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diff --git a/57460-0.txt b/57460-0.txt index 6f1f387..df39a1c 100644 --- a/57460-0.txt +++ b/57460-0.txt @@ -1,32 +1,7 @@ -The Project Gutenberg EBook of The Genetic and the operative evidence -relating to secondary sexual character, by Thomas Hunt Morgan - -This eBook is for the use of anyone anywhere 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 www.gutenberg.org/license - - -Title: The Genetic and the operative evidence relating to secondary sexual characters - -Author: Thomas Hunt Morgan - -Release Date: July 7, 2018 [EBook #57460] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE GENETIC *** - +*** START OF THE PROJECT GUTENBERG EBOOK 57460 *** -Produced by Larry B. Harrison, Bryan Ness, Chuck Greif and -the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive/American -Libraries.) @@ -5997,367 +5972,4 @@ still continued to do after the change in the feathers. End of the Project Gutenberg EBook of The Genetic and the operative evidence relating to secondary sexual character, by Thomas Hunt Morgan -*** END OF THIS PROJECT GUTENBERG EBOOK THE GENETIC *** - -***** This file should be named 57460-0.txt or 57460-0.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/5/7/4/6/57460/ - -Produced by Larry B. 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Thus, we do not necessarily -keep eBooks in compliance with any particular paper edition. - - -Most people start at our Web site which has the main PG search facility: - - http://www.gutenberg.org - -This Web site includes information about Project Gutenberg-tm, -including how to make donations to the Project Gutenberg Literary -Archive Foundation, how to help produce our new eBooks, and how to -subscribe to our email newsletter to hear about new eBooks. +*** END OF THE PROJECT GUTENBERG EBOOK 57460 *** diff --git a/57460-h/57460-h.htm b/57460-h/57460-h.htm index 09cb8c6..66c8b4b 100644 --- a/57460-h/57460-h.htm +++ b/57460-h/57460-h.htm @@ -130,44 +130,7 @@ background-color:#ffffff;font-variant:normal;font-style:normal;font-weight:norma <body> -<pre> - -The Project Gutenberg EBook of The Genetic and the operative evidence -relating to secondary sexual character, by Thomas Hunt Morgan - -This eBook is for the use of anyone anywhere 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 www.gutenberg.org/license - - -Title: The Genetic and the operative evidence relating to secondary sexual characters - -Author: Thomas Hunt Morgan - -Release Date: July 7, 2018 [EBook #57460] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE GENETIC *** - - - - -Produced by Larry B. Harrison, Bryan Ness, Chuck Greif and -the Online Distributed Proofreading Team at -http://www.pgdp.net (This file was produced from images -generously made available by The Internet Archive/American -Libraries.) - - - - - - -</pre> +<div>*** START OF THE PROJECT GUTENBERG EBOOK 57460 ***</div> <hr class="full" /> @@ -1468,5015 +1431,7 @@ and black hens (2:1:1).</p> while the exponents stand for the factors involved, viz, B for barred and b for not-barred, which here means a black bird.</p> -<pre> - Barred♂ Black♀ - P₁ ZᴮZᴮ ZᵇbW - \ / - \ / - \ / - \ / - ZᴮZ ZᴮW - F₁ Barred♂ Barred♀ - \ / - \ / - ZᴮZᴮ ZᴮZᵇ ZᴮW ZᵇW - Barred♂ Barred♂ Barred♀ Black♀ - -</pre> - -<p>In the reciprocal cross, a black cock was mated to a barred hen. The -sons were barred, the daughters black (F₁). These inbred gave (F₂) -barred males and females, black males and females in the ratio of -1:1:1:1. The chromosome scheme of inheritance is as follows:</p> - -<pre> - Black♂ Barred♀ - P₁ ZᵇZᵇ ZᴮW - \ / - \ / - \ / - ZᴮZᵇ ZᵇW - F₁ Barred♂ Black♀ - \ / - \/ - ZᴮZᵇ ZᵇZᵇ ZᴮW ZᵇW - Barred♂ Black♂ Barred♀ Black♀ -</pre> - -<p><span class="pagenum"><a name="page_28" id="page_28">{28}</a></span></p> - -<p>One back-cross test consists in mating the F₁ barred males ZᴮZᵇ (from -both crosses) to a pure black female. The expectation is for equal -numbers of barred and black males and females, and the result was -realized. The F₁ barred hen of the first cross (ZᴮW) back-crossed to a -black cock is expected to give only barred males and black females, and -this result also was obtained. The explanation of the last cross, based -on the sex chromosomes, is as follows:</p> - -<pre> - - Black♂ F₁ Barred♀ - ZᵇZᵇ ZᴮW - \ / - \ / - \ / - ZᴮZᵇ ZᵇW - Barred♂ Black♀ -</pre> - -<p>Before these experiments were finished Goodale had made other crosses -involving the barring factor, and had obtained results that showed the -sex-linked inheritance of this factor (1909). For example, he crossed -Buff Rock male (not barred) to white Plymouth Rock females. The sons -were barred and the daughters not barred. The reciprocal cross gave -barred sons and daughters. A White Rock male (carrying barring) mated to -a Brown Leghorn female gave barred sons and daughters. Reciprocally, the -chicks were of two kinds as to their down, viz, black chicks and chicks -with the down pattern of the barred rock. All these results with Barred -Plymouth Rocks show that they carry a sex-linked dominant factor for -barring. Its wild-type allelomorph would be game-color (jungle-fowl), -but since, when the dominant barring is absent in some of the -individuals in these crosses, they are black, it would seem to follow -that another dominant factor, one for black, that is not sex-linked, is -also present.</p> - -<p>Pearl and Surface have also carried out crosses with Plymouth Rocks on a -much larger scale. Their results conformed in every way to the -foregoing. They crossed Barred Plymouth Rocks and Cornish Indian games. -The plumage of the male of the latter race is black with dark red on the -back and wing-bows; the females are also black laced with mahogany -ground-color on back, breast, wing, and tail coverts. When the male game -is mated to the barred hen the sons are barred and the daughters are -black. In the reciprocal cross both sons and daughters are barred. The -back-cross tests conformed to expectation. The results were the same as -those already stated above for the Langshan-Rock cross.</p> - -<p>Sturtevant crossed Columbian Wyandottes and Brown Leghorns. The F₁ sons -were alike, whichever way the cross was made. They were fairly typical -Wyandottes, which race carries therefore more of the dominant plumage -characters (two or three?). There were two types of daughters, depending -on the direction in which the cross was made.<span class="pagenum"><a name="page_29" id="page_29">{29}</a></span> When the father is -Wyandotte, the daughters are like him (except for stippling of the -Leghorn type). When the father is Brown Leghorn the daughters are -somewhat stippled red birds. In the former case the daughters getting -their Z chromosome from their Wyandotte father resemble him; in the -latter case the daughters getting their Z chromosome from their Leghorn -father look more like him. Their failure to look exactly like him must -be due to autosomal factors derived from the Wyandotte mother that -dominate other autosomal factors from the father.</p> - -<p>Hagedoorn crossed Black Breasted Game bantams (like those used in my -Sebright crosses) to Brown-Breasted bantams. In the latter the black -breast feathers of the male are bordered by lemon; the hens are nearly -black. Black-breasted male to “brown-red” female gave both -black-breasted sons and daughters. In the reciprocal cross all the sons -were black-breasted (like the mother) and all the daughters were brown -red like the father. Evidently the factor here for Brown Breasted game -is sex-linked and recessive. In this case the new mutant sex-linked -character is recessive to the wild type.</p> - -<p>Davenport (1912) crossed Brown Leghorns to Dark Brahmas. In the cross -and its reciprocal all the sons are alike. Two dominant sex-linked -factors were found,<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a> viz, the white background characteristic of the -Dark Brahmas and the red upper wing-coverts (and back) characteristic of -the Brown Leghorns. On the other hand, the <i>daughters</i> differ in the two -crosses, in each case resembling their father in their hackle color.</p> - -<p>When two sex-linked characters are involved in a cross it is possible to -determine by suitable matings whether an interchange between the -chromosomes that bear them has taken place. In the case of the sex -chromosomes only one sex, the male, has both like chromosomes, viz, ZZ, -and we expect from analogy with the <i>Drosophila</i> work that crossing-over -would be found between the sex chromosomes only in the male. Goodale has -recently (1917) made the important discovery that in poultry -crossing-over takes place between the sex chromosomes (ZZ) in the male, -but not in the female (ZW or ZO). This relation, therefore, is the -reverse in birds and flies, for, in the one, crossing-over takes place -in the female and in the other in the male. Whether this difference -extends also to the other chromosomes in birds as it does in flies is as -yet not known.</p> - -<p>Several years ago some crosses between gold and silver Campines were -reported by Rev. E. Lewis Jones. The results are consistent with the -view that a sex-linked factor pair is responsible for this difference in -color, although the author does not apply this view to his results. The -results may be seen in the table on page 16, to which Jones has<span class="pagenum"><a name="page_30" id="page_30">{30}</a></span> -prefixed the number of individuals. The cross also involved -hen-feathering <i>versus</i> cock-feathering, which appears here (as in other -cases) to be a non-sex-linked dominant factor. As stated above there are -in the results a few apparent inconsistencies with this interpretation, -due possibly to heterozygous females having been used in the crosses.</p> - -<p>Lefevre crossed Silver Spangled Hamburgs and Brown Leghorns. The -spangling was found to be a sex-linked dominant factor. A spangled cock -bred to a Leghorn hen gives spangled sons and daughters; a spangled hen -by a Leghorn male gave spangled sons and not spangled daughters. The -daughters do not transmit spangling. Other factors may obscure the -results, especially factors for black, or the localization of the -pattern. Lefevre says “it would seem probable that multiple factors for -black, introduced by the Brown Leghorns, are present, and that these -factors may have a cumulative effect, with the result that pigmentation -is developed to varying degrees of extension.” Whether the factors for -black spoken of as coming from the Leghorns are dominant wild-type -factors that have mutant allelomorphs in the Silver Spangled Hamburg is -not entirely clear from the quotation.</p> - -<p>Baur gives in his Introduction to the Study of Heredity (1914, pp. -202-203) some results (unpublished) that Hagedoorn had obtained by -crossing gold and silver races of Assendelver birds. The factor is -sex-linked and is no doubt the same factor reported by Jones for gold -and silver Campines and by Sturtevant for Columbian Wyandottes. Silver -dominates gold and the sex relations are the same as those already -reported by others for poultry, viz, the male is ZZ, the female ZW. Gold -hens by a heterozygous silver<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a> gave 162 silver cocks, 163 silver hens, -168 gold cocks, 160 gold hens, expressed graphically (<i>g</i> for gold, <i>s</i> -for silver):</p> - -<table border="0" cellpadding="2" cellspacing="0" summary="" - class="sml"> -<tr class="c"><td colspan="4">Zᵍ—W♀ × Z—Zᵍ♂</td></tr> -<tr class="c"><td colspan="4" class="bt">ZˢZᵍ—ZᵍZᵍ—ZˢW—ZᵍW</td></tr> -<tr class="c"><td>Silver</td><td>Gold</td><td>Silver</td><td>Gold</td></tr> -<tr class="c"><td> male</td><td>male</td><td>female</td><td>female</td></tr> -</table> - -<p>When a silver hen was united to a gold cock there were 246 silver cocks -and 243 gold hens—crisscross inheritance.</p> - -<p class="c"><i>Summary.</i></p> - -<p>From the standpoint of the Brown Leghorn type representing the wild -type, the following colors and patterns represent dominant mutations -from that type:</p> - -<table border="0" cellpadding="1" cellspacing="0" summary=""> - -<tr><td class="c" colspan="2"><i>Dominants.</i></td></tr> - -<tr valign="top"><td>White of White Leghorn. <br /> -Silver of Dark Brahma.<br /> -Black of Minorca.<br /> -Lacing of Brahma.</td><td> -Barring of Plymouth Rock.<br /> -Black (?) of Plymouth Rock.<br /> -Buff (or red).</td></tr> -</table> - -<p> -<span class="pagenum"><a name="page_31" id="page_31">{31}</a></span></p> - -<p>Each of these (in heterozygous condition of course) is dominant; in some -cases completely so, in others incompletely dominant. At three different -loci in the sex chromosome a dominant mutation has occurred; at three -loci in other chromosomes dominant mutant changes have also occurred.</p> - -<table border="0" cellpadding="2" cellspacing="0" summary=""> - -<tr><td class="c" colspan="2"><i>Recessives.</i></td></tr> -<tr valign="top"> -<td>White of Rose Comb bantam. <br /> -White of Silky.<br /> -White of White Rock.</td> -<td>Brown of Brown-breasted game.<br /> -Penciling.</td></tr> -</table> - -<p>Whether the recessive white that is sometimes found in dominant White -Rock stock is different from both of the other recessive whites is not -known. There are, then, 5 or 6 recessive characters that are not -sex-linked and 1 recessive sex-linked character.</p> - -<p>Owing to the relatively large number of color dominants in poultry, some -unnecessary confusion has arisen concerning the relation of the -dominants to the wild type, and especially to other mutant characters to -which they are said to be dominant, in the sense, however, of being -epistatic. An imaginary example will illustrate this. For example, if at -some locus in the wild type a mutation occurred that gave a dominant -black (<i>i. e.</i>, a black that shows up when one gene for it is present) -and at the same time this black also showed up even when other recessive -mutant characters were present in homozygous form, then F₁ birds would -be black when black is crossed to such pure recessive stocks. Such cases -have indeed been described as dominant, but a knowledge of F₂ would have -shown at once the error of such a system. For, if black had been a real -dominant, the F₂ would have given 3 blacks to 1 of the other type (such -as the wild type), but if the case were one of epistasis, then there -would have been 9:3:3:1 classes in F₂ (or some modification of that -ratio). In this sense, then, epistasis may be defined as a result that -appears when one member of the pair of genes produces its effect -regardless of the constitution of the individual with respect to another -gene (or other pairs of genes). It is curious at least to note that in -the case of dominant white the term epistatic has been much less often -used than in the case of black. Theoretically the two situations are -exactly alike, but because black could so obviously conceal things -beneath it, while white is not thought of as doing so, it seemed -“natural” to make such a distinction. In reality it is not a question of -covering up at all, but a case of a dominant character (white or black) -preventing other colors from appearing.</p> - -<p>In the case of recessive white the situation is somewhat different and -no one, so far as I know, has gone so far as to speak of such a white as -epistatic, although when the animal is white it certainly hides, when -completely effective, all the other effects of color-producing factors, -but allows them to “show through” in some of the cases. This means not -that they do “show through,” but that they only develop<span class="pagenum"><a name="page_32" id="page_32">{32}</a></span> to a “lower” -degree. The difference between dominant and recessive whites rests on -the fact that in one case one member of a pair of factors gives white -and in the other both members are necessary. But obviously such a -distinction is not important, and if it were worth while the case might -be argued for recessive whites being also epistatic. The whole tangle -goes back to a false interpretation of presence and absence of -characters and presence and absence of factors. As I have gone over this -ground recently in my paper on the Theory of the Gene, I need not repeat -here what I tried to make clear there.</p> - -<h3><a name="ENDOCRINE_CELLS_IN_OVARY_AND_TESTES_OF_BIRDS" id="ENDOCRINE_CELLS_IN_OVARY_AND_TESTES_OF_BIRDS"></a>ENDOCRINE CELLS IN OVARY AND TESTES OF BIRDS.</h3> - -<p>The occurrence of gland-like cells with an internal secretion in the -ovary and testes of fowls has been described by a number of writers and -denied, at least for the testes, by others. The work of Boring and Pearl -has done much to bring this question to a satisfactory solution, for -they have tested out and made use of the best reagents that their -predecessors had discovered and have used a much greater amount of -material. As they have reviewed very fully the literature of the -subject, it will not be necessary to go over the ground again in detail.</p> - -<p>In the follicles of the ovary there are present, according to Boring and -Pearl, groups or nests of cells lying among the connective tissue of the -inner theca. The cells are about three times as large as the ordinary -connective-tissue cells of the ovary. The cytoplasm is clear and -vacuolated, “only occasionally containing a few acidophile granules -which stain with the fuchsin in Mallory’s stain or the eosin of Mann’s -stain, while the real interstitial cells are crowded with granules.”</p> - -<p>When the egg is set free from its follicle, the latter collapses and the -rupture becomes closed. A mass of cells collects in the center of the -collapsed structure which develop yellow pigment. The cells, lying in -the puckered edge of the follicle, may also develop such yellow color. -The cells that produce the yellow pigment come from the nests of cells -that lay originally mainly in the theca interna. Either by migration or -by division they come to fill up the central cavity. The yellow -substance in the cells is not fat, since it does not dissolve in the -clearing oils, nor can it be protein, for it does not take acid stains -as normal secretion granules of protein. It does not dissolve in HCl, -HNO₃, or H₂SO₄, nor in strong KOH, although the latter turns the pigment -a bright red color. Many other substances were also tried by Boring and -Pearl, but none of them dissolved the yellow pigment, which reacts in -this respect in the same way as does the yellow pigment in the luteal -cells of the mammal. The similarity in the nature of the pigments in the -two cases is an argument in favor of the view that the cells that -produce the pigment are the same in both groups. In the<span class="pagenum"><a name="page_33" id="page_33">{33}</a></span> mammal the -yellow corpus luteum is a large, gland-like organ that develops after -the ovum is discharged; in the bird there is also a yellow spot on the -ovary, due to the pigment in the collapsed follicle, but it is smaller -and much less conspicuous than in the mammal. The evidence concerning -luteal cells in the testes of the bird is conflicting. One of the -difficulties in the situation is the identification of the cells, which -are sometimes regarded merely as the general connective-tissue stroma of -the testis that is undoubtedly present; at other times special secretory -cells are discerned embedded in the connective tissue, as individual -cells or in islands. Boring states (1912) that in newly hatched chicks -about half of the tissue of the testes is interstitial connective -tissue; the other half consists of tubes or cords whose principal -function is the development of the germ-cells. In the paper of 1912 -Boring reached the conclusion that there are no “interstitial cells in -the testes of the domesticated chicken in the sense that this term has -been previously used,” and states that no evidence has been found that -an internal secretion of any kind is formed by any cells of the -interstitial tissue.</p> - -<p>It is not necessary to discuss whether or not connective-tissue cells -are present in the testes of birds, for is it generally conceded that -they are found at least in certain stages, but it is important to look -into the question as to whether among these interstitial cells there are -others that have an endocrine function. Mazzetti gives pictures of such -gland-cells between the seminal tubules of the cock bird, but says that -they are rare, “even though this bird has very marked secondary sexual -characters” (Boring and Pearl). It may be remarked parenthetically that -if they had been more abundant the bird might have had no secondary -sexual plumage since it will be pointed out below that such glandular -cells may have as their special function the suppression of these -characters.</p> - -<p>According to Des Cilleuls, interstitial cells are first found in males -about 30 days old and at this time the secondary sexual characters put -in their appearance. If, as will be shown in the sequel, he means by -interstitial cells the endocrine cells that suppress the development of -the male plumage in the female, the appearance of these cells at this -time would be significant; but if he implies that their occurrence in -the male incites the development of the secondary sexual characters, his -interpretation is open to serious doubt. Reeves found interstitial cells -in testes of cocks 3, 5½, 9, and 18 months—more in the earlier stages.</p> - -<p>In a later communication by Boring and Pearl the whole question is taken -up again with improved methods, etc. Previously 21 male birds had been -studied, just hatched to 12 months old. More sections of this same -material were made which were stained according<span class="pagenum"><a name="page_34" id="page_34">{34}</a></span> to Mann’s and Mallory’s -methods. In addition, a whole new series of preparations was made. A few -interstitial cells, i. e., granule containing-cells were found in newly -hatched chicks, but not in any of the 60 mature birds examined.</p> - -<h3><a name="LUTEAL-CELLS_IN_THE_TESTES_OF_THE_MALE_SEBRIGHT" id="LUTEAL-CELLS_IN_THE_TESTES_OF_THE_MALE_SEBRIGHT"></a>LUTEAL-CELLS IN THE TESTES OF THE MALE SEBRIGHT.</h3> - -<p>Finding that the testes of F₂ hen-feathered birds were often flat and -pear-shaped instead of rounded and cylindrical, as in ordinary cocks, -and that they were often black in color, suggested, as already stated, -that the testes of the Sebright might be hermaphrodite in some element. -It seemed not impossible that egg-cells might be found. I made a -considerable number of sections of the testes of these birds and -examined them under the microscope; not finding any egg or egg-like -bodies, the slides were laid aside, but the idea that in some other way -the Sebright’s testes might correspond to the ovary of the female next -recurred to my mind. Consequently, when in the summer of 1918 I had some -new material derived from a castrated Sebright male that had partly -regenerated its testes and was again going back to hen-feathering, and -pieces from one of the old testes of a castrated bird, I asked Miss -Boring, who was then in Woods Hole, to make some preparations and -examine them to see if she could detect any such elements in them as she -had found in the female. Miss Boring reported the occurrence of luteal -cells in the testes from hen-feathered males, and the results have been -published in a brief preliminary paper (1918). The abundance of these -clear cells, supposedly gland-cells with endocrine influences, in the -testes of hen-feathered birds is in sharp contrast to their absence in -the normal adult cock birds. It seems to follow, therefore, that the -hen-feathering in the Sebrights is due to the presence of these cells, -whose function is the same as of the similar cells in the female, <i>i. -e.</i>, the suppression in both of cock-feathering. Castrating the Sebright -produces its effect by the removal of these cells that are responsible -for the suppression of cock-feathering.</p> - -<p>The occurrence of luteal cells in young stages of other races of poultry -raises the question as to whether in these races the first or juvenile -plumage, that resembles that of the hen rather than that of the cock, -may not also be due to an internal secretion from these cells, or -whether this juvenile plumage is only the plumage of a characteristic -stage in development. Castration of young chicks ought to settle this -point. Such castration experiments have been made by Goodale. The -absence of any reference to any effect on the juvenile plumage in these -early castrated birds probably meant that they did not develop -precociously cock-feathering, and he writes me that he examined them -carefully and that their plumage is like that of the normal chicks. -Geoffrey Smith has reported the occurrence of two kinds of males<span class="pagenum"><a name="page_35" id="page_35">{35}</a></span> in a -race of Leghorns, the males of one of which become cock-feathered before -the other. May not this difference depend on the length of time -endocrine cells remain or begin to develop? A histological study of the -two types would be of the greatest interest.</p> - -<h3><a name="ENDOCRINE_CELLS_IN_THE_TESTES_OF_MAMMALS" id="ENDOCRINE_CELLS_IN_THE_TESTES_OF_MAMMALS"></a>ENDOCRINE CELLS IN THE TESTES OF MAMMALS.</h3> - -<p>In man and other mammals it has long been recognized that in addition to -the germinal cells of the testis there are also present other cells, -sometimes called interstitial cells, that, so far as known, have no -immediate function in connection with the germ-cells, or at least that -have other important functions outside the relation to the reproductive -organ. That some internal secretion from these cells has an important -influence on the secondary sexual characters rather than anything done -by or produced by the germinal cells has been very clearly shown by -evidence derived from three separate sources, namely, from the operation -known as vasectomy, from an exceptional condition known as -cryptorchidism, and more indirectly from X-ray treatment. Vasectomy -involves either cutting the vasa deferentia in such a way that the cut -ends do not reunite. In consequence of the closure of the outlet of the -testis the germinal cells slowly degenerate, and finally completely -disappear. How such an effect is produced we do not know. That this -result does take place is borne out by the unanimous testimony of all -those who have successfully performed the operation. Ancel and Bouin -showed (1903) that breaking the continuity of the vas deferens -suppressed spermatogenesis in 8 to 12 months. Both the Sertoli cells -(the nourishing cells of the germinal epithelium) and the interstitial -cells persist. Such animals remain sexually active and their secondary -sexual characters are not affected. Marshall states that in the hedgehog -the remarkable periodic enlargement of the testis takes place even after -vasectomy, although the germ-cells have disappeared.</p> - -<p>In mammals the testes fail at times to pass through the inguinal canal, -and, in consequence of their retention in the body-cavity, the -germ-cells fail to develop. On the other hand, the interstitial cells of -the testis develop normally. Cryptorchid individuals show the normal -secondary sexual characters of their species. How retention of the sperm -should give rise to the same result as cutting the duct, viz, absorption -of the germinal cells, is not known. A possible solution may be found in -the pressure exerted on the testes, both when retained in the abdomen -and when their outlets are stopped by tying or cutting the ducts.</p> - -<p>Finally, it has been long known that continued or repeated exposure to -X-rays or to radium causes the destruction of the germ-cells, but leaves -the interstitial cells intact and presumably functional. Destruc<span class="pagenum"><a name="page_36" id="page_36">{36}</a></span>tion of -the germ-cell by X-rays has no effect on the secondary sexual -characters.</p> - -<p>This threefold evidence demonstrates that in the male of the mammalia -most, perhaps all, of the secondary sexual characters that are affected -by castration are not affected by the destruction of the germ-cells. -This conclusion supports very strongly the view that the interstitial -cells are the cellular element in the testes that influence through -internal secretion the development of the secondary sexual characters of -the male.</p> - -<p>Equally important are the results that relate to the accessory organs of -reproduction, such as the glands that open into the vas deferens -(prostate, Cowper’s gland, etc.) and the copulatory organs also. In the -castrated mammals these organs diminish in size. On the other hand, -after destruction of the germ-cells in the testes (or even when they -fail to develop as in cryptorchid individuals) these accessory parts are -unaffected. In birds, as will be shown, the situation is entirely -different.</p> - -<h3><a name="CYCLICAL_CHANGES_IN_THE_INTERSTITIAL_CELLS_IN_HIBERNATING_MAMMALS" id="CYCLICAL_CHANGES_IN_THE_INTERSTITIAL_CELLS_IN_HIBERNATING_MAMMALS"></a>CYCLICAL CHANGES IN THE INTERSTITIAL CELLS IN HIBERNATING MAMMALS.</h3> - -<p>The changes that take place in the interstitial cells in mammals that -hibernate and in which there is a definite rutting season following -hibernation have been examined by several workers. The mole has been -studied by Regaud (1904), Lécaillon (1909), Tandler and Grosz (1911); -the marmot by Hauseman (1895) and Gaugini (1903); the hedgehog by -Marshall (1911); and the woodchuck by Rasmussan (1917). In the mole the -interstitial cells are most abundant when the tubules in which the -spermatogenesis is taking place are least developed, and <i>vice versa</i>. -In the hedgehog the increase in both tissues takes place at the same -time. In the woodchuck both tissues increase rapidly after hibernation -(during March and April), after which the spermatogenesis continues -actively for the two following months (May and June), while the -interstitial cells retrograde rapidly during April and remain at a low -level for the rest of the year. Retrogression in the germinal epithelium -begins in July, after the rutting season is past. It appears from this -evidence that the activity of the two tissues does not always run the -same course. Since the secondary sexual characters of the male, which -are not well developed in these animals, are not so far as known -affected by the condition of the testes, the evidence does not have any -very direct bearing on our present topic. How far the sexual behavior of -these mammals is determined by the quantity or by the activity of the -interstitial cells is not very clear from the evidence, although there -is a very noticeable increase in the amount of this tissue just before -and during the rutting season. In the mole also the<span class="pagenum"><a name="page_37" id="page_37">{37}</a></span> interstitial cells -begin to increase just before the mating season, and the increase -continues for several months after mating has taken place. It is -difficult to judge how great or how little the change amounts to unless -the whole organ is considered, for the relative volumes of the seminal -tubes and the interstitial tissues does not give a measure of the total -volume of these tissues, since the testes may decrease greatly in size -when the seminal tubes retrograde, and the apparent increase of the -interstitial cells at the time may not increase the total amount of that -tissue present.</p> - -<p>Probably more important than the ratio of interstitial tissue to tubules -is the activity of the former. Rasmussan states that in the woodchuck -the interstitial cells not only increase in number immediately after -hibernation, but the increase in amount of this tissue is largely due to -increase in the cytoplasm, in which there appears an accumulation of -fatty globules in the more peripheral parts of the cells. In the central -cytoplasm an abundance of fine lipoid granules develops.</p> - -<p>Marshall has made some interesting experiments on the hedgehog at -different seasons. Castration in March prior to the breeding-season has -an influence on the accessory generative organs (vesiculæ seminales, -prostates, and Cowper’s glands). They remain in the same undeveloped -stage in which they were at the time of operation. If castration is -carried out very early in the breeding-season, when the accessory -reproductive organs are about half developed, their further enlargement -is prevented. In so far as the accessory organs rank as secondary sexual -organs, their complete development is thus shown to depend on the -testes. Transection of the vasa deferentia before the beginning of the -breeding-season affects somewhat the enlargement of the testes, but -produces no effect on the accessory organs.