574">574–88</a>, - <a href="#Page_592">592–6</a>;</li> - <li class="i1">origin of vertebrate type, <b>II</b>, - <a href="#Page_600">600</a>.</li> - - <li>Strawberry: multiaxial development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page166">166</a>;</li> - <li class="i1">multiplication, <b>II</b>, - <a href="#Page_441">441</a>.</li> - - <li>Strength, a vital attribute, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page578">578</a>.</li> - - <li class="hangingindent" id="Structure">Structure: appliances for generating motion, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page75">75–7</a>;</li> - <li class="i1">biological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page125">125–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page129">129</a>;</li> - <li class="i1">size and organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page137">137</a>;</li> - <li class="i1">growth and complexity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page138">138</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page145">145</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page161">161</a>;</li> - <li class="i1">relation to environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page172">172–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page195">195–6</a>;</li> - <li class="i1">of unicellular organisms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page181">181–3</a>;</li> - <li class="i1">multicellular, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page183">183–96</a>;</li> - <li class="i1">Hertwig’s classification of tissues, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page189">189</a>;</li> - <li class="i1">continuity of units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page190">190–2</a>;</li> - <li class="i1">systems of organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page192">192</a>;</li> - <li class="i1">division into universal and particular, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page193">193–4</a>;</li> - <li class="i1">general truths, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page194">194–5</a>;</li> - <li class="i1">plant and animal, contrasted, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page195">195–6</a>;</li> - <li class="i1">precedence of function or, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page197">197</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page211">211</a>;</li> - <li class="hangingindent1">correlative complexity of function and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page200">200</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page211">211</a>;</li> - <li class="hangingindent1">progressive concomitant differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page201">201–4</a>;</li> - <li class="hangingindent1">physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page225">225–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page362">362</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page364">364</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page369">369–71</a>; <b>II</b>, - <a href="#Page_613">613</a>;</li> - <li class="i1">social and organic interdependence, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page235">235–42</a>;</li> - <li class="hangingindent1">varied by function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page334">334</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page535">535</a>; <b>II</b>, - <a href="#Page_217">217</a> (<i>see</i> <a href="#Acquired_characters">Acquired Characters</a>);</li> - <li class="i1">zoological classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page390">390–2</a>;</li> - <li class="i1">equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page521">521</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page557">557</a>;</li> - <li class="hangingindent1">progress of, and genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page590">590–1</a>; <b>II</b>, - <a href="#Page_462">462</a>;</li> - <li class="i1">co-operation with function, <b>II</b>, - <a href="#Page_3">3</a>;</li> - <li class="i1">evolution and increased, <b>II</b>, - <a href="#Page_4">4</a>;</li> - <li class="i1">retrograde metamorphosis, <b>II</b>, - <a href="#Page_12">12</a>;</li> - <li class="i1">simulated homologies, <b>II</b>, - <a href="#Page_13">13–14</a>;</li> - <li class="i1">earliest organic forms, <b>II</b>, - <a href="#Page_19">19</a>;</li> - <li class="i1">cylindrical vegetal, <b>II</b>, - <a href="#Page_57">57–62</a>;</li> - <li class="i1">permanence and complexity, <b>II</b>, - <a href="#Page_295">295</a>, - <a href="#Page_296">296</a>;</li> - <li class="i1">function and epidermic, <b>II</b>, - <a href="#Page_312">312–4</a>, - <a href="#Page_387">387</a>;</li> - <li class="i1">and muscular, <b>II</b>, - <a href="#Page_369">369</a>, - <a href="#Page_391">391</a>;</li> - <li class="i1">adaptation and equilibration, <b>II</b>, - <a href="#Page_392">392</a>;</li> - <li class="hangingindent1">persistence of force and physiological adaptation, <b>II</b>, - <a href="#Page_394">394</a>;</li> - <li class="i1">evolution, <b>II</b>, - <a href="#Page_501">501–4</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Morphology">Morphology</a>.)</li> - - <li class="hangingindent">Struggle, for nutriment among components of an organism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page562">562</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676</a>;</li> - <li class="i1">for existence (<i>see</i> <a href="#Natural_selection">Natural Selection</a>).</li> - - <li>Struthers, Sir J.: on heredity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page305">305</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314</a>;</li> - <li class="i1">digital variation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page321">321</a>;</li> - <li class="i1">rudimentary limbs of whale, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page668">668</a>.</li> - - <li>Strychnine, effects of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page54">54</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page55">55</a>.</li> - - <li>Sturgeon, size of ova and adult, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page144">144</a>.</li> - - <li>Sugars: properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page10">10–11</a>;</li> - <li class="hangingindent1">transformations, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page38">38</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page40">40</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page66">66</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page70">70</a>; <b>II</b>, - <a href="#Page_593">593</a>.</li> - - <li>Suicide, hereditary tendency to, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page307">307</a>.</li> - - <li>Sulphur: allotropic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page4">4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page59">59</a>;</li> - <li class="i1">organic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page703">703</a>.</li> - - <li>Sun (<i>see</i> <a href="#Light">Light</a>).</li> - - <li class="hangingindent">Survival of the Fittest, the expression, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page530">530</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page610">610</a>.</li> - <li class="i1">(<i>See</i> <a href="#Natural_selection">Natural Selection</a>.)</li> - - <li>Swan, vertebræ of neck, <b>II</b>, - <a href="#Page_123">123</a>.</li> - - <li>Swiftness, a vital attribute, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page578">578</a>.</li> - - <li class="hangingindent"><i>Syllis ramosa</i>, lateral branching, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page166">166</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page361">361</a>; <b>II</b>, - <a href="#Page_105">105</a>, - <a href="#Page_108">108</a>.</li> - - <li>Symbiosis, <b>II</b>, - <a href="#Page_399">399</a>, - <a href="#Page_400">400</a>.</li> - - <li>Symmetry (<i>see</i> <a href="#Morphology">Morphology</a>).</li> - - <li>Syphilis, hereditary transmission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page623">623</a>.</li> -</ul> - -<ul> - <li class="hangingindent">Tactual, Perceptiveness, heredity and the distribution of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page602">602–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page633">633</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page665">665</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page666">666</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page672">672</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>.</li> - - <li><i>Tænia</i> (see <a href="#Entozoa"><i>Entozoa</i></a>).</li> - - <li>Tansley, A. G., <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#pagevi">vi</a>; <b>II</b>, - <a href="#Page_vi">vi</a>;</li> - <li class="hangingindent1">adaptation of reproductive activity to conditions in <i>Algæ</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page288">288–9</a>;</li> - <li class="i1">shapes of <i>Caulerpa</i>, <b>II</b>, - <a href="#Page_22">22</a>;</li> - <li class="i1">stem-thickening in extinct Thallophytes, <b>II</b>, - <a href="#Page_56">56</a>;</li> - <li class="i1">natural selection and leaf-distribution, <b>II</b>, - <a href="#Page_179">179</a>.</li> - - <li>Tape-worm (see <a href="#Entozoa"><i>Entozoa</i></a>).</li> - - <li>Taste, dependent on chemical action, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page54">54</a>.</li> - - <li>Teeth: hereditary transmission, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page306">306</a>;</li> - <li class="i1">suppression of mammalian, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page457">457</a>;</li> - <li class="i1">of uncivilized and civilized, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page541">541</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>.</li> - - <li>Tegumentary organs, origin of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314–6</a>.</li> - - <li class="hangingindent">Telegony, or the Influence of a previous sire on offspring, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page624">624–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page644">644–6</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page649">649–50</a>.</li> - - <li>Temperature (<i>see</i> <a href="#Heat">Heat</a>).</li> - - <li>Tension (<i>see</i> <a href="#Strain">Strain</a>).</li> - - <li id="Termites"><i>Termites</i>: fertility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page583">583</a>; <b>II</b>, - <a href="#Page_493">493</a>;</li> - <li class="i1">late development of sexual organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page680">680</a>;</li> - <li class="i1">nutrition and differentiation of forms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page681">681</a>.</li> - - <li><i>Tetramorium</i>, utilization of aphides by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660–1</a>.</li> - - <li><i>Thallophyta</i>: size, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page138">138</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page139">139</a>;</li> - <li class="i1">low co-ordination of parts, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page164">164</a>;</li> - <li class="i1">pseudo-foliar, <b>II</b>, - <a href="#Page_28">28</a>;</li> - <li class="i1">“transition place,” <b>II</b>, - <a href="#Page_30">30</a>;</li> - <li class="i1">simulation of higher types, <b>II</b>, - <a href="#Page_32">32</a>;</li> - <li class="i1">secondary thickening in extinct species, <b>II</b>, - <a href="#Page_56">56</a>;</li> - <li class="i1">sexual and asexual genesis, <b>II</b>, - <a href="#Page_84">84</a>.</li> - <li class="i1">(See also <a href="#Algae"><i>Algæ</i></a>.)</li> - - <li>Tickling, physiology of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page76">76</a>.</li> - - <li>Tide (<i>see</i> <a href="#Sea">Sea</a>).</li> - - <li>Time, as a factor in growth, <b>II</b>, - <a href="#Page_77">77</a>.</li> - - <li>Tissue, Hertwig’s classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page189">189</a>.</li> - <li class="i1">(<i>See</i> <a href="#Physiology">Physiology</a>.)</li> - - <li>Tongue, perceptiveness of tip, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page606">606–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page665">665</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page672">672–3</a>.</li> - - <li>Tortoise: contrasted life of dog and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page103">103–4</a>;</li> - <li class="i1">natural selection and carapace, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page534">534</a>.</li> - - <li>“Transcendental Physiology,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page176">176</a>.</li> - - <li>Tree, as symbolizing phylogeny, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page428">428</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page452">452–3</a>.</li> - <li class="i1">(<i>See</i> <a href="#Plants">Plants</a>.)</li> - - <li><i>Trematoda</i>: agamogenesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page277">277</a>;</li> - <li class="i1">parasitism, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page428">428</a>;</li> - <li class="i1">alternate generation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page592">592</a>.</li> - - <li>Trembley, A., on the polyp, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page223">223</a>.</li> - - <li>Trichinosis, in Germany, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page428">428</a>.</li> - - <li class="hangingindent">Trochophore, phyletic relationships shown by, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page447">447</a>; <b>II</b>, - <a href="#Page_108">108–9</a>.