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+The Project Gutenberg eBook, On the Origin and Metamorphoses of Insects,
+by Sir John Lubbock
+
+
+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
+
+
+
+
+
+Title: On the Origin and Metamorphoses of Insects
+
+
+Author: Sir John Lubbock
+
+
+
+Release Date: December 3, 2011  [eBook #38207]
+
+Language: English
+
+Character set encoding: UTF-8
+
+
+***START OF THE PROJECT GUTENBERG EBOOK ON THE ORIGIN AND METAMORPHOSES OF
+INSECTS***
+
+
+E-text prepared by Bryan Ness, Turgut Dincer, and the Online Distributed
+Proofreading Team (http://www.pgdp.net) from page images generously made
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+      +--------------------------------------------------------------+
+      | Transcriber's note:                                          |
+      |                                                              |
+      | All non-italic genus names in the text have been italicized. |
+      +--------------------------------------------------------------+
+
+
+
+
+
+[Illustration: NATURE SERIES]
+
+
+
+
+ORIGIN AND METAMORPHOSES OF INSECTS.
+
+[Illustration]
+
+Nature Series
+
+ON THE ORIGIN AND METAMORPHOSES OF INSECTS
+
+BY
+
+Sir John Lubbock, Bart., M.P., F.R.S., D.C.L., LL.D.
+
+Principal of the London Working Men's College; President of the London
+Chamber of Commerce; and Vice-Chairman of the London County Council
+
+With Numerous Illustrations
+
+
+
+
+
+
+
+London Macmillan and Co. and New York 1890
+
+The Right of Translation and Reproduction is Reserved
+
+Richard Clay and Sons, Limited, London and Bungay.
+
+First Edition 1873. Reprinted 1874. New Edition 1890.
+
+
+
+
+PREFACE.
+
+
+For some years, much of my leisure time has been devoted to the study of
+the anatomy, development, and habits of the Annulosa, and especially of
+Insects, on which subjects I have published various memoirs, chiefly in
+the Transactions of the Royal, Linnæan, and Entomological Societies: of
+these papers I subjoin a list. Although the details, of which these
+memoirs necessarily for the most part consist, offer little interest,
+excepting to those persons who are specially devoted to Entomology,
+still there are portions which, having reference to the nature of
+metamorphoses and to the origin of insects, are of a more general
+character. I have also briefly referred to these questions in a
+Monograph of the Collembola and Thysanura, recently published by the Ray
+Society, and in the Opening Address to the Biological Section of the
+British Association at Brighton in 1872. Under these circumstances, it
+has been suggested to me that a small volume, containing, at somewhat
+greater length, in a more accessible form, and with the advantage of
+illustrations, the conclusions to which I have been led on this
+interesting subject, might not be altogether without interest to the
+general reader. The result, which has already appeared in the pages of
+_Nature_, is now submitted to the public, with some additions. I am well
+aware that it has no pretence to be in any sense a complete treatise;
+that the subject itself is one as to which our knowledge is still very
+incomplete, and on which the highest authorities are much divided in
+opinion. Whatever differences of opinion, however, there may be as to
+the views here put forward, the facts on which they are based will, I
+believe, be found correct. On this point I speak with the more
+confidence, on account of the valuable assistance I have received from
+many friends: to Mr. and Mrs. Busk and Dr. Hooker I am especially
+indebted.
+
+The papers above referred to are as follows:—
+
+   1. _On Labidocera._—Annals and Magazine of Natural History,
+        vol. xi., 1853.
+
+   2. On Two New Sub-genera of Calanidæ.—Annals and Magazine of
+        Natural History, vol. xii., 1853.
+
+   3. On Two New Species of Calanidæ.—Annals and Magazine of
+        Natural History, vol. xii., No. lxvii., 1853.
+
+   4. On Two New Species of Calanidæ.—Annals and Magazine of
+        Natural History, vol. xii., No. lxix., 1853.
+
+   5. On some Arctic Calanidæ.—Annals and Magazine of Natural
+        History, 1854.
+
+   6. On the Freshwater Entomostraca of South
+        America.—Transactions of the Entomological Society, vol.
+        iii., 1855.
+
+   7. On some New Entomostraca.—Transactions of the
+        Entomological Society, vol. iv., 1856.
+
+   8. On some Marine Entomostraca found at Weymouth.—Annals and
+        Magazine of Natural History, vol. xx., 1857.
+
+   9. On the Respiration of Insects.—Entomological Annual, 1857.
+
+  10. An Account of the Two Methods of Reproduction in
+         _Daphnia_.—Transactions of the Royal Society, 1857.
+
+  11. On the Ova and Pseudova of Insects.—Transactions of the
+        Royal Society, 1858.
+
+  12. On the Arrangement of the Cutaneous Muscles of _Pygæra
+        Bucephala_.—Linnean Society’s Transactions, vol. xxii., 1858.
+
+  13. On the Freshwater Entomostraca of South
+        America.—Entomological Society’s Transactions, 1858.
+
+  14. On _Coccus Hesperidum_.—Royal Society Proceedings, vol.
+        ix., 1858.
+
+  15. On the Distribution of Tracheæ in Insects.—Linnean
+        Society’s Transactions, vol. xxiii., 1860.
+
+  16. On the Generative Organs and on the Formation of the Egg
+        in Annulosa. Transactions of the Royal Society, 1861.
+
+  17. On _Sphærularia Bombi._—Natural History Review, 1861.
+
+  18. On some Oceanic Entomostraca.—Linnean Society’s
+        Transactions, vol. xxiii., 1860.
+
+  19. On the Thysanura. Part 1.—Linnean Society’s Transactions,
+        1862.
+
+  20. On the Development of Lonchoptera.—Entomological
+        Society’s Transactions, 1862.
+
+  21. On the Thysanura. Part 2.—Linnean Society’s Transactions,
+        1862.
+
+  22. On the Development of Chloëon. Part 1.—Linnean Society’s
+        Transactions, 1863.
+
+  23. On Two Aquatic Hymenoptera.—Linnean Society’s
+        Transactions, 1863.
+
+  24. On some little-known Species of Freshwater
+        Entomostraca.—Linnean Society’s Transactions, vol. xxiv.,
+        1863.
+
+  25. On _Sphærularia Bombi_.—Natural History Review, 1864.
+
+  26. On the Development of Chloëon. Part 2.—Linnean Society’s
+        Transactions, 1865.
+
+  27. Metamorphoses of Insects.—Journal of the Royal
+        Institution, 1866.
+
+  28. On _Pauropus_.—Linnean Society’s Transactions, 1866.
+
+  29. On the Thysanura. Part 3.—Linnean Society’s Transactions,
+        1867.
+
+  30. Address to the Entomological Society.—Entomological
+        Society’s Transactions, 1867.
+
+  31. On the Larva of Micropeplus Staphilinoides.—Entomological
+        Society’s Transactions, 1868.
+
+  32. On the Thysanura. Part 4.—Linnean Society’s Transactions,
+        1869.
+
+  33. Addresses to the Entomological Society.—Entomological
+        Society’s Transactions, 1867-1868.
+
+  34. On the Origin of Insects.—Journal of the Linnean Society,
+        vol. xi.
+
+  35. Opening Address to the Biological Section of the British
+        Association.—British Association Report, 1872.
+
+  36. Observations on Ants, Bees, and Wasps. Part 1.—Journal of
+        the Linnean Society, 1873.
+
+  37. On British Wild Flowers considered in relation to Insects,
+        1874.
+
+  38. Observations on Ants, Bees, and Wasps. Part 2.—Journal of
+        the Linnean Society, 1874.
+
+  39. Observations on Ants, Bees, and Wasps. Part 3.—Journal of
+        the Linnean Society, 1875.
+
+  40. Observations on Ants, Bees, and Wasps. Part 4.—Journal of
+        the Linnean Society, 1877.
+
+  41. On some Points in the Anatomy of Ants.—Quekett Lecture,
+        1877.—Microscopical Journal.
+
+  42. On the Colors of Caterpillars.—Entomological Society’s
+        Transactions, 1878.
+
+  43. Observations on Ants, Bees, and Wasps. Part 5.—Journal of
+        the Linnean Society, 1878.
+
+  44. Observations on Ants, Bees, and Wasps. Part 6.—Journal of
+        the Linnean Society, 1879.