</p> - -<h3><a name="HERMAPHRODITISM_IN_POULTRY_AND_THE_SECONDARY_SEXUAL_CHARACTERS" id="HERMAPHRODITISM_IN_POULTRY_AND_THE_SECONDARY_SEXUAL_CHARACTERS"></a>HERMAPHRODITISM IN POULTRY AND THE SECONDARY SEXUAL CHARACTERS.</h3> - -<p>Several hermaphrodite birds have been described (Brandt, 1889; Shattock -and Seligman, 1906; Pearl and Curtis, 1909; Smith and Thomas, 1913; -Bond, 1914; etc.). The most recent and complete account of such birds is -that by Boring and Pearl. They examined in all 8 hermaphrodites, or at -least 8 birds that showed in their plumage, or other secondary sexual -characters, peculiarities of both sexes. Five of the birds came from -Herr Houwink in Meppel, Holland, who had a stock in which there -appeared, in 1911, two hermaphrodites out of 80 birds, and in 1912, -three out of 80 birds. These were the birds studied by Boring and Pearl. -In addition, when Pearl saw Herr Houwink’s birds in 1910, “there were -then on hand a considerable number of these supposed hermaphrodite -birds.” An anatomical study of the Holland birds showed that one of them -was nearly a normal female; three, the<span class="pagenum"><a name="page_38" id="page_38">{38}</a></span> authors say, were “evidently -undeveloped females. They have infantile oviducts and embryonic -ovaries.” It should be added that there was a tumor more than twice the -size of the ovary attached to or part of the ovary. If the ovary itself -was affected by the tumor, or the tumor was a part of the ovary, the -slightly unusual condition of the birds might be accounted for. Of the -other 3 birds, 2 are also suspected to have ovarian tumors, while in the -third bird streaks of a secretion which resembles the substance of the -tumor of the other two were found. The change towards male plumage in -these 5 birds is probably due either to the incomplete development of -ovary or to the effect of the tumor on the ovary. Although luteal cells -are described as present, it seems probable that their total number -might be less than in a normal bird, and hence their insufficient -secretion would fail to suppress the development of male plumage. From -this point of view these birds are no more hermaphrodites than is a hen -with her ovary taken out.</p> - -<p>The remaining Holland birds were entirely different. On the left side -there was an ovary in an inactive condition; on the right side there was -a testis, producing spermatozoa. Sections of the testis show that it is -normal, consisting of a mass of tubules with very little connective -tissue between them. In both ovary and testis there are “a few nests of -luteal cells near the surface. The ovary contains eggs, but is abnormal -to some extent.” The authors state:</p> - -<div class="blockquot"><p>“In external appearance it is more like a male than the others, -which fact correlates well with the active condition of the testis -and inactive diseased ovary, with only one corpus luteum scar. The -interstitial cells can scarcely be held accountable for the male -secondary sex characters, as the only ones in an active secreting -condition are a few in the ovary.”</p></div> - -<p>It is not quite clear what is meant in this quotation by the statement -that the interstitial cells can scarcely be held accountable for the -male secondary characters unless to suggest that they cause the -development of these characters in the male, as they are supposed to do -in mammals—a view that the authors do not seem at other times to hold.</p> - -<p>Another hermaphrodite (Atwood’s black) had an infantile oviduct and an -ovotestis. A second bird, too, had an ovotestis—mostly testis—as well -as a rather large oviduct. Collections of luteal cells are described -between the tubules of the testicular portion. If, as suggested by the -Sebright cases, these cells tend to suppress the female plumage, their -presence here in excess might at least be made to account for the female -part of the plumage of this bird. Comparing the last two birds (that -showed active sex-behavior as males) with the best of the Holland birds, -Boring and Pearl point out that the active sex behavior of the two -former can not be due to “interstitial cells that are absent in these -<span class="pagenum"><a name="page_39" id="page_39">{39}</a></span>but present to a slight extent in the former.” They then add” -...though the differences can not be laid to the lutear cells, as they -are present in all three.” That the relative amounts of the latter or -their activity might still be accountable for the difference would not -seem entirely excluded from the evidence so far as it is given.</p> - -<p>A fourth hermaphrodite (Dexter’s) laid 12 eggs and had a large coiled -oviduct. There was present “a large, lobulated reproductive organ on the -left,” which proved to be an ovotestis. Several ovarian tumors were -present and there was testicular tissue.</p> - -<p>It is fairly evident, then, that four of these birds described by Boring -and Pearl were females with abnormal ovaries. The incomplete development -of the latter, or their abnormal condition due to tumors, may -sufficiently explain the occurrence of male secondary sexual characters. -That these tumors affect, to different degrees, such characters is -expected from what is shown by imperfectly spayed females of normal -breeds.</p> - -<p>There are a few statements in the summary of this paper that call for -comment. The statement that the “development of comb, spurs, and wattles -does not stand in direct quantitative relation to the sex of the gonad,” -appears to be only intended as a statement of fact based on the author’s -observation. But in what sense is there an expectation that they should -stand in such relation beyond the obvious fact that in the cock the comb -and wattles are larger than in the hen, and that spurs are generally -present only on the cock. But if the expression “sex of the gonad” -implies the germ-cells it is not at all certain that there is any -expectation of a quantitative relation, and there is some probability at -least that other cells than the sex-cells are involved in the -development of combs, wattles, and possibly spurs. A castrated cock has -a small comb resembling that of the female bird. On the other hand, -removal of the ovary sometimes leads to an increase in the comb and -wattles. Here we have, to say the least, a paradoxical situation, for -the result looks superficially as though something in the ovary keeps -down the hen’s comb, while something in the testes keeps up the cock’s -comb, yet when the ovary is removed the hen develops a cock’s comb; when -the testes are removed the cock develops a hen’s comb. The real meaning -is, I think, that the genetic complex for femaleness (one Z or else ZW) -stands in itself for a full-sized comb, while the genetic complex for -maleness (two Z’s) stands in itself for small comb.</p> - -<p>Boring and Pearl state that “body-shape and carriage have a genetic -relation to the sex of the gonad.” This statement means, I think, that -the amount of testicular matter present stands in some direct relation -to the shape of the body and carriage of the male. Castration, both of -the normal cock and the Sebright, seems to change the carriage somewhat -and perhaps the shape. Both lose something of the peculiar attitude of -the male, but I have not been able to my own<span class="pagenum"><a name="page_40" id="page_40">{40}</a></span> satisfaction to analyze -what this means. As has been pointed out, and as the pictures show, the -castrated Sebright changes his attitude, but whether this is a change -due to his new contour, or to a new balance resulting from a large tail, -or to a let-down resulting principally from effects on the nervous -system, is difficult to determine. The same statements apply in part to -the castrated cock of ordinary breeds, but not to the same degree, since -the change after castration, in feathering and in carriage at least, is -slight.</p> - -<p>The conclusions that the “amount of lutear cells or pigment (?) is in -precise correlation with the degree of external somatic femaleness -exhibited by the individual” is of especial interest in connection with -the Sebright evidence. It is difficult, however, to gather from the body -of the paper what the absolute amount of luteal cells is that is -present, for even in some of the more male-like birds with an ovotestis -the description leads one to suppose that there may be as much luteal -material present as in some of the more female birds with infantile -ovaries or cystic tumors.</p> - -<p>Pearl and Curtis (1909) described “a case of incomplete hermaphroditism” -in a Barred Plymouth Rock fowl. Externally the bird looked like a hen, -but “the head and neck resembled these parts in the cockerel,” -especially the comb and wattles. The bird was never seen to tread a hen, -nor did it ever crow normally. An ovary and oviduct were found on the -left side, the former no larger than that of a laying hen after removal -of the large yolks. No eggs were visible on its surface. On the right -side a testis (9 mm. by 6 mm.) and vas deferens were present. No eggs -were found in the ovary, and it gave every indication of being in a -degenerating condition, with no eggs or egg follicles in it. The testis -had no “normal seminiferous tubules”, but indications of cellular rods -were present. The organ is in all probability a degenerating testis.</p> - -<p>A Leghorn 2 years old has been described by Shattuck and Seligmann -(1906) that had the full-developed comb and wattles of the cock, but the -former drooped slightly to one side as in the hen. Well-developed spurs -were present. The plumage was mainly female, with neck-hackles -moderately developed, and with “saddle-hackles” practically absent. The -tail, though not typically female, lacks sickle feathers. The bird -excited no notice from other birds of either sex. A large left oviduct -and the distal end of a right oviduct were present. Two vasa deferentia -were also present. In the left side a flattened sex-gland (3 cm. high) -was found, made up of testicular tubules. Two small ova were found in -its posterior end. The right gonad was also tubular (testis).</p> - -<p>The occurrence of real testicular tissue in one of the Holland birds and -in three others described by Boring and Pearl, as well as in one<span class="pagenum"><a name="page_41" id="page_41">{41}</a></span> -described by Pearl and Curtis, and in another by Shattuck and Seligmann -calls for special comment, since the presence of both testicular and -ovarian tissue in the same bird is the essence of hermaphroditism. In -general there are two ways of looking at such a result. Either the -sex-determining factors have been changed so that in one part of the -body, where the reproductive organs are laid down, one condition can -prevail, in other parts other conditions; or a mixup of the sex -chromosomes has taken place. Until we get some more evidence concerning -such cases it is useless to speculate, although the former view might -seem the most probable of the two if the Holland birds of Herr Houwink’s -flock were in a high degree true hermaphrodites.</p> - -<p>But in fact three of the four described by Boring and Pearl were due to -tumors of the ovary, which, if they suppress the normal development of -this organ, would be expected to call forth the appearance of the -secondary sexual characters of the cock. If the likelihood of developing -a tumor were inherited, the frequent occurrence of hen-feathered birds -in this flock would be explained. However, one true hermaphrodite in 4 -birds is surprisingly high for a chance result, since hermaphrodite -birds are very rare.</p> - -<p>The second interpretation suggested above is one that has been advanced -and established by genetic evidence in <i>Drosophila</i>, viz., dislocation -of the sex chromosomes. In the case of birds the male is supposed to be -duplex for the sex factors (ZZ), the female simplex (ZW), and -consequently the chromosome-dislocation hypothesis must be worked out -contrawise in birds and insects. We should have to suppose that such -birds start as males (ZZ), and that at some division of the cells of the -embryo one of the Z’s became lost (left at the cell-wall for example). -All the cells that got ZZ would be male; all that got Z would be female. -If the reproductive region included cells of these two kinds, an -ovotestis would result. The rest of the body should be the same, or -nearly so, since the soma of male and female birds is alike whether ZZ -or Z, except in so far as it is affected by the secretions from the -ovaries (in most races of poultry), or from the testes if the race be -Sebright, Campines, or Hamburgs. Birds with ovotestis might, -nevertheless, be expected, on this view, to show at times an -intermediate condition of the secondary sexual characters, according to -how much internal secretion is produced in the ovotestis. In other -words, the chromosome loss might involve much more extensive regions -than the reproduction organs, but show its effects first in that organ -and then indirectly other parts of the body be affected by the luteal -cells of the testis. There is one rather good piece of evidence that -seems opposed to this interpretation. In the hermaphrodites the oviduct -is present in all cases. Its conspicuous presence in the four -hermaphrodites would seem, therefore, to indicate that the birds<span class="pagenum"><a name="page_42" id="page_42">{42}</a></span> -started as females (ZW), which is inconsistent with the dislocation -hypothesis. The alternate would be that in all these cases the Z part -always included the region of the oviduct, which seems improbable.</p> - -<p>There is another possibility, viz, that in birds a sex-factor is carried -by the W chromosome, and ZW is a female not because of one Z, but due to -the presence of W. If so, then one Z or two Z’s might give the same -result, viz, female. If a bird started as female, (ZW) and chromosomal -dislocation occurred, then the Z parts would be female and the male part -W. Until we get evidence on this point it is not worth elaborating. -Without genetic evidence from hybrids, the interpretation of -hermaphrodites in birds can have at present only a speculative interest. -We may hope some day to get the same kind of evidence as in the case of -<i>Drosophila</i>. Hermaphrodite hybrid pheasants that have been often -described might seem to furnish a hopeful field, for they appear to be -quite common and to show characteristics of both races. As yet, however, -no one has, I think, succeeded in finding a simple interpretation of the -results. It is also not unlikely that many of the pheasant cases are not -true hermaphrodites, but due to failure of normal development of the -reproductive gland, which gives an intermediate or mixed type of -secondary sexual characters.<span class="pagenum"><a name="page_43" id="page_43">{43}</a></span></p> - -<h2><a name="PART_II" id="PART_II"></a>PART II.</h2> - -<h3><a name="DARWINS_THEORY_OF_SEXUAL_SELECTION" id="DARWINS_THEORY_OF_SEXUAL_SELECTION"></a>DARWIN’S THEORY OF SEXUAL SELECTION.</h3> - -<p>Darwin seems to have felt the necessity of giving some other explanation -for the secondary sexual differences between the male and female than -that such differences were only a by-product or concomitant of sex -itself. His reason for searching further was probably a part of the -general point of view he had reached in regard to the utility of special -structures of animals, namely, that their presence finds its explanation -on the basis of utility. Believing as he did that most of the -adaptations of plants and animals have been built up by the accumulation -of small steps, it must have appeared to Darwin inconceivable that the -highly developed ornamentation exhibited in the secondary sexual -characters could have been simply the by-product of sex itself, -especially when the ornamentation may have been entirely absent in males -of closely related species. To-day we are not, I think, so oppressed -with the difficulties of the situation, for we have become familiar with -the fact that very slight genetic differences may cause very great -differences in the end-product. In a word, the problem seems less -formidable to us than it did to Darwin.</p> - -<p>Darwin appealed to three processes to account for the facts: (1) to -natural selection between the members of the same sex; (2) to choice on -the part of the “other” sex; (3) to the “inheritance of use.” Since each -of these appeals to a different procedure, let us take them up -separately.</p> - -<p>Competition of the males with each other for the female would, Darwin -said, lead to the survival of those males best endowed with organs of -offense and defense. The spurs of the cock are weapons dangerous for -other birds; the horns of the bull and those of deer are used for -offense and defense; the mane of the lion is a protection against the -teeth of other lions. It is true that these same weapons and shields -serve for attack and defense outside the species; but since the female -lacks them or has them less developed, they would not seem necessary for -survival of the individual against aggression from without. They have -developed, then, through competition within the species.</p> - -<p>Several objections of greater or less weight have been urged against -Darwin’s interpretation. It has been pointed out that the combats within -the species are seldom fatal and that the defeated rival finds another -mate. If, as a rule, there are as many females as males within the -species and monogamy is the rule, all males will find partners sooner or -later, all may have offspring, and the offspring have equally good -chances of survival. Under these circumstances it is not to be expected -that the combat would be likely to lead to the production of males with -longer spurs or larger horns.<span class="pagenum"><a name="page_44" id="page_44">{44}</a></span></p> - -<p>Darwin realized this difficulty and tried to meet it by another -assumption, viz, that the better endowed males would <i>also</i> be more -likely to have more offspring. How could this be made probable? Darwin -suggested that the strongest males would be in position to mate with the -first females to reach maturity, and if these were more likely to have -offspring, either because of maternal endowments that made them also -more prolific or because the earlier broods would have a better chance -of getting food, etc., then the successful competitor would sooner or -later impress his advantages on the race.</p> - -<p>At other times Darwin suggested that the exceptional vigor that led to -the greater development of the character in question would itself be of -value and through transmission to the offspring lead to advance in the -development of the other character in question. But here the argument -shifts to another field of inquiry and survival is ascribed to greater -vigor, while the secondary sexual character is carried along in its wake -as a sort of correlated effect.</p> - -<p>It will be conceded, I think, that such pleading does not help the -argument, but exposes rather its inherent weaknesses. There is, however, -a line of defense that is permissible. If monogamy is not the rule, if -the male captures or attracts several females and keeps a harem, as do -the fur seals and walruses, or rules a herd as does the bull, or has a -flock as does the cock, or mates more frequently with random females -than do some other males, then the advantage of his more developed -weapon might lead to more offspring. If it could be shown that such -intraspecific weapons prevail more frequently within polygamous species, -a fair argument for natural selection might be made. I do not know -whether such a census has been taken as yet, but it is true, I think, -that in most polygamous groups we find weapons of offense very highly -developed. The fur seal has a harem and the male is greater in size, in -strength, and in the development of his tusks than is the female. -Similarly for the walrus. The bull drives away rival bulls from the herd -until through age or injury, or through the development of a better -fighter, he is replaced. If the better endowment is due to a genetic -factor, we should expect natural selection to keep the race at the -highest possible level that variation supplies material for. If, then, -we confine the application of natural selection to cases of this sort, -the explanation is as valid as is the theory in other fields. Such a -conclusion becomes weakened when an attempt is made to apply it to other -groups of animals in which it appears improbable that the secondary -sexual characters of the male have any obvious value as organs of -offense. There are families of beetles, for example, in which the -development of the horns of the male are as striking as are those of the -ram or the stag. The males of these beetles are not known to fight with -each other, nor are they polygamous. It may seem that we must look here -for some other explanation, which, if found, might suffice to<span class="pagenum"><a name="page_45" id="page_45">{45}</a></span> cover -also the case of birds and mammals. In answer to this criticism it may -be argued that it is also possible that the other explanation when found -need not necessarily apply to the higher animals, where the laws of -combat may still give the true explanation. On the whole, I think that, -for our present purpose, it will suffice to state it is consistent with -the theory of natural selection to accept <i>provisionally</i> this part of -Darwin’s theory for those species in the higher groups in which polygamy -holds, conceding, however, that even here it may have to be altered when -fuller knowledge is gained.</p> - -<p>We are more concerned with that special feature of Darwin’s theory of -sexual selection that is applied to those cases where the characters are -supposed to owe their special development to selection by the -individuals of the opposite sex. It is assumed that the female <i>chooses</i> -the better endowed males, <i>because</i> of the strong appeal he makes to her -sense-organs. Here we must employ perforce or for brevity’s sake the -terms used in human psychology, and run the risk at every turn of -imputing to other animals the emotions and acquired associations which -man himself utilizes. Even granting that other animals possess somewhat -similar emotions to ours, there still remains always the danger, in the -absence of real evidence, of imputing to them the particular emotion -that we call “feeling for beauty”; and the greater danger of imputing an -esthetic sense so highly developed that the choice falls in the long run -on the suitor better ornamented than his rivals.</p> - -<h3><a name="OTHER_THEORIES_TO_ACCOUNT_FOR_SECONDARY_SEXUAL_CHARACTERS" id="OTHER_THEORIES_TO_ACCOUNT_FOR_SECONDARY_SEXUAL_CHARACTERS"></a>OTHER THEORIES TO ACCOUNT FOR SECONDARY SEXUAL CHARACTERS.</h3> - -<p>Wallace has always been an opponent of Darwin’s theory of sexual -selection in so far as it is based on female choice. As already stated, -he believes that the difference between the plumage of the male and -female in birds is due to natural selection keeping down the -ornamentation and high coloration in the female, because these would be -expected to expose the female while sitting on the nest to the attacks -of enemies, more especially of hawks. In support of this view he points -to a long series of species which build exposed nests and in them the -female is plainly and inconspicuously colored, while he also points out -that in such birds as parrots, toucans, woodpeckers, hangnests, and -starlings, which nest in holes or have covered nests, the female is -often as highly colored as the male. It can not be denied that he makes -out rather a strong case in support of this view, despite the fact that -there are other birds, like the Baltimore oriole, that have covered -nests and in which the sexes are very markedly different.</p> - -<p>Wallace tries to meet cases like the last one by assuming that the -covering keeps off the rain; but, if so, why are the sexes still so -different? In the case of other highly colored birds, such as jays, -magpies, hawks, and crows, Wallace believes that these birds are all -aggressive, hence<span class="pagenum"><a name="page_46" id="page_46">{46}</a></span> can protect their nests if attacked. As a further -support of his view, Wallace points out that in the few cases where the -female is more highly colored than the male (as the dotterel, species of -phalarope, an Australian creeper) the male incubates the eggs.</p> - -<p>Wallace’s suggestion still leaves unexplained the ornamentation of the -male, which he tries to account for as the direct result of the greater -vitality of the male. He tries to show that excessive ornaments and high -coloration develop especially in those parts of the body to which there -is an unusual supply of blood or where nerves and blood-vessels emerge -to go to the skin or to the muscles.</p> - -<div class="blockquot"><p>“If we have found a <i>vera causa</i> for the origin of ornamental -appendages of birds and other animals in a surplus of vital energy, -leading to abnormal growths in those parts of the integument where -muscular and nervous action are greatest, the continuous -development of these appendages will result from the ordinary -action of natural selection in preserving the most healthy and -vigorous individuals, and the still further selective agency of -sexual struggle in giving to the very strongest and most energetic -the parentage of the next generation. And, as all the evidence goes -to show that, so far as female birds exercise any choice, it is for -‘the most vigorous, defiant, and mettlesome male,’ this form of -sexual selection will act in the same direction, and help to carry -on the process of plume development to its culmination. That -culmination will be reached when the excessive length or abundance -of the plumes begins to be injurious to the bearer of them; and it -may be this check to the further lengthening of the peacock’s train -that has led to the broadening of the feathers at the ends, and the -consequent production of the magnificent eye-spots which now form -its crowning ornament.</p> - -<p>“The display of these plumes will result from the same causes which -led to their production. Just in proportion as the feathers -themselves increased in length and abundance, the skin-muscles -which serve to elevate them would increase also; and the nervous -development as well as the supply of blood to these parts being at -a maximum, the erection of the plumes would become a habit at all -periods of nervous or sexual excitement. The display of the plumes, -like the existence of the plumes themselves, would be the chief -external indication of the maturity and vigor of the male, and -would, therefore, be necessarily attractive to the female. We have, -thus, no reason for imputing to her any of those esthetic emotions -which are excited in us, by the beauty of form, color, and pattern -of these plumes; or the still more improbable esthetic tastes, -which would cause her to choose her mate on account of minute -differences in their forms, colors, or patterns.”</p></div> - -<p>Wallace says, referring to the immense tuft of golden plumage in the -best known birds of paradise (<i>Paradisea apoda</i> and <i>P. minor</i>) that -springs from a very small area on the side of the breast, that Mr. Frank -E. Beddard, who has kindly examined a specimen, says that “this area -lies upon the pectoral muscles, and near to the point where the fibers -of the muscle converge towards their attachment to the humerus. The -plumes arise, therefore, close to the most powerful muscle of the body, -and near to where the activities of that muscle would be at a maximum. -Furthermore, the area of attachment of the plumes is just<span class="pagenum"><a name="page_47" id="page_47">{47}</a></span> above the -point where the arteries and nerves for the supply of the pectoral -muscles, and neighboring regions, leave the interior of the body. The -area of attachment of the plume is, also, as you say in your letter, -just above the junction of the coracoid and sternum.” “Ornamental plumes -of considerable size rise from the same part in many other species of -paradise birds, sometimes extending laterally in front, so as to form -breast shields. They also occur in many hummingbirds, and in some sun -birds and honey-suckers; and in all these cases there is a wonderful -amount of activity and rapid movement, indicating a surplus of vitality, -which is able to manifest itself in the development of these accessory -plumes.”<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a></p> - -<p>There are two serious defects in such an attempt to explain the facts. -In the first place, it has been shown in several cases that have been -studied that it is not the lessened “vitality” of the female but the -suppression caused by the ovary that keeps down the development of the -full plumage in that sex. In the second place, the anatomical influences -appealed to are imaginary rather than real, for it is by no means -apparent that the local exits of blood-vessels and nerves to muscles are -at all correlated with the location of the ornamental parts, in the -skin. Even when larger blood-vessels run to the region of excessive -development of feather ornaments it may well be that they go there -because the ornaments in question use them for their nourishment; in -other words, Wallace puts the cart before the horse. The top of the -head, where crests so often develop, the throat coloration and throat -shields of hummingbirds and birds of paradise, the two long tail -feathers of several species of hummingbirds, etc., do not arise, so far -as known, from regions which are conspicuous for a rich supply of blood -and nerves. Wallace’s appeal to underlying organs such as muscles that -supposedly influence the special development of the feathers in the skin -above does not strike one as a fortunate appeal to physiological -principles.</p> - -<p>Hudson, in his interesting book, “The Naturalist in La Plata,” has also -criticized Darwin’s theory of sexual selection. He has brought together -a considerable number of interesting observations that go to show that -the displays—dancing, singing, and combats—of males and females have -no relation to mating. Many of them involve birds already mated, -sometimes several males participating, sometimes males and females -together. Some of the tourneys he describes are more elaborate than the -mating instincts themselves, yet are not concerned with mating. He -attempts to explain them as overflow phenomena, <i>i. e.</i>, as expressions -of the high vitality of the males, especially at this time. If he is -right, then elaborate exhibitions of these kinds have evolved that have -no special connection with mating. Are we<span class="pagenum"><a name="page_48" id="page_48">{48}</a></span> called upon for a different -explanation for other differences that distinguish the sexes? One -example will suffice to bring out a curious emotional (?) display that, -elaborate as it is, has no apparent connection with mating (p. 269):</p> - -<div class="blockquot"><p>“The lapwing display, called by the natives its ‘dance’ or ‘serious -dance’—by which they mean square dance—requires three birds for -its performance, and is, so far as I know, unique in this respect. -The birds are so fond of it that they indulge in it all the year -round, and at frequent intervals during the day, also on moonlight -nights. If a person watches any two birds for some time—for they -live in pairs—he will see another lapwing, one of a neighboring -couple, rise up and fly to them, leaving his own mate to guard -their chosen ground; and instead of resenting this visit as an -unwarranted intrusion on their domain, as they would certainly -resent the approach of almost any other bird, they welcome it with -notes and signs of pleasure. Advancing to the visitor, they place -themselves behind it; then all three, keeping step, begin a rapid -march, uttering resonant drumming notes in time with their -movements; the notes of the pair behind being emitted in a stream, -like a drumroll, while the leader utters loud single notes at -regular intervals. The march ceases; the leader elevates his wings -and stands erect and motionless, still uttering loud notes; while -the other two, with puffed-out plumage and standing exactly -abreast, stoop forward and downward until the tips of their beaks -touch the ground, and sinking their rythmical voices to a murmur -remain for some time in this posture. The performance is then over -and the visitor goes back to his own ground and mate, to receive a -visitor himself later on.”