</li> - - <li><i>Tubicolæ</i>: development, <b>II</b>, - <a href="#Page_100">100</a>;</li> - <li class="i1">bilateral symmetry, <b>II</b>, - <a href="#Page_197">197</a>.</li> - - <li id="Tunicata"><i>Tunicata</i>: gemmation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page588">588</a>; <b>II</b>, - <a href="#Page_445">445</a>;</li> - <li class="i1">alternate generation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page592">592</a>;</li> - <li class="i1">integration, <b>II</b>, - <a href="#Page_93">93–4</a>;</li> - <li class="i1">tertiary aggregation, <b>II</b>, - <a href="#Page_124">124</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_194">194–5</a>.</li> - - <li>Tunny, size of ova and adult, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page144">144</a>.</li> - - <li><i>Turbellaria</i>: segmentation, <b>II</b>, - <a href="#Page_102">102</a>;</li> - <li class="i1">symbiosis, <b>II</b>, - <a href="#Page_400">400</a>.</li> - - <li>Turnip: chlorophyll in roots, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page209">209</a>; <b>II</b>, - <a href="#Page_254">254</a>;</li> - <li class="i1">vascular system, <b>II</b>, - <a href="#Page_281">281</a>, - <a href="#Page_284">284</a>, - <a href="#Page_578">578</a>, - <a href="#Page_591">591</a>, - <a href="#Page_596">596</a>.</li> - - <li>Twins: similarity of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page324">324</a>;</li> - <li class="i1">traits of women bearing, <b>II</b>, - <a href="#Page_457">457</a>.</li> - - <li>“Types, persistent,” Huxley on, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page408">408</a>.</li> -</ul> - -<ul> - <li>Ulcer, dermal structure, <b>II</b>, - <a href="#Page_306">306</a>.</li> - - <li>Ultimate Reality, incomprehensibility of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page120">120</a>.</li> - - <li><i>Ulva</i>: cell multiplication, <b>II</b>, - <a href="#Page_26">26</a>;</li> - <li class="i1">outer tissue, <b>II</b>, - <a href="#Page_256">256</a>.</li> - - <li><i>Umbelliferæ</i>: floral symmetry, <b>II</b>, - <a href="#Page_171">171</a>;</li> - <li class="i1">axial and foliar organs, <b>II</b>, - <a href="#Page_541">541–6</a>.</li> - - <li>United States: cases of telegony, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page644">644–5</a>;</li> - <li class="i1">birth-rate, <b>II</b>, - <a href="#Page_520">520</a>.</li> - - <li>Units: differentiation and dissimilarity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page20">20</a>;</li> - <li class="i1">“protyle,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page22">22–3</a>;</li> - <li class="i1">shapes in higher types, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page164">164</a>;</li> - <li class="i1">differential assimilation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page180">180</a>;</li> - <li class="i1">primordial organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page181">181</a>;</li> - <li class="hangingindent1">morphological composition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page184">184–7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page194">194</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page252">252</a>; <b>II</b>, - <a href="#Page_5">5</a>, - <a href="#Page_7">7–9</a>, - <a href="#Page_21">21</a>, - <a href="#Page_79">79</a>, - <a href="#Page_85">85–6</a>;</li> - <li class="i1">segregation and organic repair, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page221">221–2</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page222">222–6</a>;</li> - <li class="hangingindent1">chemical, morphological, and physiological, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page225">225–6</a>; <b>II</b>, - <a href="#Page_612">612</a>;</li> - <li class="i1">stability, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page339">339</a>;</li> - <li class="i1">instability and heterogeneity of organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page350">350</a>;</li> - <li class="i1">Darwin’s gemmules, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page356">356–60</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page362">362</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page372">372</a>;</li> - <li class="i1">Weissmann’s germ-plasm (<i>q. v.</i>) <i>ib.</i>;</li> - <li class="i1">sociological comparison, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page363">363–8</a>;</li> - <li class="i1">specific proclivities in embryogeny, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page458">458</a>;</li> - <li class="i1">phænogamic, <b>II</b>, - <a href="#Page_73">73</a>, - <a href="#Page_151">151</a>;</li> - <li class="i1">annulose, <b>II</b>, - <a href="#Page_105">105</a>;</li> - <li class="i1">incident force and homologous, <b>II</b>, - <a href="#Page_159">159</a>;</li> - <li class="i1">morphological summary, <b>II</b>, - <a href="#Page_233">233</a>.</li> - <li class="i1">(<i>See also</i> <a href="#Physiological_Units">Physiological Units</a>.)</li> - - <li>“Universal Postulate,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>.</li> - - <li>Unsymmetrical, definition, <b>II</b>, - <a href="#Page_131">131</a>.</li> - - <li>Urea, muscular energy and excretion, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page72">72</a>.</li> -</ul> - -<ul> - <li>Van Beneden, P. J., on <i>Tænia</i>, <b>II</b>, - <a href="#Page_103">103</a>.</li> - - <li>Variation: digital, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page331">331</a>;</li> - <li class="i1">effects of parental conditions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page324">324</a>;</li> - <li class="i1">of altered function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page325">325</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page334">334</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>;</li> - <li class="hangingindent1">dissimilarity of initial conditions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page327">327–32</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page333">333</a>;</li> - <li class="i1">“spontaneous,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page328">328</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page513">513</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page697">697</a>; <b>II</b>, - <a href="#Page_529">529</a>;</li> - <li class="i1">persistence of force, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page335">335</a>;</li> - <li class="hangingindent1">physiological units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page348">348–54</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page360">360</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page369">369</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page371">371–3</a>; <b>II</b>, - <a href="#Page_614">614–7</a>, - <a href="#Page_622">622–3</a>;</li> - <li class="hangingindent1">Weismann’s germ-plasm theory, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page357">357–8</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page372">372–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page671">671</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page677">677</a>; <b>II</b>, - <a href="#Page_622">622</a>;</li> - <li class="i1">equilibration and vegetal, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page523">523–5</a>;</li> - <li class="hangingindent1">Weismann’s panmixia theory, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page561">561–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page649">649</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page667">667–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page671">671</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>;</li> - <li class="i1">reproductive organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page570">570</a>;</li> - <li class="hangingindent1">natural selection and concomitant, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page614">614–21</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page653">653</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page664">664</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page674">674</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page692">692</a>;</li> - <li class="i1">and disused organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page648">648</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page668">668</a>;</li> - <li class="i1">plus and minus. <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page667">667</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>;</li> - <li class="hangingindent1">Masters on correlated, in plants, <b>II</b>, - <a href="#Page_298">298</a>, - <a href="#Page_621">621–2</a>;</li> - <li class="i1">equilibration of favourable, <b>II</b>, - <a href="#Page_394">394</a>.</li> - - <li class="hangingindent" id="Vascular_System">Vascular System: effects of vegeto-alkalies, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page55">55</a>;</li> - <li class="i1">nutrition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page146">146</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page148">148</a>;</li> - <li class="i1">embryonic development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page169">169</a>;</li> - <li class="i1">structural traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page192">192</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page193">193</a>;</li> - <li class="i1">function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page199">199</a>;</li> - <li class="i1">of Ascidians. <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page202">202</a>;</li> - <li class="hangingindent1">functional differentiation and integration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page205">205–6</a>;</li> - <li class="i1">organic repair, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page217">217</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page221">221–2</a>;</li> - <li class="i1">effect of function, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page229">229</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page234">234–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page236">236</a>;</li> - <li class="i1">equilibration, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page535">535</a>;</li> - <li class="i1">community in compound organisms, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page588">588</a>;</li> - <li class="hangingindent1">development of vegetal, <b>II</b>, - <a href="#Page_273">273–5</a>, - <a href="#Page_279">279–84</a>, - <a href="#Page_285">285–8</a>, - <a href="#Page_388">388</a>;</li> - <li class="i1">differentiation of, summary, <b>II</b>, - <a href="#Page_288">288–90</a>, - <a href="#Page_388">388</a>;</li> - <li class="i1">differentiation of animal, <b>II</b>, - <a href="#Page_339">339–44</a>;</li> - <li class="i1">osseous development, <b>II</b>, - <a href="#Page_347">347–51</a>;</li> - <li class="i1">muscularity, <b>II</b>, - <a href="#Page_364">364</a>;</li> - <li class="i1">muscular colour, <b>II</b>, - <a href="#Page_365">365–9</a>;</li> - <li class="i1">heart-motor apparatus, <b>II</b>, - <a href="#Page_374">374</a>;</li> - <li class="hangingindent1">differentiation and integration in animal, <b>II</b>, - <a href="#Page_376">376–9</a>, - <a href="#Page_383">383</a>;</li> - <li class="i1">wood formation, <b>II</b>, - <a href="#Page_567">567–92</a>;</li> - <li class="i1"><i>résumé</i> of wood formation, <b>II</b>, - <a href="#Page_592">592–7</a>.</li> - - <li><i>Vaucheria</i>, reproduction, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page279">279</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page289">289</a>.</li> - - <li class="hangingindent">Vegetative System, co-ordination of actions in, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page578">578</a>.</li> - - <li>Vegeto-alkalies, physiological effects of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page54">54–5</a>.</li> - - <li>Velocity, of moving bodies, <b>II</b>, - <a href="#Page_219">219–20</a>.