+
+  45. On the Anatomy of Ants.—Linnean Society’s Transactions,
+        1880.
+
+  46. Observations on Ants, Bees, and Wasps. Part 7.—Journal of
+        the Linnean Society, 1880.
+
+  47. Observations on Ants, Bees, and Wasps. Part 8.—Journal of
+        the Linnean Society, 1881.
+
+  48. On Fruits and Seeds.—Journal of the Royal Institution,
+        1881.
+
+  49. Observations on Ants, Bees, and Wasps. Part 9.—Journal of
+        the Linnean Society, 1881.
+
+  50. On the Limits of Vision among some of the lower
+        Animals.—Journal of the Linnean Society, 1881.
+
+  51. Observations on Ants, Bees, and Wasps. Part 10.—Journal
+        of the Linnean Society, 1882.
+
+
+
+
+CONTENTS.
+
+
+  CHAPTER I.
+
+  THE CLASSIFICATION OF INSECTS.
+
+  Introduction.—Stages in the Life of an Insect.—Classification
+    of Insects.—Characters derived from the Wings; from the parts
+    of the Mouth; from the Metamorphoses.—The Classes of Insects:
+    Hymenoptera, Strepsiptera, Coleoptera, Euplexoptera,
+    Orthoptera, Thysanoptera, Neuroptera, Trichoptera, Diptera,
+    Aphaniptera, Heteroptera, Homoptera, Lepidoptera          _page_ 1-26
+
+
+  CHAPTER II.
+
+  THE INFLUENCE OF EXTERNAL CONDITIONS ON THE FORM AND STRUCTURE
+  OF LARVÆ.
+
+  Larvæ depend partly on the group to which they
+    belong.—Wood-eating Larvæ.—Larvæ of Lamellicorns.—Larvæ
+    depend also in part on mode of life.—Larvæ of Hymenoptera, of
+    _Sirex_; of _Tenthredo_; of Ichneumons; of Bees.—Rudimentary
+    legs of Bee Embryo.—Beetles, _Weevils_, _Scolytus_,
+    _Crioceris_, _Sitaris_, Metamorphoses of Pteromalidæ.
+    _Platygaster_, _Polynema_.—Influence of external
+    conditions.—Developmental and adaptive Metamorphoses    _page_ 27-41
+
+
+  CHAPTER III.
+
+  THE NATURE OF METAMORPHOSES.
+
+  The life history of an Insect must be considered as a
+    whole.—Vagueness of the term Larva.—Some larvæ much more
+    advanced than others.—Organs develope in different order, in
+    different groups.—Suppressed stages.—Apod condition of
+    _Phryganea_; of _Aphis_; of
+    _Chrysopa_.—Libellulidæ.—_Donacia_.—Spiders.—Myriapods.—Apod
+    stage of Homomorphous Insects once probably longer than
+    now.—Suppression of embryonic stages.—Metamorphoses of
+    Hydroida, Crustacea, Isopods, and
+    Amphipods.—Echinoderms.—Variations in development induced by
+    the influence of external conditions.                    _page_ 41-62
+
+
+  CHAPTER IV.
+
+  THE ORIGIN OF METAMORPHOSES.
+
+  Origin of Metamorphoses.—Views of Messrs. Kirby and
+    Spence.—Nature of the question.—Young animals often more
+    similar than mature.—Views of Darwin, Herbert Spencer,
+    Johannes Müller, Fritz Müller, and Agassiz.—Effect of size of
+    egg.—Insects leave the egg in a more or less developed
+    condition.—Consideration of pupal condition.—Quiescence of
+    pupa.—Period of quiescence at each moult.—Changes not so
+    abrupt as generally supposed.—Change in
+    mouth-parts.—Difficulty in reference to Darwinian
+    theory.—Mouth-parts of _Campodea_ and Collembola, as
+    intermediate between the mandibulate and haustellate
+    types.—Change in mouth-parts as connected with pupal
+    conditions.—Origin of wings.—Use of wings under
+    water.—Connection of metamorphoses with alternation of
+    generations.—Parthenogenetic larvæ of _Cecidomyia_.—In
+    alternation of generations one form always agamic.—Dimorphism
+    and Dieidism.—Summary and Conclusions                   _page_ 62-81
+
+
+  CHAPTER V.
+
+  THE ORIGIN OF INSECTS.
+
+  The Origin of Insects.—Mistaken views of Darwinian
+    theory.—Natural selection a _vera causa_.—Application of
+    Darwin’s views to Insects.—Similarity of young Crustacea as
+    compared with mature forms; ditto in Insects.—Type of
+    Insecta.—Two principal types of larvæ: Hexapod and
+    Apod.—Conclusions to be drawn from them.—_Campodea_ the modern
+    representative of the Insect-stock.—_Campodea_, perhaps
+    derived from Tardigrade.—Vermiform or Apod type of
+    larva.—Views of Fritz Müller, Brauer, and Packard.—Represents
+    a still earlier ancestor.—Modern representatives.—_Notommata_,
+    _Albertia_, _Lindia_.—Earlier forms difficult to trace.—Lowest
+    forms of animal life.—Yolk-segmentation.—Embryology and
+    Evolution.—Light thrown by the evolution of the individual on
+    that of the species                                     _page_ 82-108
+
+  DESCRIPTION OF THE PLATES.
+
+
+  PLATE I. p. 7.
+
+  FIG.
+
+  1. Cricket. Westwood, Intro. to the Modern Classification of
+       Insects, vol. i. p. 440.
+
+  2. Earwig. Westwood, loc. cit. vol. i. p. 399.
+
+  3. _Aphis_. Packard, Guide to the Study of Insects, pp. 521, 522.
+
+  4. _Scolytus_. Westwood, loc. cit. vol. i. p. 350.
+
+  5. _Anthrax_. Westwood, loc. cit. vol. ii. p. 538.
+
+  6. _Balaninus_.
+
+  7. _Cynips_. Westwood, loc. cit. vol. ii. p. 121.
+
+  8. Ant (_Formica_). Westwood, loc. cit. vol. ii. p. 218.
+
+  9. Wasp. Ormerod, Nat. Hist. of Wasps, pl. i. fig. 1.
+
+
+  PLATE II. p. 8.
+
+  FIG.
+
+  1. Larva of Cricket. Westwood, loc. cit. vol. i. p. 440.
+
+  2. Larva of _Aphis_. Packard, loc. cit. pp. 521, 522.
+
+  3. Larva of Earwig. Westwood, loc. cit. vol. i. p. 399.
+
+  4. Larva of _Scolytus_. Westwood, loc. cit. vol. i. p. 350.
+
+  5. Larva of _Anthrax_. Westwood, loc. cit. vol. ii. p. 546.
+
+  6. Larva of _Balaninus_.
+
+  7. Larva of _Cynips_. Westwood, loc. cit. vol. ii. p. 121.
+
+  8. Larva of Ant (_Formica_). Westwood, loc. cit. vol. ii. p. 226.
+
+  9. Larva of Wasp. Newport, Art. Insecta, Todd’s Cycl. Anat. and
+       Phys., p. 871.
+
+
+  PLATE III. p. 14.
+
+  FIG.
+
+  1. _Chloëon_. Linn. Trans. 1866.
+
+  2. _Meloë_. Spry and Shuckard, Coleoptera Delineated, pl. 56.
+
+  3. _Calepteryx_.
+
+  4. _Sitaris_. Spry and Shuckard, loc. cit. pl. 56.
+
+  5. _Campodea_. Suites à Buffon. Aptéres.
+
+  6. _Acilius_. Westwood, loc. cit. vol. i. p. 100.
+
+  7. _Termes_. Westwood, loc. cit. vol. ii. p. 12.
+
+  8. _Stylops_. Duncan, Met. of Insects, p. 387; Packard, p. 482.
+
+  9. _Thrips_. Westwood, loc. cit. vol. ii. p. 1.
+
+
+  PLATE IV. p. 15.
+
+  FIG.
+
+  1. Larva of _Chloëon_. Linn. Trans. 1863.
+
+  2. Larva of _Meloë_. Chapuis and Candèze, Mem. Soc. Roy. Liége,
+       1853, pp. 1, 7.