<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a></p></div> - -<p>Cunningham, who has brought together many interesting cases of secondary -sexual differences in his book on “Sexual Dimorphism in the Animal -Kingdom,” attempts to show that the development of the secondary sexual -characters of the males are due directly to the use of certain parts of -the body during courtship—the use of the parts leading to the -enlargement and excessive growth of the parts. The effects are believed -by him to be inherited, and he tries, furthermore, to show the way in -which such acquired characters could be inherited. He makes use of the -modern idea of hormones—substances that are elaborated in many organs -of the body, whose effects are often most conspicuously produced in -other parts of the body. He imagines these hormones to be collected in -the germ-cells and transmitted to the next generation, where their -presence contributes to the further development of the special region -(when it develops) that corresponds to the region in its parent in which -the hormone was made. His speculation meets in the first place with the -general objections inherent in Lamarck’s theory—objections so well -recognized to-day that I need not go over them here. His special appeal -to the hormone theory makes use of that theory in a way to which it was -never intended to be put, by assuming that an internal secretion formed -in one organ can be stored up in another organ, eggs and sperm—an -assumption not only unsupported by any evidence, but, as I have stated, -one quite foreign to the hor<span class="pagenum"><a name="page_49" id="page_49">{49}</a></span>mone theory. In fact, Cunningham’s -suggestion is nothing more than Darwin’s old idea of pangens, which, -being imaginary, could be endowed with all desirable properties. But one -can not invoke a chemical substance, even a hormone, and then at the -critical moment endow it with special virtues.</p> - -<p>A rather unique explanation of the origin of secondary sexual characters -is made by Stolzmann. His argument runs as follows: (1) There is a great -excess of males in birds; (2) the males left over after mating are -useless to the species, since they can not propagate and they consume -food needed by the reproducing part of the population; (3) the -conspicuous coloration of the male has been evolved in order that he -could be seen more readily by birds of prey and the objectionable excess -of males removed; the comb of the cock has developed in order that he -may be the more easily killed by other cocks.</p> - -<p>Stolzmann’s account of the origin of the plumes of the birds of paradise -should be immortalized in the literature of the subject:</p> - -<div class="blockquot"><p>“Nous comprendrons aussi facilement la présence de longues plumes -chez les males de nombreuses espèces, comme p. e. chez les oiseaux -de paradis, chez les veuves (<i>Vidua</i>) et chez l’engoulevent -africain (<i>Cosmetornis</i>). Telles plumes ont probablement pour but -de relantir le vol des males. J’ai constate chez la <i>Loddigesia -mirabilis</i> (oiseaumouche péruvien), que le vieux male posséde -l’aile quelques millimetres plus courte que le jeune male ou la -femelle. Cet avortement des remiges provient assurément a cause de -développement extraordinaire de retrices externes chez le vieux -male de cet oiseaumouche. Si donc d’une part les retrices allongees -rendent le vol plus difficile et d’hautre les ailes plus petites -diminuent sa vélocité, le vol du male doit ètre plus lent que celui -de la femelle, le poids du corps restant la même. Le développement -extraordinaire soit des remiges soit des rectrices, en -<i>relantissant</i> le vol des males, rend leur rôle plus difficile, en -facilitant en même temps celui des femelles. Nous pouvons prendre -comme exemple le <i>Cosmetornis</i>, qui, comme tous les engoulevents, -se nourrit d’insectes, qu’il attrape au vol. Chez cet oiseau -quelques plumes des ailes se developpent extraordinairement pendant -l’époque de reproduction, en retardant visiblement son vol. Il est -donc facile a remarquer, qu’alors le male, ayant les mouvements -plus lourds, n’est pas en êtat de se procurer la même quantité -d’insectes qu’auparavant; ainsi donc la femelle a plus de chances -de trouver une nourriture plus abondante.”<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></p></div> - -<p>Equally worthy of perpetuation is Stolzmann’s explanation of dancing and -singing birds:</p> - -<div class="blockquot"><p>“Toutes les réunions des males, leurs danses bizarres, leur chant, -enfin, ne servent pas probablement a séduire les femelles, mais -pour distraire les males, ce qui rend plus faciles les besognes -maternelles des femelles et au surplus les protege contre -l’assiduite nuisible des célibataires. Darwin lui-mème constate le -fait, qu’ordinairement pendant les réunions des males, quand ces -derniers sont trop occupes par le combat ou la danse, la femelle -s’echappe avec un d’eux pour copuler. Ainsi donc dans ce cas c’est -bien la selection naturelle et non la selection sexuelle, qui agit -pour la conservation d’équilibre sexuel.”<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a></p></div><p><span class="pagenum"><a name="page_50" id="page_50">{50}</a></span></p> - -<h3><a name="DISPLAY_OF_THE_MALE" id="DISPLAY_OF_THE_MALE"></a>DISPLAY OF THE MALE.</h3> - -<p>The antics of male birds at the mating season, their courtship -so-called, has played an important rôle in Darwin’s theory of sexual -selection. The behavior of many birds at this time is of such a kind as -to suggest that the male is exhibiting his plumage before the female for -the “purpose” of influencing her choice. The whole paraphernalia of -human psychology is imported into the situation and both the -consciousness of the male, his intentions so to speak, and the supposed -esthetic response or choice of the female is invoked. Even though it be -granted that the words that we must make use of, borrowed from human -behavior, are such as to imply much more in the direction of -consciousness and purpose than is desirable, and that most of the -behavior of animals should be stated in a more roundabout and objective -way, yet the theory will only work out on the assumption that the female -<i>chooses</i> in some sense the more brilliant or ornamental (or effective) -male, whether she is “conscious” or unconscious of intention. I doubt if -anyone to-day would care to defend seriously the theory on the grounds -of consciousness or esthetic value of the exhibition, despite the fact -that Darwin’s language often takes this turn and the less-guarded -statements of some of his disciples, such as Romanes, show little -hesitation in anthropo-morphologizing the entire situation. It is, -however, not necessary for the working out of the theory that this -complication be introduced into it, for if the female is more likely to -mate with a more brilliantly colored than a less brilliantly colored -male, the theory may be made to apply regardless of whether she is -“conscious” or not of the difference to which she responds.</p> - -<p>But there are weighty arguments against such an interpretation of the -behavior of the male and female during courtship. In the first place, -there is almost no direct evidence to show that the female mates with -the more ornamental male. As this is the all-essential requirement of -the theory, the almost complete absence of facts in its support leaves -the theory resting on a theoretical assumption. It can scarcely pass -unnoticed that while there exists a large mass of data describing the -secondary sexual characters, there is practically nothing in this -accumulation to show that the female makes her selection on differences -in coloration or ornamentation. And on the other hand, there is some -evidence showing that the female is ready to succumb to the -aggressiveness of the male rather than that she “chooses” him.</p> - -<p>The behavior of the male under sexual excitement is often described to -be of a kind to exhibit before the female his peculiar adornments. That -the “purpose” of his exhibition is to show himself off before the female -may be conceded, with reservations as to what is meant here by -“purpose.” That the male is conscious of the probable results of his -conduct is scarcely probable the first time he courted; but that he may<span class="pagenum"><a name="page_51" id="page_51">{51}</a></span> -have found out the most probable result after the first attempt through -“associative memory” is in accord with what the study of “animal -behavior” has shown to be possible. In this sense purpose would mean a -line of conduct that experience had shown to lead to a certain end. -Anticipation or far-sightedness would henceforth characterize such a -reaction. Here, however, we venture on very dubious grounds. But the -display of the male may be purposeful in a much simpler sense. His -activity may be an inborn reflex to visual or other sensory stimuli that -is a part of his attack on the female, or possibly a series of reflexes -that we may register under the old unanalyzed terms of “desire and -fear.” The action calls forth a responsive reflex in the female, for the -sexual act is not entirely active on one side, passive on the other, but -consists of a series of interreactions on the part of each sex, which, -if they pursue a given course, leads to the final mating. The mutual -responses appear to follow an automatic course in many cases if the -individuals are sexually ready to mate and the environment is -propitious. Types of behavior of this kind must be familiar to anyone -who has observed domesticated and semi-domesticated animals. The purpose -of the display may mean no more than a reaction that leads to a result -propitious to the perpetuation of the species if the situation is ripe -for such an outcome.</p> - -<p>This conclusion still leaves open the question as to whether the display -is more likely to be successful, if certain special characters possessed -by the species are exhibited. In the absence of any sufficient evidence -to show that this is so, and in the light of the very great danger of -projecting “our human standards” into the world of other animals, and in -view of the fact that related species without such marks are as -successful in maintaining themselves, I can not but think that at -present we have a good deal to lose in the way of scientific procedure -and nothing to gain of scientific value in accepting Darwin’s -interpretation of sexual selection based on the display of the male as -furnishing an opportunity to the female to make the “best” selection -amongst her suitors on the basis of his adornment.</p> - -<p>An excellent opportunity to study the problem as to “choosing” by the -female is furnished by the mutant races of <i>Drosophila</i>, some of which, -differing in a single mutant gene, have wings as different in coloration -as black, yellow, or gray, and eyes as differently colored as white, -vermilion, or red. Sturtevant put a yellow female with a gray -(wild-type) male and a yellow male. The male that first mated was noted -and the trio discarded. The female “chose” the gray males 25 times and -the yellow only 8 times. In the control combination, where a gray female -“chose” between the same two kinds of males, she took the gray male 60 -times and the yellow male 12 times. In both cases it “appears” that the -female “prefers” the gray male, but this deduction may give an entirely -wrong impression as to what is taking place, for<span class="pagenum"><a name="page_52" id="page_52">{52}</a></span> the result would be -the same in kind if the gray male were more active and mated quicker. -This was tested by putting a gray and a yellow female with a gray male -and then for control a gray and a yellow female with a yellow male. The -result was as follows:</p> - -<table border="0" cellpadding="4" cellspacing="0" summary="" - class="sml"> - -<tr><td rowspan="2" valign="middle">Red ♂ </td><td>{Gray ♀ </td><td> 25 </td><td rowspan="2"></td><td rowspan="2" valign="middle"> Yellow ♂ </td><td>{Gray ♀ </td><td> 12</td></tr> -<tr><td>{Yellow ♀ </td><td> 31 </td><td> {Yellow ♀ </td><td> 30 </td></tr> -</table> - -<p>Here the gray male mated slightly oftener with the yellow female than -with the other, whereas the yellow male mated much oftener with the -yellow female than with the gray one. Both results are explicable on the -view that the yellow female, being less active, is more easily captured -by the yellow male than is the gray female. This view fits in also with -the former experiment, where the yellow male is much less successful -than the more active gray male. Such a conclusion gives a more -consistent explanation of all the facts than does the theory of female -choice, for on the latter we must suppose that the yellow females prefer -the gray males and the yellow male prefers the yellow females, etc.</p> - -<p>The following results were obtained by Sturtevant when red and white -eyed flies were competing:</p> - -<table border="0" cellpadding="4" cellspacing="0" summary="" - class="sml"> - -<tr><td rowspan="2" valign="middle">Red ♂ </td> -<td> {Red ♀ </td><td> 54 </td> -<td rowspan="5"> </td> -<td rowspan="2" valign="middle"> Red ♀ </td> -<td> {Red ♂ </td><td> 53</td></tr> - -<tr><td>{White ♀ </td><td> 82 </td> -<td> {White ♂ </td><td> 14</td></tr> - -<tr><td> </td></tr> - -<tr><td rowspan="2" valign="middle">White ♂ </td> -<td> {Red ♀ </td><td> 40 </td> -<td rowspan="2" valign="middle"> White ♀</td> -<td> {Red ♂ </td><td> 62</td></tr> -<tr><td>{White ♀ </td><td> 93 </td> -<td> {White ♂ </td><td> 19</td></tr> -</table> - -<p>The outcome can be interpreted in the same way as the yellow-gray -competition. The red male wins by virtue of his greater activity, while -the white female is chosen more often, especially by the white male, -because of her passivity (or weaker resistance). It may be claimed that -these results do not show that the female does not choose, for such -choice, if made, would be swamped by another condition of the -experiment, viz, the greater aggressiveness of one kind of male and -greater passivity of the other kind of female. This, of course, is true, -but the experiment still shows that in these flies other influences are -so much greater than “choice” by the female, if it exists, that the -postulated effect of the latter practically disappears from the -situation.</p> - -<p>Mayer’s experiments with the large moth <i>Callosamia promethea</i> furnish -important information as to the factors involved in mating. The results -are all the more significant from our present point of view because the -colors of male and female are in this species markedly different. The -wings of the male are black, those of the female reddish brown; the -antennæ of the male are large and bushy, those of the female small and -slender. Mayer found that the males are attracted by the female from -some distance when the latter are put into a glass jar covered by only -coarse mosquito-netting, but if the same jars are turned upside down the -males are unable to find the female. Females<span class="pagenum"><a name="page_53" id="page_53">{53}</a></span> concealed in loose cotton -attracted males. Females were put into a box with an open chimney at one -end, the other open end being covered by mosquito-netting. A current of -air blew into the open end and out of the chimney. The males flew to the -end of the chimney from which the air came and fluttered about in the -neighborhood. Males are attracted to places where a female has been kept -even several hours after her removal. The male finds the female through -the sense-organs in his antennæ, for a male whose abdomen has been cut -off and the sides of whose thorax are covered with shellac will still -fly to the female, but if his antennæ he coated with any substance he no -longer seeks the female. If the eyes of the males are blackened they -will mate with females “in the normal manner.”</p> - -<p>Mayer cut off the wings of females and glued male wings in their places, -so that the female looked like a male. Males readily mated with these -females. The wings of males were cut off and female wings glued in their -place. Mating occurred “with normal frequency, and I was unable to -detect that the female displayed any unusual aversion” to such males. -Males with female wings pass unnoticed by other males.</p> - -<p>In a later paper (1901) Mayer and Soule describe how, when the wings of -the male were painted scarlet or green, the males were accepted as -readily as normals in competition with them. Experiments were also made -by them with the gipsy moth. Wingless males met with more “resistance” -from the female than do normal males, but when the eyes were covered the -wingless males succeeded as often as the normal males, but the number of -observations on which this statement is were far too few to be of any -value, and there are several other observations that make any such -conclusion from the evidence highly uncertain.</p> - -<p>That it is the odor of the females that attracts the male can not be -doubted. It might still be claimed that the female chooses amongst her -suitors the darkest males, but the evidence gives no grounds for -inferring such a choice, and since she will even accept males with -female wings when they attempt to mate with her, it does not appear -probable that the color of the male is a factor in the result, or at -least if it is, then it must be entirely subordinate to the sense of -smell in finding the female and of touch after he arrives. There is -little or nothing in the behavior of these moths, or in that of the -silkworm moth, according to Kellogg, to suggest that vision plays any -significant rôle in courtship.</p> - -<p>Concerning the genetic situation in insects, there are only a few cases -that have been studied. The most instructive are those in which more -than a single kind of male exists (two or three), one of which may be -like the female, the other quite different. The best worked out cases -are <i>Papilio memnon</i> and <i>P. polytes</i>. De Meijere and Punnett have<span class="pagenum"><a name="page_54" id="page_54">{54}</a></span> -shown from the breeding data that it is possible to frame an explanation -of such a sort that the aberrant female differs from the female -resembling the male in only a single genetic factor—one not sex-linked -(<i>i. e.</i>, not carried by an X chromosome), but autosomal. The gene would -be of such a sort that it affects the female only—producing no visible -effect on the male. Such a conclusion, if established, helps, -theoretically at least, toward simplifying the situation in other -species, for it shows that genetic factors occur whose influence is on -one sex alone; hence the difference between the male and one type of -female does in such cases result from a single gene present in both but -causing them to be differently colored. There would be no need, then, to -assume that the difference had been slowly built up by selection, but -rather that the difference arose at some time by a single mutant step. -The incorporation of the step in the species would then follow if the -effect of the gene were useful in mating or if it had some other primary -significance for the welfare of the species, the different effect -produced on the male and female being only an unimportant by-product of -its action. On the other hand, it should be emphasized that because a -single factor difference between the two kinds of females will explain -the genetic results, it does not necessarily follow that the difference -did arise as a single mutation. The foregoing argument does no more than -imply that the difference in question may have arisen in this way, and -if so, that the situation, as it exists, would be the more easily -comprehended.</p> - -<p>In insects and spiders, where dimorphism is as marked as in birds, the -mating habits have been studied by a number of naturalists. Here also -there are numerous accounts of the display of the male during courtship. -The account given by Dr. and Mrs. Peckham are particularly detailed and -call for careful consideration on account of their well-recognized -accuracy in observational work. Moreover, as a result of their -observations, along with those of Montgomery, Petrunkewitsch, and -others, we have really fuller information concerning the courtship of -spiders than of birds and of mammals.</p> - -<p>In the great majority of species where the sexes are different the male -is more brightly colored or more ornamental. For example, in a group -such as the Attidæ of France, where both sexes are known, the Peckhams -state that in 26 cases the male is more conspicuous than the female; in -55 cases the sexes are alike, or if they differ the male is more -conspicuous. It appears that in other genera there are cases where the -female is more conspicuous than the male. The Peckhams state that -possibly as many as 250 species are in this condition. Those females -with brighter colors than the males are usually well armed by strong -spines. When very young they are like the males and begin to assume the -adult form and color when they are a quarter to a third grown. Whether -the change depends on changes in the ovary is not known.<span class="pagenum"><a name="page_55" id="page_55">{55}</a></span></p> - -<p>The mating behavior of <i>Saitis pulex</i>, a species in which the males and -females are much alike, is described by the Peckhams as follows:</p> - -<div class="blockquot"><p>“On May 24th we found a mature female and placed her in one of the -larger boxes, and the next day we put a male in with her. He saw -her as she stood perfectly still, twelve inches away; the glance -seemed to excite him and he at once moved toward her; when some -four inches from her he stood still and then began the most -remarkable performances that an amorous male could offer to an -admiring female. She eyed him eagerly, changing her position from -time to time so that he might be always in view. He, raising his -whole body on one side by straightening out the legs, and lowering -it on the other by folding the first two pairs of legs up and -under, leaned so far over as to be in danger of losing his balance, -which he only maintained by sidling rapidly toward the lowered -side. The palpus, too, on this side was turned back to correspond -to the direction of the legs nearest it. (Fig. 13.) He moved in a -semi-circle for about two inches and then instantly reversed the -position of the legs and circled in the opposite direction, -gradually approaching nearer and nearer to the female. Now she -dashes toward him, while he, raising his first pair of legs, -extends them upward and forward as if to hold her off, but withal -slowly retreats. Again and again he circles from side to side, she -gazing toward him in a softer mood, evidently admiring the grace of -his antics. This is repeated until we have counted 111 circles made -by the ardent little male. Now he approaches nearer and nearer and -when almost within reach whirls madly around and around her, she -joining and whirling with him in a giddy maze. Again he falls back -and resumes his semi-circular motions, with his body tilted over; -she, all excitement, lowers her head and raises her body so that it -is almost vertical; both draw nearer; she moves slowly under him, -he crawling over her head, and the mating is accomplished.</p> - -<p>“After they have paired once, the preliminary courtship is not so -long. When this same pair mated a second time, there was no -whirling movement, nor did the female lift her body, as at first.” -(pp. 37-38).<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a></p></div> - -<p>The courtship of another species, <i>Dendryphantes capitatus</i>, in which -the sexes are entirely different, is described as follows:</p> - -<div class="blockquot"><p>“The males of <i>capitatus</i> are very quarrelsome, sparring whenever -they meet, chasing each other about, and sometimes clinching. It is -a very abundant spider with us, so that we often put eight or ten -males into a box to see them fight. It seemed cruel sport at first, -but it was soon apparent that they were very prudent little -fellows, and were fully conscious that ‘he who fights and runs away -will live to fight another day.’ In fact, after two weeks of hard -fighting we were unable to discover one wounded warrior. When the -males are approaching each other, they hold the first legs up in a -vertical direction. Sometimes they drop the body on to one side as -they jump about each other. These movement are very quick, and they -are always ready for a passage at arms. When courting the females -they have another movement. They approach her rapidly until within -two to five inches, when they stop and extend the first legs -directly forward, close to the ground, the legs being slightly -curved with the tips turned up. (Fig. 18). Whether it be -intentional or not, this position serves admirably to expose the -whole of the bronze and white face to the attentive female, who -watches him closely from a little distance. (Fig. 19.) The males -also give their palpi a circular movement, much as a person does -when washing his hands. As he grows more excited, he lies down<span class="pagenum"><a name="page_56" id="page_56">{56}</a></span> on -one side with his legs still extended. These antics are repeated -for a very long time, often for hours, when at last the female, -either won by his beauty or worn out by his persistence, accepts -his addresses.” (Pp. 45, 46.)</p></div> - -<p>In another species, <i>Dendryphantes elegans</i>, both sexes are brilliantly -colored.</p> - -<div class="blockquot"><p>“The male is covered with iridescent scales, his general color -being green; in the female the coloring is dark, but iridescent, -and in certain lights has lovely rosy tints. In the sunlight both -shine with the metallic splendor of hummingbirds. The male alone -has a superciliary fringe of hairs on either side of his head, his -first legs being also longer and more adorned than those of his -mate. The female is much larger, and her loveliness is accompanied -by an extreme irritability of temper which the male seems to regard -as a constant menace to his safety, but his eagerness being great, -and his manners devoted and tender, he gradually overcomes her -opposition. Her change of mood is only brought about after much -patient courting on his part. While from three to five inches -distant from her he begins to wave his plumy first legs in a way -that reminds one of a wind-mill. She eyes him fiercely and he keeps -at a proper distance for a long time. If he comes close she dashes -at him and he quickly retreats. Sometimes he becomes bolder and -when within an inch, pauses, with the first legs outstretched -before him, not raised as is common in other species; the palpi -also are held stiffly out in front with the points together. Again -she drives him off, and so the play continues. Now the male grows -excited as he approaches her, and while still several inches away -whirls completely around and around; pausing, he runs closer and -begins to make his abdomen quiver as he stands on tip-toe in front -of her. Prancing from side to side, he grows bolder and bolder, -while she seems less fierce, and yielding to the excitement lifts -up her magnificently iridescent abdomen, holding it at one time -vertically and at another sideways to him. She no longer rushes at -him, but retreats a little as he approaches. At last he comes close -to her, lying flat, with his first legs stretched out and -quivering. With the tips of his front legs he gently pats her; this -seems to arouse the old demon of resistance, and she drives him -back. Again and again he pats her with a caressing movement, -gradually creeping nearer and nearer, which she now permits without -resistance until he crawls over her head to her abdomen, far enough -to reach the epigynum with his palpus”. (Pp. 46-47.)</p></div> - -<p>If we lay no emphasis on the implied emotional elements in the behavior -of the spiders in this description—terms of emotion borrowed direct -from human psychology—there still remain the several types of -apparently significant reactions associated with courtship. The -statements leave no room for doubt that vision plays an important rôle -in the complex reflexes that lead gradually to successful mating. The -Peckhams insist that the display of the male is always of a kind to -bring before the female the special adornments of the male in whatever -part of the body they may lie. The chance of subjective interpretation -here is so great that unless the results are carefully checked up by -studies of the attitudes assumed by males in species in which the males -are without ornament, their interpretation must be taken with the -greatest reserve. Assigning, as our authors do, so much by gratuitous -implication to the emotional side of the picture prejudices<span class="pagenum"><a name="page_57" id="page_57">{57}</a></span> one, -perhaps too greatly, against accepting a special (even an implied -intentional) exhibition of the specially ornamented parts. On the other -hand, if it be conceded that the conspicuousness of the male is an -element in the reaction, the very special adornments visible from the -front might be supposed to enhance the effect produced in the female. -Similar displays of special ornamentation in the male have been -described both for birds and insects, but here, too, the question has -been raised as to whether such exhibitions are more than an accidental -accompaniment of the posturing of the male, for the same kind of -behavior is known to occur in other cases where the male is unornamented -and resembles the female. Had such a male special ornamentation it would -no doubt appear to us that his behavior was “calculated” to display his -ornaments.</p> - -<p>Dr. and Mrs. Peckham point out that their observations are entirely -inconsistent with Wallace’s interpretation of the origin of secondary -sexual characters. They find no evidence in favor of his view that the -male possesses greater “vital activity.” On the contrary, the female is -the more active and pugnacious of the two. They also object to Wallace’s -statement of a total absence of any evidence that the female notices the -display of the male. In spiders the females “<i>observe</i>” the males with -close attention during their courtship. They point out also that, in -spiders at least, as the female gradually becomes adult, a male if -preferred will have a chance of mating with several females, “and as the -mating season lasts for two or three weeks the more brilliant males may -easily be selected again and again.” In regard to Wallace’s argument as -to the distribution of accessory plumes in humming birds, the Peckhams -point out that—</p> - -<div class="blockquot"><p>“The pectoral muscles reach their highest development in the -hummingbirds, the diurnal birds of prey, and the swallows, and we -may, therefore, fairly use these groups to test Mr. Wallace’s -explanation of breast plumes. In the swallows and birds of prey we -find no such appendages, in spite of their further claim to them, -on the ground of great vigor and activity. As to the humming-birds, -we find in the genus <i>Aglæactis</i> six species with more or less -developed breast-plumes, which are also found in nine other -species, scattered through different genera—in all, only fifteen -species out of four hundred and twenty-six; while we find in -fifty-six species the lengthened and modified tail-feathers, which, -according to Mr. Wallace’s view, should be peculiar to the -Gallinaceæ.</p> - -<p>“Again, there are elongated feathers from the throat or from the -side of the neck in thirty-five species, while seventeen have -crests from the top of the head, and seventeen, downy puffs from -the tarsi.”