</li> - - <li id="Vertebrata"><i>Vertebrata</i>: size, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page139">139</a>;</li> - <li class="i1">size at birth and maturity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page144">144</a>;</li> - <li class="i1">axial structure, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page165">165</a>;</li> - <li class="i1">embryonic development and self-mobility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page175">175</a>;</li> - <li class="i1">functional differentiation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page206">206</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page591">591</a>;</li> - <li class="i1">reparative power, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page219">219</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page223">223</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page589">589</a>;</li> - <li class="i1">homogenesis universal, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>;</li> - <li class="i1">distinctive traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page392">392</a>; <b>II</b>, - <a href="#Page_35">35</a>;</li> - <li class="i1">distribution in time, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page408">408</a>;</li> - <li class="i1">classificatory value, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page446">446</a>;</li> - <li class="i1">embryonic mammalian respiratory system, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page456">456</a>;</li> - <li class="i1">embryological pre-adaptation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page461">461</a>;</li> - <li class="i1">evolution and vertebral column, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page470">470</a>;</li> - <li class="i1">rudimentary organs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page473">473</a>;</li> - <li class="i1">evolution and varied media, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page479">479–85</a>;</li> - <li class="i1">size of head and vertebræ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page512">512</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page537">537</a>;</li> - <li class="i1">segregation and evolution of vertebræ, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page515">515</a>;</li> - <li class="i1">fertility and development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page583">583</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page598">598–9</a>;</li> - <li class="i1">Weismann on reproductive cells, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page635">635</a>;</li> - <li class="i1">limb locomotion, <b>II</b>, - <a href="#Page_15">15</a>;</li> - <li class="hangingindent1">adaptive segmentation, <b>II</b>, - <a href="#Page_117">117–23</a>, - <a href="#Page_125">125–7</a>, - <a href="#Page_223">223</a>, - <a href="#Page_602">602</a>, - <a href="#Page_605">605–7</a>;</li> - <li class="i1">supernumerary vertebræ, <b>II</b>, - <a href="#Page_123">123</a>;</li> - <li class="i1">bilateral symmetry, <b>II</b>, - <a href="#Page_203">203–6</a>;</li> - <li class="i1">internal organic symmetry, <b>II</b>, - <a href="#Page_208">208</a>;</li> - <li class="i1">genesis of rudimentary axis, <b>II</b>, - <a href="#Page_212">212–6</a>;</li> - <li class="hangingindent1">natural selection and genesis of structure, <b>II</b>, - <a href="#Page_216">216</a>, - <a href="#Page_227">227</a>;</li> - <li class="i1">origin of notochord, <b>II</b>, - <a href="#Page_216">216–8</a>;</li> - <li class="i1">spinal segmentation, <b>II</b>, - <a href="#Page_218">218–22</a>, - <a href="#Page_224">224</a>;</li> - <li class="i1">skull development, <b>II</b>, - <a href="#Page_222">222</a>, - <a href="#Page_227">227</a>;</li> - <li class="i1"><i>résumé</i> of axis development, <b>II</b>, - <a href="#Page_224">224</a>;</li> - <li class="i1">Cope on author’s theory, <b>II</b>, - <a href="#Page_225">225–7</a>;</li> - <li class="i1">nerve differentiation, <b>II</b>, - <a href="#Page_304">304</a>;</li> - <li class="i1">sensory organs, <b>II</b>, - <a href="#Page_318">318</a>;</li> - <li class="i1">air-chambers, <b>II</b>, - <a href="#Page_334">334</a>;</li> - <li class="i1">osseous differentiation, <b>II</b>, - <a href="#Page_344">344–55</a>;</li> - <li class="i1">activity and muscular colour, <b>II</b>, - <a href="#Page_365">365–9</a>;</li> - <li class="i1">heart-motor apparatus, <b>II</b>, - <a href="#Page_374">374</a>;</li> - <li class="i1">cost of genesis, <b>II</b>, - <a href="#Page_436">436</a>;</li> - <li class="i1">agamogenesis unknown, <b>II</b>, - <a href="#Page_445">445</a>;</li> - <li class="i1">growth and genesis, <b>II</b>, - <a href="#Page_454">454</a>;</li> - <li class="i1">heat expenditure and genesis, <b>II</b>, - <a href="#Page_468">468–9</a>, - <a href="#Page_474">474</a>;</li> - <li class="i1">Owen, theory of skeleton, <b>II</b>, - <a href="#Page_548">548–66</a>;</li> - <li class="i1">evolution of vertebræ, <b>II</b>, - <a href="#Page_563">563–6</a>;</li> - <li class="i1">origin of type, <b>II</b>, - <a href="#Page_598">598–600</a>.</li> - - <li><i>Vestiges of Creation</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page491">491</a>.</li> - - <li>Vibrissæ, function of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page75">75</a>.</li> - - <li>Vitalism, hypothesis examined, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page114">114–7</a>.</li> - - <li>Vittadini, C., on silkworm disease, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page622">622–3</a>.</li> - - <li>Viviparons genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page271">271</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page274">274–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page278">278</a>.</li> - - <li>Voice, correlated sexual traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page371">371–2</a>.</li> - - <li>Volcano, definition of life and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page85">85</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page89">89</a>.</li> - - <li><i>Volvocineæ</i>: unicentral development, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page163">163</a>;</li> - <li class="i1">individuality, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page245">245</a>;</li> - <li class="i1">disintegration of genesis, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page276">276</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page587">587</a>;</li> - <li class="i1">spherical aggregation, <b>II</b>, - <a href="#Page_24">24</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_137">137</a>, - <a href="#Page_187">187</a>;</li> - <li class="i1">fertility, <b>II</b>, - <a href="#Page_441">441</a>.</li> - - <li>Vomiting, alimentary canal development, <b>II</b>, - <a href="#Page_328">328</a>.</li> - - <li><i>Vorticella</i>: secondary aggregate, <b>II</b>, - <a href="#Page_90">90</a>;</li> - <li class="i1">symmetry, <b>II</b>, - <a href="#Page_188">188</a>.</li> -</ul> - -<ul> - <li class="hangingindent">Wallace, A. R.: “The Origin of the Human Races,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page553">553</a>;</li> - <li class="hangingindent1">the expression “Survival of the Fittest,” <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page530">530</a>;</li> - <li class="hangingindent1">his association of natural with artificial selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page609">609</a>;</li> - <li class="i1">co-adaptation in giraffe, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page615">615</a>;</li> - <li class="i1">skin sensitiveness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646</a>.</li> - - <li class="hangingindent">Wasp: co-ordination of instincts in Mason-, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page574">574</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page679">679–80</a>;</li> - <li class="i1">genesis of worker, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page654">654–7</a>.</li> - - <li>Waste, animal, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page69">69</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page213">213–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page228">228</a>;</li> - <li class="i1">relation to activity, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page196">196</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page220">220–1</a>;</li> - <li class="i1">in plants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page213">213</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page220">220</a>.</li> - - <li>Water: properties, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page7">7</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page9">9</a>;</li> - <li class="i1">colloidal affinity for, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page28">28</a>;</li> - <li class="i1">organic change from, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page29">29</a>;</li> - <li class="i1">organic need for, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page147">147</a>;</li> - <li class="hangingindent1">proportion in mammalian adult and fœtus, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page154">154</a>;</li> - <li class="i1">motion through, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page156">156</a>;</li> - <li class="hangingindent1">organic development and environment, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page173">173</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page177">177</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page479">479</a>;</li> - <li class="i1">terrestrial organisms inhabiting, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page400">400</a>;</li> - <li class="hangingindent1">adaptation of organisms to change of media, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page479">479–85</a>;</li> - <li class="i1">vegetal tissue differentiation, <b>II</b>, - <a href="#Page_253">253</a>;</li> - <li class="i1">molecular re-arrangement, <b>II</b>, - <a href="#Page_359">359</a>;</li> - <li class="i1">colloidal contraction, <b>II</b>, - <a href="#Page_361">361–2</a>.</li> - - <li>Water-weed, American, invasion of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page399">399</a>.</li> - - <li class="hangingindent">Watts, Dr., on <i>The Principles of Biology</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#pageix">ix</a>.</li> - - <li>Wax, foliar deposit, <b>II</b>, - <a href="#Page_260">260–1</a>.</li> - - <li>Weber, on tactual discriminativeness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page602">602</a>.</li> - - <li class="hangingindent">Weight: relation to environment of organic, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page174">174</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page177">177</a>;</li> - <li class="hangingindent1">varying as cube of dimensions, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page151">151</a>; <b>II</b>, - <a href="#Page_434">434</a>, - <a href="#Page_470">470</a>.</li> - - <li class="hangingindent" id="Weismann">Weismann, Aug.: reproductive tissue in <i>Medusæ</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page281">281</a>;</li> - <li class="i1">in <i>Daphnidæ</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page290">290</a>;</li> - <li class="hangingindent1">his theory of the differentiated germ-plasm and its fundamental units, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page357">357</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page622">622–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page628">628–30</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page633">633–44</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page646">646</a>; <b>II</b>, - <a href="#Page_618">618–9</a>, - <a href="#Page_622">622</a>;</li> - <li class="hangingindent1">the alleged differentiation and plant-phenomena, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page359">359–60</a>;</li> - <li class="i1">and regenerative processes, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page360">360</a>;</li> - <li class="i1">false joints, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page362">362</a>;</li> - <li class="i1">implied complexity of determinants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page370">370</a>;</li> - <li class="hangingindent1">theory inadequate to explain correlation of sexual traits, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page372">372</a>;</li> - <li class="hangingindent1">and variations in peacock’s tail feather, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page372">372–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page695">695</a>; <b>II</b>, - <a href="#Page_618">618</a>;</li> - <li class="hangingindent1">his view of natural selection as sole factor in organic evolution, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page559">559</a>;</li> - <li class="hangingindent1">the doctrine of panmixia, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page561">561–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page632">632</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page649">649</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page667">667–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page671">671</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page689">689</a>;</li> - <li class="hangingindent1">arguments against inheritance of acquired characters, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page612">612–3</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page651">651–65</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page669">669–71</a>;</li> - <li class="i1">blindness of cave-animals, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page613">613</a>;</li> - <li class="i1">current acceptance of his views, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page631">631</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page690">690</a>;</li> - <li class="hangingindent1">cannot explain the process of natural selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page651">651</a>;</li> - <li class="hangingindent1">the degradation of the little toe in man, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page652">652</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page669">669</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page673">673</a>;</li> - <li class="hangingindent1">caste gradations of social insects, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page654">654</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page658">658–65</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page678">678–84</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>;</li> - <li class="hangingindent1">food-seeking instinct in Amazon ants, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page660">660</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>;</li> - <li class="hangingindent1">the co-adaptation of co-operative parts, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page663">663–4</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page670">670</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page674">674</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page675">675</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676</a>;</li> - <li class="i1">tactual discriminativeness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page665">665</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page672">672</a>;</li> - <li class="i1">intra-selection, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page676">676–8</a>;</li> - <li class="hangingindent1">effect of nutrition on fertility of blow-fly, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page678">678–9</a>.