+
+  3. Larva of _Calepteryx_. Dufour, Ann. Sci. Nat. 1852.
+
+  4. Larva of _Sitaris_. Duncan, Met. of Insects, p. 309.
+
+  5. Larva of _Campodea_. Gervais’ Suites à Buffon. Aptéres.
+
+  6. Larva of _Acilius_. Westwood, loc. cit. vol. i. p. 100.
+
+  7. Larva of _Termes_. Duncan, loc. cit. p. 348.
+
+  8. Larva of _Stylops_. Westwood, Trans. Ent. Soc. 1839, vol. ii.
+       pl. xv. fig. 13a.
+
+  9. Larva of _Thrips_. Westwood, loc. cit. vol. ii. p. i.
+
+
+  PLATE V. p. 99.
+
+  FIG.
+
+  1-5. _Protamœba_.
+
+  6-9. _Protamyxa aurantiaca_. Haeckel Beit. zur. Monog. der
+         Moneren, pl. 1.
+
+  10-18. _Magosphœra planula_. Haeckel, loc. cit. pl. v.
+
+
+  PLATE VI. p. 105.
+
+  FIG.
+
+  1-4. Yolk-segmentation in _Laomedea_. After Allman. Mon. of
+         Tubularian Hydroids. Ray Society.
+
+  5-9. Yolk-segmentation in _Filaria_. After Van Beneden. Mem. sur
+         les Vers Intestinaux.
+
+  10-13. Yolk-segmentation in _Echinus_. After Derbès. Ann. des.
+           Sci. Nat. 1847.
+
+  14-17. Yolk-segmentation in _Lacinularia_. After Huxley. J. of
+           Mic. Sci. 1853.
+
+  18-21. Yolk-segmentation in _Purpura_. After Koren and
+           Danielssen. Ann. des. Sci. Nat. 1853.
+
+  22-24. Yolk-segmentation in _Amphioxus_. After Haeckel.
+           Naturliche Schöpfungsgeschichte, pl. x.
+
+  25-29. Yolk-segmentation in Vertebrate. After Allen Thompson.
+           Art. Ovum. Cyclop. of Anatomy and Physiology.
+
+
+  DESCRIPTION OF THE FIGURES.
+
+
+  FIG. 1. Larva of the Cockchafer (_Melolontha_)
+
+   2. Larva of _Cetonia_.
+
+   3. Larva of _Trox_.
+
+   4. Larva of _Oryctes_.
+
+   5. Larva of _Aphodius_.
+
+   6. Larva of _Lucanus_.
+
+   7. Larva of _Brachytarsus_.
+
+   8. Larva of _Crioceris_.
+
+   9. Larva of _Sitaris humeralis_.
+
+  10. Larva of _Sitaris humeralis_, in the second stage.
+
+  11. Larva of _Sitaris humeralis_, in the third stage.
+
+  12. Larva of _Sitaris humeralis_, in the fourth stage.
+
+  13. Pupa of _Sitaris_.
+
+  14. Larva of _Sirex_.
+
+  15. Egg of _Rhynchites_, showing the parasitic larva.
+
+  16. The parasitic larva, more magnified.
+
+  17. Egg of _Platygaster_.
+
+  18. Egg of _Platygaster_, showing the central cell.
+
+  19. Egg of _Platygaster_, after the division of the central cell.
+
+  20. Egg of _Platygaster_, more advanced.
+
+  21. Egg of _Platygaster_, more advanced.
+
+  22. Egg of _Platygaster_, showing the rudiment of the embryo.
+
+  23. Larva of _Platygaster_.—_mo_, mouth; _a_, antenna; _kf_,
+        hooked feet; _r_, toothed process; _lfg_, lateral
+        process; _f_, branches of the tail.
+
+  24. Larva of another species of _Platygaster_. (The letters
+        indicate the same parts as in the preceding figure.)
+
+  25. Larva of a third species of _Platygaster_. (The letters
+        indicate the same parts as in the preceding figure.)
+
+  26. Larva of _Platygaster_ in the second stage.—_mo_, mouth;
+        _slkf_, œsophagus; _gsae_, supra-œsophagal ganglion;
+        _lm_, muscles; _bsm_, nervous system; _gagh_, rudiments
+        of the reproductive glands.
+
+  27. Larva of _Platygaster_ in the third stage.—_mo_, mouth;
+        _ma_, mandibles; _gsae_, supra-œsophagal ganglion; _slk_,
+        œsophagus; _ag_, ducts of the salivary glands; _bnm_,
+        ventral nervous system; _sp_, salivary glands; _msl_,
+        stomach; _im_, imaginal discs; _tr_, tracheæ; _fk_, fatty
+        tissue; _ed_, intestine; _ga_, rudiments of reproductive
+        organs; _ew_, wider portion of intestine; _ao_, posterior
+        opening.
+
+  28. Embryo of _Polynema_.
+
+  29. Larva of _Polynema_.—_asch_, rudiments of the antennæ;
+        _flsch_, of the wings; _bsch_, of the legs; _vfg_,
+        lateral projections; _gsch_, rudiments of the ovipositor;
+        _fk_, fatty tissue.
+
+  30. Egg of _Phryganea_ (Mystacides).—_A_¹, mandibular segment;
+        _C_¹-_C_⁵, maxillary, labial, and three thoracic
+        segments; _D_, abdomen.
+
+  31. Egg of _Phryganea_ somewhat more advanced.—_b_, mandibles;
+        _c_, maxillæ; _cfs_, rudiments of the three pairs of
+        legs.
+
+  32. Egg of _Pholcus opilionides_, showing the Protozonites.
+
+  33. Embryo of _Julus_.
+
+  34. Colony of _Bougainvillea fruticosa_, natural size, attached
+        to the underside of a piece of floating timber.
+
+  35. Portion of the same, more magnified.
+
+  36. The Medusa from the same species.
+
+  37. Larva of Prawn, Nauplius stage.
+
+  38. Larva of Prawn, more advanced, Zoëa stage.
+
+  39. Larva of Echino-cidaris œquituberculata seen from above ×
+        6/10.
+
+  40. Larva of _Echinus_ × 100.—_A_, front arm; _F_, arms of the
+        mouth-process; _B_, posterior side arm; _E_¹, accessory
+        arm of the mouth-process; _a_, mouth; _a_¹, œsophagus;
+        _b_, stomach; _b_¹, intestine; _o_, posterior orifice;
+        _d_, ciliated bands; _f_, ciliated epaulets; _c_, disc of
+        future _Echinus_.
+
+  41. _Comatula rosacea_.
+
+  42. Larva of _Comatula rosacea_.
+
+  43. Larva of _Comatula rosacea_, more advanced.
+
+  44. Larva of _Comatula rosacea_, in the Pentacrinus state.
+
+  45. Larva of Starfish (Bipinnaria), × 100.
+
+  46. Larva of Starfish (Bipinnaria), × 100, seen from the
+  side.—_a_, mouth; _b_, œsophagus; _c_, stomach; _c_¹,
+  intestine.
+
+  47. Larva of another Bipinnaria, showing the commencement of
+  the Starfish.—_g_, canal of the ciliated sac; _i_, rudiments
+  of tentacles; _d_, ciliated band.
+
+  48. Larva of Moth (_Agrotis_).
+
+  49. Larva of Beetle (_Haltica_).
+
+  50. Larva of Saw-fly (_Cimbex_).
+
+  51. Larva of _Julus_.
+
+  52. _Agrotis suffusa_.
+
+  53. _Haltica_.
+
+  54. _Cimbex_.
+
+  55. _Julus_.
+
+  56. Tardigrade.
+
+  57. Larva of _Cecidomyia_.
+
+  58. _Lindia torulosa_.
+
+  59. _Prorhynchus stagnalis_.
+
+  60. Egg of Tardigrade.
+
+  61. Egg of Tardigrade, after the yolk has subdivided.
+
+  62. Egg of Tardigrade, in the next stage.
+
+  63. Egg of Tardigrade, more advanced.
+
+
+
+
+
+ON THE ORIGIN AND METAMORPHOSES OF INSECTS.
+
+
+
+
+CHAPTER I.
+
+  _THE CLASSIFICATION OF INSECTS._
+
+
+About forty years ago the civil and ecclesiastical authorities of St.