<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a></p></div> - -<p>From this brief survey of the family we see that, contrary to what we -should expect from Mr. Wallace’s theory, although the breast muscles are -the seat of the highest activity, breast plumes are the least frequent -of all the forms of ornamental plumage.<span class="pagenum"><a name="page_58" id="page_58">{58}</a></span></p> - -<div class="blockquot"><p>“We may fairly say, then, that the humming-birds completely refute -the proposition that there is any relation between the development -of color and accessory plumes and ‘surfaces where muscular and -nervous development is considerable.’<span class="lftspc">”</span><a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a></p></div> - -<p>What is true for birds is even more obvious for spiders where the -special ornaments are not confined to parts of the body with high -muscular development, etc. The writers make the very pertinent criticism -that while Wallace objects to assuming the emotional states in females, -he is less careful in regard to the males’ emotions when he speaks of -the display “under the influence of jealousy or sexual excitement.... -The males, in their rivalry with each other, <i>would see what plumes were -most effective; and each would endeavor to excel his enemy</i> as far as -voluntary exertion would enable him.”<a name="FNanchor_13_13" id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a></p> - -<div class="blockquot"><p>“If the males have so complex an emotion as jealousy, and further, -if they are conscious of the value of the plumes, may it not be -asked why the female is unable to ‘see what plumes are most -effective?’ The mental state in the male is without meaning unless -we suppose the female to be affected and pleased.” (Peckham, <i>loc. -cit.</i>, p. 144.)</p></div> - -<p>In regard to another interpretation of the courtship, the Peckhams point -out:</p> - -<div class="blockquot"><p>“Mr. Pocock has suggested that the attitude of observant interest -on the part of the female spider might be taken to indicate that -she was preparing to spring upon her mate and devour him; or that -it might simply mean that she was warily guarding herself from his -approach. Neither of these suppositions is admissible. In some -species the male is not attacked by the female, and when she does -wish, as frequently happens, either to avoid or to destroy him, her -attitude is totally different. In the former case she turns about -and runs rapidly away, or suspends herself by a thread of web. In -the second, there is a contraction of all the muscles, the legs are -drawn together, and in this crouching position she creeps slowly -toward him, as she might if he were a fly, only with something more -malignant in her aspect. When she takes this stand the male -incontinently flees. When, on the contrary, the female is -interested in the male display, she seems perfectly absorbed in -watching him, the muscles are all relaxed, unconscious of herself -she directs her glance now here, now there, as he moves about; as -he continues his mad antics, her appearance gives every indication -of pleasurable excitement, and as he comes closer and closer, she -yields herself to the impulses which he has awakened in her, and, -as in <i>pulex</i>, joins in his dance and whirls around and around as -though intoxicated. We claim, then, to have completely answered Mr. -Wallace’s first objection.” (Peckham, <i>loc. cit.</i>, pp. 145, 146.)</p></div> - -<p>Finally, in regard to the specific character of the display of the -males, the Peckhams make the following significant statement:<span class="pagenum"><a name="page_59" id="page_59">{59}</a></span></p> - -<div class="blockquot"><p>“The spider has four pairs of legs, and all are equally available -for display or locomotion, and since all the movements are slow and -on the ground they are entirely open to observation and study, and -we are thus in a position to decide by facts whether their activity -is simply an outlet for superfluous energy, and therefore -meaningless, or whether there is a purpose in it. If the purpose of -the antics is only to let off energy, then we should expect one -pair to be flourished around quite as often as another, and that -the pair flourished should as frequently be one that was not -ornamented as one that was; and, moreover, their movements ought -not to be of such a nature as to display the color or ornament, -more frequently than the law of chance would explain. If the spider -almost always moves the ornamented legs, and in such a way, too, as -to bring out their beauty, it would seem to us, to say the least, -highly improbable that the dance of the spider was merely a -meaningless overflow of surplus energy. Such an explanation leaves -much that needs explanation. The facts are, that the best foot is -put forward; and this is just what Darwin’s theory requires and -explains. Under Mr. Wallace’s view the facts are inexplicable. The -better to show that these movements are not simply meaningless -outlets of high vigor, we illustrate the several positions by -figures taken from nature (figs. 7-12). The figures would seem to -prove that the legs that are ornamented or contrasted in color are -also the legs that are usually flourished; that where none of the -legs have special ornament, then all are used; or, as sometimes -happens, when an unornamented leg is used the movements are of such -a character as to display some ornament that would otherwise have -been more or less hidden from the female.” (Peckham, <i>loc. cit.</i>, -p. 147.)</p></div> - -<p>In the tarantula, Petrunkewitsch finds that sight plays no rôle in -mating—that it is due entirely to accidental contact between the male -and female. Here the sexes are closely alike, except for a pair of hooks -on the front legs of the male, by means of which he grasps the mandibles -of the female, holding them during the elaborate process of transference -to her genital opening the sperm that he has already collected in the -genital spoon on his palpi. The hooks serve to guard the male against -injury or death, while at the same time they aid him in the act of -coitus.</p> - -<p>In a common spider, <i>Mœvia villata</i>, two kinds of males exist. Both have -been seen to mate with the same female. No preference is given to either -type. The difference between them, according to Painter, is connected -with or caused by an additional pair of chromosomes in the gray male. -The two types may therefore have no connection with sexual selection, -but be directly due to a difference in the chromosome group.</p> - -<p>Montgomery, who made observations on the courting habits of several -species of spiders, states that his “general theoretical conclusions -were quite different from those of the Peckhams.” It turns out, however, -that his objection to their view is based entirely on their assumption -that the male is conscious of his display and that the female is guided -by an esthetic sense in selecting the more beautiful male. It should be -pointed out that even after the removal of these<span class="pagenum"><a name="page_60" id="page_60">{60}</a></span> gratuitous assumptions -as to the cause of the evolution of the male and female, enough still -remains in Montgomery’s own observations to include his results on -courtship under Darwin’s theory of sexual selection. For example, -Montgomery says:</p> - -<div class="blockquot"><p>“The adult male is excited simultaneously by fear of and desire for -the female, and his courtship motions are for the most part -exaggerations of ordinary motions of fear and timidity. By such -motions he advertises himself to the female as a male, but there is -no proof that he consciously seeks to arouse her eagerness by -esthetic display—there seems to be no good reason to hold that the -female is actuated in her choice by sensations of beauty.... Thus -my opinion was opposed to Darwin’s theory.”</p></div> - -<p>Now, it is obvious that if a more brightly colored male has a better -chance of “advertising himself” to the female all the essential -requirements of Darwin’s theory are fulfilled, regardless of whether the -male is conscious of his ornamentation or the female makes use of an -“esthetic sense.” In another passage (p. 173) Montgomery concedes all -that any modern critical advocate of Darwin’s theory is likely to ask:</p> - -<div class="blockquot"><p>“We have previously seen that conscious aesthetic choice by the -female probably does not account for such male characters -[secondary sexual characters with their ‘conspicuous color -markings’]; that they are accordingly, probably not due to sexual -selection. These characters of the males may be most readily -explained as being conceived by simple natural selection. Peculiar -ornamentation would be selected because unusually greater sex -recognition therefore prompted mating.”</p></div> - -<p>It is evident that Montgomery has only shifted the situation, although -to advantage, I think, but is essentially in accord with Darwin’s theory -of sexual selection, despite his protest to the contrary. The difference -lies in Darwin’s and especially in the Peckhams’ use of the term -“choice,” “aesthetic sense,” etc., to stand for the fact that the female -more promptly mates (as Montgomery prefers to put it) with a male -peculiarly ornamental.</p> - -<p>The most critical observations on sexual selection that have been made -in the group of insects are those by Sturtevant on the pomace fly. The -courtship is described as follows:</p> - -<div class="blockquot"><p>“The first and most noticeable act in courtship occurs when the -male, being near the female, extends one wing at about right angles -to his body, and vibrates it for a few seconds. The wing is then -returned to the normal position and the process is repeated, -usually with the other wing. But between times there is a -scissors-like movement of the wings repeated several times. This -vibrating of the wings is often repeated many times, and may be -done in any position relative to the female, though the male always -faces her. Usually, in fact, he swings quickly around her in a -semicircle once, or oftener, during the process. Soon the male -begins to protrude his genitalia and, if the female remains quiet, -to lick her posterior end. Some white matter now protrudes from her -ovipositor, and other males in the same vial are usually observed -to become excited now and begin courting, indicating odor as a -cause of sexual excitement. If the female runs or flies away the -male is excited, moves his<span class="pagenum"><a name="page_61" id="page_61">{61}</a></span> wings jerkily, and walks around -rapidly, but seems unable to follow the female accurately or to -locate her quickly. The penis is directed forward by bending up the -abdomen underneath, towards the thorax, and is jerked toward the -female (the male always standing facing her at this stage), but not -always toward her genitalia, as I have seen it strike her in the -eye. (The male in this case, however, had white eyes, and so was -perhaps blind. Normally the aim is accurate.) If it does strike the -mark the male mounts on the female’s back, between her wings. -Mounting never takes place until after the actual copulation has -occurred, in which respect <i>Drosophila</i> differs from some related -flies (<i>e. g.</i>, Muscidæ, Anthomyidæ, Sepsidæ, Borboridæ, and -Ephydrichæ, so far as my observations go). In these forms the male -flies and lights on the female, after which copulation may or may -not take place, probably depending upon the way the female -responds.”<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" class="fnanchor">[14]</a></p></div> - -<p>To test whether the wings have any significance in courtship, the wings -of a male were clipped off and he was put into competition with a normal -male of the same stock, age, and size. A virgin female sexually mature -was given to these two males. The normal male mated 72 times before the -other, the clipped male 53 times. It might appear that the female -selected the normal male in preference to the clipped one, or possibly -that the male with normal wings drove the other male away. That the -operation on the wings may have an influence on the male himself is -shown in McEwen’s results. He found that clipped males lost their -heliotropism. It was also possible that the courtship of the normal male -might make the female ready to copulate and then she would mate with -either male. Sturtevant tested the last supposition by placing single -pairs in vials, testing each day an equal number of normal and clipped -males. The length of time before copulation was noted. The clipped male -began to court as soon as the normal, but a larger number of normal -males mated in the first 12 minutes than clipped males (50 to 25). Had -the females discriminated against the clipped males to an equal extent -we would have expected a much greater excess than 72 to 53 when they -were in competition. It appears, then, that the wings are useful in -shortening the time between the meeting of the individuals and -copulation. The display acts, however, almost as favorably for the other -male as for the exhibitor himself. The results show, therefore, that -here an esthetic sense of the female need not be postulated, for she -actually shows little preference when she has been brought to the point -of mating between the male that aroused her and the other male that did -not. This critical test puts the problem in a different relation from -that which Darwin’s theory of female choice was meant to throw light -upon.</p> - -<p>The reverse experiment—a clipped and a normal female of the same age, -size, etc.—showed that the mate did not discriminate between them, for -in 52 first trials the normal female was paired with 25 times, the -clipped 27 times.<span class="pagenum"><a name="page_62" id="page_62">{62}</a></span></p> - -<h2><a name="PART_III" id="PART_III"></a>PART III.<br /><br /> -THE GENETIC AND THE OPERATIVE EVIDENCE.</h2> - -<p>The genetic and operative evidence shows that there has been included -under the general term “secondary sexual characters” a complex of cases -that are the outcome of diverse physiological processes. Sex-linked and -sex-limited characters have often been confused; some characters depend -on the gonad; some of these involve the ovary, others the testes. Still -other characters fall under none of these groups, but are the direct -product of the male or female genetic constitution. It is not -surprising, therefore, that theories proposed on the information derived -from certain of these data are controverted by information derived from -other data. The theory of sexual selection, in its attempt to bring all -the facts under one point of view, has not escaped these difficulties, -even although it may be said that neither natural selection nor sexual -selection is concerned with the origin or even the kind of variations -with which it works. Nevertheless, the latter theory, by ignoring the -origin or the physiological process concerned in the production of -secondary sexual characters, may make assumptions that are difficult to -harmonize with the facts in the case, and we shall find several -instances of this sort. For example, if the hen had selected the cock -for his fine plumage (which, as we have seen, depends in part on -autosomal genes producing their effect without the cooperation of the -testes), she would be expected to endow herself with the same adornments -(if her selection worked), unless her ovary were already producing some -substance inimical to those that she is “calling forth” by selection of -the male. The problem is evidently, then, more complex than appears on -the surface, and is not so simple as it seemed when these essential -facts were unknown or ignored.</p> - -<p>In the case of other theories, such as those of Wallace and of -Cunningham (that appeal more directly to the causes that are producing -the variation out of which the secondary sexual characters are built -up), the absence of information, physiological or genetic, has only too -often given these writers the opportunity to speculate without the -restraints which a more recent knowledge of the facts has imposed on us.</p> - -<p>It is obvious from what we have learned that we shall have to proceed -with more caution in disentangling the evidence before we can hope to -“explain” it. Despite the meagerness of our present information, enough -has been found out to indicate that we must be content for a while with -tentative and partial explanations even in the best-known cases, and we -must, I think, be prepared to admit that no one theory may be able to -account for all of the secondary sexual differences that exist between -the sexes.</p> - -<p>The genetic evidence shows, in the case of cock-feathering versus -hen-feathering in birds, that only one or two Mendelian factor -differ<span class="pagenum"><a name="page_63" id="page_63">{63}</a></span>ences are involved. The result may seem to mean that the -secondary sexual <i>characters</i> themselves have been acquired historically -by a single evolutionary step, and that in consequence the opportunity -for selection to have accomplished such a result has been enormously -facilitated. Such an argument rests, however, as we know to-day, on a -false interpretation of Mendelian heredity. What the evidence really -shows is that one or two genes if present cause the testes to produce -some substance that prevents the cock-feathering from developing. The -genetic complex may require a hundred or a thousand or more special -factors that are directly and indirectly concerned with the development -of the cock-feathering, but one or two other factors may suffice to -block this machinery; or, to change the metaphor, these dominant factors -may be no more than so much sand poured into the clock. The clock may -have been slowly built up historically by many contributory “factors,” -but a little sand may spoil its activity. Similarly in the hen something -produced by the ovary prevents the fullest possible genetic action from -taking place. Here at present we do not know whether a single factor or -a hundred “special” factors are necessary to produce such an inhibition, -but if, as one would like to suppose, it is the same or partly the same -genes involved in the ovary, and in the testes of hen-feathered males, -then a relatively few, one or two, factors will suffice to bar -cock-feathering from the female.</p> - -<p>In a case like the clover butterfly, where the genetic relations work -out on the theory of one pair of factors that produce two types of -females and one type of male, it seems more reasonable to infer that -such a difference has not been slowly acquired by many smaller -mutational changes, because the two types are not adapted to live under -two different environments for which their differences fit them -respectively, but to live in the same environment. It has never been -claimed, so far as I know, that these two types of females have arisen -through some males preferring one, some another kind of female, so that -even although it may seem probable that the genetic situation is simple, -the simplicity can not be turned to the advantage of the theory of -sexual selection. It is unnecessary to discuss further the origin of the -factor or factors suppressing the development of one type in the male or -the probability of the multiplicity of such factors. In the case of such -species as <i>Papilio memnon</i> and <i>P. polytes</i>, with three types of -females, the situation is the same as above, with the addition of the -theory of mimicry, that “explains” some advantage accruing to each type -of female. Since the latter is only a form of natural selection, we are -not further concerned with the change here. Punnett’s excellent -treatment of the problems involved in his recent book on mimicry brings -the subject down to date.</p> - -<p>Meager as is the genetic and surgical evidence at present, it is enough -to show that only by further work along these lines can we hope to lay<span class="pagenum"><a name="page_64" id="page_64">{64}</a></span> -a firm foundation for a scientific study of the subject. It is equally -important that critical evidence be obtained in regard to the effect on -the female of males of different types in competition. The instinctive -reactions of animals in these respects, their first reaction, the -associations that may or may not result, are practically an open field -for investigation. The entire equipment of human psychology of the -introspective school, that has been appealed to for help in a situation -itself little understood, reads often more like fiction than like -science.</p> - -<p>So far as one branch of the subject goes—the possible interpretation of -ornamentation in the male—there seem to be two ways at least in which -the subject calls for immediate investigation: First, if it can be shown -that, other things being equal, a more adorned male rouses the female to -prompter mating, it may be inferred with some probability that in the -long run such conduct would lead to the establishment of the more -effective individual, but this would not be true unless the males mate, -as a rule, more than once, for any advantage that might accrue to a more -ornamented male would not affect the course of evolution of the species -if every other male found a mate too. Second, if it could be shown that -the special ornamentation of the male is only one of several effects of -a gene whose main effect is in some other direction, then the advantage -gained through natural selection in this other direction would carry in -its wake the advance in ornamentation, and if the change affects one sex -more than the other, owing to the difference in the genetic complex of -the two sexes, it would be called a secondary sexual character.</p> - -<h4>A. <span class="smcap">Evidence from Mammals.</span></h4> - -<p>Owing to the differences in the secondary sexual characters of different -breeds of sheep, we have more genetic information about such characters -in this group than in other groups of mammals. Fortunately, also, in -some of the breeds both castration and ovariotomy have been performed, -and consequently we are in position to utilize both sources of -information for interpreting the situation. In certain breeds both males -and females have horns (Dorsets), in which case the horns of the male -are larger than those of the female. In other breeds neither males nor -females have horns (Suffolks). In still other breeds the males have -horns and the females are hornless (Merinos and Herdwicks). The clearest -evidence that we have, both genetic and operative, is that obtained by -Woods, as reported by Bateson, in which horned (Dorsets) and hornless -(Suffolks) breeds were crossed. In the Dorsets, where both sexes have -horns, those of the male are larger than those in the female. When the -young male is castrated the horns develop, but only as far as in the -female. It appears, therefore, that the presence of the testis, probably -through some secretion from it,<span class="pagenum"><a name="page_65" id="page_65">{65}</a></span> contributes to the development of the -horns. The other race, the Suffolks, have no horns in either sex. -Castration produces no change in their hornless condition.</p> - -<p>When a Dorset ram is crossed to a Suffolk ewe the sons have horns, the -daughters lack them. The reciprocal cross gives the same results. The -factor or factors involved are therefore not sex-linked. When the F₁’s -from the cross or from its reciprocal are inbred, four classes of -offspring are produced, namely: Horned male, 3; hornless male, 1; horned -female, 1; hornless female, 3. The ratios, as above, are approximately -3:1:1:3.</p> - -<p>A simple Mendelian explanation covers the results. If we assume that the -Dorsets, both male and female, are homozygous in a factor for horns, H, -that is not in the sex chromosome, and that the Suffolks “lack this -factor,” <i>i. e.</i>, that they have an allelemorphic factor for -hornlessness, the germ-cells are H-H and h-h, respectively. Only one -kind of individual, Hh, results in F₁. Since the male with this formula -develops horns, we must conclude that the presence of the testis -(through its secretions) causes horns to develop, while in the female of -this same composition horns are not produced because of the absence of -the testes. The sex-cells in these F₁ individuals are H-h and H-h. -Chance meeting of these gametes will give 3 classes of individuals, -irrespective of sex, namely, (1) HH, (2) Hh, (1) hh. The expectation for -the males is that those of the composition (1) HH and (2) Hh will -develop horns, while those of the composition hh will not develop horns. -There should be 3 horned to 1 hornless male. In the females we expect -those with the composition (1) HH to develop horns, since they have the -same formula as the pure Dorset; those with the formula Hh are not -expected to develop horns, because the F₁ females of this composition do -not have horns; those with the formula hh are not expected to develop -horns, because they have the same composition as have the pure Suffolk. -There should be 3 hornless to 1 horned female. Combining both sexes, the -expectation for F₂ is 4 horned to 4 hornless. Arranged according to sex, -these give the classes realized: Horned male, 3; hornless male, 1; -horned female, 1; hornless female, 3. That this is the correct -explanation is borne out by back-crossing the hornless F₁ female to a -hornless Suffolk ram. The former has two kinds of gametes, H and h, the -latter only gametes that bear the h factor. Half the sons should be -horned, half hornless, because half of them are Hh and half hh. But none -of the daughters should have horns, because neither the Hh nor the hh -females produce horns. This is the result realized, viz, 3 hornless -offspring to 1 horned.</p> - -<p>The preceding account of the inheritance of the factor for horns is -based on the combination of Dorsets and Suffolks used by Wood. That -other conditions may exist in other breeds and even in races of<span class="pagenum"><a name="page_66" id="page_66">{66}</a></span> the -same breed is claimed by Arkell as a result of a large number of crosses -that he has carried out. He states, for instance, that in the great -Merino class, with its various sub-breeds, there are flocks in which the -males only are horned, but even here there may be individual males that -are hornless “and at times the females may also show some signs of horn -growth.” In America, Arkell states, there are three types of -Merinos—the American, the Delaine, and the Rambouillet. He quotes Plumb -(Types and Breeds of Farm Animals, Boston, 1906) as stating that “the -American Merino ram carries heavy, spirally twisted horns, but the ewes -are hornless; ... that the rams of the National Standard or Victor-Beald -Delaines may or may not have horns; that the Dickinson Delaines may have -small horns, but a polled head is preferred,” etc. These conditions -suggest that there may be more than a single factor for horns in sheep -or that there may be modifying factors in certain breeds. In fact, -Arkell and Davenport attempt to cover the results of Arkell’s -experiments by assuming that there is an inhibiting factor for horns -that is carried by the sex chromosome. Such an inhibitor (I) would be -double in the XX female and single in the X male. It is assumed to be -incapable of preventing the development of horns in the heterozygous Hh -male, the inhibitor being there simplex (<i>i.e.</i>, one I), while the -double inhibitor is capable of preventing the horns in the heterozygous -(Hh) condition, but not of preventing the development of horns when the -homozygous (HH) condition occurs. There are several objections to this -scheme: first, that there is no evidence that a <i>sex-linked</i> inhibitor -is present that affects the hornless breeds, for the evidence indicates -rather that there is no factor for horns present in them, at least in -the Suffolks; second, the peculiar balance between the factors for horns -and the inhibitor seems an extremely artificial statement. Arkell and -Davenport intimate that races with horned males and hornless females do -not exist in a pure state. That breeds impure in these respects may -exist need not be denied, but that pure races for such a dimorphic -condition do exist seems probable. Castle states, for instance, that he -knows at first hand of such races of Merinos. Castle also states that -castrated Merino rams in this race do not develop horns, and this result -is in accordance with statements made by Marshall for Herdwicks (a race -with horned males and hornless females). Under the circumstances it is -certain that the presence of the testes is one of the factors in -determining whether horns develop at all (as in Merinos), or in -determining the extent to which they develop (as in the Dorsets), rather -than that the difference between the sexes is due only to an inhibiting -genetic factor. Nevertheless, it may be well to keep open the -possibility that there may be different factors for horns in different -races (allelomorphs or others), or conversely, that the genetic -composition of the races is different, the factor for horns remaining -the same, but producing a different effect.<span class="pagenum"><a name="page_67" id="page_67">{67}</a></span></p> - -<p>It may be pointed out in passing that if, as Arkell assumes, the -hornless races are due to the presence in them of an inhibitor for -horns, the results can be worked out without postulating that the -inhibitor is sex-linked. For example, if the hornless male and female be -HHII and the horned male and female HHii, the F₁ horned males and -hornless females will be HHIi. The germ-cells will be HI and Hi in each -sex, which, by chance meeting, as shown below, gives the results -obtained by Wood. Thus:</p> - -<table border="0" cellpadding="2" cellspacing="0" summary="" - class="sml"> -<tr><td>HI </td><td rowspan="2" class="c"><big>×</big></td><td> Hi.....female.</td></tr> -<tr><td>HI </td><td>Hi.....male.</td></tr> -<tr class="c"><td colspan="3" class="bt">1HIHI+2, HIHi+1, HiHi.</td></tr> - -</table> - -<p>These formulæ give 3 horned males, 1 hornless male, 1 horned female, 3 -hornless females. This formulation, while appealing apparently to a -different set of factors from those used by Arkell, is in reality the -same in principle, since the heterozygous condition is here represented -by Ii (instead of Hh) and sex determines that the heterozygous male is -horned and the female hornless.</p> - -<p>The genetic relations of the Merino with horned males and hornless -females to the Dorsets, in which both sexes are horned (but in the male -the horns are larger), must be different from the genetic relation in -the other cross. There are two theoretical possibilities, viz., that a -different factor for horns is present that is either an allelomorph or -another different factor; or second, that a modifier is present in the -Merino that keeps down the development of the horns in the female. An -answer could be obtained by breeding Merinos to horned and to hornless -and getting F₂ from both crosses. Arkell’s data is not sufficient to -settle the question, because his numbers are often too small, but -chiefly because it appears that there were two genetic types present in -his flock of Merinos, one of which is characterized by scurs (very short -horns) in the females, the other by hornlessness in the female. He found -in a cross between a hornless father and Merino mother (that had knobs -or scab-like growths) that the daughters had horns or scurs and carried -a determiner for horns (as subsequent generations showed). On the other -hand, in other cases where the Merino mother was without horns, her F₁ -daughters had no horns. In both cases the F₁ sons had horns. Arkell -cites this cross as “proving” that the knobs of Merino ewes depend for -their development upon two horn determiners (H´H´). It is not at all -evident that the results lead to such a conclusion, as other -explanations will cover the case as well.