</li> - - <li>Whale: weight of brain, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page599">599</a>;</li> - <li class="i1">rudimentary limbs, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page668">668–9</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page685">685</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page693">693</a>.</li> - - <li>Wheat, adaptive variations, <b>II</b>, - <a href="#Page_298">298</a>.</li> - - <li>Whistling, definition of life and, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page112">112</a>.</li> - - <li class="hangingindent">White-Cooper, Mr., on inheritance of abnormal vision, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page306">306</a>.</li> - - <li>Willow, nutrition and growth, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page294">294</a>.</li> - - <li>Wilson, E. B.: composition of chromatin, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page260">260</a>;</li> - <li class="hangingindent1">separation of segmentation spheres of <i>Amphioxus</i> ovum, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page691">691</a>.</li> - - <li>Wind: and vegetal bilateral symmetry, <b>II</b>, - <a href="#Page_142">142</a>;</li> - <li class="hangingindent1">and inner vegetal tissue differentiation, <b>II</b>, - <a href="#Page_275">275–9</a>, - <a href="#Page_285">285</a>, - <a href="#Page_288">288</a>, - <a href="#Page_388">388</a>;</li> - <li class="i1">and proliferation of <i>Bryophyllum</i>, <b>II</b>, - <a href="#Page_295">295</a>;</li> - <li class="i1">and vegetal sap movement, <b>II</b>, - <a href="#Page_583">583</a>, - <a href="#Page_584">584</a>, - <a href="#Page_587">587</a>;</li> - <li class="i1"><i>résumé</i>, - <a href="#Page_592">592–6</a>.</li> - - <li class="hangingindent">Wolff, C.: vegetal fructification and nutrition, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page283">283</a>; <b>II</b>, - <a href="#Page_179">179–80</a>;</li> - <li class="i1">vegetal vascular system, <b>II</b>, - <a href="#Page_283">283</a>.</li> - - <li>Women (<i>see</i> <a href="#Man">Man</a>).</li> - - <li>Wood (<i>see</i> <a href="#Plants">Plants</a>).</li> -</ul> - -<ul> - <li>Yeast: fermentation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page38">38</a>;</li> - <li class="i1">fertility, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page581">581</a>; <b>II</b>, - <a href="#Page_440">440</a>;</li> - <li class="i1">linear aggregation, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page587">587</a>; <b>II</b>, - <a href="#Page_23">23</a>.</li> -</ul> - -<ul> - <li>Zebra marks in horses, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page314">314</a>.</li> - - <li>Zoology, classification, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page124">124–5</a>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page380">380–9</a>.</li> - - <li>Zoophytes, structural indefiniteness, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page173">173</a>.</li> - - <li>Zoospores, unit-life of, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page185">185</a>.</li> - - <li>Zygote, of conjugating <i>Algæ</i>, <b>I</b>, - <a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#page283">283</a>.</li> -</ul> - - -<p class="center p-left sm">THE END.</p> - - -<div class="footnotes"><h2>FOOTNOTES:</h2> - -<div class="footnote"> - -<p><a id="Footnote_1" href="#FNanchor_1" class="label">[1]</a> It seems needful here to say, that allusion is made in -this paragraph to a proposition respecting the ultimate natures of -Evolution and Dissolution, which is contained in an essay on <i>The -Classification of the Sciences</i>, published in March, 1864. When -the opportunity comes, I hope to make the definition there arrived -at, the basis of a re-organization of the second part of <i>First -Principles</i>: giving to that work a higher development, and a greater -cohesion, than it at present possesses. [The intention here indicated -was duly carried out in 1867.]</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_2" href="#FNanchor_2" class="label">[2]</a> Let me here refer those who are interested in this -question, to Prof. Huxley’s criticism on the cell-doctrine, published -in the <i>Medico-Chirurgical Review</i> in 1853.</p> - -<p>A critic who thinks the above statements are “rather misleading” -admits that the lowest types of organisms yield them support, saying -that “there are certainly masses of protoplasm containing many nuclei, -but no trace of cellular structure, in both animals and plants. Such -non-cellular masses may exist during development and later become -separated up into cells, but there are certain low organisms in which -such masses exist in the adult state. They are called by some botanists -non-cellular, by others multi-nucleate cells. Clearly the difference -lies in the criteria of a cell. There are also some <i>Protozoa</i>, -and the <i>Bacteria</i>, in which no nucleus has certainly been -demonstrated. But it is usual to consider the bodies of such organisms -as cells nevertheless, and it is supposed that such cells represent a -stage of development in which the nucleus has not yet been evolved, -though the chemical substance ‘nuclein’ has been formed in some of -them.”</p> - -<p>Perhaps it will be most correct to say that, excluding the minute, -non-nucleated organisms, all the higher organisms—<i>Metazoa</i> and -<i>Metaphyta</i>—are composed throughout of cells, or of tissues -originally cellular, or of materials which have in the course of -development been derived from cells. It must, however, be borne in -mind that, according to sundry leading biologists, cells in the strict -sense are not the immediate products either of the primitive fissions -or of subsequent fissions; but that the multiplying so-called cells -are nucleated masses of protoplasm which remain connected by strands -of protoplasm, and which acquire limiting membranes by a secondary -process. So that, in the view of Mr. Adam Sedgwick and others, the -substance of an organism is in fact a continuous mass of vacuolated -protoplasm.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_3" href="#FNanchor_3" class="label">[3]</a> In further illustration, Mr. Tansley names the fact that -in the genus <i>Caulerpa</i> we have extremely complicated forms often -of considerable size produced in the same way. The various species -simulate very perfectly the members of different groups among the -higher plants, such as Horse-tails, Mosses, Cactuses, Conifers and the -like.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_4" href="#FNanchor_4" class="label">[4]</a> It may be objected that in <i>Cladophora</i> the separate -compartments of the thallus severally contain many nuclei, making it -doubtful whether they descend from uni-nucleate cells. If, however, -they do not they simply illustrate another form of integration.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_5" href="#FNanchor_5" class="label">[5]</a> The great mass of early ancestral types—plant and -animal—consisting of soft tissues, have left no remains whatever, and -we have no reason to suppose that those which left remains fell within -the direct ancestral lines of any existing forms. Contrariwise, we have -reason to suppose that they fell within lines of evolution out of which -the lines ending in existing forms diverged. We must therefore infer -that the difficulties of affiliation which arise if we contemplate -divergent types now existing, would not arise if we had before us all -the early intermediate types. The Mammalia differ in sundry respects -from all other kinds of Vertebrata—Fishes, Reptiles, Birds; and if -the absence of hair, mammæ, and two occipital condyles, in these other -vertebrates were taken to imply a fundamental distinction, it might, in -the absence of any known fossil links, be inferred that the Mammalia -belonged to a separate phylum. But these differences are not held to -negative the assumed relationship. Similarly among plants. We must -not reject an hypothesis respecting a certain supposed type, because -the existing types it must have been akin to present traits which it -could not have had. We are justified in assuming, within limits, a -hypothetical type, unlike existing types in traits of some importance. -Hence results the answer to a criticism passed on the above argument, -that it implies relations between the undeveloped and developed forms -of the <i>Jungermanniaceæ</i> such as the facts do not show us. This -objection is met on remembering that the types in which the supposed -transition took place disappeared myriads of years ago.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_6" href="#FNanchor_6" class="label">[6]</a> There is much force in the criticism passed on the above -paragraph, and by implication on some preceding paragraphs, that -though in plants which tend to produce compound leaves the production -is largely dependent on the supply of nutriment, yet the unqualified -statement of this relation as a general one, is negatived by the -existence of plants which bear only simple leaves, however much high -nutrition causes growth. But mostly valid though this objection is, -it is probably not universally valid. I am led to say this by what -occasionally occurs in flowers. The flowering stem of the Hyacinth -is single; but I have seen a cultivated Hyacinth in which one of -the flowers had developed into a lateral spike. Still more striking -evidence was once supplied to me by Agrimony. All samples of this plant -previously seen had single flowering spikes, but some years ago I met -with one, extremely luxuriant, in which some flowers of the primitive -spike were replaced by lateral spikes; and I am not sure that some of -these, again, did not bear lateral spikes. Now if in plants which, -in probably millions of cases, have their flowering stems single, -excessive nutrition changes certain of their flowers into new spikes, -it is a reasonable supposition that in like manner plants which are -thought invariably to bear only single leaves, will, under kindred -conditions, bear compound leaves.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_7" href="#FNanchor_7" class="label">[7]</a> See <i>British and Foreign Medico-Chirurgical Review</i> -for January, 1862.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_8" href="#FNanchor_8" class="label">[8]</a> Schleiden, who chooses to regard as an axis that which -Mr. Berkeley, with more obvious truth, calls a mid-rib, says:—“The -flat stem of the Liverworts presents many varieties, consisting -frequently of one simple layer of thin-walled cells, or it exhibits in -its axis the elements of the ordinary stem.” This passage exemplifies -the wholly gratuitous hypotheses which men will sometimes espouse, -to escape hypotheses they dislike. Schleiden, with the positiveness -characteristic of him, asserts the primordial distinction between -axial organs and foliar organs. In the higher Archegoniates he sees an -undeniable stem. In the lower Archegoniates, clearly allied to them -by their fructification, there is no structure having the remotest -resemblance to a stem. But to save his hypothesis, Schleiden calls -that “a flat stem,” which is obviously a structure in which stem and -leaf are not differentiated. He is the more to be blamed for this -unphilosophical assumption, since he is merciless in his strictures on -the unphilosophical assumptions of other botanists.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_9" href="#FNanchor_9" class="label">[9]</a> To this interpretation it is objected that “the -more-developed <i>Jungermanniaceæ</i>” do not appear to have arisen from the -lower forms of <i>Jungermanniaceæ</i>—that is to say, from such lower -forms as are now existing. It may, however, be contended that this fact -does not exclude the interpretation given; since the higher forms may -well have been evolved, not from any of the lower forms we now know, -but from lower forms which have become extinct. This, indeed, is the -implication of the evolutionary process as pointed out in the note to -Chap. I. If then we assume some early type of intermediate structure, -the explanation may not improbably hold.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_10" href="#FNanchor_10" class="label">[10]</a> I am indebted to Dr. Hooker for pointing out further -facts supporting this view. In his <i>Flora Antarctica</i>, he -describes the genus <i>Lessonia</i> (see Fig. <a href="#i_030">37</a>), and especially -<i>L. ovata</i>, as having a mode of growth simulating that -of the dicotyledonous trees, not only in general form but in -internal structure. The tall vertical stem thickens as it grows, -by the periodical addition of layers to its periphery. That even -Thallophytes should thus, under certain conditions, present a -transversely-increasing axis, shows that there is nothing absolutely -characteristic of Phanerogams in their habit of stem-thickening. -Mr. Tansley gives me further verification by the statement that -“it is also now certain that members of the <i>Equisetineæ</i> -and <i>Lycopodineæ</i>, as well as some Ferns which flourished in -Carboniferous times, had secondary thickening in their stems quite -comparable to that of modern Dicotyledonous trees.”</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_11" href="#FNanchor_11" class="label">[11]</a> See note at the end of the chapter.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_12" href="#FNanchor_12" class="label">[12]</a> Since this paragraph was put in type [this refers -to the first edition], I have observed that in some varieties of -<i>Cineraria</i>, as probably in other plants, a single individual -furnishes all these forms of leaves—all gradations between -unstipulated leaves on long petioles, and leaves that embrace the axis. -It may be added that the distribution of these various forms is quite -in harmony with the rationale above given.