+Fernando in Chili arrested a certain M. Renous on a charge of
+witchcraft, because he kept some caterpillars which turned into
+butterflies.[1] This was no doubt an extreme case of ignorance; it is
+now almost universally known that the great majority of insects quit the
+egg in a state very different from that which they ultimately assume;
+and the general statement in works on entomology has been that the life
+of an insect may be divided into four periods.
+
+Thus, according to Kirby and Spence,[2] “The states through which
+insects pass are four: the _egg_, the _larva_, the _pupa_, and the
+_imago_.” Burmeister,[3] also, says that, excluding certain very rare
+anomalies, “we may observe four distinct periods of existence in every
+insect,—namely, those of the egg, the larva, the pupa, and the imago,
+or perfect insect.” In fact, however, the various groups of insects
+differ widely from one another in the metamorphoses they pass through:
+in some, as in the grasshoppers and crickets, the changes consist
+principally in a gradual increase of size, and in the acquisition of
+wings; while others, as for instance the common fly, acquire their full
+bulk in a form very different from that which they ultimately assume,
+and pass through a period of inaction in which not only is the whole
+form of the body altered, not only are legs and wings acquired, but even
+the internal organs themselves are almost entirely disintegrated and
+re-formed. It will be my object, after having briefly described these
+changes, to throw some light on the causes to which they are due, and on
+the indications they afford of the stages through which insects have
+been evolved.
+
+The following list gives the orders or principal groups into which the
+Class Insecta may be divided. I will not, indeed, here enter upon my own
+views, but will adopt the system given by Mr. Westwood in his excellent
+“Introduction to the Modern Classification of Insects,” from which also,
+as a standard authority, most of the figures on Plates I. to IV., when
+not otherwise acknowledged, have been taken. He divides insects into
+thirteen groups, and with reference to eight of them it may be said that
+there is little difference of opinion among entomologists. These orders
+are by far the most numerous, and I have placed them in capital
+letters. As regards the other five there is still much difference of
+opinion. It must also be observed that Prof. Westwood omits the
+parasitic Anoplura, as well as the Thysanura and Collembola.
+
+
+ORDERS OF INSECTS ACCORDING TO WESTWOOD.
+
+   1. HYMENOPTERA   Bees, Wasps, Ants, &c.
+   2. STREPSIPTERA  _Stylops_, _Zenos_, &c.
+   3. COLEOPTERA    Beetles.
+   4. EUPLEXOPTERA  Earwigs.
+   5. ORTHOPTERA    Grasshoppers, Crickets, Cockroaches, &c.
+   6. THYSANOPTERA  _Thrips_.
+   7. NEUROPTERA    _Ephemeras_, &c.
+   8. TRICHOPTERA   _Phryganea_.
+   9. DIPTERA       Flies and Gnats.
+  10. APHANIPTERA   Fleas.
+  11. HETEROPTERA   Bugs.
+  12. HOMOPTERA     _Aphis_, _Coccus_, &c.
+  13. LEPIDOPTERA   Butterflies and Moths.
+
+Of these thirteen orders, the eight which I have placed in capital
+letters—namely the first, third, fifth, seventh, ninth, eleventh,
+twelfth, and thirteenth, are much the most important in the number and
+variety of their species; the other five form comparatively small
+groups. The Strepsiptera are minute insects, parasitic on Hymenoptera:
+Rossi, by whom they were discovered, regarded them as Hymenopterous;
+Lamarck placed them among the Diptera; by others they have been
+considered to be most closely allied to the Coleoptera, but they are now
+generally treated as an independent order.
+
+The Euplexoptera or Earwigs are only too familiar to most of us. Linnæus
+classed them among the Coleoptera, from which, however, they differ in
+their transformations. Fabricius, Olivier, and Latreille regarded them
+as Orthoptera; but Dr. Leach, on account of the structure of their
+wings, considered them as forming the type of a distinct order, in which
+view he has been followed by Westwood, Kirby, and many other
+entomologists.
+
+The Thysanoptera, consisting of the Linnæan genus _Thrips_, are minute
+insects well known to gardeners, differing from the Coleoptera in the
+nature of their metamorphoses, in which they resemble the Orthoptera and
+Hemiptera. The structure of the wings and mouth-parts, however, are
+considered to exclude them from these two orders.
+
+The Trichoptera, or Caddis worms, offer many points of resemblance to
+the Neuroptera, while in others they approach more nearly to the
+Lepidoptera. According to Westwood, the genus _Phryganea_ “forms the
+connecting link between the Neuroptera and Lepidoptera.”
+
+The last of these small aberrant orders is that of the Aphaniptera,
+constituted for the family Pulicidæ. In their transformations, as in
+many other respects, they closely resemble the Diptera. Strauss
+Durckheim indeed said that “_la puce est un diptère sans ailes_.”
+Westwood, however, regards it as constituting a separate order.
+
+As indicated by the names of these orders, the structure of the wings
+affords extremely natural and convenient characters by which the various
+groups may be distinguished from one another. The mouth-parts also are
+very important; and, regarded from this point of view, the Insecta have
+been divided into two series—the Mandibulata and Haustellata, or
+mandibulate and suctorial groups, between which, as I have elsewhere
+shown,[4] the Collembola (_Podura_, _Smynthurus_, &c.) occupy an
+intermediate position. These two series are:—
+
+MANDIBULATA.
+
+  Hymenoptera.
+  Strepsiptera.
+  Coleoptera.
+  Euplexoptera.
+  Orthoptera.
+  Trichoptera?
+  Thysanoptera?
+
+HAUSTELLATA.
+
+  Lepidoptera.
+  Diptera.
+  Aphaniptera.
+  Hemiptera.
+  Homoptera.
+
+Again—and this is the most important from my present point of
+view—insects have sometimes been divided into two other series,
+according to the nature of their metamorphoses: “Heteromorpha,” to use
+the terminology of Prof. Westwood,[5] “or those in which there is no
+resemblance between the parent and the offspring; and Homomorpha, or
+those in which the larva resembles the imago, except in the absence of
+wings. In the former the larva is generally worm-like, of a soft and
+fleshy consistence, and furnished with a mouth, and often with six short
+legs attached in pairs to the three segments succeeding the head. In the
+Homomorpha, including the Orthoptera, Hemiptera, Homoptera, and certain
+Neuroptera, the body, legs, and antennæ are nearly similar in their form
+to those of the perfect insect, but the wings are wanting.”
+
+HETEROMORPHA.
+
+  Hymenoptera.
+  Strepsiptera.
+  Coleoptera.
+  Trichoptera.
+  Diptera.
+  Aphaniptera.
+  Lepidoptera.
+
+HOMOMORPHA.
+
+  Euplexoptera.
+  Orthoptera.
+  Hemiptera.
+  Homoptera.
+  Thysanoptera.
+  Neuroptera.
+
+But though the Homomorphic insects do not pass through such striking
+changes of form as the Heteromorphic, and are active throughout life,
+still it was until within the last few years generally (though
+erroneously) considered, that in them, as in the Heteromorpha, the life
+fell into four distinct periods; those of (1) the egg, (2) the larva,
+characterized by the absence of wings, (3) the pupa with imperfect
+wings, and (4) the imago, or perfect insect.
+
+I have, however, elsewhere[6] shown that there are not, as a matter of
+fact, four well-marked stages, and four only, but that in many cases the
+process is much more gradual.
+
+The species belonging to the order Hymenoptera are among the most
+interesting of insects. To this order belong the gallflies, the
+sawflies, the ichneumons, and, above all, the ants and bees. We are
+accustomed to class the Anthropoid apes next to man in the scale of
+creation, but if we were to judge animals by their works, the chimpanzee
+and the gorilla must certainly give place to the bee and the ant. The
+larvæ of the sawflies, which live on leaves, and of the Siricidæ or
+long-tailed wasps, which feed on wood, are very much like caterpillars,
+having three pairs of legs, and in the former case abdominal pro-legs
+as well: but in the great majority of Hymenoptera the larvæ are legless,
+fleshy grubs (Plate II., Figs. 7-9); and the various modes by which the
+females provide for, or secure to, them a sufficient supply of
+appropriate nourishment constitutes one of the most interesting pages of
+Natural History.