</p> - -<p>Arkell’s mating between Dorsets and Merinos (tables <small>IX</small> and <small>XVI</small>) -corroborates his view “that the knob of the Merino female is represented -in the germ-plasm by the double determiner.” The 5 F₁ sons had long -horns, 3 F₁ daughters had horns present, and 2 had them absent (table -<small>XVI</small>). If some of the Merino mothers used were homozygous for a factor -that inhibits the development of horns in the female<span class="pagenum"><a name="page_68" id="page_68">{68}</a></span> we can account for -the hornless daughters, and if other mothers did not have this factor -(or were heterozygous for it) we can account for the horned daughters. -Evidently more evidence is needed. Arkell himself assigns a -corresponding difference to the mothers in these cases, based on the -observed fact that the mother that had knobs or scurs were the ones that -gave birth to the horned daughters. If the above suggestion proves true, -it shows that the Merino condition dominates the Dorset condition. The -result is in harmony with the view that both have a common factor for -horns, but that in addition the Merinos have a non-sex-linked modifier -that holds down the development of the horns in the ewe.</p> - -<p>What bearing have these results on the theory of sexual selection? -Clearly the Merino male, as constituted at present, develops horns -because he is a male, but only in the sense that his testes secrete some -substance that makes his horns grow. That maleness does not in itself -necessarily produce horn is shown by the absence of horns in the Suffolk -breed. Is it the same factor, present in the Merino, that produces horns -in both sexes of Dorsets when homozygous and in the male only when -heterozygous? If originally the ancestral race had no horns, the -appearance of factors for horns would, even in a heterozygous condition, -have sufficed in the males for the development of horns. If this gave -them any advantage either over the enemies of the race or in the eyes of -the female, such factors might be perpetuated, and through transferrence -to the females ultimately become homozygous in both sexes. Both would -then have horns, whether horns were or were not of any advantage to the -female, which would have them because they have an advantage to the -other sex.</p> - -<p>Because the genetic evidence shows that a single factor difference -between the breeds with and without horns accounts for the horned -condition in one of them, it by no means follows that horns as they -exist arose as a single mutant factor change. True, they may have arisen -as a new single factor difference, but the Mendelian evidence can not be -claimed as evidence for this view. The <i>a priori</i> argument based on the -relation of horns in an adaptive sense to the rest of the body would -appear rather to indicate that they could not have arisen at a single -mutational step.</p> - -<p>Concerning the still broader bearing of this evidence on the theory of -sexual selection, two distinct questions are involved: first, how has -the present racial difference in horns arisen in domesticated sheep, and -secondly, what was the original condition of sheep. Reversing the order -of these questions, we find that sheep were domesticated in Asia and -Europe before the dawn of history. “Whether our well-known and useful -animal is derived from any one of the existing wild species, or from the -crossing of several, or from some now extinct species, is quite a matter -of conjecture” (Flower and Lydekker’s “Mammals”).<span class="pagenum"><a name="page_69" id="page_69">{69}</a></span> Most of the wild -species of the genus (of which about 12 are recognized) have horns in -both sexes, but larger in the male. There are 3 wild species in which -the horns are lacking in the female, according to Flower and Lydekker. -If these have been crossed into the domesticated breeds the condition -shown by the Merino may go back to the wild state. The third condition -found in domesticated races, viz, hornlessness, may have appeared under -domestication. Such a change might have arisen in either of the two -other types and would be comparable to well-known losses of characters -shown by domesticated animals and plants. These losses of characters are -usually ascribed to actual losses of genes; any lost gene in the complex -of factors necessary for the production of horns might cause such a -change. But there is no advantage, in fact, in ascribing the <i>loss</i> in -the character to a <i>loss</i> in one of the factors producing that -character, for any change of any kind in the factor complex might bring -about the same result and the evidence from multiple allelomorphs should -put us on our guard against the all too easy assumption that a loss in a -character involves necessarily loss of a factor in the real sense in -which loss is used in ordinary speech.</p> - -<p>The operative and genetic evidence for sheep shows that if the horns in -the male were developed through natural or sexual selection we should -expect them to develop also in the female. The greater development in -the male seems to be due to secretions from the testes which probably -are due to special factors that call them forth, but whether such -factors were also acquired to reinforce the effects being produced -through selection or were already present (reinforcement for horns being -only a by-product of their activity) can not of course be known. We can -suppose that special factors that suppress the development of horns in -the female may have arisen in the wild or in the domesticated races and -have been perpetuated because of some imagined benefit conferred; or -that in certain races factors were already present that kept down the -development of horns in the female. In any case such factors do not -cause their effects through secretions from the ovary, because after -ovariotomy horns do not develop; nor are they sex-linked factors. Any -speculation as to how natural or sexual selection has brought about the -evolution of the horns in sheep must reckon with the conditions imposed -on such speculation by the preceding information. So far as I can see, -it leaves the situation in this respect neither better nor worse off -than before.</p> - -<p>In deer the effects of castration are well known, but there is no -genetic evidence to show the kind of factors involved, since no crosses -have been made between species with differences in their horns. If the -young male deer is castrated before the antlers have appeared, no horns -develop. If castrated at the time when the antlers have begun to -develop, incomplete or imperfect development follows. The antlers<span class="pagenum"><a name="page_70" id="page_70">{70}</a></span> -remain covered with the velvet, and are said not to be thrown off -periodically as in the normal male. If the adult stag with antlers is -castrated, the horns are precociously dropped, and, if replaced at all, -the new antlers are imperfect and are not renewed. I do not know of any -cases in which females have been spayed, but no doubt the ovaries must -sometimes become diseased. There are, however, a few records of horns -developing in this sex in old age, or presumably after disease of the -ovaries. Both male and female reindeer are horned. Castration produces -no effect on the development of the horns.</p> - -<p>In the case of deer it is evident that the presence of the testes in the -male causes the horns to develop. The genetic factor, or factors, for -horns may be supposed to be carried by both sexes, but the effects of -the factor can be seen only when the testes are present. In the reindeer -and eland, on the other hand, the genetic factor for sex can produce -horns without the need of the environment produced by the testes.<a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15" class="fnanchor">[15]</a> -Whether we are dealing here with the same factor or whether the rest of -the hereditary complex makes the result different can not be known -without breeding experiments.</p> - -<p>There is apparently a connection between the stage of development of the -horns and the age of the animal, as the following statement by -Yarrell<a name="FNanchor_16_16" id="FNanchor_16_16"></a><a href="#Footnote_16_16" class="fnanchor">[16]</a> (1858) indicates:</p> - -<div class="blockquot"><p>“The fallow-buck is at his best in his sixth, or at most in his -seventh year; after which, though the carcass may increase, the -horns become smaller, and irregularly going back annually through -something like their former stages of increase, a very old buck has -from the state of his horns been mistaken for a young one. In the -osteological department of the Museum at Paris there was, and may -be now, the skeleton of a female reindeer in which the horns were -reduced to little more than a rudiment of the beam and the -brow-antler; this animal was so old that the molar teeth were worn -down to the edges of the alveolar cavities.”</p></div> - -<p>At first sight these results in the fallow deer appear to be only an age -condition, but since in old age a reverse process sets in, it may appear -more probable that the amount of secretion by the testes or other glands -may be the conditioning agent. In the case of the reindeer one may -hesitate to ascribe the change to the ovary without further evidence.</p> - -<p>In cattle the effects of castration as seen in oxen have been studied. -There is little here that is useful for our present purpose. The horns -are not inhibited and may even be larger than in the bull. The absence -of horns in certain races of cattle is apparently a dominant character, -but as the character is neither sex-limited nor sex-linked, the evidence -has no further bearing on the present topic.<span class="pagenum"><a name="page_71" id="page_71">{71}</a></span></p> - -<p>The effect of removal of the ovary from female calves has been studied -by Tandler and Keller. The height of the ovariotomized female is less -than that of the cow. The same difference is found between bull and ox. -Tandler and Keller call attention to the similarity of the head in male -and female lacking the gonads. They conclude that the ovariotomized -female does not come to resemble the male, but that removal of the gonad -causes both sexes to converge to a common type.</p> - -<p>Castration is frequently performed in horses, dogs, and cats, but as the -secondary sexual differences, aside from size and behavior, are not very -well marked in these animals, the results need not be here considered.</p> - -<p>Steinach’s experiments with rats are important, because by grafting -ovarian tissue into the castrated male, the male was caused to assume -certain characteristics peculiar to the female. The mammary glands that -are rudimentary in the male became much enlarged—not only the glandular -tissue increased in amount, but the mammæ themselves were greatly -developed. The hair of the male is coarser than that of the female. In -the feminized male the hair was soft like that of the female. The size -was smaller than that of the male. The skeleton also was affected, and -Steinach thinks that it changed in the direction of a female skeleton. -Even more striking was the sexual behavior of the feminized rat. The -individual no longer reacted as male, but showed some of the reflexes -peculiar to the female. These results, that stand almost alone, appear -to show that several of the secondary sexual characters of the female -rat are due directly to the presence of the ovary.</p> - -<p>One of the most striking and definite results shown by castrated rats -(Steinach), guinea-pigs (Pirsche, Steinach), rabbits (Pauncet), hedgehog -(Marshall), and man is to be seen in the effect on the accessory glands -connected with the male ducts as well as on the penis. These remain -small and infantile. Some substances produced by the testes are -essential for the development of these parts. Natural selection rather -than sexual selection would be the agency that here comes into play.</p> - -<p>In man the effects of castration have been often described. Eunuchs have -had a commercial value in some countries, as in Turkey and China, and -castration has been deliberately practiced on young children. Certain -religious sects, such as the Skops of Russia, have advocated and carried -out the operation. Disease has also at times necessitated the removal of -the testis, more often in adults than in the young. The full effects are -shown only when the operation has been carried out before the secondary -sexual characters have developed. The more striking difference between -the sexes involve the beard, and the hair on other parts of the body, -the voice, the shape of the pelvis, and the mammary glands. For a -detailed account of the results, the publications of Tandler and Grosz -and Marshall’s book on the “Physiology of Reproduction” should be -consulted.<span class="pagenum"><a name="page_72" id="page_72">{72}</a></span></p> - -<p>The two most obvious changes in the eunuch are the absence of the beard -and mustache and the small larynx, which produces a high-pitched voice. -In both these respects man differs from woman; in both, however, the -eunuch is like the boy as much as he is like the woman. It is not -evident, therefore, whether the eunuch has retained the juvenile -condition or has become more like the female. Moreover, there is the -possibility that there is no difference in the present case between -these two conditions. The distribution of hair on the pubis of the -eunuch is often said to be more like that in the woman than that in the -man, but there is apparently no sufficient evidence to show that this is -more than the juvenile condition or an undeveloped condition of the -male. As to the voice, there is no way of determining whether the voice -of the eunuch is feminine or juvenile. The development of the mammæ in -the eunuch would be a better test, but it does not appear from the -literature on the subject that the mammary glands and the nipples of the -eunuch are changed toward the female type. On the contrary, it appears -rather that there is no such change. It is true that the tendency toward -the accumulation of fat may give the eunuch a somewhat feminine -appearance (since one of the foci of fat accumulation is in the region -of the breasts), but this in itself can scarcely be claimed to be -feminization, but due rather to the more slothful habit of the eunuch -that tends to obesity.</p> - -<p>A more suggestive resemblance is found in the narrowness of the shoulder -girdle and broadness of the hips in the eunuch, but even these -resemblances to the female should be regarded skeptically, since other -changes in the bones that result from castration are certainly not a -development toward the female type, but a peculiar specific effect of -the absence of testes on the growth of the bones. For instance, the -bones of the arms and legs are much longer in the eunuch than in either -the normal man or woman, in fact, more in the direction of the male, who -has longer legs than the female. The explanation usually given is that -the ossification at the ends of the bones and of the epiphyses does not -take place so soon as in normal men and women. The condition here is -that characteristic of the juvenile state that is carried over into the -adult, but whether the narrowness of the chest and shoulder girdle of -the eunuch is correlated in some way with the more prolonged growth of -the other bones has not, so far as I know, been determined. That there -is no <i>apparent</i> connection between the shortness of the one and the -greater length of the other does not necessarily lead to the conclusion -that there is no such connection. For the present I think we must hold -this point in reserve.</p> - -<p>Steinach’s evidence for the feminized rats, if it may be extended to -man, indicates that some of the female characteristics are due to the -presence of the ovary holding in check the genetic possibilities of the -female, as well as leading to the development of such characteristic<span class="pagenum"><a name="page_73" id="page_73">{73}</a></span> -traits as the mammæ, etc. In the case of the pelvis the female departs -from the juvenile type of both sexes, and here one might look for a -better criterion. It is stated that the pelvis of the ox is more like -that of the female than it is like that of the male, and it has been -said that this is true for the castrated rat and guinea-pig, but whether -a simple enlargement of the juvenile pelvis would make it resemble the -female type more than that of the male has not, so far as I know, been -carefully examined. Should it prove here that this is the case, the -evidence on this point would be no stronger than that for other -character differences. As has been stated, Tandler and Grosz think that -the changes in the skeleton of the ox, as well as those in the castrated -cow (skull, pelvis, and limb bones), are due directly to loss of the -gonads and are much the same in both. But their resemblance may possibly -be due more to an enlarged juvenile condition rather than that either of -them changes toward the normal skeleton of the other sex.</p> - -<p>The statements that have been published concerning the effects of -removal of the ovaries in woman are, on the whole, unsatisfactory and -often contradictory. That the uterus and oviducts become smaller is -expected from what is known to occur in other mammals, and is definitely -recorded in the human female. That the breasts become smaller is stated -to be the case, but whether because of an actual decrease in the -glandular portion has not, so far as I know, been shown. That hair is -likely to develop on the upper lip of woman without ovaries is also -claimed as likely to occur, and this, too, is sometimes seen in old -women, but if it is interpreted to mean an approach to the bearded -condition of man it should be admitted that the development is hardly -sufficient to invite such a comparison. Finally, it has been stated that -the voice becomes deeper, more, therefore, like the male, but this has -also been denied. If it could be established that the voice changes and -that it was brought about by an enlargement of the larynx, similar to -that which takes place when the larynx of the boy changes to that of the -man, it might seem not improbable that the change was toward that of the -opposite sex. This would mean that the ovary produces some substance -that prevents the enlargement of the larynx in the female. But since it -has been shown that the enlargement in the male is caused by the -development of the testes, and that this enlargement is prevented by -castration, a paradoxical situation would present itself, viz, that the -testes cause the larynx to enlarge in the male and the ovary prevents -the enlargement in the female. Until convincing evidence is forthcoming, -the question is better left undecided.</p> - -<h4>B. <span class="smcap">Evidence from Birds.</span></h4> - -<p>Probably a greater difference in the secondary sexual characters is -shown in birds than in any other group. It is true that there are<span class="pagenum"><a name="page_74" id="page_74">{74}</a></span> -species, such as the doves and pigeons, in which the plumage of the male -is much like that of the female, but this is the exception rather than -the rule. At the other extreme are species like birds of paradise, -hummingbirds, fowls, pheasants, ducks, and many passerines, in which the -plumage of the two sexes is entirely different. Our knowledge as to the -relation between the nuptial plumage of the male and the condition of -the sex-organs rests largely on information gained by castration in -poultry and ducks and on the assumption of the nuptial plumage in -several species only at the mating season.</p> - -<p>John Hunter in 1780 described a pheasant with male plumage. His account -of a similar change in a pea fowl is so complete that I venture to quote -it in full:</p> - -<div class="blockquot"><p>“Lady Tynte had a favorite pyed pea-hen, which had produced -chickens eight several times; having moulted when she was about -eleven years old, she astonished the lady and her family by showing -the feathers peculiar to the other sex, and appearing like a pyed -peacock. In this process the tail, which was similar to that of a -cock, first appeared after moulting. In the following year she -moulted again, and produced the same feathers. In the third year -she did the same; at the same time she had spurs similar to those -of a cock. She died in the following winter during the hard frost, -namely, in the winter 1775-6. She never bred after this change in -her plumage. This bird is now preserved in the Museum of Sir Ashton -Lever.”<a name="FNanchor_17_17" id="FNanchor_17_17"></a><a href="#Footnote_17_17" class="fnanchor">[17]</a></p> - -<p>“From what has been related of these two birds, may it not -reasonably be inferred that it seems probable that all those wild -pheasants of the female sex, which are found with the feathers of -the cock, had changed the nature of their feathers, particularly at -a certain age?</p> - -<p>“If this idea be just, it shews that there is a disposition in the -female to come nearer and nearer to the male, at least in the -secondary properties; or it may rather be said that the female is -later in producing this change than the male is; for it has already -been observed that both sexes when young differ not from each other -in these respects, but that the male appears to be the one that by -degrees separates from the female in its secondary properties.”</p></div> - -<p>Statements in regard to the effect of castration on poultry go back, it -appears, to Aristotle. Yarrel in 1811 and again in 1850 has given an -excellent account of many of the effects produced. His account of the -effects on the cock seem to be based partly on hearsay, and while they -contain much accurate information, yet the statement that the plumage of -the capon is intermediate between that of the cock and hen is incorrect. -The further statement that by cutting the oviduct the hen assumes the -plumage of the capon has been shown by Sellheim to be erroneous. The -operation referred to by Yarrel must have been one in which the ovary -was removed.<span class="pagenum"><a name="page_75" id="page_75">{75}</a></span></p> - -<p>Yarrel described a female pheasant that had assumed some of the -characteristic colors of the male. On dissection he found that the ovary -was diseased as well as the oviduct. He correctly assigns the change in -plumage to the condition of the ovary. He states furthermore that most -of the female pheasants that he had examined that had male plumage had -not assumed the complete coloration of the male. In one case, however, a -complete change had taken place. The change in pheasants he thought was -due to old age accompanied by partial or complete loss of function of -the ovary. For poultry he states:</p> - -<div class="blockquot"><p>“In the imperfect female the comb increases; a short spur or spurs -appear; the plumage undergoes an alteration, getting what is -usually called ‘foul-feathered;’ she ceases to produce any eggs, -and makes an imperfect attempt to imitate the crow of the cock. -Being profitless in this state, she is usually made away with. The -proverb says:</p> - -<div class="poetry"> -<div class="poem"><div class="stanza"> -<span class="i0">A whistling woman and a crowing hen<br /></span> -<span class="i0">Are neither good for gods nor men.<br /></span> -</div></div> -</div> - -<p class="nind">Our neighbors and allies the French, who seem to take a wider range -in their prejudice against habits which they consider irregular, -have the following proverb, which says:</p> - -<div class="poetry"> -<div class="poem"><div class="stanza"> -<span class="i0">Poule qui chante, Prêtre qui danse<br /></span> -<span class="i2">Et Femme qui parle latin,<br /></span> -<span class="i2">N’arrivent jamais à belle fin.<br /></span> -</div></div> -</div> - -<p>“I have seen two instances in which females of the wild duck have -assumed to a considerable extent the appearance of the plumage of -the mallard, even to the curled feathers of the tail. One of these -birds, in my own collection, was given me when alive by my kind -friend the late John Morgan, esq. When this bird was examined after -death, the sexual organs were found to be diseased, as in the case -of the hen pheasants referred to, and figured in the 2d volume of -the History of our British Birds. In the published illustrations to -his Fauna of Scandinavia, M. Nilsson has given a colored figure of -a duck in this state of plumage (plate 163), which is called a -barren female, and in which the curled tail-feathers are made very -conspicuous.</p> - -<p>“From the general similarity in these females to the appearance -assumed for a time by healthy males in July, I am disposed to refer -this seasonal change in males, in this and in other species of -ducks, to a temporary exhausted state of the male generative -organs, and their consequent diminished constitutional influence on -the plumage.</p> - -<p>“A male shut up by himself from early spring to the end of July -undergoes no change in his plumage; but if he is allowed to -associate with females till their season of incubation commences, -he then goes through the change, and this appears to indicate the -cause of the partial summer moulting.</p> - -<p>“The appearance is somewhat different, but yet very interesting in -insects and crustacea. In these classes the sexual organs are -double and distinct, arranged one on each side of the elongated -mesial line. It sometimes happens, that a species in which the -sexes are of a different color, or markings, or form has one sexual -organ of each sort, male and female, in which case each half of the -same insect is developed under the exclusive influence of the -sexual organ on its own side. Instances are preserved among our -collections of butterflies, mothes and beetles; and I have seen it -twice in the common lobster.<span class="pagenum"><a name="page_76" id="page_76">{76}</a></span></p> - -<p>“Nor is the human race exempt from the operation of the law which -prevails in the Mammalia. In women, at an advanced age, hair -appears on the chin and upper lip, and the voice alters, becoming -deep in its tone. The beard in old men becomes thin and soft, and -our own inimitable Shakespeare has told us,</p> - -<div class="poetry"> -<div class="poem"><div class="stanza"> -<span class="i6">* * * his big manly voice<br /></span> -<span class="i0">Turning again toward childish treble, pipes<br /></span> -<span class="i0">And whistles in his sound.”<br /></span> -</div></div> -</div> -</div> - -<p>Gurney (1888) has recorded several cases in which female birds have -assumed male plumage. For instance, he describes a female merganser, -<i>Mergus serrator</i>, assuming male plumage that showed no signs of disease -in the ovary. Mr. Cecil Smith had a female widgeon (<i>Mareca penelope</i>) -on his ponds near Trenton, which assumed the male plumage some years -ago, and which, so far as he knew, had not had young nor laid eggs.</p> - -<div class="blockquot"><p>“On May 16th, 1887, a chaffinch (<i>Fringilla cœelebs</i>) in full male -plumage was shot at Chapel Town, near Leeds, in Yorkshire, by the -son of Mr. W. L. Jackson, M. P.; it was skinned by G. R. Grassham, -assistant to Mr. W. E. Clarke at the Museum, who, much to his -surprise, found that it was a female, and contained an egg, ready -for laying, of a pale blue, without markings, and another egg in a -less forward state. This chaffinch is in every way in perfect male -plumage, and I am indebted to Mr. Clarke for his kindness in -sending these particulars with the specimen, which he received from -Grassham a few hours after the latter had dissected the bird.</p> - -<p>“In the ‘Norwich Nat. Trans.,’ an enumeration was given of female -Redstarts (<i>Ruticilla phoenicurus</i>) assuming male plumage (<i>l.c.</i>) -to which the following may be added: a hen <i>R. phoenicurus</i> -assuming male plumage, and very like Mr. Millais’ described in the -‘Norwich Nat. Trans.’ iv., p. 182, was caught by Mr. W. E. Clarke -sitting upon her eggs, at Wike, near Leeds, in June, 1886; at the -same time Mr. Clarke saw the cock close by, which appeared to be in -the ordinary male plumage. The late Mr. Henry Doubleday’s -collection contained a hen Redstart (<i>R. phoenicurus</i>) in male -plumage, which had the ovaries ‘quite perfect and full of eggs’ -(<i>cf.</i> B. of Norf., i, p. 370, note), probably one of those alluded -to by Yarrell (Brit. B. 1st ed. i, p. 240) in the remarks made by -him on the plumage of this species. I have some recollection of -this Redstart at the dispersal of Mr. Doubleday’s collection, but -do not know who was the purchaser of it. There can be no doubt that -more would soon turn up if looked for; and now that attention has -been drawn to the subject, and the practice of dissection is -getting more general among bird stuffers, it is certain to be the -case, not only in <i>Ruticilla</i>, but in other genera besides. Why it -should happen in <i>Ruticilla phoenicurus</i> oftener than in other -Passerine birds is hard to explain, but such is evidently the -case.”</p> - -<p>“The same is recorded to have happened five or six times with the -female Red-backed Shrike (<i>Lanius colluria</i>); see ‘the Field,’ June -17, 1871, and April 25, 1885; Mag. N. H., iv, p. 344; ‘B. of -Suffolk,’ p. 45; ‘Ibis,’ 1863, p. 292; but the number of hen -Redstarts which have donned masculine attire is greater.</p> - -<p>“The following is a list of the species in which one or more -instances of females assuming male plumage are ascertained to have -occurred:</p> - -<ul> -<li>Falco aesalon, fide Scully. (Cf. Sharpe, ‘Cat. Birds Brit. Mus.,’ i, p. 407).</li> -<li>Tinnunculus alaudarius, fide Sharpe; col. fig. P. Z. S., 1874, p. 580.</li> -<li>Lanius collurio, fide Hoy.</li> -<li>Lanius vittatus, fide Blyth.</li> -<li><span class="pagenum"><a name="page_77" id="page_77">{77}</a></span>Ruticilla phœnicurus, fide Millais, Clarke and others.</li> -<li>Fringilla cœlebs, fide Clarke.</li> -<li>Linota cannabina, fide Blyth.</li> -<li>Linota rufescens, fide Blyth.</li> -<li>Nectarinia asiatica, fide Blyth.</li> -<li>Gallus (domestic fowl), fide Yarrell and others; col. fig. “B. of Sherwood,” p. 183.</li> -<li>Pavo (peahen), fide Latham; fig. “Synopsis,” ii, pl. 60.</li> -<li>Meleagris (Turkey), fide Bechstein.</li> -<li>Phasianus colchicus, fide Edwards and others. Of common occurrence in a semi-domesticated state.</li> -<li>Thaumalea picta, fide Edwards.</li> -<li>Euplocamus nycthemerus, fide Yarrell.</li> -<li>Pucrasia nipalensis, fide Blyth.</li> -<li>Tetrao tetrix, fide Bond; col. fig. Dresser, “B. of Eur.,” vi, 205.</li> -<li>Tetrao urogallus, fide Nilsson; col. fig. “Unser Auer-, Rackel- und Birkwild und seine Abarten,” by A. B. Meyer.</li> -<li>Otis tarda, fide Tiedmann.</li> -<li>Anas (domestic duck), fide Rowley; col. fig. “Orn. Misc.,” i, p. 118.</li> -<li>Anas boschas, fide Hancock; fig. col. “Scandinavisk Fauna,” pl. 163.</li> -<li>Fuligula marila, fide Blyth; see also P. Z. S., 1885, p. 246.</li> -<li>Mergus serrator, fide Gurney.</li> -<li>Mareca penelope, fide Cecil Smith.</li> -</ul> - -<p>“Perhaps the Kestrel (<i>Tinnunculus alaudarius</i>) ought not to be -included in this catalogue, for so many have been seen with the -lower part of the back blue or bluish, as to leave little doubt -that the female generally becomes so if she lives long enough.</p> - -<p>“It is said that the females in <i>Oriolus</i> generally become as -bright as males in time (‘Ibis,’ 1864, p. 412; ‘Field,’ June 24th -and July 8th, 1871).”</p> - -<p>“P. S.—Mr. W. Tegetmeier tells me he has known a barnyard cock -moult into hen’s plumage, which is the converse of the instances -narrated in this paper, and rather resembles the annual change -which takes place in <i>Anas boschas</i> and others of that tribe.”</p></div> - -<p>In a later notice Gurney makes the following statement:</p> - -<div class="blockquot"><p>“The bearded tit (<i>Panurus biarmicus</i>) may be added to the list of -female birds which are known to occasionally assume male plumage. -In the summer of 1882 a bearded tit, two years old, in Mr. J. G. -Keulemans’ aviary, hatched five eggs and moulted, during which -operation she suffered much from cold and stiffness, and when she -recovered her plumage it was partly that of the male (<i>cf.</i> ‘The -Field,’ Sept. 14, 1872).”</p></div> - -<p>Brandt, who has reviewed the literature very thoroughly, cites the -following cases:</p> - -<div class="blockquot"><p>“Galeinacei: Gallus bankiva domest., Phasianus pictus, torquatus, -colchicus, mongolicus and nycthemerus, Pavo cristatus domest., -Meleagris gallopave domest., Perdix einerea, Tetrao urogallus, -tetrix und bonasia.