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_13" href="#FNanchor_13" class="label">[13]</a> Since these figures were put on the block, it has -occurred to me that the relations would be still clearer, were the -primary frond represented as not taking part in these processes of -modification, which have been described as giving rise to the erect -form; as, indeed, the rooting of its under surface will prevent it from -doing in any considerable degree. In such case, each of the Figs. <a href="#i_071">111 -to 117</a>, should have a horizontal rooted frond at its base, homologous -with the pro-embryo among Acrogens. This primary frond would then more -manifestly stand in the same relation to the rest, as the cotyledon -does to the plumule—both by position, and as a supplier of nutriment. -Fig. <a href="#i_071">117<i>a</i></a>, which I am enabled to add, shows that this would -complete the interpretation. Of the dicotyledonous series, it is -needful to add no further explanation than that the difference in habit -of growth, will permit the second frond to root itself as well as the -first; and so to become an additional source of nutriment, similarly -circumstanced to the first and equal with it.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_14" href="#FNanchor_14" class="label">[14]</a> How the element of time modifies the result, is shown by -the familiar fact that crystals rapidly formed are small, and become -relatively large when left to form more slowly. If the quantity of -molecules contained in a solution is relatively great, so that the -mutual polarities of the molecules crowded together in every place -throughout the solution are intense, there arises a crystalline -aggregation around local axes; whereas, in proportion as the local -action of molecules on one another is rendered less intense by their -wider dispersion, they become relatively more subordinate to the forces -exerted on them by the larger aggregates of molecules that are at -greater distances, and thus are left to arrange themselves round fewer -axes into larger crystals.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_15" href="#FNanchor_15" class="label">[15]</a> It is objected that these transformations should be much -commoner than they are, were they caused solely by the variations of -nutrition described. The reply is that they are comparatively rare -in uncultivated plants, where such variations are not frequent. The -occurrence of them is chiefly among cultivated plants which, being -artificially manured, are specially liable to immense accessions of -nutriment, caused now by sudden supplies of fertilizing matters, and -now by sudden arrival of the roots at such matters already deposited in -the soil. It is to these great <i>changes</i> of nutrition, especially -apt to take place in gardens, that these monstrosities are ascribed; -and it seems to me that they are as frequent as may be expected.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_16" href="#FNanchor_16" class="label">[16]</a> Since this paragraph was published in 1865, much has been -learned concerning cell-structure, as is shown in Chapter VI<sup>A</sup> of Part -I. While some assert that there exist portions of living protoplasm -without nuclei, others assert that a nucleus is in every case present, -and that where it does not exist in a definite aggregated form it -exists in a dispersed form. As remarked in the chapter named, “the -evidence is somewhat strained to justify this dogma.” Words are taken -in their non-natural senses, if one which connotes an individualized -body is applied to the widely-diffused components of such a body; and -this perverting of proper meanings leads to obscuration of what may -perhaps be an essential truth. As argued in the chapter named (<a href="http://www.gutenberg.org/files/54612/54612-h/54612-h.htm#sect74">§§ 74<i>e</i>, 74<i>f</i></a>), -nuclear matter is, as shown by its chemical -character, an extremely unstable substance, the molecular changes of -which, perpetually going on, initiate shocks, producing changes all -around. In the earlier stages of cell-evolution this unstable substance -is dispersed throughout the cytoplasm; whereas in the more advanced -stages it is gathered together in one mass. If so, instead of saying -there is a dispersed nucleus we should say there are the materials of a -nucleus not yet integrated.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_17" href="#FNanchor_17" class="label">[17]</a> This statement seems at variance with the figure; but the -figure is very inaccurate. Its inaccuracy curiously illustrates the -vitiation of evidence. When I saw the drawing on the block, I pointed -out to the draughtsman, that he had made the surrounding curves much -more obviously related to the contained bodies, than they were in the -original (in Dr. Carpenter’s <i>Foraminifera</i>); and having looked -on while he in great measure remedied this defect, thought no further -care was needed. Now, however, on seeing the figure in the printer’s -proof, I find that the engraver, swayed by the same supposition as the -draughtsman that such a relation was meant to be shown, has made his -lines represent it still more decidedly than those of the draughtsman -before they were corrected. Thus, vague linear representations, like -vague verbal ones, are apt to grow more definite when repeated. -Hypothesis warps perceptions as it warps thoughts.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_18" href="#FNanchor_18" class="label">[18]</a> Though the subdivision into chambers of the shell does -not correspond to the subdivision into cell-units it may still be held -that since in the solitary types the subdivision of the nucleus is -followed by formation of new individuals which separate, and since in -the compound types the subdivision of the nucleus is followed by growth -and formation of new chambers, the compound type must be regarded as an -aggregate of the second order.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_19" href="#FNanchor_19" class="label">[19]</a> A critic says the question is “what are the forces -internal or external which produce union or separation.” A proximate -reply is—degree of nutrition. As in a plant new individuals or -rudiments of them are cast off where nutrition is failing, so in a -compound animal. The connecting part dwindles if it ceases to carry -nutriment.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_20" href="#FNanchor_20" class="label">[20]</a> It has been pointed out that I have here understated -the evidence of physiological integration. An instance of it among -<i>Hydrozoa</i> is shown in Fig. <a href="#i_092">151</a>, but by a strange oversight -I have forgotten to name the various cases furnished by the -<i>Siphonophora</i> in which the individual polypes of a compound -aggregate are greatly specialized in adaptation to different functions.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_21" href="#FNanchor_21" class="label">[21]</a> Recently Mr. T. H. Morgan has made elaborate experiments -which show that <i>Planaria Maculata</i> may be cut into many pieces -from various parts and of various shapes—even a slice out of the -side—and each, if not too small, will produce a perfect animal.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_22" href="#FNanchor_22" class="label">[22]</a> Since this was written in 1865 there has come to light -evidence more completely to the point than any at that time known. In -the subdivision of <i>Platyhelminthes</i> known as <i>Turbellaria</i>, -there are some, the <i>Microstomida</i> which, by a process of -segmentation form “chains of 4, then 8, then 16, and sometimes even 32 -individuals.” “Each forms a mouth [lateral] and for some time the chain -persists, but the individuals ultimately become sexually matured and -then separate.” (Shipley, <i>Zoology of the Invertebrata</i>, p. 92.) -Here it should be remarked that the lateral mouths enable the members -of a string to feed separately, and that nutrition not being interfered -with they doubtless gain some advantage by temporary maintenance of -their union—probably in creeping.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_23" href="#FNanchor_23" class="label">[23]</a> I find that the reasons for regarding the segment of -a <i>Tænia</i> as answering to an individual of the second order -of aggregation, are much stronger than I supposed when writing the -above. Van Beneden says:—“Le Proglottis (segment) ayant acquis tout -son développement, se détache ordinairement de la colonie et continue -encore à croître dans l’intestin du même animal; il change même souvent -de forme et semble doué d’une nouvelle vie; ses angles s’effacent, -tout le corps s’arrondit, et il nage comme une Planaire au milieu des -muscosités intestinales.”</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_24" href="#FNanchor_24" class="label">[24]</a> Though this was doubtful in 1865 it is no longer -doubtful. In an individual <i>Ctenodrilus monostylus</i>, which -multiplies by dividing and subdividing itself, “parts arise which are -destitute of both head and anus and at times consist of only a single -segment.” In another species, <i>C. pardalis</i>, there is separation -into many segments; and each segment before separating forms a budding -zone out of which other segments are afterwards produced, completing -the animal (Korschelt and Heider, <i>Embryology</i>, i, 301–2).</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_25" href="#FNanchor_25" class="label">[25]</a> In place of those originally here instanced about which -there are disputes, I may give an undoubted one described by McIntosh, -the <i>Syllis ramosa</i>, a species of chætopod living in hexactinellid -sponges from the Arafura Sea, which branches laterally repeatedly so as -to extend in all directions through the canals of the sponge. In most -cases the buds terminate in oval segments with two long cirri each. -But male and female buds were found, provided each with a head, and -containing ovaries and testes. Sometimes these sexual buds had become -separate from the branched stock.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_26" href="#FNanchor_26" class="label">[26]</a> The name <i>Annulosa</i>, once used to embrace the -<i>Annelida</i> and <i>Arthropoda</i>, has of late ceased to be used. -It seems to me better than <i>Appendiculata</i>, both as being more -obviously descriptive and as being more exclusive.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_27" href="#FNanchor_27" class="label">[27]</a> The fusion of the segments forming the Arthropod head -and the extreme changes, or perhaps in some cases disappearances, of -their appendages, put great difficulties in the way of identification; -so that there are differences of opinion respecting the number of -included segments. Prof. MacBride writes:—“It is highly probable that -a primary head (præoral lobe or præstomium) has been derived from -annelid ancestors, but the secondary fusion of body-segments with this -head, in other words the formation of a secondary head, has gone on -independently in the different classes of the phylum <i>Arthropoda</i>, -viz., <i>Arachnida</i>, <i>Crustacea</i>, and <i>Tracheata</i> -(including Insects and Myriapods). Judged by the number of appendages -(which gives an inferior limit) the head of a malacostracous Crustacean -consists of præstomium and 8 segments; the head of an insect of -præstomium and 4 segments; the head of a Myriapod of præstomium and 3 -segments; and the head of an Arachnid of præstomium and 3 segments.” -Again, the comment of Mr. J. T. Cunningham is:—“According to Claus and -most modern authorities there are only 5 segments in the head of an -Arthropod, the eyes not counting as appendages; and further it should -be noted that the second pair of antennæ are wanting in Insects.”</p> - -<p>Of course difference of opinion respecting the number of somites in the -head involves difference of opinion respecting the number constituting -the entire body, which, in the higher Arthropods, is said by some to -be 19 and by others 20. But those who thus differ in detail, agree in -regarding all the segments of head and body as homologous, and this is -the essential point with which we are here concerned.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_28" href="#FNanchor_28" class="label">[28]</a> Prof. MacBride corrects this statement by saying that -“The ctenidia or gills (which in <i>Mollusca</i> generally are -represented only by a single pair) are here represented by a large -number of pairs; they do not, however, correspond in either number or -position to the shell plates.” It may, I think, be contended that if -these had any morphological significance, they would not differ in -arrangement from the shell plates, and would not be limited to this -special type of Mollusc.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_29" href="#FNanchor_29" class="label">[29]</a> Though it is alleged that at a later stage the posterior -part of the skull is formed by fusion of divisions which are assumed to -represent vertebræ, yet it is admitted that the anterior part of the -skull never shows any signs of such division. Moreover in both parts -the bones show no trace of primitive segmentation.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_30" href="#FNanchor_30" class="label">[30]</a> See note at the end of the chapter.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_31" href="#FNanchor_31" class="label">[31]</a> A qualifying fact should be named. When the production -of vertebral segments has become constitutionally established, so that -there is an innate tendency to form them, there arises a liability to -form supernumerary ones; and this, from time to time recurring, may -lengthen the series, as in the body of a snake or the neck of a swan. -This qualification, however, affects equally the hypothesis of an ideal -type and the hypothesis of mechanical genesis.