+
+The species of Hymenoptera are very numerous; in this country alone
+there are about 3,000 kinds, most of which are very small. In the pupa
+state they are inactive, and show distinctly all the limbs of the
+perfect insect, encased in distinct sheaths, and folded on the breast.
+In the perfect state they are highly organized and very active. The
+working ants and some few species are wingless, but the great majority
+have four strong membranous wings, a character distinguishing them at
+once from the true flies, which have only one pair of wings.
+
+The saw-flies are so called because they possess at the end of the body a
+curious organ, corresponding to the sting of a wasp, but which is in the
+form of a fine-toothed saw. With this instrument the female sawfly cuts
+a slit in the stem or leaf of a plant, into which she introduces her
+egg. The larva much resembles a caterpillar, both in form and habits. To
+this group belongs the nigger, or black caterpillar of the turnip, which
+is often in sufficient numbers to do much mischief. Some species make
+galls, but the greater number of galls are formed by insects of another
+family, the Cynipidæ.
+
+[Illustration: PLATE I.[7]—MATURE INSECTS.
+
+Fig. 1, Cricket; 2, Earwig; 3, _Aphis_; 4, _Scolytus_; 5, Anthrax;
+6, _Balaninus_; 7, _Cynips_; 8, Ant; 9, Wasp.]
+
+[Illustration: PLATE II.—LARVÆ OF THE INSECTS REPRESENTED ON PLATE I.
+
+Fig. 1, Larva of Cricket; 2, Larva of Aphis; 3, Larva of Earwig; 4,
+Larva of _Scolytus_ (Beetle); 5, Larva of _Anthrax_ (Fly); 6, Larva of
+_Balaninus_ (Nut Weevil); 7, Larva of _Cynips_; 8, Larva of Ant;
+9, Larva of Wasp.]
+
+In the Cynipidæ (Plate I., Fig. 7) the female is provided with an organ
+corresponding to the saw of the sawfly, but resembling a needle. With
+this she stings or punctures the surface of leaves, buds, stalks, or
+even roots of various plants. In the wound thus produced she lays one or
+more eggs. The effects of this proceeding, and particularly of the
+irritating fluid which she injects into the wound, is to produce a
+tumour or gall, within which the egg hatches, and on which the larva, a
+thick fleshy grub (Plate II., Fig. 7), feeds. In some species each gall
+contains a single larva; in others, several live together.
+
+The oak supports several kinds of gallflies: one produces the well-known
+oak-apple, one a small swelling on the leaf resembling a currant,
+another a gall somewhat like an acorn, another attacks the root; the
+species making the bullet-like galls, which are now so common, has only
+existed for a few years in this country; the beautiful little spangles
+so common in autumn on the under side of oak leaves are the work of
+another species, the _Cynus longipennis_. One curious point about this
+group is, that in some of the commonest species the females alone are
+known, no one yet having ever succeeded in finding a male.
+
+Another great family of the Hymenoptera is that of the ichneumons; the
+females lay their eggs either in or on other insects, within the bodies
+of which the larvæ live. These larvæ are thick, fleshy, legless grubs,
+and feed on the fatty tissues of their hosts, but do not attack the
+vital organs. When full-grown, the grubs eat their way through the skin
+of the insect, and turn into chrysalides. Almost every kind of insect
+is subject to the attacks of these little creatures, which are no doubt
+useful in preventing the too great multiplication of insects, and
+especially of caterpillars. Some species are so minute that they
+actually lay their eggs within those of other insects (Figs. 15, 16).
+These parasites assume very curious forms in their larval state.
+
+But of all the Hymenoptera, the group containing the ant, the bee, and
+the wasp is the most interesting. This is especially the case with the
+social species, though the solitary ones also are extremely remarkable.
+The solitary bee or wasp, for instance, forms a cell generally in the
+ground, places in it a sufficient amount of food, lays an egg, and
+closes the cell. In the case of bees, the food consists of honey; in
+that of wasps, the larva requires animal food, and the mother therefore
+places a certain number of insects in the cell, each species having its
+own special prey, some selecting small caterpillars, some beetles, some
+spiders. _Cerceris bupresticida_, as its name denotes, attacks beetles
+belonging to the genus _Buprestis_. Now if the Cerceris were to kill the
+beetle before placing it in the cell, it would decay, and the young
+larva, when hatched, would find only a mass of corruption. On the other
+hand, if the beetle were buried uninjured, in its struggles to escape it
+would be almost certain to destroy the egg. The wasp has, however, the
+instinct of stinging its prey in the centre of the nervous system, thus
+depriving it of motion, and let us hope of suffering, but not of life;
+consequently, when the young larva leaves the egg, it finds ready a
+sufficient store of wholesome food.
+
+Other wasps are social, and, like the bees and ants, dwell together in
+communities. They live for one season, dying in autumn, except some of
+the females, which hibernate, awake in the spring, and form new
+colonies. These, however, do not, under ordinary circumstances, live
+through a second winter. One specimen which I kept tame through last
+spring and summer, lived until the end of February, but then died. The
+larvæ of wasps (Plate II., Fig. 9) are fat, fleshy, legless grubs. When
+full-grown they spin for themselves a silken covering, within which they
+turn into chrysalides. The oval bodies which are so numerous in ants’
+nests, and which are generally called ants’ eggs, are really not eggs
+but cocoons. Ants are very fond of the honey-dew which is formed by the
+Aphides, and have been seen to tap the Aphides with their antennæ, as if
+to induce them to emit some of the sweet secretion. There is a species
+of _Aphis_ which lives on the roots of grass, and some ants collect these
+into their nests, keeping them, in fact, just as we do cows. Moreover
+they collect the eggs in the autumn and tend them through the winter
+(when they are of no use) with the same care as their own, so as to have
+a supply of young Aphides in the spring. This is one of the most
+remarkable facts I know in the whole history of animal life. One species
+of red ant does no work for itself, but makes slaves of a black kind,
+which then do everything for their masters. The slave makers will not
+even put food into their own mouths, but would starve in the midst of
+plenty, if they had not a slave to feed them. I found, however, that I
+could keep them in life and health for months if I gave them a slave for
+an hour or two in a week to clean and feed them.
+
+Ants also keep a variety of beetles and other insects in their nests.
+That they have some reason for this seems clear, because they readily
+attack any unwelcome intruder; but what that reason is, we do not yet
+know. If these insects are to be regarded as the domestic animals of the
+ants, then we must admit that the ants possess more domestic animals
+than we do.
+
+Some indeed of these beetles produce a secretion which is licked by the
+ants like the honey-dew; there are others, however, which have not yet
+been shown to be of any use to the ants, and yet are rarely, if ever,
+found, excepting in ants’ nests.
+
+M. Lespès, who regards these insects as true domestic animals, has
+recorded[8] some interesting observations on the relations between one
+of them (_Claviger Duvalii_) and the ants (_Lasius niger_) with which it
+lives. This species of _Claviger_ is never met with except in ants’
+nests, though on the other hand there are many communities of _Lasius_
+which possess none of these beetles; and M. Lespès found that when he
+placed _Clavigers_ in a nest of ants which had none of their own, the
+beetles were immediately killed and eaten, the ants themselves being on
+the other hand kindly received by other communities of the same species.
+He concludes from these observations that some communities of ants are
+more advanced in civilization than others; the suggestion is no doubt
+ingenious, and the fact curiously resembles the experience of navigators
+who have endeavoured to introduce domestic animals among barbarous
+tribes; but M. Lespès has not yet, so far as I am aware, published the
+details of his observations, without which it is impossible to form a
+decided opinion. I have sometimes wondered whether the ants have any
+feeling of reverence for these beetles; but the whole subject is as yet
+very obscure, and would well repay careful study.
+
+[Illustration: PLATE III.—MATURE INSECTS.
+
+Fig. 1, _Chloëon_; 2, _Meloë_ (after Shuckard); 3, _Calepteryx_;
+4, _Sitaris_ (after Shuckard); 5, _Campodea_ (after Gervais);
+6, _Acilius_; 7, _Termes_; 8, _Stylops_ (female); 9, _Thrips_.]