</p> - -<p>“Passeres: Fringilla coelebs, Pyrrhula vulgaris, coccinea, Loxia -chloris, Turdus merula, Ruticilla phoenicurus, ochrura, -chrysogastra, Cyanecula Wolfii, Sturnus vulgaris, Ampelis cotinga.</p> - -<p>“Scansores: Cuculus canorus, Edolius glandarius.</p> - -<p>“Grallatores: Machetes pugnax.</p> - -<p>“Natatores: Anas boschas domest.</p> - -<p>“Es ware denkbar, dass die Hahnenfedrigkeit, wenn auch in -verkapptem Grade, allen Vögeln, selbst denjenigen zukomme, deren -Gefieder uns geschlechtlich uniform zu sein scheint. Wie dem auch -sei, einzelne Genera und Species scheinen mehr, andere weniger zur -Arrhenoidie prädisponirt. So<span class="pagenum"><a name="page_78" id="page_78">{78}</a></span> bemerkt J. Geoffrey St. Hilaire (p. -511), dass Fasanen häufiger selbst als die Hühner hahnenfedrig -werden, während für den Pfau, den man doch stets eines natürlichen -Todes sterben lässt, ihm nur ein einziger Fall (der von Hunter) -bekannt geworden. Während Lorenz (vide Tichomirow) auf dem Moskauer -Markt häufiger hahnenfedrige Weibchen von Phasianus colchicus and -mongolicus aufgefunden, ist ihm dieses fur Ph. chrysomelas bisher -kein einziges Mal gelungen, obgleich die Zahl der jährlich in -Moskau feilgebotenen Exemplare dieser Art sich auf 8000 Stück -belaufen möchte.”</p></div> - -<p>The preceding cases relate to exceptional changes in the plumage as -observed in nature, or in birds kept under domestication. We may next -examine the cases where the ovary or the testis has been removed.</p> - -<p>The earlier observations of Berthold, Wagner, Hanau, Samuel, Sellheim, -Pirsche, Foges, Shattock, and Seligman are sufficiently covered by later -work quoted below. Sellheim’s work, however, is especially to be noted, -since he gives some measurements covering the weight of the brain, -heart, and body of the cock and capon, as well as observations on the -skull and skeleton. The weight of the brain is slightly less in the -capon, but the body-weight is greater. He questions whether the ovary -has ever been successfully removed, and he shows that the operation of -resecting the oviduct does not, as was supposed, lead to the -degeneration of the ovary. On the contrary, he found that after the -effects of the operation had been removed the ovary began again its -functions.</p> - -<p>From Goodale’s careful summing up of the effects of castration only the -following points need be recalled: The feathers are little changed; some -of them, the hackles especially, become longer. The lowermost tier of -wing coverts are elongated as compared with those of the cock. The spurs -are practically the same in the capon and cock. The capon is disinclined -to give voice, but at times he crows. The molting is not affected. The -size of the capon is larger. He pays little attention to the hens. He is -not pugnacious, and if attacked will not often fight. As a rule he does -not pursue the hens, but if a hen squats down as the capon approaches he -will mount and go through the characteristic mating reaction. The comb -is extremely small, much smaller than that of the female of the same -race; it is infantile rather than feminine.</p> - -<p>Comparing these results with those that I have observed in the castrated -Sebright, we find that aside from the assumption of the full plumage of -the cock-feathered bird the Sebright shows all of the characteristic -features of the capon. The spurs develop, perhaps even more fully than -in the normal Sebright cock. He seldom crows, and then weakly. The birds -appear large, but the excessive development of the feathers produces the -effect. I have not weighed them to show whether an actual increase in -size takes place. Two of my birds are notably large for Sebrights, but -the others are smaller. Both large and small cocks occur in the strain -that I have used. My Sebright and other capons neglect the hens, but I -have seen them tread the hens<span class="pagenum"><a name="page_79" id="page_79">{79}</a></span> on occasion. They will fight each other, -if two strangers meet, but the attacks are not violent or prolonged. A -normal male beats them easily, and afterwards they run away from such -birds. The combs and wattles are very small and pale. If a piece of the -testis is left in, the comb is a fair index of its size. In the birds -that changed back toward a Sebright the comb slowly enlarged. After the -second operation it decreased again as the plumage once more changed to -that of the cock.</p> - -<p>Goodale’s results with ovariotomized females are especially noteworthy, -since here for the first time we have definite information as to the -effects of the operation. By using a well-established breed, the brown -Leghorn, in which the dimorphism of the sexes is very striking, the -results are made all the more convincing. Goodale found that it was -possible to completely remove the ovary of young birds, for at an early -age the ovary is sufficiently compact to make its entire removal -possible. Later the ovary becomes more diffuse, and complete removal is -almost impossible. In a few successful cases, in which the ovary had -been completely removed, the bird assumed the full plumage of the -Leghorn cock, with red back, black breast, and long, pointed hackle and -saddle feathers. Spurs developed in all the operated females, even when -the ovary was not entirely removed. There can be little doubt that the -ovary holds back the development of the spurs, but as some hens -sometimes develop spurs, especially in certain breeds, it is not -entirely certain that in these cases the loss of the ovary is the cause -of the appearance. The comb (and wattles) developed to different -degrees; in some birds it was as large as in the cocks, in others no -larger than in the normal hen, but in all cases it was larger than in -the capon. What to conclude is doubtful. Tentatively it may be suggested -that the genetic complex that gives the female (ZW) produces a comb as -large as that shown by the female independently of the ovary, but beyond -this point the ovary inhibits the further development of the comb, -presumably by means of the same internal secretion that holds down the -cock plumage in the hen. In the male, on the other hand, the genetic -complex (ZZ) produces a comb much smaller than that of the female (no -more than that of the capon), and the testes produce a substance that -causes this comb to grow to the size of that of the cock. Possibly, -however, other internal secretions are involved.</p> - -<p>The operated hens are quiet and nearly voiceless. None of Goodale’s -birds were heard to crow, yet this seems to be a well-known peculiarity -of old hens that have become cock-feathered. The operated hens are not -larger than the normal hens of the same breed. Their legs remain short, -as in the normal hen; and in this respect and in size the ovariotomized -bird is externally a female. The poullards “never visit the nests, never -sing or cackle, show none of the normal female reactions, and few or -none of the male.<span class="pagenum"><a name="page_80" id="page_80">{80}</a></span>”</p> - -<p>The influence of the ovary in suppressing the cock plumage has been -convincingly shown in an experiment of Goodale’s, in which, after -removal of both testes from the young Leghorn cock, pieces of ovaries -were inserted into the body-cavity. As dissection showed later, several -of these implanted pieces grew onto the wall of the body-cavity. The -birds developed the plumage of a hen, although some traces of the male -plumage were at times present. The difference between the sexes is so -great in Brown Leghorns that the hen-feathering of the feminized -cockerels leaves no doubt that the presence of the ovary had produced -the female coloration.</p> - -<p>Geoffrey Smith and Mrs. Haig Thomas (1913) have examined a number of -hybrid pheasants, some of which were sterile. They found that the ovary -(and oviduct) was often small and degenerate. There was a more or less -corresponding tendency for such female hybrids to show male feathering, -at least in a part of the plumage. The degeneration of the sex element, -however, does not take place until after the time of synapsis, so that -the younger germ-cells may be normal. The later degeneration of these -cells is not likely to influence the secondary sexual characters, but -may be an index of changes in other parts of the ovary.</p> - -<p>Geoffrey Smith had a breed of White Leghorns with cocks of two -classes—those that assumed cock plumage at 6 months, and those that are -like the hens for 8 months, after which they slowly assume the -cock-feathering. The difference is hereditary and appears to segregate. -Possibly this breed had one factor at least for hen-feathering that is -more effective for young birds than for older ones.</p> - -<p>Smith states that birds and crabs (see <i>infra</i>) appear to give opposite -results, since removal of the ovary in the former leads to development -of secondary male characters and removal of testes in the latter to -secondary female characters. But he adds that he thinks the results are -really the same, because in the crab it is not the suppression of the -testis but the feminization of the male by the Sacculina that causes the -change.</p> - -<p>There are a number of observations on ducks. Several cases have been -recorded where in old age the female assumed the male plumage (Darwin, -Shattock, and Sellheim). Also a few cases in which the testes were -removed. Those of Goodale are the most complete and striking. The male -duck has two characteristic plumages, one called the nuptial, also -called the summer or breeding plumage that is assumed at the molt in the -autumn, and the other the eclipse plumage, which is not identical with -but much like that of the female. Here, then, we find a new situation, -and one that invites comparison with the condition in Sebrights, in so -far as the male becomes hen-feathered at certain seasons.<span class="pagenum"><a name="page_81" id="page_81">{81}</a></span></p> - -<p>Throughout the greater part of the year the Rouen drake has the nuptial -plumage. The head is green and the breast is claret. Two median tail -feathers are strongly curved; the next two are also often curved. These -four are called the sex feathers. At the close of the breeding-season -(July) both sexes molt. The male now has the same coat as the female, or -nearly so. The green head becomes brown to buff; the sex feathers are -straight. The change back again to the nuptial plumage begins at the end -of summer and is completed early in October. Thus in the race of Rouens -the eclipse plumage lasts only a very short time. In the mallard it -lasts longer. The eclipse plumage develops, therefore, only when the -testes are active, or, as Goodale puts it, “the presence of the active -testis is necessary for the drake to assume this plumage.” Conversely, -the nuptial plumage comes on in the late summer, when mating is over, -and when the testes have shrunken and are not active, at least as far as -the sex-cells are concerned. In some respects the situation is like that -in the fowls, for in both the testes are not necessary for the -development of the full plumage, but in other respects the situation is -different, because at the time in the ducks when the testes are active -the eclipse plumage develops. Are we to suppose that at the time of -sexual activity a substance is produced analogous to that produced by -the ovary of the female? This seems the most plausible assumption, for -we know that if the testis is removed the eclipse plumage does not -appear. Such a situation suggests a comparison with the Sebright, where -it has been shown that the testis must actively produce some substance -which, like that in the ovary, keeps down cock-feathering. It is -plausible, even if it can not be established, that the substance in the -duck and the inhibitory substance in the male Sebright are the same as -that produced in the female.</p> - -<p>Goodale’s results with females (ducks) are not so clear cut, because the -ovariotomized females turned out to be of two sorts. One sort is almost -identical with the male, the other is more intermediate. There are -sufficient reasons for thinking, he says, that these differences are not -due to defective operations. Goodale suggests a genetic difference in -the females used, but this is apparently even to Goodale himself not a -very satisfactory solution. For our present purpose the important fact -is that the ovariotomized female may assume the perfect male plumage. -Evidently the ovary produces some substance which, as in the hen, -suppresses the potential plumage of the male. One such female known to -have had all the ovary removed never assumed the summer (eclipse) -plumage of the drake. On the other hand, another female developed first -the nuptial plumage, but this was replaced by the summer coat “of the -male of this variety.” Again, in the summers of 1914 and 1915 the change -to the eclipse plumage was followed in the autumn by a return to the -nuptial plumage.<span class="pagenum"><a name="page_82" id="page_82">{82}</a></span></p> - -<p>How can we explain the apparent discrepancy of Goodale’s results? In one -case, the nuptial plumage was molted to nuptial plumage; in the other -case an eclipse plumage appeared at the breeding-season. Goodale regards -the latter case as a more perfect approach to the male than the former, -but this view undoubtedly offers serious theoretical difficulties. It -seems to me possible to suppose that in those cases where the summer -plumage appeared there was in reality enough ovarian tissue (or related -tissue) left after the operation to produce an effect at the normal -season for such ovarian tissue to become most active. It might then -suffice to eclipse the male plumage sufficiently to make it very similar -to the eclipse of the normal male. At any rate, on this basis we have a -consistent explanation of the entire complex of phenomena.</p> - -<p>What bearing have these results relating to castration and -transplantation on the theory of sexual selection? Granting, of course, -that selection takes the materials as it finds them, there may still be -restrictions imposed on the theory by the kind of material offered. For -instance, the development of the plumage of the cock is independent of -the condition of his testes. Hence, if the female selected the more -vigorous male, she would not necessarily obtain one more ornate than his -less vigorous rivals. If the taste of the hen has built up the plumage -of the cock, it has been carried out then independently of the vigor -resulting from the greater activity of the testis. In a word, the more -vigorous male is not necessarily the most highly colored one. Darwin -concedes that these two conditions, high color and vigor, must go -together to insure success, or at least that the most vigorous and -therefore the most highly colored male will have more offspring. -Wallace’s contention that the greater vigor of the male accounts for his -greater development of plumage gets scant support from the facts of -castration. One might rather contend that the female must be more -vigorous, since she is obliged to suppress plumage that is allowed to -run riot in the male.</p> - -<p>Wallace’s argument in favor of natural selection holding down the -plumage in the female as a protection to her while nesting might appear -to fit the facts better were it not that the quest for an explanation of -the male’s plumage is thereby abandoned. It should not be forgotten in -this connection that the nest is generally only partly concealed, that -bright color at rest need not be conspicuous, and that the male, exposed -as he is through a considerable part of the year, still manages to -maintain himself in about equal numbers with the female. Suppose, -however, for the sake of argument, that natural selection has kept under -the full possibilities of the female. The <i>modus operandi</i> would be -competition between the least adorned females, suppression being brought -about by the activity of the ovary; while the male is left therefore to -exhibit the full possibilities of the genetic complex of<span class="pagenum"><a name="page_83" id="page_83">{83}</a></span> his race -without restraint. The facts in the case are that the plumage of the -male is the direct result of his genetic composition; the female has the -same genetic composition (the sex-linked characters are duplex), but the -ovary produces a substance that holds them in restraint. Put in this -way, there is nothing further to be explained, unless we insist on -finding an explanation as to how the species came to have its genetic -constitution. In other words, if we are not satisfied with the statement -as to the actual situation, we must explain it by a utilitarian appeal -to a relation between the plumage and the world outside of the -individual or the species. To those who feel unsatisfied to leave the -case as it stands on a physiological basis, there is another -hypothetical means of escape. It may be assumed that the genetic factors -that are instrumental in producing the secondary sexual characters have -also other but unknown influences in the economy of the species, color -and ornamentation being by-products of these factors whose utility in -other directions accounts for their presence. Such a philosophy has -perhaps one redeeming feature, since it suggests the possibility of -searching for other influences—influences that only incidentally give -the striking coloration and ornamentation of the males.</p> - -<p>At first sight the absence of cock-feathering in the Sebright may seem -to furnish the occasion for such a quest. It might appear that since -only one or two genetic factor differences are responsible for the -“nuptial” plumage of the male, that this plumage may have originated in -one or two genetic changes. Such an argument is fallacious, however, for -very many genetic factors may historically have been necessary to build -up the nuptial plumage of the male. The breeding experiment shows no -more than that one or two other factors have appeared that counteract -the effect of all that the others are capable of producing; the -experiment throws no light upon how many or how few these other factors -may be. That the nuptial complex is still present in the Sebright is -evident after castration. Castration shows only that the testes in the -Sebright produce some material that keeps down the effects of all the -other factors combined. This conclusion, it is true, somewhat simplifies -the problem for those who appeal to natural selection as suppressing in -the female the feathering of the cock, because it shows that this could -have been accomplished by one or two Mendelian factors that appeared of -such a kind that they caused the ovary to produce a substance -antagonistic to the influences coming from the genetic complex of the -species.</p> - -<p>With this by way of provisional exposition, let us return to the -question as to whether the Sebright-game cross throws any other light on -the possibly useful character of the genetic factor or factors that -produce cock-feathering. It is obvious that the evidence gives us no -clue at all, for with the exception of the normal allelomorphs of the -dominant factor for hen-feathering, all the other factors are still<span class="pagenum"><a name="page_84" id="page_84">{84}</a></span> -present in the Sebright. The normal allelomorph in question need not -have had any relation to the other complex; in fact, it seems not to -have any, because the castrated Sebright (with both normal allelomorphs -replaced by genes for hen-feathering) still develops the characteristic -cock-feathering.</p> - -<p>The outcome in the duck with its double male plumage is still more -puzzling when we attempt to analyze the situation in the light of the -selection theory. At the height of the breeding-season, when his testes -are enlarged and functioning actively, a substance is being produced -that leads to the eclipse of the nuptial plumage. If the male were -selected by his partner for his plumage, he would be chosen for a -plumage that develops in the absence of the functioning testes. If the -male is chosen because of his greater aggressiveness or “activity” or -“vitality” due to the development of his testes, the result would be to -select males that would probably develop a better eclipse plumage. The -case is interesting because it gives an opportunity to distinguish -between a plumage that develops under the influence of the sexual organs -and one that does not; and the latter is paradoxically the nuptial -plumage. It is true that the male might be selected for his nuptial -suit, and, theoretically at least, female choice might still be made -responsible for this plumage, but this merely shifts the problem, for it -leaves “unexplained” the appearance historically of the effect of the -activity of the testes in suppressing this plumage for a short time -after maturity. No doubt an attempt might be made to show that natural -selection comes in at this time of the year in giving a protective color -to the male, but so long as any evidence is lacking as to the need of -this protection the argument serves rather to further complicate an -already difficult situation.</p> - -<p>Goodale has written to me that there is an account, in the Agricultural -Journal, Union of South Africa, <span class="smcap">IV</span>, 1912, of the effects of the removal -of the ovary of the female ostrich. I have not been able to see the -account, but according to my informant such female individuals assume -the male secondary characters.</p> - -<p>Of unusual interest in connection with the seasonal change of plumage in -males of dimorphic species are Beebe’s experiments with scarlet tanagers -and bobolinks. In both species the males in their nuptial plumage are -very different from the females. Full-plumaged males of both species, at -the height of their “vocal and physical condition,” were confined in -small cages. The supply of light was gradually cut off and a slight -increase of the amount of food was allowed them. The birds became less -active in consequence and increased in weight. “The time for the fall -molt came and passed and not a single feather was shed.” The birds had -skipped the autumn molt and remained in their nuptial plumage. The song -soon died away; “the birds seldom uttered even a chirp.” From time to -time a bird was gradually brought into<span class="pagenum"><a name="page_85" id="page_85">{85}</a></span> the light for a week or two and -meal-worms were added to the diet. This invariably resulted in a full -resumption of song.</p> - -<div class="blockquot"><p>“I found that a sudden alteration in temperature—either lower or -higher—wrought a radical change in the physical metabolism of the -birds. They would stop feeding almost altogether, and one tanager -lost weight rapidly. A few feathers on the neck fell out, and in -the course of some two weeks this bird moulted almost every feather -and came strongly into his normal winter plumage of olive green. -The metabolism set up by the change in temperature, in its intent -and rapidity, seems comparable only to the growth of a deer’s -antlers.</p> - -<p>“Early in the following spring individual tanagers and bobolinks -were gradually brought under normal conditions and activities, with -quick result; just as the wild birds in their winter haunts in -South America were at that time shedding their winter garb and -assuming the most brilliant hues of summer, so the birds under my -observation also moulted into the colors appropriate to the season. -The old scarlet and black feathers fell from the tanagers and were -replaced by others of the same color; from buff, cream, and black, -the bobolinks moulted into buff, cream, and black! There was no -exception; the moult was from nuptial to nuptial, not from nuptial -to winter plumage. The dull colors of the winter season had been -skipped.”</p></div> - -<p>How are these results to be interpreted? Obviously the environment -prevented the autumn molting; hence the birds necessarily retained their -nuptial plumage. But is this the whole story? Did they not also remain -sexually active with their testes producing sperm as in the mating -season? In other words, if feathers had been plucked from them, would -not the new feathers have been like those already present? Despite the -author’s statement that not a single feather was molted, is it not -likely that occasionally a feather must have been accidentally lost. If -even one had been lost and an eclipse feather had replaced it, the -effect would not have escaped so keen an observer as Dr. Beebe. It seems -to me not unlikely that an occasional feather may have been lost and -replaced by a nuptial one. If so, then the results are most probably -interpreted as due to the birds having remained sexually active. This -condition suppressed the autumn molt, and at the same time would cause -any single feather lost to be like those still present. In support of -such a conclusion I can appeal to Beebe’s statement that after a week in -the light a full resumption of the song took place. It is unlikely that -sexual maturity would be attained in so short a time unless the birds -were already in the condition of sexual vigor. Perhaps one can appeal -also to Beebe’s other statement, viz, that after a sudden change in -temperature, followed by a changed metabolism and loss of weight, the -birds molted and assumed the eclipse (winter) plumage. Here I should -interpret the facts cited possibly to mean that the males lost their -sexual activity and in consequence developed the eclipse plumage.</p> - -<p>Until further information is obtained judgment must be suspended. If, as -Beebe’s statements strongly suggest, the external conditions,<span class="pagenum"><a name="page_86" id="page_86">{86}</a></span> acting -directly on the “metabolism,” cause the changes observed, then the -experiments mean that environmental conditions affect directly the -development of the nuptial and the eclipse plumage; but if, as I suggest -here, the effects observed are due directly to the environmental action -through its effects on the testes, then the results fall more nearly -into line with those of Goodale on ducks, etc.</p> - -<h4>C. <span class="smcap">Evidence from Amphibia.</span></h4> - -<p>The thumbs of frogs enlarge at the breeding-season and shrink -afterwards. The enlarged thumb is used by the male in clasping the -female during copulation, and the rough papillæ that appear over its -surface at this time may also help to anchor the male in his precarious -position on the back of the female. Since the pads and their papillæ are -used in copulation, they belong rather in the class of accessory organs -of reproduction than in the class of secondary sexual characters. Smith -and Schuster state for <i>Rana fusca</i> that the testes are at their -smallest size in March and April after the breeding-season. From that -time until August they steadily increase in size and reach their maximum -size in September. From September to March they are inactive and full -size, until the shedding of the sperm in March brings them soon -afterward to their lowest point again. It is to be noted that the -increase after March is associated with the increase in division rate of -the spermatogonia. The ripening of the sperm is finished in October.</p> - -<p>The thumb-pads with their pigmented papilla are “cast off” immediately -after the breeding-season, the thumb remaining smooth from May to -September. The reduction of the pad is usually due to the reduction of -the glands and the disappearance of the papillæ. Smith and Schuster -state: “During the months when the most active growth of the testis is -taking place the thumb-pads remain inactive and smooth.” The -implication, apparently, is that one ought to expect the growth in the -thumb to take place when the germ-cells are most actively dividing, if -its growth is connected with their activity; but there are no grounds -for such expectations, because the influence of the gonad may have -nothing to do with the division rate of the germ-cells, but rather with -interstitial or other cells, and even here less with their division rate -than with their period of greater secretive activity.</p> - -<div class="blockquot"><p>“In August and September the epidermal papillæ begin to be obvious, -and from this time onwards until about February a continuous -increase of the epidermal papillæ and pigmentation occurs. During -the greater part of this time, when the thumb-pads are attaining -their characteristic rough and pigmented appearance, the testes -remain inactive and unchanged—a fact which has been too readily -overlooked by writers on the correlation of the primary and -secondary sexual characters.”</p></div> - -<p>Nussbaum (1909) and later Meisenheimer (1911) found that after -castration the thumb-pads disappear. Smith confirms this report in all -essential respects, although in certain details concerning the papillæ<span class="pagenum"><a name="page_87" id="page_87">{87}</a></span> -he does not agree with the two former observers. His results show that -castration at the breeding-season is rapidly followed by the loss of the -outer papillated layer of the thumb-pads, but castration at any other -season does not have “any marked effect,” the papillæ remaining for 5 -months and more in the same condition as at the time of castration. The -essential point here, however, is that the excessive and even special -development at the breeding-season does not take place nor is again -assumed (apparently), if castration has taken place at some other time -of the year.</p> - -<p>Smith and Schuster’s attempts to transplant the testes into other males -or females were unsuccessful, as the testes degenerate after a time. -Auto-transplantation of the testes were more successful.</p> - -<p>Removal of the ovary had no effect on the thumbs of the female, and even -the injection of testes extracts into such females did not cause them to -develop pads. Nussbaum and Meisenheimer had found that transplantation -of pieces of the testes, and even injection of testes extract, into -castrated frogs caused an enlargement of the thumb-pads. Smith shows -that this conclusion rests on uncritical evidence. At any rate, his own -more carefully planned experiments extending over the year show that the -results obtained by Nussbaum and by Meisenheimer may be accounted for on -other grounds than the effect of the injection or implantation.</p> - -<p>The following statement by Smith is not without interest, since it bears -directly on an important question as to how internal secretions may -produce their effects.</p> - -<div class="blockquot"><p>“The deduction, therefore, which has been unduly based on -Nussbaum’s experiments, that the testis of the frog contains an -internal secretion, which, on being circulated in the blood, calls -for the development of the secondary sexual characters, either with -or without the mediation of the nervous system, is without -experimental foundation.... The fact that the developmental cycle -of the thumb depends for its normal course on the presence of -normal living testicular tissue can be equally well explained on -the theory that the testicular cells enter into a chain of -metabolic processes in the body which do not pursue their normal -course in the absence of the testicular cells. This disturbance of -the normal metabolic processes of the body, resulting in the -failure of the metabolic organs of the body to give rise to their -normal products in normal quantities, may have the result of -inhibiting the further development of the secondary sexual -characters. The development of these latter characters may depend, -therefore, not directly on the action of an internal secretion or -hormone derived from the gonad, but on the elaboration of other -products in other organs of the body in their due proportions. -These substances may be tentatively called ‘sexual formative -substances,’ but we have no reason for supposing that they are -entirely devoted to sexual or reproductive purposes, and that they -take no part in the ordinary metabolic processes of the body.”