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_32" href="#FNanchor_32" class="label">[32]</a> Here and throughout, the word <i>radial</i> is applied -equally to the spiral and the whorled structures. These, as being alike -on all sides, are similarly distinguished from arrangements that are -alike on two sides only.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_33" href="#FNanchor_33" class="label">[33]</a> It should be added that this change of distribution is -not due to change in the relative positions of the insertions of the -leaves but to their twistings.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_34" href="#FNanchor_34" class="label">[34]</a> We may note that some of these leaves, as those of the -Lime, furnish indications of the ratio which exists between the effects -of individual circumstances and those of typical tendencies. On the -one hand, the leaves borne by these drooping branches of the Lime are -with hardly an exception unsymmetrical more or less decidedly, even -in positions where the causes of unsymmetry are not in action: a fact -showing us the repetition of the type irrespective of the conditions. -On the other hand, the degree of deviation from symmetry is extremely -variable, even on the same shoot: a fact proving that the circumstances -of the individual leaf are influential in modifying its form. But the -most striking evidence of this direct modification is afforded by the -suckers of the Lime. Growing, as these do, in approximately upright -attitudes, the leaves they bear do not stand to one another in the way -above described, and the causes of unsymmetry are not in action; and -here, though there is a general leaning to the unsymmetrical form, a -large proportion of the leaves become quite symmetrical.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_35" href="#FNanchor_35" class="label">[35]</a> It was by an observation on the forms of leaves, that I -was first led to the views set forth in the preceding and succeeding -chapters on the morphological differentiation of plants and animals. -In the year 1851, during a country ramble in which the structures -of plants had been a topic of conversation with a friend—Mr. G. H. -Lewes—I happened to pick up the leaf of a buttercup, and, drawing -it by its foot-stalk through my fingers so as to thrust together its -deeply-cleft divisions, observed that its palmate and almost radial -form was changed into a bilateral one; and that were the divisions to -grow together in this new position, an ordinary bilateral leaf would -result. Joining this observation with the familiar fact that leaves, in -common with the larger members of plants, habitually turn themselves to -the light, it occurred to me that a natural change in the circumstances -of the leaf might readily cause such a modification of form as that -which I had produced artificially. If, as they often do with plants, -soil and climate were greatly to change the habit of the buttercup, -making it branched and shrub-like; and if these palmate leaves were -thus much overshadowed by one another; would not the inner segments -of the leaves grow towards the periphery of the plant where the light -was greatest, and so change the palmate form into a more decidedly -bilateral form? Immediately I began to look round for evidence of the -relation between the forms of leaves and the general characters of the -plants they belong to; and soon found some signs of connexion. Certain -anomalies, or seeming anomalies, however, prevented me from then -pursuing the inquiry much further. But consideration cleared up these -difficulties; and the idea afterwards widened into the general doctrine -here elaborated. Occupation with other things prevented me from giving -expression to this general doctrine until Jan. 1859; when I published -an outline of it in the <i>Medico-Chirugical Review</i>.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_36" href="#FNanchor_36" class="label">[36]</a> It is objected to the above interpretation that “many -flowers of sizes intermediate between the Hollyhock and the Agrimony -are radially symmetrical and yet grow sideways. I may mention -various <i>Liliaceæ</i>, e.g. <i>Chlorophytum</i>, <i>Eucomis</i>, -<i>Muscari</i>, <i>Anthericum</i>. <i>Sagittaria</i>, also, has many -of its flowers in this position. Further, if the higher insects alight -on flowers in a definite way, as they do, the parts of the flower -must bear different relations to the visiting insect, however large, -so that flowers unvisited ought all to be zygomorphic.” My reply is -that in the sense which here concerns us, the different petals of -the Hollyhock-flower do not bear different relations to the visiting -insect; since, practically, the upper and lateral petals bear no -physical relations at all: in so far as the visiting bee is concerned -they are non-existent. The argument implies that change in the form of -a flower from the radial to the bilateral is likely to take place only -when the contact-relations of the petals to the visiting insect, are -such as to make some forms facilitate its action more than others; and -the large petals of the Hollyhock cannot facilitate its action at all. -In respect of the <i>Liliaceæ</i> instanced, it is needful to inquire -whether the structures are such that this alleged cause of bilateral -symmetry can come into play.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_37" href="#FNanchor_37" class="label">[37]</a> I had intended here to insert a figure exhibiting these -differences; but as the Cow-parsnip does not flower till July, and as -I can find no drawing of the umbel which adequately represents its -details, I am obliged to take another instance.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_38" href="#FNanchor_38" class="label">[38]</a> It has been pointed out to me that “the extreme -development of the corolla so often found in the outer flowers or on -the outer side of the outer flowers in closely-packed inflorescences, -associated as it often is with disappearance of stamens or carpels or -both, is usually put down to specialization of these outer flowers for -attractive purposes. Since the whole inflorescence is increased in -conspicuousness by such a modification, it is supposed that natural -selection favoured those plants which sacrificed a portion of their -seed-bearing capacity for the supposed greater advantage of securing -more insect visits.” But granting this interpretation, it may still -be held that increase of attractiveness due to increase of area must -be achieved by florets at the periphery, and that their ability to -achieve it depends on their having an outer, unoccupied, space which -the inner florets have not; so that, though in a more indirect way, -their different development is determined by different exposure to -conditions.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_39" href="#FNanchor_39" class="label">[39]</a> One of my critics writes:—“This chapter might of course -be enormously extended, not only as in the preceding ones by citation -of quite similar cases, but by the introduction of fresh groups of -cases.”</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_40" href="#FNanchor_40" class="label">[40]</a> Natural selection may have operated in establishing -a constitutional tendency to other sudden abridgments. Mr. Tansley -alleges that this is a part-cause of the varying distribution of -leaves. He says:—“I have myself made some observations on the length -of internodes in the Beech, and am satisfied that it follows quite -other laws, connected with the suitable disposition of the leaves on -the branch. Although I have not had the opportunity of following up -this line of work so as in any way to generalize the results, I suspect -that ‘indirect equilibration’ is a widespread cause of such variation.”</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_41" href="#FNanchor_41" class="label">[41]</a> It is but just to the memory of Wolff, here to point out -that he was immensely in advance of Goethe in his rationale of these -metamorphoses. Whatever greater elaboration Goethe gave to the theory -considered as an induction, seems to me more than counter-balanced -by the irrationality of his deductive interpretation; which unites -mediæval physiology with Platonic philosophy. A dominant idea with him -is that leaves exist for the purpose of carrying off crude juices—that -“as long as there are crude juices to be carried off, the plant must -be provided with organs competent to effect the task”; that while “the -less pure fluids are got rid of, purer ones are introduced” and that -“if nourishment is withheld, that operation of nature (flowering) is -facilitated and hastened; the organs of the nodes (leaves) become -more refined in texture, the action of the purified juices becomes -stronger, and the transformation of parts having now become possible, -takes place without delay.” This being the proximate explanation, the -ultimate explanation is, that Nature wishes to form flowers—that when -a plant flowers it “attains the end prescribed to it by nature”; and -that so “Nature at length attains her object.” Instead of vitiating -his induction by a teleology that is as unwarranted in its assigned -object as in its assigned means, Wolff ascribes the phenomena to a -cause which, whether sufficient or not, is strictly scientific in its -character. Variation of nutrition is unquestionably a “true cause” of -variation in plant-structure. We have here no imaginary action of a -fictitious agency; but an ascertained action of a known agency.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_42" href="#FNanchor_42" class="label">[42]</a> The <i>Natural History Review</i> for July, 1865, -contained an article on the doctrine of morphological composition set -forth in the foregoing Chaps. I. to III. In this article, which unites -exposition and criticism in a way that is unhappily not common with -reviewers, it is suggested that the spiral structure may be caused by -natural selection. When this article appeared, the foregoing five pages -were standing over in type, as surplus from No. 14, issued in June, -1865.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_43" href="#FNanchor_43" class="label">[43]</a> A verifying comment on this paragraph runs as -follows:—“In the Hypotricha Infusoria, which creep over solid -surfaces, there is a differentiation between ventral and dorsal surface -and an approach to bilateral symmetry. The ventral surface is provided -with movable cilia, the dorsal with immobile setæ.”</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_44" href="#FNanchor_44" class="label">[44]</a> Criticisms on the above passage have shown the need -for naming sundry complications. These complications chiefly, if -not wholly, arise from changes in modes of life—changes from -the locomotive to the stationary, and from the stationary to the -locomotive. Referring to my statement that (ignoring the spherical) -the radial type is the lowest and must be taken as antecedent -to the bilateral type, it is alleged that all existing “radial -animals above Protozoa are probably derived from free-swimming, -bilaterally-symmetrical animals.” If this is intended to include -the planulæ of the hydroid polyps, then it seems rather a straining -of the evidence. These locomotive embryos, described as severally -having the structure of a gastrula with a closed mouth, can be said -to show bilateralness only because the first two tentacles make their -appearance on opposite sides of the mouth—a bilateralness which lasts -only till two other tentacles make their appearance in a plane at -right angles, so giving the radial structure. I think the criticism -applies only to cases furnished by Echinoderms. The larvæ of these -creatures have bilaterally-symmetrical structures, which they retain -as long as they swim about and which such of them as fix themselves -lose by becoming similarly related to conditions all round: the radial -structure being retained by those types which, becoming subsequently -detached, move about miscellaneously. But, as happens in some of the -Sea-urchins and still more among the Holothurians, the structure is -again made bilaterally-symmetrical by a locomotive life pursued with -one end foremost. Should it be contended that the conditions and the -forms are reciprocally influential—that either may initiate the other, -it still remains unquestionable that ordinarily the conditions are the -antecedents, as is so abundantly shown by plants.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_45" href="#FNanchor_45" class="label">[45]</a> Should it be proved that the Ascidian is a degraded -vertebrate, then the argument will be strengthened; since loss -of bilateral symmetry has gone along with change to asymmetrical -conditions.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_46" href="#FNanchor_46" class="label">[46]</a> A critical comment made on this sentence runs as -follows:—“The aërial roots of most epiphytic orchids contain -chlorophyll in their cortex throughout their length, but the cortex -being covered by a ‘velamen’ of air-containing cells which break up and -reflect incident light, the green colour is not visible through this -opaque coat. When moistened the cells of the velamen take up water and -the green colour immediately shows through. Such roots do not however -possess stomata. The roots of certain species of <i>Angræcum</i>, -however, contain the whole of the assimilating tissue of the plant.”