+
+[Illustration: PLATE IV. YOUNG FORMS OF THE INSECTS REPRESENTED ON PLATE
+III.—Fig. 1, Larva of _Chloëon_; 2, Larva of _Meloë_ (after Chapuis and
+Candèze); 3, Larva of _Calepteryx_ (after Léon Dufour); 4, Larva of
+_Sitaris_; 5, Larva of _Campodea_; 6, Larva of _Acilius_;
+7, Larva of Termes (after Blanchard); 8, Larva of _Stylops_; 9, Larva
+of _Thrips_.]
+
+The order Strepsiptera are a small, but very remarkable group of
+insects, parasitic on bees and wasps. The larva (Pl. IV., Fig. 8) is
+minute, six-legged, and very active; it passes through its
+transformations within the body of the bee or wasp. The male and female
+are very dissimilar. The males are minute, very active, short-lived, and
+excitable, with one pair of large membranous wings. The females (Pl.
+III., Fig. 8), on the contrary, are almost motionless, and shaped very
+much like a bottle; they never quit the body of the bee, but only thrust
+out the top of the bottle between the abdominal rings of the bee.
+
+In the order Coleoptera, the larvæ differ very much in form. The
+majority are elongated, active, hexapod, and more or less depressed; but
+those of the Weevils (Pl. II., Fig. 6), of _Scolytus_ (Pl. II., Fig. 4),
+&c., which are vegetable feeders, and live surrounded by their
+food,—as, for instance, in grain, nuts, &c.,—are apod, white, fleshy
+grubs, not unlike those of bees and ants. The larvæ of the Longicorns,
+which live inside trees, are long, soft, and fleshy, with six short
+legs. The Geodephaga, corresponding with the Linnæan genera _Cicindela_
+and _Carabus_, have six-legged, slender, carnivorous larvæ; those of
+_Cicindela_, which waylay their prey, being less active than the hunting
+larvæ of the Carabidæ. The Hydradephaga, or water-beetles (Dyticidæ and
+Gyrinidæ), have long and narrow larvæ (Pl. IV., Fig. 6), with strong
+sickle-shaped jaws, short antennæ, four palpi, and six small eyes on
+each side of the head; they are very voracious. The larvæ of the
+Staphylinidæ are by no means unlike the perfect insect, and are found in
+similar situations; their jaws are powerful, and their legs moderately
+strong. The larvæ of the Lamellicorn beetles (Figs. 1-6)—cockchafers,
+stag-beetles, &c.—feed on vegetable substances or on dead animal
+matter. They are long, soft, fleshy grubs, with the abdomen somewhat
+curved, and generally lie on their side. The larvæ of the Elateridæ,
+known as wireworms, are long and slender, with short legs. That of the
+glowworm (Lampyridæ) is not unlike the apterous female. The male
+glowworm, on the contrary, is very different. It has long, thin, brown
+wing-cases, and often flies into rooms at night, attracted by the light,
+which it probably mistakes for that of its mate.
+
+The metamorphoses of the Cantharidæ are very remarkable, and will be
+described subsequently. The larvæ are active and hexapod. The Phytophaga
+(_Crioceris_, _Galeruca_, _Haltica_, _Chrysomela_, &c.) are vegetable
+feeders, both as larvæ and in the perfect state. The larvæ are furnished
+with legs, and are not unlike the caterpillars of certain Lepidoptera.
+
+The larva of _Coccinella_ (the Ladybird) is somewhat depressed, of an
+elongated ovate form, with a small head, and moderately strong legs. It
+feeds on Aphides.
+
+Thus, then, we see that there are among the Coleoptera many different
+forms of larvæ. Macleay considered that there were five principal types.
+
+1. Carnivorous hexapod larvæ, with an elongated, more or less flattened
+body, six eyes on each side of the head, and sharp falciform mandibles
+(_Carabus_, _Dyticus_, &c.).
+
+2. Herbivorous hexapod larvæ, with fleshy, cylindrical bodies, somewhat
+curved, so that they lie on their side.
+
+3. Apod grub-like larvæ, with scarcely the rudiments of antennæ
+(_Curculio_).
+
+4. Hexapod antenniferous larvæ, with a subovate body, the second segment
+being somewhat larger than the others (_Chrysomela_, _Coccinella_).
+
+5. Hexapod antenniferous larvæ, of oblong form, somewhat resembling the
+former, but with caudal appendages (_Meloë_, _Sitaris_).
+
+The pupa of the Coleoptera is quiescent, and “the parts of the future
+beetle are plainly perceivable, being encased in distinct sheaths; the
+head is applied against the breast; the antennæ lie along the sides of
+the thorax; the elytra and wings are short and folded at the sides of
+the body, meeting on the under side of the abdomen; the two anterior
+pairs of legs are entirely exposed, but the hind pair are covered by
+wing-cases, the extremity of the thigh only appearing beyond the sides
+of the body.”[9]
+
+In the next three orders—namely, the Orthoptera (grasshoppers, locusts,
+crickets, walking-stick insects, cockroaches, &c.), Euplexoptera
+(earwigs), and Thysanoptera, a small group of insects well known to
+gardeners under the name of _Thrips_ (Pl. I. and II., Figs. 1 and 2)—the
+larvæ when they quit the egg already much resemble the mature form,
+differing, in fact, principally in the absence of wings, which are more
+or less gradually acquired, as the insect increases in size. They are
+active throughout life. Those specimens which have rudimentary wings
+are, however, usually called pupæ.
+
+The Neuroptera present, perhaps, more differences in the character of
+their metamorphoses than any other order of insects. Their larvæ are
+generally active, hexapod little creatures, and do not vary from one
+another in appearance so much, for instance, as those of the Coleoptera,
+but their pupæ differ essentially; some groups, namely, the Psocidæ,
+Termitidæ, Libellulidæ, Ephemeridæ, and Perlidæ, remaining active
+throughout life, like the Orthoptera; while a second division, including
+the Myrmeleonidæ, Hemerobiidæ, Sialidæ, Panorpidæ, Raphidiidæ, and
+Mantispidæ, have quiescent pupæ, which, however, in some cases, acquire
+more or less power of locomotion shortly before they assume the mature
+state; thus that of _Raphidia_, though motionless at first, at length
+acquires strength enough to walk, even while still enclosed in the pupa
+skin, which is very thin.[10]
+
+One of the most remarkable families belonging to this order is that of
+the Termites, or white ants. They abound in the tropics, where they are
+a perfect pest, and a serious impediment to human development. Their
+colonies are extremely numerous, and they attack woodwork and furniture
+of all kinds, generally working from within, so that their presence is
+often unsuspected, until it is suddenly found that they have completely
+eaten away the interior of some post or table, leaving nothing but a
+thin outer shell. Their nests, which are made of earth, are sometimes
+ten or twelve feet high, and strong enough to bear a man. One species,
+_Termes lucifugus_, is found in the South of France, where it has been
+carefully studied by Latreille. He found in these communities five kinds
+of individuals—(1) males; (2) females, which grow to a very large size,
+their bodies being distended with eggs, of which they sometimes lay as
+many as 80,000 in a day; (3) a form described by some observers as Pupæ,
+but by others as neuters. These differ very much from the others, having
+a long, soft body without wings, but with an immense head, and very
+large, strong jaws. These individuals act as soldiers, doing apparently
+no work, but keeping watch over the nest and attacking intruders with
+great boldness. (4) Apterous, eyeless individuals, somewhat resembling
+the winged ones, but with a larger and more rounded head; these
+constitute the greater part of the community, and, like the workers of
+ants and bees, perform all the labour, building the nest and collecting
+food. (5) Latreille mentions another kind of individual which he regards
+as the pupa, and which resembles the workers, but has four white
+tubercles on the back, where the wings afterwards make their appearance.
+There is still, however, much difference of opinion among entomologists,
+with reference to the true nature of these different classes of
+individuals. M. Lespès, who has recently studied the same species,
+describes a second kind of male and a second kind of female, and the
+subject, indeed, is one which offers a most promising field for future
+study.
+
+Another interesting family of Neuroptera is that of the Ephemeræ, or
+Mayflies (Pl. III., Fig. 1), so well known to fishermen. The larvæ (Pl.