</p></div> - -<p>The arbitrary distinctions that Smith here sets up do not seem to me to -contribute anything to the situation, and in fact in the end it amounts -to practically the same thing whether the hormone acts<span class="pagenum"><a name="page_88" id="page_88">{88}</a></span> directly on some -specific part of the body or whether in doing so it acts on other parts -as well. While it is more or less customary to limit the term “hormone” -to substances that do produce specific effects in a particular organ, no -one would, I suppose, deny that a substance was acting as a hormone if -at the same time it acted on other parts of the body also, or even if -its immediate action were on some part and its ultimate action on -another part of the animal. Moreover, there is nothing in the evidence -appealed to by Smith that supports one rather than the other contention. -It is not apparent that the simpler idea of hormone action may not still -apply. Failure to implant the testes in castrated male or female, and -failure of injections to produce the results sought for, may mean no -more than that the experimenter failed to fulfill some one of the -conditions present in the normal frog at the breeding-season. Granting -that the results recorded by Nussbaum and Meisenheimer are open to the -serious objections, pointed out by Smith and Schuster, the facts -recorded by all three writers indicate that the maximum development of -the pad takes place when the testes are at their greatest development -and that the pad suddenly decreases if at this time the testes are -removed. It would seem to follow that since the swelling is connected -with the presence of a certain condition of the testes, its enlargement -is to be referred directly to the latter, and the case comes under the -general category of “secondary sexual differences,” depending on the -gonad.</p> - -<p>The secondary sexual characters of <i>Triton cristatus</i> can not, as can -those of the frog, be supposed to be mechanically useful in mating, but -seem to be comparable in every respect with the secondary sexual -ornaments of higher animals. The work of Bresca has shown that their -development is under the influence of the testes. The most important -secondary sexual characters of the male are the dorsal comb and the -white stripes of the tail. The comb extends along the dorsal surface of -the body and of the tail (with a slight dip in the pelvic region). It is -fully developed during the breeding-season, when it reaches a height of -1.5 cm. In winter it is only 0.66 mm. high, or even less. The white -stripes also are fully developed in the breeding-season. They extend on -each side from the cloaca to the end of the tail. In the female the -white stripe is sometimes faintly seen. The angles of the tail and of -the cloaca thickening are black-brown or black. The belly of the male is -bright orange or “Ziegel rot”; that of the female sulphur-yellow or -orange, but the difference is not constant. The upper surface of the -head of the male is marbled, especially during the breeding-season -almost disappearing during the rest of the year. Bresca found, when the -testes were removed from sexually mature males, that in the course of a -year all the important secondary sexual characters disappeared, -including the comb, the white tail stripes, and the marbling of the -upper surface. Removal of the ovaries did not affect the characters of<span class="pagenum"><a name="page_89" id="page_89">{89}</a></span> -the female. The black lower corner of the tail in the male is not -changed by castration.</p> - -<p>When the skin along the middle line of the back of the female is -transplanted upon the back of a normal male (in place of his own comb) -the transplanted tissue develops into a comb. In other words, under the -influence of the testis, the dorsal mid-line tissues of the female -change into those characteristic of the male. When pieces of skin of a -male with the white tail stripes are grafted on the side of the tail of -another male, the stripe remains, but when grafted similarly on a female -the stripe slowly disappears. The result shows that its presence depends -on the testis.</p> - -<p>A remarkably clear case of hermaphroditism in amphibians was found by V. -la Vallette St. George. He found an individual of <i>Triton tæniatus</i> that -was outwardly a male with well-formed dorsal comb. In the interior were -two large testes in normal position and just lateral to these on each -side a large ovary. Sections showed ripe sperm in the testes and typical -ova in the ovary. Sperm-ducts were present, but no oviducts. The -presence of the testes will, of course, account for the development of -the secondary sexual characters of the male.</p> - -<p>Other cases amongst the Anura have been recorded by Loisel and by -Marshall, Spengel, and Knappe. In the early stages of the gonad in frogs -there appears to be an hermaphroditic stage in which egg mother-cells -and sperm mother-cells are both present, at least in those individuals -that will later become males (Kusakowitsch).</p> - -<p>The normal hermaphroditism of certain fish (<i>Serranus</i>) and its rare -occurrence in other species (recorded by Shattuck and Seligmann) need -not be recorded here.<a name="FNanchor_18_18" id="FNanchor_18_18"></a><a href="#Footnote_18_18" class="fnanchor">[18]</a></p> - -<h4>D. <span class="smcap">Evidence from Crustaceans.</span></h4> - -<p>In the Crustacea the secondary sexual characters are not marked, except -in a few cases. In the amphipods, Holmes has shown direct contact plays -the chief rôle in mating, and in the crayfish it has been shown by -Dearborn, Andrews, and Pearse that sex recognition is largely tactile. -Chidester also has shown this in crayfish. Even in crabs, and especially -those living on land which have well-developed eyes and good vision, -secondary sexual differences are as a rule slight and the mating -instincts simple. On the other hand, the enormous chela of the male of -the fiddler is supposed to be a secondary sexual difference (mainly -because no other use for it has been found). Pearse suggests that the -waving of this claw by the male is used as a sex signal, although he is -disinclined to accept Alcock’s view that it has become “conspicuous and -beautiful in order to attract the female.”</p> - -<p>The most remarkable case known of a change in the secondary sexual -characters of one sex into those of the other was discovered by<span class="pagenum"><a name="page_90" id="page_90">{90}</a></span> Giard -in 1886. As a result of infection by parasitic crustacea (<i>e. g.</i>, -<i>Sacculina</i>), the male crab develops the secondary sexual characters of -the female. It has been generally supposed, following Giard, that this -result is due to the destruction of the testes of the male by the roots -of the parasite that invades the spaces between the organs of the host, -and, in the case of the testis, ultimately brings about its partial or -complete destruction. Not unnaturally the results here were supposed to -be parallel to those of castration in vertebrates, and received in fact -the name of “parasitic castration.” More recently Geoffrey Smith has -studied this phenomenon in the crab <i>Inachus</i>, infected by the parasite -<i>Sacculina</i>, and has reached the conclusion that the change is not due -to injury or to destruction of the testes, but to a change in the -metabolism of the crab brought about by the parasite.</p> - -<p>Taking Geoffrey Smith’s case of <i>Inachus-Sacculina</i> as typical, the -changes brought about are as follows: The parasites attach themselves to -the young crabs before the external secondary sexual differences have -appeared. In the females, the effect is to cause them to develop -prematurely the distinctively female characters. In the male, on the -other hand, the narrow abdomen of the male changes after a molt into the -broad abdomen of the female, which also develops ovigerous appendages on -its ventral surface like those of the female in every detail. The larger -claw of the male changes into that of the female, which is different in -form as well as in size. Some years ago I ventured to raise the question -as to whether these effects on the male might not be interpreted as -retention of the juvenile characters rather than development of the -female characters in the male. This might appear more especially the -case in the somewhat more juvenile shape of the anterior abdominal -appendages and possibly also in the shape of the broader abdomen; but -Smith has later shown that the results can not be interpreted as -juvenile, for when the changed organs are examined in detail they are -found to differ from the same organs in the juvenile condition, and to -be identical with those of the adult female. I think, therefore, that we -must accept this interpretation of Giard and of Smith as correct. But -Smith goes further and believes that the effects may be carried so far -that eggs develop in the old testes; in other words, that the testis -changes to an ovary. It seems to me that the evidence to support this -last point should be much stronger than that advanced by Smith before we -can accept this interpretation, for we lack the essential control for -this evidence. In only a single case were eggs found—in the testis of a -male that had been infected, but from which the parasite had fallen off, -and which was presumably recovering from the effects of its presence. -Now, it is known that in the testes of some male animals a few eggs may -occasionally be found where there is no suspicion that the animal has -changed its sex. In some crustacea, in scorpions, and in insects, -isolated instances of this kind have been found. Abnormal division<span class="pagenum"><a name="page_91" id="page_91">{91}</a></span> of a -spermatogonial cell, of such a kind that both sex chromosomes (in the -case of insects at least) got into the same cell might be expected to -cause such a cell to become, even in the male, an egg-cell rather than a -sperm-cell. The degenerative changes of the testes in the hermit crab -caused by the parasite might be imagined to favor such abnormal division -with its consequences. More significant, however, is the fact that the -parasite causes the absorption of the ovary when it infects a young -female, so that even all its eggs disappear. In other words, the -parasite is as injurious to the peculiarly female organ as it is to the -testis. Why then, one can not but ask, should an influence that causes -such effects on the ovary first change a male into a female so long as -it is present and then when the parasite has disappeared leave an -influence behind of a kind that causes the ovary to develop—an organ -which the parasite destroys when the parasite is present? Is it not more -probable that only the secondary sexual organs were changed, without -change in sex, the single case of eggs observed being caused in another -way? This point can only be settled by direct experimentation either by -removal of the testis, by injuring it, or by injection, grafting, or -feeding experiments. The extent of the testis and its position make it -impossible to remove it by an operation, as I have found after repeated -attempts. It seemed easier to destroy it by radium. This I have tried to -do, using very powerful tubes, treating the crab (fiddler crabs) for -several hours. The crabs had had one claw removed—the enormously large -one—and were kept until the next molt, that occurred from a week to six -weeks later. In none of the cases was any change produced. The large -claw of the male regenerated, of course, not full size after only one -molt, but after several nearly full size and always with the -peculiarities of the male crab. The abdomen and the appendages were not -changed. Whether the significant cells of the testes, if there are such -cells apart from the germ-cells, were destroyed, can not be told, for as -yet the histological examination of the material has not been made. -Until a successful operation has been done, I think we must hesitate to -accept Smith’s argument, although based as it is on a series of -interesting observations. His speculation is as follows:</p> - -<div class="blockquot"><p>“The reason why <i>Sacculina</i> causes the assumption of the adult -female state in <i>Inachus</i> is found in the facts: (1) that the roots -of <i>Sacculina</i> elaborate a yolk-substance from the blood of -<i>Inachus</i> of a similar nature to that which is elaborated in the -ovaries of an adult <i>Inachus</i>; (2) that in order to elaborate this -yolk-substance the roots take up from the blood of <i>Inachus</i> the -female sexual formation substance, which is the necessary material -for forming the yolk; (3) that the female sexual formative -substance being absorbed by the <i>Sacculina</i> roots is regenerated in -excess; (4) that the presence of the female formative substance -continually circulating in large quantities in the body-fluids of -the infected crabs causes the production of adult female secondary -sexual characters, and, when the parasite dies, of yolk-containing -eggs.”</p></div> - -<p>In brief, the evidence consists in showing that in the parasite a -yolk-substance appears, which Smith says comes from the blood of the -crab<span class="pagenum"><a name="page_92" id="page_92">{92}</a></span> that produces it under the influence of the parasite. -Incidentally, as it were, this is said to be the same yolk-substance -(but no sufficient evidence that it is the same is given) that the egg -stores up inside itself, and it is <i>assumed</i> that it is a formative -substance that causes the cell that gets it (or contains it or secretes -it—details are wanting) to become an egg-cell. It is the excess of this -substance produced by the male crab, while still a male, under the -influence of the parasite, that affects the abdomen and its appendages -in such a way that they assume the female condition. There are too many -assumptions in the argument, some of which are scarcely of a kind that -our knowledge of development, incomplete as it is, can allow us to -accept without more direct evidence in their support, to make this view -very plausible. Until better evidence is forthcoming, I fail to be -convinced by Smith’s interpretation of his facts.</p> - -<p>Into Smith’s and Robson’s interesting observations on the blood of -crabs, described in Smith’s later paper (part 7, 1911), it is not -necessary to enter here, since the evidence taken as a whole offers -little further in support of his view than had been already assumed. The -argument on page 263 should not, however, pass unchallenged. Smith says:</p> - -<div class="blockquot"><p>“It is clear that the old and familiar idea of an internal -secretion produced by the gonad being the stimulus for the -development of the secondary sexual character could not be applied -here, since at the time that the alterations in the secondary -sexual characters take place no ovary is present to give rise to -the required stimulus. It is suggested, therefore, that in some way -the stimulus must reside in the roots of the <i>Sacculina</i>,” etc.</p></div> - -<p>The argument seems to imply that, since the secondary sexual characters -of the female can not be produced by an ovary in the infected male, -therefore the <i>Sacculina</i> must take the place of the ovary. But why make -such a supposition, for if the testes simply keep down the development -of the female characters, as Giard supposes, there is no need either for -an ovary or for a <i>Sacculina</i> to develop them. One might as well argue -that since the cock does not develop the secondary sexual characters of -the hen that an ovary is essential for their development—which is true, -but not in the sense implied.</p> - -<p>Stamati (1888) states that he attempted to remove the testes of adult -crayfish and apparently succeeded, but since no effects are expected -until after a molt occurs (that may not take place for two years or -more), no results were obtained. Injections of the gonads with an acid -failed, since the animals died.</p> - -<h4>E. <span class="smcap">Evidence from Insects.</span></h4> - -<p>In 1899 Oudemans succeeded in finding a method of removing the testes -and ovaries from caterpillars, using a dimorphic species, <i>Ocneria -dispar</i>, the gipsy moth. The results were negative; none of the -secondary sexual characters of the male or female moths or the accessory -organs of copulation were in the least affected by the operation. The -castrated male copulated as readily with the female as did the normal<span class="pagenum"><a name="page_93" id="page_93">{93}</a></span> -male, while the spayed females also behaved as normal individuals of -that sex behave. Kellogg, in 1904, repeated the same operation in the -silkworm moth on a small scale with the same results. Kopec and -Meisenheimer, in 1909, repeated in a more detailed way Oudemans’s work. -A further important addition was made by Kopec and by Meisenheimer. They -transplanted ovaries into a castrated male and testes into a spayed -female. Neither gonad produced any effect on the characters of the other -sex. It is interesting to note that the testes underwent their normal -development in the body of a spayed female, and even in one with the -ovaries present, and that the ovary also underwent normal development in -the body of the male. In other words, there is no intolerance of the -tissue of one sex to the gonad of the other. This result is all the more -unexpected, because other observations have shown that the color of the -blood, and its chemical properties, is quite different in the male and -female moths of certain species.</p> - -<p>In the case of moths, therefore, if these cases be regarded as typical, -the situation from the point of view of sexual selection is much simpler -than in birds in the sense that the secondary sexual characters are -directly the product of the genetic constituents of all the cells, and -not influenced indirectly by the secretions from the testes or the -ovaries. Sexual selection, therefore, if it is an agent in the evolution -of the differences between males and females, has acted on the genetic -complex to produce these effects on either sex without the result being -involved in the condition of the ovary or the testes.</p> - -<p>Regen castrated crickets, <i>Gryllus campestris</i>, in the larval stages and -found no effects on the adult structures. The castrated males chirped -like normal males and mated with the females. Spayed females were like -normal females; they bored holes in the ground, but laid no eggs in -them, of course, as the ovary had been completely removed.</p> - -<p>The only genetic evidence in the group of insects, outside of the -vinegar fly, relating to the secondary sexual inheritance of the -secondary sexual characters is the following important experiments made -by Foot and Strobell:</p> - -<p>The male of one of the bugs, <i>Euchistus variolarius</i>, has a black spot -on the end of the abdomen—a spot that is not present in the female. -Foot and Strobell crossed a female of this species to another bug, <i>E. -servus</i>, that lacks the spot in both sexes. The daughters had no spot, -the sons a faint spot less developed than in <i>variolarius</i>. These inbred -gave (in F₂) 249 females without a spot, 107 males with a spot, and 84 -males without a spot. The results are explicable on the view that a -single dominant Mendelian factor, not-sex-linked, causes the spot in the -males, but the presence of the gene in the female produces no effect. -The effect, therefore, is sex-limited, <i>i. e.</i>, its expression is -determined by the rest of the complex male or female.</p> - -<p>The very important breeding experiments carried out by Goldschmidt on -varieties of the gipsy moth should be referred to in this<span class="pagenum"><a name="page_94" id="page_94">{94}</a></span> connection, -but as I have recently reviewed these results in the paper on -gynandromorphs written in collaboration with C. B. Bridges,<a name="FNanchor_19_19" id="FNanchor_19_19"></a><a href="#Footnote_19_19" class="fnanchor">[19]</a> I need -only refer to that account here.</p> - -<div class="blockquot"><p class="c">[Note added April 21, 1919.]</p> - -<p>Shortly after the preceding paper was finished a theses by A. -Pézard on the secondary sexual characters of birds reached me. In -it the author gives an account of a number of experiments that he -has made with poultry and with pheasants. His description of the -changes that take place after castration are more exact and more -detailed than any other so far recorded; but in general the results -obtained by Pézard, through castration, are the same as those that -had been obtained by others. Castration of 4 male silver pheasants -are reported. No change in the plumage results, although the -changes that take place in the comb and wattles are the same in -kind as those observed in fowls. The sexual instincts and -peculiarities of the voice and their belligerency are also lost. -Similarly 4 golden pheasants that were operated on gave the same -results.</p> - -<p>Three pheasants with mixed plumage (<i>Phasianus colchicus</i>) were -examined. Their testes proved, on histological examination, to be -imperfectly developed. It is not evident what relation existed -between the facts and the mixed plumage. The suggestions made by -Pézard seem inadequate to cover the cases.</p> - -<p>Testicular tissue transplanted into castrated cocks whose comb, -wattles, etc., had undergone retrogressive changes brought about a -return to the normal conditions after an interval during which the -implanted nodules had begun to regenerate.</p> - -<p>Testicular extract from the cryptorchid testes of swine was -injected into castrated cocks. In one case this resulted in a rapid -growth in size of the comb, which, after 2 months, had reached its -full size. Cessation of the injections led immediately to a -cessation of growth. Before injection the bird exhibited the -pacifistic characteristics of the capon, but the injections brought -out little by little the aggressive behavior of the normal male. -The voice reappeared and “nous assistons á une véritable crise de -puberte.”</p> - -<p>A histological study of the testes of the fowl and of pheasants -showed that much connective tissue is characteristic of young -birds. In the adult cock, and during the mating season of the -pheasant, the connective tissue becomes largely crowded out by the -enlargement of the tubules. Pézard concludes that the -“interstitial” cells in birds have nothing to do with the secondary -sexual characters, but that these come rather under the influence -of the germinal cycle of cells of the testes. The submergence of -the connective-tissue cells of pheasants during the breeding-season -and their reappearance during the rest of the year might appear to -have some relation to the facts that I have recently described in -Sebrights, but as the nuptial plumage of the male remains the same -throughout the year we can not ascribe any direct influence to this -tissue. Nevertheless, the different tissues of the testes in birds -that show seasonal dimorphism of plumage should be carefully -examined.</p> - -<p>Pézard made a few observations on hens whose ovary had been -removed. His results are in accord with those of Goodale, except -that he thinks that the ovary has no influence on the erectile -organs (comb, etc.) which acquire in the spayed bird the same -<i>length</i> as that of the normal female.</p> - -<p>Two hens showing male characteristics and a pheasant similarly -affected are described. In all three cases an examination of the -ovary was found to be undeveloped or abnormal.</p></div><p><span class="pagenum"><a name="page_95" id="page_95">{95}</a></span></p> - -<h2><a name="PART_IV" id="PART_IV"></a>PART IV.<br /><br /> -SUMMARY AND CONCLUSIONS.</h2> - -<p>1. The two principal results obtained were: (<i>a</i>) that castration of -hen-feathered Sebright males causes them to develop the full plumage -characteristic of the cock-bird; (<i>b</i>) that complete hen-feathering is -due to two dominant Mendelian genes.</p> - -<p>2. A striking change takes place when the Sebright male is castrated -(<a href="#plt_1">plate 1</a>, figs. 3, 4; <a href="#plt_3">plate 3</a>, fig. 1). The new feathers on the upper -surface of the head, neck, back, wings, rump, and tail-coverts assume a -different color and distribution of their pigment; they take on a new -shape, and in those regions where in the cock the barbules are absent -from a part of the margin of the feather, the same absence occurs in the -castrated birds. Such feathers are present on the neck, back, wing-bow, -and rump. The transition is shown in the figures in <a href="#plt_6">plate 6</a>, where for -comparison one of the old and one of the new feathers lie side by side. -The tail-coverts in the hen-feathered bird are short, and like those in -the hen do not cover the true tail. After castration they become -excessively long—longer, in fact, than in many cocks—and cover the -true tail feathers. The tail feathers themselves, moreover, become -increased in length, as do the posterior row of feathers of the -wing-coverts. On the breast and sides the change is less marked. The -castrated Sebright loses his erect carriage, but how far this is due to -the changes in his plumage and how far is real (as a result of a new -balance due possibly to the lengthening tail and its coverts) I can not -decide.</p> - -<p>3. While castration causes the hen-feathered male to make additions in -color, length, and size of many feathers, it causes at the same time the -other retrogressive changes characteristic of the capon (a castrated -cock-feathered bird); the comb and wattles shrink and become pale, the -birds almost cease crowing, and become timid. They do not make much -effort to mate with the hens, but when they do they show the usual -copulatory reactions.</p> - -<p>4. If feathers are removed at the time of castration, the new feathers -show the full effect of the removal of the testes, although they must -have begun to develop immediately afterward. It is suggested that by -means of this delicate test the time relations of the internal secretion -can be profitably studied.</p> - -<p>5. Feathers that may have started their development at the time of the -operation show the old influence at the tip of the feathers (<a href="#plt_10">plate 10</a>) -and the new one in the rest of the feather. The change is abrupt, -although the transition is perfect.</p> - -<p>6. Incomplete castration of the hen-feathered male leads to smaller -changes in the same direction than those following complete castration.</p> - -<p>Where such small pieces of the testis were left that complete -cock-feathering followed, the bird slowly changed back to -hen-feathering<span class="pagenum"><a name="page_96" id="page_96">{96}</a></span> as the testes began to regenerate. When the regenerated -pieces were removed the bird became cock-feathered again.</p> - -<p>7. One Sebright male whose testes appear to have been completely removed -did not change the character of the plumage. No testes were found on -autopsy. It is suggested that some other endocrine organs have taken -over the function of the testes, but as yet none such can be indicated.</p> - -<p>8. In one case an old hen-feathered (F₁) male began to change over to -cock-feathering. It was found that his testes had dwindled (probably -through disease) to very small size (10 by 5 mm.).</p> - -<p>9. The F₁ male of the cross between the Sebright and game is also -hen-feathered (<a href="#plt_2">plate 2</a>, fig. 1). After castration he becomes -cock-feathered (<a href="#plt_2">plate 2</a>, fig. 4) and shows thereby the genetic type of -the heterozygous cock-feathered class in which his hen belongs. The -change in this male is even more striking than that in the Sebright. The -change in the individual feathers is shown in <a href="#plt_7">plate 7</a>, figs. 1 and 1<i>a</i>.</p> - -<p>10. Three types of F₂ hen-feathered castrated males are shown in plate -2, figure 3, and <a href="#plt_3">plate 3</a>, figure 3 and figure 4. The first was a dark -bird that changed to a lighter red above. The third a gray bird that -became bright red; the second was a light yellow that became deep -yellow, etc. The class of hens to which such males belong, as -cock-feathered birds, can thus be found out by castration. In this way -the F₂, and back-cross, hen-feathered cocks can be classified with the -corresponding F₂ cock-feathered males.</p> - -<p>11. In the F₂ generation, made up of birds from the direct and -reciprocal crosses taken together, there were 29 hen-feathered and 26 -cock-feathered males. In the back-cross (F₁ hen by game male) the -classes were 2 and 7. The results seem in better accord with the -assumption that two factors are present in the Sebright that stand for -hen-feathering; that either alone will give hen-feathered birds -(intermediate type?), but that both together give the extreme type of -hen-feathering seen in the Sebright.</p> - -<p>12. The difference in color in the two races (Sebright and Black -Breasted Game bantams) is very great. The former have almost uniformly -laced feathers, while the latter has the varied plumage of the -jungle-fowl. The game is strongly dimorphic in color and color-pattern; -the Sebright has the same type of coloration and pattern both in the -male and female, but this is deceptive, as castration shows, because the -castrated male is as strikingly different from the normal Sebright -female as is the cock of other birds from the hen. The resemblance of -male and female in this race is due to the suppression of the true male -plumage by something produced in the testes. Therefore the heredity of -dimorphism resolves itself here into the problem of the heredity of -hen-feathering. That the female Sebright has the same genetic factors as -the male is shown by the fact that she trans<span class="pagenum"><a name="page_97" id="page_97">{97}</a></span>mits hen-feathering in the -same way as does the male, and also by the fact, as Darwin pointed out, -that an old female Sebright whose ovaries had degenerated developed not -the hen-feathered plumage of her own cock, but cock-feathered plumage -like that of most male poultry.</p> - -<p>13. The color of the F₁ birds is shown in <a href="#plt_2">plate 2</a>, figs. 1 and 2. In -general, the feathers are stippled, black and light yellow being the two -most conspicuous ingredients. Since hen-feathering dominates, the -dimorphism is absent, or at least is so slight as to not attract -attention—little more, in fact, than in the Sebright race. The carriage -of the male is like that of the Sebright male. The F₁ male and female -are alike in the direct cross and the reciprocal, or at least no -conspicuous difference is found between the two classes of hens, -indicating that no important sex-linked factors are involved in the -cross.</p> - -<p>14. The F₂ birds show a great variety of color and pattern, but those -obtained can be approximately grouped into 16 classes. The classes are, -however, admittedly not uniform, indicating minor factors not here -reckoned with. The classification of the hens is easiest; the F₂ -hen-feathered males can then in many cases be referred to the proper -classes; the F₂ cock-feathered males can not be accurately classified -with their corresponding hens, except in the case of those that resemble -the two P₁ males, the F₁ male, and those that castration experiments of -the hen-feathered males have shown to belong to certain hen types.</p> - -<p>15. Despite the admitted difficulties of classification, it is suggested -that three factor-pairs of differences will cover the main color classes -seen in the F₂ and in the back-cross. One or two of these seem to be -incompletely dominant, since the F₁ birds are not like either parent in -any single character, nor are they like the wild type in so far as this -is represented by the game.</p> - -<p>16. A histological examination of the testis of the male Sebright by -Boring and Morgan has shown that it contains cells like those present in -the ovary of all breeds of poultry. These cells are called luteal cells -by Pearl and Boring, from their resemblance to the cells of that name -found in the corpora lutea of mammals. In the mammals similar cells are -supposed to produce internal secretions that act as hormones. Their -function in the female bird is unknown, but the fact that after the -removal of the ovary the female develops the secondary sexual plumage of -the male suggests that some secretion from these cells performs this -function. Their occurrence in the male Sebright and their complete -absence, or paucity, in the males of other races supports strongly the -view that these cells are concerned with the suppression of the -secondary sexual plumage.