</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_47" href="#FNanchor_47" class="label">[47]</a> The current doctrine that chlorophyll is <i>the</i> -special substance concerned in vegetal assimilation, either as an -agent or as an incidental product, must be taken with considerable -qualification. Besides the fact that among the <i>Algæ</i> there are -many red and brown kinds which thrive; and besides the fact that -among the lower Archegoniates there are species which are purple or -chocolate-coloured; there is the fact that Phænogams are not all -green. We have the Copper-Beech, we have the black-purple <i>Coleus -Verschaffeltii</i>, and we have the red variety of Cabbage, which seems -to flourish as well as the other varieties. Chlorophyll, then, must be -regarded simply as the most general of the colouring matters found in -those parts of plants in which assimilation is being effected by the -agency of light. Though it is always present <i>along with</i> the red -and brown pigments, yet there is much evidence to show that these are -the actual assimilative pigments.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_48" href="#FNanchor_48" class="label">[48]</a> This seems as fit a place as any for noting the fact, -that the greater part of what we call beauty in the organic world, is -in some way dependent on the sexual relation. It is not only so with -the colours and odours of flowers. It is so, too, with the brilliant -plumage of birds; and it is probable that the colours of the more -conspicuous insects are in part similarly determined. The remarkable -circumstance is, that these characteristics, which have originated -by furthering the production of the best offspring, while they are -naturally those which render the organisms possessing them attractive -to one another, directly or indirectly, should also be those which are -so generally attractive to us—those without which the fields and woods -would lose half their charm. It is interesting, too, to observe how the -conception of human beauty is in a considerable degree thus originated. -And the trite observation that the element of beauty which grows out of -the sexual relation is so predominant in æsthetic products—in music, -in the drama, in fiction, in poetry—gains a new meaning when we see -how deep down in organic nature this connexion extends.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_49" href="#FNanchor_49" class="label">[49]</a> Students of vegetal physiology, familiar with the -controversies respecting sundry points dealt with in this chapter, will -probably be surprised to find taken for granted in it, propositions -which they have habitually regarded as open to doubt. Hence it seems -needful to say that the conclusions here set forth, have resulted -from investigations undertaken for the purpose of forming opinions on -several unsettled questions which I had to treat, but which I could -find in books no adequate data for treating. The details of these -investigations, and the entire argument of which this chapter is partly -an abstract, will be found in Appendix C.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_50" href="#FNanchor_50" class="label">[50]</a> To this implied inference it is objected that “excess -of nutritive material does not necessarily lead to correspondingly -increased growth.” My reply is that a concomitant factor is activity of -the tissue, and that in its absence growth is not to be expected.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_51" href="#FNanchor_51" class="label">[51]</a> In recent years (since 1890) Prof. Wilhelm Roux, in -essays on functional adaptation, has set forth some views akin to the -foregoing in respect to the general belief they imply, though differing -in respect of the physiological processes he indicates. The following -relevant passage has been translated for me from an article of his in -the <i>Real-Encyclopädie der gesammten Heilkunde</i>:—“A more complete -theory of functional adaptation by the author is founded on the -assumption that the ‘functional’ stimulus, or ‘the act of exercising -the function’ (in muscles and glands), and especially, in the case of -bones, the concussion and tension caused by stress and strain, exert -a ‘trophic’ stimulus on the cells, in consequence of which, and along -with an increased absorption of nutriment, they grow and eventually -increase (or the osteoblasts at the point of greater stimulus form more -bone); while, conversely, with continued inactivity, by absence of -these stimuli the nourishment of the cell declines so that the waste is -insufficiently replaced (or otherwise that the bone-substance gradually -loses its power of resistance to the osteoblasts formed as a result of -inactivity”).</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_52" href="#FNanchor_52" class="label">[52]</a> An outline of the doctrine set forth in the following -chapters, was originally published in the <i>Westminster Review</i> for -April, 1852, under the title—<i>A Theory of Population deduced from -the General Law of Animal Fertility</i>; and was shortly afterwards -republished with a prefatory note stating that it must be accepted as a -sketch which I hoped at some future time to elaborate. In now revising -and completing it, I have omitted a non-essential part of the argument, -while I have expanded the remainder by adding to the number of facts -put in evidence, by meeting objections which want of space before -obliged me to pass over, and by drawing various secondary conclusions. -The original paper, with omissions, will be found in Appendix A to -Volume I of this work.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_53" href="#FNanchor_53" class="label">[53]</a> I was here thinking only of the cases which are general -among insects, but it seems that vertebrate animals, too, furnish -cases. Mr. Cunningham writes:—“There is a curious instance of this in -the Conger: the female grows to 6 or 7 feet long and a weight of 60 -lbs. and upwards and then ceases to feed for 6 months while the eggs -develop, and when the eggs are shed dies.”</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_54" href="#FNanchor_54" class="label">[54]</a> I say “normal” for the purpose of excluding not only -morbid growths but excess of fat.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_55" href="#FNanchor_55" class="label">[55]</a> To meet a possible criticism it should be remarked that -this calculation assumes that the power of asexual reproduction is -not exhausted by the end of the month. It has been found that “the -successive fissions of <i>Paramœcium</i> cannot continue indefinitely. -After some hundreds of generations the products of fission are small, -have no mouth, and die unless before this they have been allowed to -conjugate with individuals of another brood.” It may, however, be -fairly taken for granted that “some hundreds of generations” would take -longer than a month.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_56" href="#FNanchor_56" class="label">[56]</a> Even this number is far exceeded. Dr. Edward Klein, in a -lecture he gave at the Royal Institution on June 2, 1898, asserted that -246 bacteria in a cubic centimetre of nutritive liquid would multiply -to 20,000,000 in the course of twenty-four hours: a rate which, at -the end of the <i>third</i> day, would give, as the offspring of one -individual, 537,367,797,000,000.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_57" href="#FNanchor_57" class="label">[57]</a> It has since been shown that in <i>Myrianida fasciata</i> -as many as 29 attached groups exist. See <i>Cambridge Natural -History</i>, Vol. II, <i>Worms, Rotifers and Polyzoa</i>, p. 280.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_58" href="#FNanchor_58" class="label">[58]</a> To this passage Prof. MacBride appends the remark:—“This -is quite proven now, and the statement as it stands is quite correct; -but far better and more minutely worked out cases are to be found -amongst the <i>Infusoria</i>. In <i>Paramœcium</i> for example, there -are normally present a large macronucleus and a small micronucleus -lying alongside of it. When two individuals adhere preparatory to -conjugation, the macronucleus breaks up into fragments which are -absorbed: the micronucleus—which has some time previously divided into -two—begins to break up further and eventually forms eight bodies; all -of these except one disappear; this last piece then divides into two; -of these two one represents a male genital cell, for it passes over -into the body of the other <i>Paramœcium</i> and fuses with one of the -two corresponding nuclei there; thus each of the two individuals which -adhere fertilizes the other. The two individuals then separate and the -nucleus (result of fusion of male and female nuclei) in each divides -into four. Of these, two move to one end of the animal and two to the -other. The animal then divides into two transversely—each of the -products thus having two nuclei which form the micro-and macronucleus -of it. Thus it appears that the function of sexual union is simply -to give increased vigour to all the vital processes <i>including -fission</i>. Since as mentioned above (p. 443) if it is prevented, the -products of fission are eventually unable to feed themselves.”</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_59" href="#FNanchor_59" class="label">[59]</a> A passage translated for me from the German may be here -given in verification. Dr. Dionys Hellin in an essay on the origin of -Multiparity and Twin-births, refers to the thesis above set forth, and -says that “the fact that it is generally women of small growth who bear -twins is in complete agreement with it.” He adds that “Puech is right -in his opinion that twin pregnancies are a direct result of relatively -large ovaries (<i>i.e.</i>, in comparison with the whole body). He has -observed that for the same size of body the ovarium of a pluriparous -animal is always of greater volume than that of a uniparous animal ... -a sow has ovaries as large as a cow’s; but while the latter bears only -one calf [at a time], the sow brings forth 6–15 at each litter. Even -in animals of the same species but belonging to different races these -relations may be verified,” <i>e.g.</i>, Barbary sheep and ordinary -sheep.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_60" href="#FNanchor_60" class="label">[60]</a> When, after having held for some years the general -doctrine elaborated in these chapters, I agreed, early in 1852, -to prepare an outline of it for the <i>Westminster Review</i>, -I consulted, among other works, the just-issued third edition -of Dr. Carpenter’s <i>Principles of Physiology, General and -Comparative</i>—seeking in it for facts illustrating the different -degrees of fertility of different organisms, I met with a passage, -quoted above in <a href="#sect339">§ 339</a>, which seemed tacitly to assert that individual -aggrandizement is at variance with the propagation of the race; but -nowhere found a distinct enunciation of this truth. I did not then -read the Chapter entitled “General View of the Functions,” which held -out no promise of such evidence as I was looking for. But on since -referring to this chapter, I discovered in it the definite statement -that—“there is a certain degree of antagonism between the Nutritive -and Reproductive functions, the one being executed at the expense of -the other. The reproductive apparatus derives the materials of its -operations through the nutritive system, and is entirely dependent -upon it for the continuance of its function. If, therefore, it be -in a state of excessive activity, it will necessarily draw off from -the individual fabric some portion of the aliment destined for its -maintenance. It may be universally observed that, when the nutritive -functions are particularly active in supporting the <i>individual</i>, -the reproductive system is in a corresponding degree undeveloped,—and -<i>vice versâ</i>.” P. 592.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_61" href="#FNanchor_61" class="label">[61]</a> The climate, the locality, and the kind of food, are of -course all factors; and hence, probably, the differences between the -statements of different authorities concerning these several cases. -Prof. MacBride writes:—</p> - -<p>“According to Flower (<i>Mammals, Living and Extinct</i>) the Ferret is -a domesticated variety of the common polecat, which has 3 to 8 young. -Darwin (<i>Animals and Plants</i>) says that the wild sow often breeds -twice a year and produces a litter of 4 to 8, and sometimes even 12. -The domestic sow breeds twice and would breed oftener if permitted, and -if any good at all produces 8 in litter.”</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_62" href="#FNanchor_62" class="label">[62]</a> It is worth while inquiring whether unfitness of the food -given to them, is not the chief cause of that sterility which, as Mr. -Darwin says, “is the great bar to the domestication of animals.” He -remarks that “when animals and plants are removed from their natural -conditions, they are extremely liable to have their reproductive -systems seriously affected.” Possibly the relative or absolute arrest -of genesis, is less due to a direct effect on the reproductive -system, than to a changed nutrition of which the reproductive system -most clearly shows the results. The matters required for forming an -embryo are in a greater proportion nitrogenous than are the matters -required for maintaining an adult. Hence, an animal forced to live on -insufficiently-nitrogenized food, may have its surplus for reproduction -cut off, but still have a sufficiency to keep its own tissues in -repair, and appear to be in good health—meanwhile increasing in bulk -from excess of the non-nitrogenous matters it eats.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_63" href="#FNanchor_63" class="label">[63]</a> Huxley, <i>Anatomy of Invertebrated Animals</i>, p. 274.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_64" href="#FNanchor_64" class="label">[64]</a> Shipley, <i>Zoology of Invertebrata</i>, p. 112.