+IV., Fig. 1) are semi-transparent, active, six-legged little creatures,
+which live in water; having at first no gills, they respire through the
+general surface of the body. They grow rapidly and change their skin
+every few days. After one or two moults they acquire seven pairs of
+branchiæ, or gills, which are generally in the form of leaves, one pair
+to the segment. When the larvæ are about half grown, the posterior
+angles of the two posterior thoracic segments begin to elongate. These
+elongations become more and more marked with every change of skin. One
+morning, in the month of June, some years ago, I observed a full-grown
+larva, which had a glistening appearance, owing to the presence of a
+film of air under the skin. I put it under the microscope, and, having
+added a drop of water with a pipette, looked through the glass. To my
+astonishment, the insect was gone, and an empty skin only remained. I
+then caught a second specimen, in a similar condition, and put it under
+the microscope, hoping to see it come out. Nor was I disappointed. Very
+few moments had elapsed, when I had the satisfaction of seeing the
+thorax open along the middle of the back; the two sides turned over; the
+insect literally walked out of itself, unfolded its wings, and in an
+instant flew up to the window. Several times since, I have had the
+pleasure of witnessing this marvellous change, and it is really
+wonderful how rapidly it takes place: from the moment when the skin
+first cracks, not ten seconds are over before the insect has flown away.
+
+Another family of Neuroptera, the Dragon-flies, or Horse-stingers, as
+they are sometimes called, from a mistaken idea that they sting severely
+enough to hurt a horse, though in fact they are quite harmless, also
+spend their early days in the water. The larvæ are brown, sluggish, ugly
+creatures, with six legs. They feed on small water-animals, for which
+they wait very patiently, either at the bottom of the water, or on some
+aquatic plant. The lower jaws are attached to a long folding rod; and
+when any unwary little creature approaches too near the larva, this
+apparatus is shot out with such velocity that the prey which comes
+within its reach seldom escapes. In their perfect condition, also,
+Dragon-flies feed on other insects, and may often be seen hawking round
+ponds. The so-called Ant-lions in many respects resemble the
+Dragon-flies, but the habits of the larvæ are very dissimilar. They do
+not live in the water, but prefer dry places, where they bury themselves
+in the loose sand, and seize with their long jaws any small insect which
+may pass. The true Ant-lion makes itself a round, shallow pit in loose
+ground or sand, and buries itself at the bottom. Any inattentive little
+insect which steps over the edge of this pit immediately falls to the
+bottom, and is instantaneously seized by the Ant-lion. Should the insect
+escape, and attempt to climb up the side of the pit, the Ant-lion is
+said to throw sand at it, knocking it down again.
+
+One other family of Neuroptera which I must mention, is the
+Hemerobiidæ. The perfect insect is a beautiful, lace-winged, very
+delicate, green creature, something like a tender Dragon-fly, and with
+bright, green, touching eyes. The female deposits her eggs on leaves,
+not directly on the plant itself, but attached to it by a long white
+slender footstalk. The larva has six legs and powerful jaws, and makes
+itself very useful in destroying the Hop-fly.
+
+The insects forming the order Trichoptera are well known in their larval
+condition, under the name of caddis worms. These larvæ are not
+altogether unlike caterpillars in form, but they live in water—which is
+the case with very few lepidopterous larvæ—and form for themselves
+cylindrical cases or tubes, built up of sand, little stones, bits of
+stick, leaves, or even shells. They generally feed on vegetable
+substances, but will also attack minute freshwater animals. When full
+grown, the larva fastens its case to a stone, the stem of a plant, or
+some other fixed substance, and closes the two ends with an open grating
+of silken threads, so as to admit the free access of water, while
+excluding enemies. It then turns into a pupa which bears some
+resemblance to the perfect insect, “except that the antennæ, palpi,
+wings, and legs are shorter, enclosed in separate sheaths, and arranged
+upon the breast.” The pupa remains quiet in the tube until nearly ready
+to emerge, when it comes to the surface, and in some cases creeps out of
+the water. It is not therefore so completely motionless as the pupæ of
+Lepidoptera.
+
+The Diptera, or Flies, comprise insects with two wings only, the hinder
+pair being represented by minute club-shaped organs called “haltères.”
+Flies quit the egg generally in the form of fat, fleshy, legless grubs.
+They feed principally on decaying animal or vegetable matter, and are no
+doubt useful as scavengers. Other species, as the gadflies, deposit
+their eggs on the bodies of animals, within which the grubs feed, when
+hatched. The mouth is generally furnished with two hooks which serve
+instead of jaws. The pupæ of Diptera are of two kinds. In the true
+flies, the outer skin of the full-grown larva is not shed, but contracts
+and hardens, thus assuming the appearance of an oval brownish shell or
+case, within which the insect changes into a chrysalis. The pupæ of the
+gnats, on the contrary, have the limbs distinct and enclosed in sheaths.
+They are generally inactive, but some of the aquatic species continue to
+swim about.
+
+One group of Flies, which is parasitic on horses, sheep, bats, and other
+animals, has been called the Pupipara, because it was supposed that they
+were not born until they had arrived at the condition of pupæ. They come
+into the world in the form of smooth, ovate bodies, much resembling
+ordinary dipterous pupæ, but as Leuckart has shown,[11] they are true,
+though abnormal, larvæ.
+
+The next order, that of the Aphaniptera, is very small in number,
+containing only the different species of Flea. The larva is long,
+cylindrical, and legless; the chrysalis is motionless, and the perfect
+insect is too well known, at least, as regards its habits, to need any
+description.
+
+The Heteroptera, unlike the preceding orders of insects, quit the egg in
+a form differing from that of the perfect insect principally in the
+absence of wings, which are gradually acquired. In their metamorphoses
+they resemble the Orthoptera, and are active through life. The majority
+are dull in colour, though some few are very beautiful. The species
+constituting this group, though very numerous, are generally small, and
+not so familiarly known to us as those of the other large orders, with
+indeed one exception, the well-known Bug. This is not, apparently, an
+indigenous insect, but seems to have been introduced. The word is indeed
+used by old writers, but either as meaning a bugbear, or in a general
+sense, and not with reference to this particular insect. In this country
+it never acquires wings, but is stated to do so sometimes in warmer
+climates. The Heteroptera cannot exactly be said either to sting or
+bite. The jaws, of which, as usual among insects, there are two pairs,
+are like needles, which are driven into the flesh, and the blood is then
+sucked up the lower lip, which has the form of a tube. This peculiar
+structure of the mouth prevails throughout the whole order; consequently
+their nutriment consists almost entirely of the juices of animals or
+plants. The Homoptera agree with the Heteroptera in the structure of the
+mouth, and in the metamorphoses. They differ principally in the front
+wings, which in Homoptera are membranous throughout, while in the
+Heteroptera, the front part is thickened and leathery. As in the
+Heteroptera, however, so also in the Homoptera, some species do not
+acquire wings. The Cicada, celebrated for its chirp, and the lanthorn
+fly, belong to this group. So also does the so-called Cuckoo-spit, so
+common in our gardens, which has the curious faculty of secreting round
+itself a quantity of frothy fluid which serves to protect it from its
+enemies. But the best known insects of this group are the Aphides or
+Plant-lice; while the most useful belong to the Coccidæ, or scale
+insects, from one species of which we obtain the substance called lac,
+so extensively used in the manufacture of sealing-wax and varnish.
+Several species also have been used in dyeing, especially the Cochineal
+insect of Mexico, a species which lives on the cactus. The male _Coccus_
+is a minute, active insect, with four large wings; while the female, on
+the contrary, never acquires wings, but is very sluggish, broad, more or
+less flattened, and in fact, when full grown, looks like a small brown,
+red, or white scale.
+
+The larva of the order Lepidoptera are familiar to us all, under the
+name of caterpillars. The insects of this order in their larval
+condition are almost all phytophagous, and are very uniform both in
+structure and in habits. The body is long and cylindrical, consisting of
+thirteen segments; the head is armed with powerful jaws; the three
+following segments, the future prothorax, mesothorax, and meta-thorax,
+each bears a pair of simple articulated legs. Of the posterior segments,
+five also bear false or pro-legs, which are short, unjointed, and
+provided with a number of hooklets. A caterpillar leads a dull and
+uneventful life; it eats ravenously, and grows rapidly, casting its skin
+several times during the process, which generally lasts only a few
+weeks; though in some cases, as for instance that of the goat-moth, it
+extends over a period of two or three years, after which the larva
+changes into a quiescent pupa or chrysalis.