</p> - -<p>17. While in mammals the interstitial cells have been supposed to -produce an internal secretion that causes the development of some of the -secondary sexual characters of the male, and the fuller elaboration of -others, in birds no such connection exists, if we except the case<span class="pagenum"><a name="page_98" id="page_98">{98}</a></span> of -the Sebright. Castration of ordinary males does not affect deleteriously -the secondary sexual plumage (although it does the comb, behavior, -etc.), in fact may even enhance their effects. But, while in the mammal -a secretion is necessary for the full development of the secondary -sexual characters, in the Sebright a secretion inhibits certain of them. -What element in the ordinary bird and in the Sebright causes the full -development of the comb, wattles, sexual behavior, etc., is not known. -Possibly it is the sexual elements themselves, but possibly it is a -secondary influence of the luteal cells producing a contrary effect on -these parts from its effects on the feathers; but possibly more than one -kind of secretory cell is present in the testis of the cock.</p> - -<p>18. The causes of the development of the secondary sexual characters are -seen to be of such diverse physiological kinds that one may well -hesitate to apply the same explanation as to their evolution. In fact, -it is pointed out that several of the theories that have been suggested -run counter to the conditions that bring about the development of the -secondary sexual characters.</p> - -<p>19. An attempt is made to give a critical review of Darwin’s theory of -sexual selection in the light of the modern genetic and operative -results on the secondary sexual characters of the vertebrates. It is -pointed out that far from extending the general theory in its -applications, the modern work has shown in the first place that the -underlying conditions that call forth the development of the secondary -sexual differences are so diverse in the different groups of animals -that it is a priori very unlikely that this evolution can have been -directed by the same external agent, such as the choice of the female, -for such an assumption carries with it in several cases other -implications concerning the causes of the suppression of these same -characters in the female herself, etc. In the second place, it is -pointed out that the problem of the excessive development of certain -characters in the male whose genes are present in both sexes no longer -oppresses us as it did Darwin, for it has been shown both by the genetic -and by the operative work that a single factorial difference may be at -the root of exceedingly great differences in the individual. Such -results, while they admittedly do not <i>in most cases</i> tell us that the -differences involved have arisen at a single progressive step, show us -nevertheless that such differences may depend on very simple initial -differences, and if so, the entire problem becomes enormously -simplified. To Darwin the excessive development of color and -ornamentation appeared due to a long, slow process of evolution -laboriously brought about by the female through selection of those males -a little more ornamented than their fellows. To-day we have found out -that in many cases the genetic composition of a male with such -ornamentation and of a female without it may be almost identical, except -that the genes in one chromosome are duplex in one sex and simplex in -the other. Owing to this initial difference, the<span class="pagenum"><a name="page_99" id="page_99">{99}</a></span> female in birds -produces an internal secretion that suppresses in her the ornamentation -shown by the male, and in the mammal an internal secretion produced by -the testes causes the full development in the male of the secondary -sexual characters. If, as seems probable, these secretions are some -particular kind of substance, the condition that led to their appearance -historically need not have been very complex; and if not, the problem -appears simplified. It still remains to give some reasonable explanation -as to why such substances should continue to be produced if their -products—the secondary sexual characters—possess no “beauty” for the -female. Here more work is necessary, but the modern genetic point of -view may possibly give an important clue. We are coming to realize more -fully that the hereditary genes generally have more than a single effect -on the characters of the animal. The secondary sexual characters may, -then, be only by-products of genes whose important function lies in some -other direction. If, for example, the secretion produced by the cells of -the male have an important influence on his output of energy, or -strength, or activity, their secondary influence over certain parts of -the body would not call for any further explanation on the modern view -of natural selection. If the secretions of the ovary of the female bird -have some direct relation to her physiological processes that are -important in the development of the oviduct, for instance, it would be a -matter of no importance from an evolutionary point of view if that same -secretion suppresses in her the development of the high color shown by -the male.<span class="pagenum"><a name="page_100" id="page_100">{100}</a></span></p> - -<h2><a name="BIBLIOGRAPHY" id="BIBLIOGRAPHY"></a>BIBLIOGRAPHY.</h2> - -<div class="blockquott"><p><span class="smcap">Alcock, A.</span>, 1892. On the habits of <i>Galasimus annulipes</i>. An. Mag. -Nat. Hist., VI.</p> - -<p><span class="smcap">Ancel, P., et Bouin</span>, 1906. Sur l’effet des injections d’extrait de -glande interstitielle du testicule sur la croissance. Compt. Rend. -Acad. Sc. Paris, CXLII.</p> - -<p><span class="smcap">Arkell, T. R.</span>, 1912. Some data on the inheritance of horns in -sheep. N. H. Agr. Exp. Sta. Bull., 160.</p> - -<p>—— ——, 1912. 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Anat. -und Ent.-ges., XV.</p> - -<p>—— ——, 1909, Hoden und Brunstorgane des braunen Landfrosches -(<i>Rana fusca</i>). Arch. f. d. gesamte Phys., CXXVI.</p> - -<p><span class="smcap">Oudemans, H. Th.</span>, 1899. Falter aus kastrierten Raupen, wie sie -aussehen und wie sie sich benehmen. Zoolog. Jahrb., Abt. Syst., -XII.</p> - -<p><span class="smcap">Packard, A. S.</span>, 1875. On gynandromorphism in the Lepidoptera. Mem. -Boston Soc. Nat. Hist., II.</p> - -<p><span class="smcap">Painter, T. S.</span>, 1913. On the dimorphism of the males of <i>Mœvia -vittata</i>, a jumping spider. Zool. Jahrb. Abt., Syst., XXXV.</p> - -<p><span class="smcap">Pearl, R.</span>, and <span class="smcap">M. R. Curtis</span>, 1909. Studies on the physiology of -reproduction in the domestic fowl. Biol. Bull., XVII.</p> - -<p>—— ——, 1910. Studies on hybrid poultry. Rept. Maine Agri. Exp. -Station.</p> - -<p>—— ——, and <span class="smcap">F. M. Surface</span>, 1910. 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An experiment dealing with sex-linkage in fowls. -Journ. Exp. Zool., XII.</p> - -<p>—— ——, 1915. Experiments on sex recognition and the problem of -sexual selection in <i>Drosophila</i>. Journ. of Animal Behav., V.</p> - -<p><span class="smcap">Swift, C. H.</span>, 1914. Origin and early history of the germ cells of -the chick. Amer. Jour, of Anat., XV.</p> - -<p><span class="smcap">Tandler, J.</span>, und <span class="smcap">K. Kellar</span>. Die Körperform der weiblichen -Fruehkastraten des Rindes. Archiv Entw-mech., XXXI.</p> - -<p>—— ——, und <span class="smcap">S. Grosz</span>, 1909, 1910. Ueber den Einfluss der -Castration auf den Organismus. Archiv f. Entw-mech., XXVII, XXIX, -XXX, 1909.</p> - -<p>—— ——, und <span class="smcap">S. Grosz</span>, 1913. Die biologischen Grundlagen der -sekundären Geschlechtscharaktere. Berlin.</p> - -<p><span class="smcap">V. la Valette St. George</span>, 1895. Zwitterbildung beim kleinen -Wassermolch. Arch. Mik. Anat., XLV.</p> - -<p><span class="smcap">Walker, C. E.</span>, 1908. The influence of the testis upon the secondary -sexual characters of fowls. Proc. Royal Soc. of Med.</p> - -<p><span class="smcap">Wallace, A. R.</span>, 1891. Darwinism: An exposition of the theory of -natural selection. London.</p> - -<p>—— ——, 1891. Natural selection and tropical nature. London.</p> - -<p><span class="smcap">Weber, M.</span>, 1890. Über einen Fall von Hermaphroditismus bei -<i>Fringilla coelebs</i>, Zool. Anz., XIII.</p> - -<p><span class="smcap">Yarrell, W.</span>, 1827. On the changes in the plumage of some -hen-pheasants, Phil. Trans., 117.</p> - -<p>—— ——, 1857. On the influence of the sexual organ in modifying -external character. Journ. Proc. Linn. Soc., I.</p></div><p><span class="pagenum"><a name="page_106" id="page_106">{106}</a></span></p> - -<h2><a name="DESCRIPTION_OF_PLATES" id="DESCRIPTION_OF_PLATES"></a>DESCRIPTION OF PLATES.</h2> - -<table border="0" cellpadding="0" cellspacing="0" summary="" -style="border: 2px black solid;margin:auto auto;max-width:50%; -padding:1%;"> -<tr><td><p class="c"><span class="nonvis">In certain versions of this etext [in certain browsers] -clicking on the image of the plate will bring up a larger version.</span></p> - -<p class="c">(etext transcriber's note)</p></td></tr> -</table> - -<p class="c"><span class="smcap"><a href="#plt_1">Plate 1.</a></span></p> - -<div class="blockquott"><p><span class="smcap">Fig. 1.</span> Black-Breasted Game bantam cock. He is typically -cock-feathered, but, as in all games, his hackles and tail-coverts -are shorter than in the cocks of other breeds. The comb was dubbed -by the breeder.</p> - -<p><span class="smcap">Fig. 2.</span> Black-Breasted Game bantam hen. The great contrast in color -between the cock and hen is practically the same as that in the -Brown Leghorn, in most races of Tosa fowls, and in the wild type -<i>Gallus bankiva</i>.</p> - -<p><span class="smcap">Fig. 3.</span> Sebright cock, “hen-feathered.” The short hackles, the -rounded feathers of the back and saddle, and the shortness of the -tail-coverts are characteristic features of these males. For -details of individual feathers from different regions see <a href="#plt_6">plate 6</a> -and <a href="#plt_8">plate 8</a>.</p> - -<p><span class="smcap">Fig. 4.</span> A castrated Sebright male. The drawing was made about a -year after the operation. This particular bird developed a lighter -color than did other castrated Sebrights (see <a href="#plt_3">plate 3</a>, fig. 1). The -entire dorsal region has changed its color, and the feathers have -also changed in shape, length, etc. Note especially the very long -hackle and saddle feathers (for details see <a href="#plt_6">plate 6</a>, fig. 1<i>a</i>) and -the change in the wing-bow. The tail-coverts have also grown long.</p></div> - -<p class="c"><span class="smcap"><a href="#plt_2">Plate 2.</a></span></p> - -<div class="blockquott"><p><span class="smcap">Fig. 1.</span> F₁ hen-feathered male out of Game by Sebright. The -hen-feathering in this bird is as complete as in the Sebright.</p> - -<p><span class="smcap">Fig. 2.</span> F₁ female out of Game by Sebright.</p> - -<p><span class="smcap">Fig. 3.</span> Castrated male originally hen-feathered (292), nearly black -in color, as shown by the individual feathers of <a href="#plt_7">plate 7</a>, figure 2. -After castration the bird has become red above, with black -iridescent tail-coverts, and deeper yellow (or red) below.</p> - -<p><span class="smcap">Fig. 4.</span> Castrated F₁ male, originally like figure 1. Note -especially the change in color of the whole upper surface that has -become red, like that of the jungle-fowl. The tail-coverts have -grown long and are now iridescent black. The breast has changed -least, but is a richer yellow. The comb and wattles and ear lobes -are shrunken, as in all capons.</p></div> - -<p class="c"><span class="smcap"><a href="#plt_3">Plate 3.</a></span></p> - -<div class="blockquott"><p><span class="smcap">Fig. 1.</span> A castrated Sebright male. The operation was performed on a -juvenile bird; the drawing was made a year later. The bird is -typical as to the change in color that takes place in the Sebright. -He was darker red than the bird shown in <a href="#plt_1">plate 1</a>, figure 4. The red -was more mahogany than the picture shows. The original feathers -were like those in <a href="#plt_6">plate 6</a>, fig. 2 (there erroneously referred to -as those of light-colored Sebright).</p> - -<p><span class="smcap">Fig. 2.</span> An F₂ hen-feathered very dark male. The condition of his -plumage at the time of the operation is shown in this figure. The -change that took place after castration is shown in the next -figure.</p> - -<p><span class="smcap">Fig. 3.</span> The change that took place in the bird drawn in figure 2 is -shown here. The whole upper surface has become red, except the -tail-coverts, which are iridescent black. Note also the change in -color on the wing-bow. For the details of the feathers see <a href="#plt_9">plate 9</a>, -figures 1, 1<i>a</i>.</p> - -<p><span class="smcap">Fig. 4.</span> A castrated F₂ bird that had been hen-feathered and had -changed over to cock-feathering, as shown here. The color and the -details of the original hen-feathering are shown in <a href="#plt_9">plate 9</a>, -figures 2 and 2<i>a</i>.</p></div><p><span class="pagenum"><a name="page_107" id="page_107">{107}</a></span></p> - -<p class="c"><span class="smcap"><a href="#plt_4">Plate 4.</a></span></p> - -<div class="blockquott"><p><span class="smcap">Fig. 1.</span> One of the original Black-Breasted Game males used in the -breeding experiments. Compare with colored drawing, <a href="#plt_1">plate 1</a>, figure -1.</p> - -<p><span class="smcap">Fig. 2.</span> A Black-Breasted Game hen used in the breeding experiments. -Compare with colored drawing, <a href="#plt_1">plate 1</a>, figure 2.</p> - -<p><span class="smcap">Fig. 3.</span> A Sebright male. The bird was used in the later -back-crosses and not in the original experiments. He is typical of -his breed.</p> - -<p><span class="smcap">Fig. 4.</span> A Sebright female. One of the birds used in the original -experiments.</p> - -<p><span class="smcap">Fig. 5.</span> An F₁ male. This bird had just reached maturity and was -younger than the one drawn in <a href="#plt_2">plate 2</a>, figure 1.</p> - -<p><span class="smcap">Fig. 6.</span> An F₁ hen of the same age as the last. The pattern changed -a little as the bird became older.</p></div> - -<p class="c"><span class="smcap"><a href="#plt_5">Plate 5.</a></span></p> - -<div class="blockquott"><p><span class="smcap">Fig. 1.</span> An adult Sebright male for comparison with the next figure.</p> - -<p><span class="smcap">Fig. 2.</span> A castrated Sebright male. This photograph shows the same -bird from which the drawing, <a href="#plt_1">plate 1</a>, figure 4, was made. It is the -lighter colored bird referred to in the text.</p> - -<p><span class="smcap">Fig. 3.</span> One of the two F₁ castrated birds. For comparison see the -colored drawing in <a href="#plt_2">plate 2</a>, figure 4.</p> - -<p><span class="smcap">Fig. 4.</span> A castrated Sebright. This bird is darker, and in this -sense more typical than figure 2.</p> - -<p><span class="smcap">Fig. 5.</span> One of the castrated Sebright males which at one time after -castration was as extremely cock-feathered as figure 2, but slowly -“went back” towards hen-feathering, as the figure shows especially -in the hackle and saddle. The details are much better shown in the -feathers photographed in <a href="#plt_8">plate 8</a>, figures 1, 2, 3, 4, 1<i>a</i>, 2<i>a</i>, -3<i>a</i>, 4<i>a</i>, 1<i>b</i>, 2<i>b</i>, 3<i>b</i>, 4<i>b</i>.</p> - -<p><span class="smcap">Fig. 6.</span> The same bird was opened and the regenerated pieces of the -testis removed. He returned later, as shown here, to full -cock-feathering.</p></div> - -<p class="c"><span class="smcap"><a href="#plt_6">Plate 6.</a></span></p> - -<div class="blockquott"><p><span class="smcap">Figs. 1, 1a.</span> Typical old (1) and new (1<i>a</i>) feathers (after -castration) of the same bird. This is the “lighter” male drawn in -<a href="#plt_1">plate 1</a>, figure 4, and photographed in <a href="#plt_5">plate 5</a>, figure 2.</p> - -<p><span class="smcap">Figs. 2, 2a.</span> Typical old (2) and new (2<i>a</i>) (after castration) -feathers of another Sebright. This bird developed after castration -darker feathers than did the last bird. Its feathers were more like -those that other castrated Sebrights developed. Legend on <a href="#plt_6">plate 6</a> -erroneous as far as 2 and 2a are concerned.</p></div> - -<p class="c"><span class="smcap"><a href="#plt_7">Plate 7.</a></span></p> - -<div class="blockquott"><p><span class="smcap">Figs. 1, 1a.</span> Typical old (1) and new (1<i>a</i>) (after castration) -feathers of an F₁ bird. (See <a href="#plt_2">plate 2</a>, figures 1 and 4.)</p> - -<p><span class="smcap">Figs. 2, 2a.</span> Typical old (2) and new (2<small>A</small>) (after castration) -feathers of bird shown in <a href="#plt_3">plate 3</a>, figures 2 and 3 (No. 292).</p></div> - -<p class="c"><span class="smcap"><a href="#plt_8">Plate 8.</a></span></p> - -<div class="blockquott"><p>Typical feathers of “dark” Sebright (1, 2, 3, 4) that after -incomplete castration changed to cock-feathering (1<i>a</i>, 2<i>a</i>, 3<i>a</i>, -4<i>a</i>), then later, as pieces of the testes that had been left -behind in the old situs regenerated, began to go back towards -hen-feathering (1<i>b</i>, 2<i>b</i>, 3<i>b</i>, 4<i>b</i>). The bird was then opened -again, and the regenerated pieces removed, when it again became -cock-feathered (1<i>c</i>, 2<i>c</i>, 3<i>c</i>, 4<i>c</i>), and has so remained for -more than a year.</p></div><p><span class="pagenum"><a name="page_108" id="page_108">{108}</a></span></p> - -<p class="c"><span class="smcap"><a href="#plt_9">Plate 9.</a></span></p> - -<div class="blockquott"><p><span class="smcap">Figs. 1, 1a.</span> Typical feathers of hackle and saddle from -hen-feathered bird (No. 68) <a href="#plt_3">plate 3</a>, figure 2, that changed over to -the cock-feathered bird of <a href="#plt_3">plate 3</a>, figure 3.</p> - -<p><span class="smcap">Figs. 2, 2a.</span> Typical feathers of an F₁ male (2) that changed over -partly as a result of degeneration of his testes, into a -cock-feathered bird (2<small>A</small>). The change was not so great as it is -after castration.</p> - -<p><span class="smcap">Figs. 3, 3a.</span> Typical feathers of Sebright male that slightly -changed towards cock-feathering (old hackle feather missing).</p></div> - -<p class="c"><span class="smcap"><a href="#plt_10">Plate 10.</a></span></p> - -<div class="blockquott"><p><span class="smcap">Figs. 1, 1a.</span> Old (1) and new (1<small>A</small>) wing-coverts of normal Sebright -(1) and castrated (1<small>A</small>).</p> - -<p><span class="smcap">Figs. 2a, 2b.</span> Upper row, to right, “Transitional” hackle feathers -(2<small>A</small>), and a slightly later changed-over feather from wing-bow (2<small>A</small>), -and from back (2<span class="smcap">B</span>). Second row, to left, old (2), transitional -(2<i>a</i>), and changed-over feather (2<i>b</i>), from saddle of Sebright.</p> - -<p><span class="smcap">Fig. 3.</span> Three feathers (tail-covert, wing-bow, and saddle) of an F₂ -hen-feathered game-like male.</p> - -<p><span class="smcap">Fig. 4.</span> A series of breast feathers from an F₂ bird. At one end of -the series (the left) the feather is spangled, at the other barred.</p> - -<p><span class="smcap">Fig. 5.</span> A series of breast feathers from another F₂ bird. At one -end of the series (the left) the feathers are penciled, at the -other end they are barred.</p></div><p><span class="pagenum"><a name="page_109" id="page_109">{109}</a></span></p> - -<div class="figcenter"> -<a name="plt_1" id="plt_1"></a> -<br /> -<a href="images/i_plate01_lg.jpg"> -<img src="images/i_plate01_sml.jpg" width="374" height="550" alt="[Image unavailable.]" /></a> -<div class="caption"><p class="c">PLATE 1</p> - -<table border="0" cellpadding="0" cellspacing="0" summary="" -style="text-align:left;"> - -<tr><td>1. Black Breasted Game Bantam male. <br /> -2. Female.<br /></td> -<td>3. Sebright male.<br /> -4. Castrated Sebright male.</td></tr> -</table> -</div> -</div> - -<p><span class="pagenum"><a name="page_111" id="page_111">{111}</a></span></p><p><span class="pagenum"><a name="page_110" id="page_110">{110}</a></span></p> - -<div class="figcenter"> -<a name="plt_2" id="plt_2"></a> -<br /> -<a href="images/i_plate02_lg.jpg"> -<img src="images/i_plate02_sml.jpg" width="365" height="550" alt="[Image unavailable.]" /></a> -<div class="caption"><p class="c">PLATE 2<br /></p> -<table border="0" cellpadding="0" cellspacing="0" summary="" -style="text-align:left;"> - -<tr><td> -1. Hen-feathered F₁ male. <br /> -2. F₁ female.<br /></td><td> -3. Castrated F₂ male.<br /> -4. Castrated F₁ male (Fig. 1).<br /></td> -</tr> -</table> -</div> -</div> - -<p><span class="pagenum"><a name="page_113" id="page_113">{113}</a></span></p><p><span class="pagenum"><a name="page_112" id="page_112">{112}</a></span></p> - -<div class="figcenter"> -<a name="plt_3" id="plt_3"></a> -<br /> -<a href="images/i_plate03_lg.jpg"> -<img src="images/i_plate03_sml.jpg" width="366" height="550" alt="[Image unavailable.]" /></a> -<div class="caption"><p class="c">PLATE 3<br /></p> - -<table border="0" cellpadding="0" cellspacing="0" summary="" -style="text-align:left;"> - -<tr><td> -1. Castrated Sebright male. <br /> -2. F₂ Hen-feathered male.<br /></td><td> -3. Same castrated.<br /> -4. F₂ Castrated male.<br /></td></tr> -</table> -</div> -</div> - -<p><span class="pagenum"><a name="page_115" id="page_115">{115}</a></span></p><p><span class="pagenum"><a name="page_114" id="page_114">{114}</a></span></p> - -<div class="figcenter"> -<a name="plt_4" id="plt_4"></a> -<br /> -<a href="images/i_plate04_lg.jpg"> -<img src="images/i_plate04_sml.jpg" width="374" height="550" alt="[Image unavailable.]" /></a> -<div class="caption"><p class="c">PLATE 4<br /></p> - -<table border="0" cellpadding="0" cellspacing="0" summary="" -style="text-align:left;"> - -<tr><td> -1. Black-Breasted Game male.<br /> -2. Black-Breasted Game female. <br /> -3. Sebright male.<br /></td><td> -4. Sebright female.<br /> -5. Hybrid male.<br /> -6. Hybrid female.<br /></td></tr> -</table></div> -</div> - -<p><span class="pagenum"><a name="page_117" id="page_117">{117}</a></span></p><p><span class="pagenum"><a name="page_116" id="page_116">{116}</a></span></p> - -<div class="figcenter"> -<a name="plt_5" id="plt_5"></a> -<br /> -<a href="images/i_plate05_lg.jpg"> -<img src="images/i_plate05_sml.jpg" width="394" height="550" alt="[Image unavailable.]" /></a> -<div class="caption"><p class="c">PLATE 5<br /></p> -<table border="0" cellpadding="0" cellspacing="0" summary="" -style="text-align:left;"> - -<tr><td> -1. Adult Sebright male.<br /> -2. Castrated Sebright male. <br /> -3. Castrated F₁ male.<br /></td><td> -4. Another castrated Sebright male.<br /> -5. Castrated Sebright male with testes regenerating.<br /> -6. Same as 5 after second removal of testes.</td></tr> -</table> -</div> -</div> - -<p><span class="pagenum"><a name="page_119" id="page_119">{119}</a></span></p><p><span class="pagenum"><a name="page_118" id="page_118">{118}</a></span></p> - -<div class="figcenter"> -<a name="plt_6" id="plt_6"></a> -<br /> -<a href="images/i_plate06_lg.jpg"> -<img src="images/i_plate06_sml.jpg" width="366" height="550" alt="[Image unavailable.]" /></a> -<div class="caption"><p class="c">PLATE 6<br /></p> - -<p class="c">Feathers of “light” colored Sebright (1, 2) that changed to -cock-feathers after castration (1ªa, 2ª).</p></div> -</div> - -<p><span class="pagenum"><a name="page_121" id="page_121">{121}</a></span><span class="pagenum"><a name="page_120" id="page_120">{120}</a></span></p> - -<div class="figcenter"> -<a name="plt_7" id="plt_7"></a> -<br /> -<a href="images/i_plate07_lg.jpg"> -<img src="images/i_plate07_sml.jpg" width="366" height="550" alt="[Image unavailable.]" /></a> -<div class="caption"><p class="c">PLATE 7<br /></p> - -<p class="c">Feathers of F₁ hen-feathered male before (1), and after (1ª) castration.</p> - -<p class="c">Feathers of a darker hen-feathered male before (2), and after (2ª) -castration.</p></div> -</div> - -<p><span class="pagenum"><a name="page_123" id="page_123">{123}</a></span><span class="pagenum"><a name="page_122" id="page_122">{122}</a></span></p> - -<div class="figcenter"> -<a name="plt_8" id="plt_8"></a> -<br /> -<a href="images/i_plate08_lg.jpg"> -<img src="images/i_plate08_sml.jpg" width="365" height="550" alt="[Image unavailable.]" /></a> -<div class="caption"><p class="c">PLATE 8<br /></p> - -<p>Feathers from hen-feathered male Sebright (1, 2, 3, 4) that changed to -cock-feathered male (1ª, 2ª, 3ª, 4ª) after castration; and then began to -go back as the testes regenerated (1ᵇ, 2ᵇ, 3ᵇ, 4ᵇ); then changed again -to cock-feathering after castration (1ᶜ, 2ᶜ, 3ᶜ, 4ᶜ).</p></div> -</div> - -<p><span class="pagenum"><a name="page_125" id="page_125">{125}</a></span><span class="pagenum"><a name="page_124" id="page_124">{124}</a></span></p> - -<div class="figcenter"> -<a name="plt_9" id="plt_9"></a> -<br /> -<a href="images/i_plate09_lg.jpg"> -<img src="images/i_plate09_sml.jpg" width="358" height="550" alt="[Image unavailable.]" /></a> -<div class="caption"><p class="c">PLATE 9<br /></p> - -<p class="c">Feathers showing complete (1) or incomplete (2 and 3) change from -hen-feathering to cock-feathering (1ª, 2ª, 3ª) after castration.</p></div> -</div> - -<p><span class="pagenum"><a name="page_127" id="page_127">{127}</a></span><span class="pagenum"><a name="page_126" id="page_126">{126}</a></span></p> - -<div class="figcenter"> -<a name="plt_10" id="plt_10"></a> -<br /> -<a href="images/i_plate10_lg.jpg"> -<img src="images/i_plate10_sml.jpg" width="359" height="550" alt="[Image unavailable.]" /></a> -<div class="caption"><p class="c">PLATE 10<br /></p> - -<p class="c">Normal. 1, 2; transitional, 1ª, 2ª, and changed-over feathers, 2ᵇ, of -Sebright, 3, 4 and 5. Feathers from F₂ birds.</p></div> -</div> - -<div class="footnotes"><p class="cb">FOOTNOTES:</p> - -<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> The expectation for 1 dominant and 1 recessive factor is so -nearly the same as for 1 dominant alone that for the numbers obtained no -difference between the two cases could be detected.</p></div> - -<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> There is one other bird, not given in the above list, that -is pure Sebright except that his legs are yellow. Until I find out by -further breeding of the Sebright stock whether yellow legs are present -in it, this case must remain doubtful. On the basis of a two factor -color-difference one Sebright (as to color) is expected in 16 birds, and -one in 64 on a three factor basis. Some Sebrights had been raised along -with the back cross, hence the possibility of contamination.</p></div> - -<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> Provided that the blue classification was based on the -adult plumage and not on down color.</p></div> - -<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> If the recessive mutation occurs first in the Z chromosome -of an egg of the female it will not appear in the next generation; then -if it has passed into a male, half his daughters will show it. The -single factor-pair involved is carried by the sex chromosomes ZZ.</p></div> - -<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> One may be either sex-linked or sex-limited so far as the -evidence goes.</p></div> - -<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> No mention is made by Baur that a heterozygous male instead -of a pure silver male was used, although the male is made heterozygous -in the formulæ.</p></div> - -<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> For activity and pugnacity in hummingbirds, see Tropical -Nature, pp. 130, 213.</p></div> - -<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a> The Naturalist in La Plata, W. H. Hudson, London, 1892, pp. -269-270.</p></div> - -<div class="footnote"><p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> Proceedings of the Zoological Society of London, 1885, p. -431, Quelques remarques sur le dimorphisme sexuel. Jean Stolzmann.</p></div> - -<div class="footnote"><p><a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a> George W. and Elizabeth G. Peckham. Observations on Sexual -Selection in Spiders of the Family Attidæ. Nat. Hist. Soc. of Wisconsin, -Vol. I, 1889, pp, 46, 47.</p></div> - -<div class="footnote"><p><a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11]</span></a> <i>Loddigesia mirabilis</i> has the tail about three times as -long as the body. Similar modifications are found in the genera -<i>Sappho</i>, <i>Cynanthus</i>, <i>Lesbia</i>, <i>Stegnura</i>, <i>Discura</i>, <i>Gouldia</i>, <i>et -al.</i></p></div> - -<div class="footnote"><p><a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12"><span class="label">[12]</span></a> Among the most remarkable of this wonderful family are the -nine species of coquettes (<i>Lophornis</i>), which have elongated feathers, -with metallic tips, springing from the sides of the neck; some have also -beautiful crests. (George W. and Elizabeth G. Peckham, Additional -Observations on Sexual Selection in Spiders of the Family Attidæ, Nat. -Hist. Soc. of Wisconsin, 1889, vol. I, pp. 141, 142.)</p></div> - -<div class="footnote"><p><a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a> Tropical Nature, p. 210. The italics are ours.</p></div> - -<div class="footnote"><p><a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span class="label">[14]</span></a> A. H. Sturtevant, Experiments on Sex Recognition and the -Problem of Sexual Selection in <i>Drosophila</i>. Journ. Animal Behavior, -Sept.-Oct. 1915, vol. 5, No. 5, pp. 352, 353.</p></div> - -<div class="footnote"><p><a name="Footnote_15_15" id="Footnote_15_15"></a><a href="#FNanchor_15_15"><span class="label">[15]</span></a> In the eland as well as in the reindeer, in which both -sexes have horns that begin in the latter at least to develop before the -gonads ripen, it is stated that castration does not prevent the -development of the horns in the male, but whether they are as large as -in the normal male is apparently not definitely stated.</p></div> - -<div class="footnote"><p><a name="Footnote_16_16" id="Footnote_16_16"></a><a href="#FNanchor_16_16"><span class="label">[16]</span></a> Yarrell also states that after the fallow buck has reached -the height of its maturity and has 6 prongs in its antler, removal of -one testis causes the next antler to have but 5 prongs.</p></div> - -<div class="footnote"><p><a name="Footnote_17_17" id="Footnote_17_17"></a><a href="#FNanchor_17_17"><span class="label">[17]</span></a> It might be supposed that this bird was really a cock -which had been changed for a hen; but the following facts put this -matter beyond a doubt: First, there was no other pyed pea-fowl in the -country. Secondly, the hen had knobs on her toes, which were the same -after her change. Thirdly, she was as small after the change as before, -therefore too small for a cock. Fourthly, she was a favorite bird, and -was generally fed by the lady, and used to come for her meat, which she -still continued to do after the change in the feathers.</p></div> - -<div class="footnote"><p><a name="Footnote_18_18" id="Footnote_18_18"></a><a href="#FNanchor_18_18"><span class="label">[18]</span></a> See the latter also for references to <i>Lacertilia</i> and -<i>Chelonia</i>.</p></div> - -<div class="footnote"><p><a name="Footnote_19_19" id="Footnote_19_19"></a><a href="#FNanchor_19_19"><span class="label">[19]</span></a> Carnegie Inst. Wash. Pub. No. 278, 1918.</p></div> - -</div> - -<hr class="full" /> - - - - - - - -<pre> - - - - - -End of the Project Gutenberg EBook of The Genetic and the operative evidence -relating to secondary sexual character, by Thomas Hunt Morgan - -*** END OF THIS PROJECT GUTENBERG EBOOK THE GENETIC *** - -***** This file should be named 57460-h.htm or 57460-h.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/5/7/4/6/57460/ - -Produced by Larry B. 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