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_65" href="#FNanchor_65" class="label">[65]</a> I am told that “Wagner, who described the larva, found -that it bored into the bark of trees. It attacks also the wheat plant, -and is a most destructive parasite.” Apparently this statement is at -variance with the foregoing inference. It is clear, however, that -since these heaps of nitrogenous refuse in which it has been found are -artificial and recent, they cannot be its natural habitats; and it -seems not improbable that these larvæ, suddenly supplied with a more -nutritive food in unlimited amount, may have as a consequence acquired -this habit of agamogenetic multiplication which did not characterize -the species under its natural conditions and relatively low nutrition.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_66" href="#FNanchor_66" class="label">[66]</a> This is exactly the reverse of Mr. Doubleday’s doctrine; -which is that throughout both the animal and vegetable kingdoms, -“over-feeding checks increase; whilst, on the other hand, a limited or -deficient nutriment stimulates and adds to it.” Or, as he elsewhere -says—“Be the range of the natural power to increase in any species -what it may, the <i>plethoric</i> state invariably checks it, and the -<i>deplethoric</i> state invariably develops it; and this happens in -the exact ratio of the intensity and completeness of each state, until -each state be carried so far as to bring about the actual death of the -animal or plant itself.”</p> - -<p>I have space here only to indicate the misinterpretations on which Mr. -Doubleday has based his argument.</p> - -<p>In the first place, he has confounded normal plethora with what I have, -in <a href="#sect355">§ 355</a>, distinguished as abnormal plethora. The cases of infertility -accompanying fatness, which he cites in proof that over-feeding checks -increase, are not cases of high nutrition properly so-called; but -cases of such defective absorption or assimilation as constitutes -low nutrition. In Chap. IX, abundant proof was given that a truly -plethoric state is an unusually fertile state. It may be added that -much of the evidence by which Mr. Doubleday seeks to show that among -men, highly-fed classes are infertile classes, may be out-balanced by -counter-evidence. Many years ago Mr. G. H. Lewes pointed this out: -extracting from a book on the peerage, the names of 16 peers who had, -at that time, 186 children; giving an average of 11·6 in a family.</p> - -<p>Mr. Doubleday insists much on the support given to his theory by the -barrenness of very luxuriant plants, and the fruitfulness produced -in plants by depletion. Had he been aware that the change from -barrenness to fruitfulness in plants, is a change from agamogenesis to -gamogenesis—had it been as well known at the time when he wrote as it -is now, that a tree which goes on putting out sexless shoots, is thus -producing new individuals; and that when it begins to bear fruit, it -simply begins to produce new individuals after another manner—he would -have perceived that facts of this class do not tell in his favour.</p> - -<p>In the law which Mr. Doubleday alleges, he sees a guarantee for the -maintenance of species. He argues that the plethoric state of the -individuals constituting any race of organisms, presupposes conditions -so favourable to life that the race can be in no danger; and that -rapidity of multiplication becomes needless. Conversely, he argues -that a deplethoric state implies unfavourable conditions—implies, -consequently, unusual mortality; that is—implies a necessity for -increased fertility to prevent the race from dying out. It may be -readily shown, however, that such an arrangement would be the reverse -of self-adjusting. Suppose a species, too numerous for its food, to -be in the resulting deplethoric state. It will, according to Mr. -Doubleday, become unusually fertile; and the next generation will be -more numerous rather than less numerous. For, by the hypothesis, the -unusual fertility due to the deplethoric state, is the cause of undue -increase of population. But if the next generation is more numerous -while the supply of food has not increased in proportion, then this -next generation will be in a still more deplethoric state, and will be -still more fertile. Thus there will go on an ever-increasing rate of -multiplication, and an ever-decreasing share of food, for each person, -until the species disappears. Suppose, on the other hand, the members -of a species to be in an unusually plethoric state. Their rate of -multiplication, ordinarily sufficient to maintain their numbers, will -become insufficient to maintain their numbers. In the next generation, -therefore, there will be fewer to eat the already abundant food, which -becoming relatively still more abundant, will render the fewer members -of the species still more plethoric, and still less fertile, than their -parents. And the actions and reactions continuing, the species will -presently die out from absolute barrenness.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_67" href="#FNanchor_67" class="label">[67]</a> A good deal of this chapter retains its original form; -and the above paragraph is reprinted verbatim from the <i>Westminster -Review</i> for April, 1852, in which the views developed in the -foregoing hundred pages were first sketched out. This paragraph shows -how near one may be to a great generalization without seeing it. Though -the struggle for life is the alleged motive force; though the process -of natural selection is recognized; and though to it is ascribed a -share in the evolution of a higher type; yet the conception is not -that which Mr. Darwin has worked out with such wonderful skill and -knowledge. In the first place, natural selection is here described -only as furthering direct adaptation—only as aiding progress by the -preservation of individuals in whom functionally-produced modifications -have gone on most favourably. In the second place, there is no trace -of the idea that natural selection may by co-operation with the -cause assigned, or with other causes, produce <i>divergences</i> -of structure; and of course, in the absence of this idea, there is -no implication that natural selection has anything to do with the -origin of species. And in the third place, the all-important factor -of variation—“spontaneous,” or incidental as we may otherwise call -it—is wholly ignored. Though use and disuse are, I think, much more -potent causes of organic modification than Mr. Darwin supposes—though, -while pursuing the inquiry in detail, I have been led to believe that -direct equilibration has played a more active part even than I had -myself at one time thought; yet I hold Mr. Darwin to have shown beyond -question, that a great part of the facts—perhaps the greater part—are -explicable only as resulting from the survival of individuals which -have deviated in some indirectly-caused way from the ancestral type. -Thus, the above paragraph contains merely a passing recognition of the -selective process; and indicates no suspicion of the enormous range -of its effects, or of the conditions under which a large part of its -effects are produced.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_68" href="#FNanchor_68" class="label">[68]</a> For the information of those who may wish to examine -metamorphoses of these kinds, I may here state that I have found nearly -all the examples described, in the neighbourhood of the sea—the -last-named, on the shore of Locheil, near Fort William. Whether it is -that I have sought more diligently for cases when in such localities, -or whether it is that the sea-air favours that excessive nutrition -whence these transformations result, I am unable to say.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_69" href="#FNanchor_69" class="label">[69]</a> These two dyes have affinities for different components -of the tissues, and may be advantageously used in different cases. -Magenta is rapidly taken up by woody matter and other secondary -deposits; while logwood colours the cell-membranes, and takes but -reluctantly to the substances seized by magenta. By trying both of them -on the same structure, we may guard ourselves against any error arising -from selective combination.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_70" href="#FNanchor_70" class="label">[70]</a> Those who repeat these experiments must be prepared for -great irregularities in the rates of absorption. Succulent structures -in general absorb much more slowly than others, and sometimes will -scarcely take up the dye at all. The differences between different -structures, and the same structure at different times, probably depend -on the degrees in which the tissues are charged with liquid and the -rates at which they are losing it by evaporation.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_71" href="#FNanchor_71" class="label">[71]</a> It may be added here that, on considering the mechanical -actions that must go on, we are enabled in some measure to understand -both how such inosculating channels are initiated, and how the -structures of their component cells are explicable. What must happen -to one of these elongated prosenchyma-cells if, in the course of -its development, it is subject to intermittent compressions? Its -squeezed-out liquid while partially escaping laterally, will more -largely escape upwards and downwards; and while repeated lateral -escape will tend to form lateral channels communicating with -laterally-adjacent cells, repeated longitudinal escape will tend to -form channels communicating with longitudinally-adjacent cells—so -producing continuous though irregular longitudinal canals. Meanwhile -each cell into and out of which the nutritive liquid is from time to -time squeezed through small openings in its walls, cannot thicken -internally in an even manner: deposition will be interfered with by the -passage of the currents through the pores. The rush to or from each -pore will tend to maintain a funnel-shaped depression in the deposit -around; and the opening from cell to cell will so acquire just that -shape which the microscope shows up—two hollow cones with their apices -meeting at the point where the cell-membranes are in contact. Moreover, -as confirming this interpretation, it may be remarked that we are thus -supplied with a reason for the differences of shape between these -passages from one pitted cell to another, and the analogous passages -that exist between cells otherwise formed and otherwise conditioned. -In the cells of the medulla, and others which are but little exposed -to compression, the passages are severally formed more like a tube -with two trumpet-mouths, one in each cell. This is just the form which -might be expected where the nutritive fluid passes from cell to cell in -moderate currents, and not by the violent rushes caused by intermittent -pressures. Of course it is not meant that in each individual cell -these structures are determined by these mechanical actions. The -facts clearly negative any such conclusion, showing us, as they in -many cases do, that these structures are assumed in advance of these -mechanical actions. The implication is, that such mechanical actions -initiated modifications that have, with the aid of natural selection, -been accumulated from generation to generation; until, in conformity -with ordinary embryological laws, the cells of the parts exposed to -such actions assume these special structures irrespective of the -actions—the actions, however, still serving to aid and complete the -assumption of the inherited type.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_72" href="#FNanchor_72" class="label">[72]</a> Some exceptions to this occur in plants that have -retrograded in the character of their tissues towards the simpler -vegetal types. Certain very succulent leaves, such as those of -<i>Sempervivum</i>, in which the cellular tissue is immensely developed -in comparison with the vascular tissue, seem to have resumed to a -considerable extent what we must regard as the primitive form of -vegetal circulation—simple absorption from cell to cell. These, -when they have lost much of their water, will take up the dye to -some distance through their general substance, or rather through its -interstices, even neglecting the vessels. At other times, in the same -leaves, the vessels will become charged while comparatively little -absorption takes place through the cellular tissue. Even in these -exceptional cases, however, the movement through cellular tissue is -nothing like as fast as the movement through vessels.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_73" href="#FNanchor_73" class="label">[73]</a> It seems probable, however, that osmotic distention is -here, especially, the more important of the two factors. The rising -of the sap in spring may indirectly result, like the sprouting of the -seed, from the transformation of starch into sugar. During germination, -this change of an oxy-hydro-carbon from an insoluble into a soluble -form, leads to rapid endosmose; consequently to great distention of -the seed; and therefore to a force which thrusts the contained liquids -into the plumule and radicle, and gives them power to displace the -soil in their way: it sets up an active internal movement when neither -evaporation nor the change which light produces can be operative. And -similarly, if, in the spring, the starch stored-up in the roots of a -tree passes into the form of sugar, the unusual osmotic absorption that -arises will cause an unusual distention—a distention which, being -resisted by the tough bark of the roots and stem, will result in a -powerful upward thrust of the contained liquid.</p> - -</div> -</div> - - -<p class="transnote">Transcriber’s Note:<br /> - -1. Obvious printers’, spelling and punctuation errors have been -silently corrected.<br /> - -2. 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