+
+
+
+
+CHAPTER II.
+
+_THE INFLUENCE OF EXTERNAL CONDITIONS ON THE FORM AND STRUCTURE OF
+LARVÆ._
+
+
+The facts recapitulated briefly in the preceding chapter show, that the
+forms of insect larvæ depend greatly on the group to which they belong.
+Thus the same tree may harbour larvæ of Diptera, Hymenoptera,
+Coleoptera, and Lepidoptera; each presenting the form typical of the
+family to which it belongs.
+
+If, again, we take a group, such, for instance, as the Lamellicorn
+beetles, we shall find larvæ extremely similar in form, yet very
+different in habits. Those, for instance, of the common cockchafer (Fig.
+1) feed on the roots of grass; those of _Cetonia aurata_ (Fig. 2)
+inhabit ants’ nests; the larvæ of the genus _Trox_ (Fig. 3) are found on
+dry animal substances; of _Oryctes_ (Fig. 4) in tan-pits; of _Aphodius_
+(Fig. 5) in dung; of _Lucanus_ (the stag-beetle, Fig. 6) in wood.
+
+[Illustration: FIG. 1, Larva of the Cockchafer (_Melolontha_).
+(Westwood, Int. to the Modern Classification of Insects, vol. i. p.
+194.). 2, Larva of _Cetonia_. 3, Larva of _Trox_. 4, Larva of _Oryctes_.
+5, Larva of _Aphodius_ (Chapuis and Candèze, Mém. Soc. Roy. Liège,
+1853). 6, Larva of _Lucanus_. (Packard, Guide to the Study of Insects,
+Fig. 403).]
+
+On the other hand, in the present chapter it will be my object to show
+that the form of the larva depends very much on the conditions of its
+life. Thus, those larvæ which are internal parasites, whether in
+animals or plants, are vermiform, as are those which live in cells, and
+depend on their parents for food. On the other hand, larvæ which burrow
+in wood have strong jaws and generally somewhat weak thoracic legs;
+whilst those which feed on leaves have the thoracic legs more developed,
+but less so than the carnivorous species. Now, the Hymenoptera, as a
+general rule, belong to the first category: the larvæ of the Ichneumons,
+&c., which live in animals,—those of the Cynipidæ, inhabiting
+galls,—and those of ants, bees, wasps, &c., which are fed by their
+parents, are fleshy, apodal grubs; though the remarkable fact that the
+embryos of bees in one stage of their development possess rudiments of
+thoracic legs which subsequently disappear, seems to show, not indeed
+that the larvæ of bees were ever hexapod, but that bees are descended
+from ancestors which had hexapod larvæ, and that the present apod
+condition of these larvæ is not original, but results from their mode of
+life.
+
+On the other hand, the larvæ of _Sirex_ (Fig. 14) being wood-burrowers,
+possess well-developed thoracic legs. Again, the larvæ of the
+Tenthredinidæ, which feed upon leaves, closely resemble the caterpillars
+of Lepidoptera, even to the presence of abdominal pro-legs.
+
+[Illustration: FIG. 7, Larva of _Brachytarsus_ (Ratzeburg, Forst.
+Insecten). 8, Larva of _Crioceris_ (Westwood, loc. cit.).]
+
+The larvæ of most Coleoptera (Beetles) are active, hexapod, and more or
+less flattened: but those which live inside vegetable tissues, such as
+the weevils, are apod fleshy grubs, like those of Hymenoptera. Pl. II.,
+Fig. 6, represents the larva of the nut-weevil, _Balaninus_ (Pl. I., Fig.
+6), and it will be seen that it closely resembles Pl. II., Fig. 5, which
+represents that of a fly (_Anthrax_), Pl. I., Fig. 5, and Pl. II., Figs.
+7, 8, and 9, which represent respectively those of a _Cynips_ or gall-fly
+(Pl. I., Fig. 7), an ant (Pl. I., Fig. 8), and wasp (Pl. I., Fig. 9).
+Nor is _Balaninus_ the only genus of Coleoptera which affords us examples
+of this fact. Thus in the genus _Scolytus_ (Pl. I., Fig. 4), the larvæ
+(Pl. II., Fig. 4), which, as already mentioned, feed on the bark of the
+elm, closely resemble those just described, as also do those of
+_Brachytarsus_ (Fig. 7). On the other hand, the larvæ of certain beetles
+feed on leaves, like the caterpillars of Lepidoptera; thus that of
+_Crioceris Asparagi_ (Fig. 8)—which, as its name denotes, feeds on the
+asparagus—closely resembles the larvæ of certain Lepidoptera, as for
+instance of _Thecla spini_. From this point of view the transformations
+of the genus _Sitaris_ (Pl. III., Fig. 4), which have been very carefully
+investigated by M. Fabre, are peculiarly interesting.[12]
+
+[Illustration: FIG. 9, Larva of _Sitaris numeralis_ (Fabre, Ann. des Sci.
+Nat., sér. 4, tome vii.). 10, Larva of _Sitaris humeralis_, in the second
+stage. 11, Larva of _Sitaris humeralis_, in the third stage. 12, Larva of
+_Sitaris humeralis_, in the fourth stage. 13, Pupa of _Sitaris_.]
+
+The genus _Sitaris_ (a small beetle allied to Cantharis, the blister-fly,
+and to _Meloë_, the oil-beetle) is parasitic on a kind of Bee
+(Anthophora), which excavates subterranean galleries, each leading to a
+cell. The eggs of the _Sitaris_, which are deposited at the entrance of
+these galleries, are hatched at the end of September or beginning of
+October; and M. Fabre not unnaturally expected that the young larvæ,
+which are active little creatures with six serviceable legs (Fig. 9),
+would at once eat their way into the cells of the Anthophora. No such
+thing: till the month of April following they remain without leaving
+their birthplace, and consequently without food; nor do they in this
+long time change either in form or size. M. Fabre ascertained this, not
+only by examining the burrows of the _Anthophoras_, but also by direct
+observation of some young larvæ kept in captivity. In April, however,
+his captives at last awoke from their long lethargy, and hurried
+anxiously about their prisons. Naturally inferring that they were in
+search of food, M. Fabre supposed that this would consist either of the
+larvæ or pupæ of the Anthophora, or of the honey with which it stores
+its cell. All three were tried without success. The first two were
+neglected, and the larvæ, when placed on the latter, either hurried
+away, or perished in the attempt, being evidently unable to deal with
+the sticky substance. M. Fabre was in despair: “Jamais expérience,” he
+says, “n’a éprouvé pareille déconfiture. Larves, nymphes, cellules,
+miel, je vous ai tous offert; que voulez-vous donc, bestioles maudites?”
+The first ray of light came to him from our countryman, Newport, who
+ascertained that a small parasite found by Léon Dufour on one of the
+wild bees, and named by him Triungulinus, was, in fact, the larva of
+_Meloë_. The larvæ of _Sitaris_ much resembled Dufour’s Triungulinus;
+and acting on this hint, M. Fabre examined many specimens of Anthophora,
+and found on them at last the larvæ of his _Sitaris_. The males of
+Anthophora emerge from the pupæ sooner than the females, and M. Fabre
+ascertained that, as they come out of their galleries, the little
+_Sitaris_ larvæ fasten upon them. Not, however, for long: instinct
+teaches them that they are not yet in the straight path of development;
+and, watching their opportunity, they pass from the male to the female
+bee. Guided by these indications, M. Fabre examined several cells of the
+Anthophora: in some, the egg of the Anthophora floated by itself on the
+surface of the honey; in others, on the egg, as on a raft, sat the still
+more minute larva of the _Sitaris_. The mystery was solved. At the
+moment when the egg is laid the _Sitaris_ larva springs upon it. Even
+while the poor mother is carefully fastening up her cell, her mortal
+enemy is beginning to devour her offspring: for the egg of the
+Anthophora serves not only as a raft, but as a repast. The honey which
+is enough for either, would be too little for both; and the _Sitaris_,
+therefore, at its first meal, relieves itself from its only rival. After
+eight days the egg is consumed, and on the empty shell the _Sitaris_
+undergoes its first transformation, and makes its appearance in a very
+different form, as shown in Fig. 10.
+
+The honey which was fatal before is now necessary; the activity which
+before was necessary is now useless; consequently, with the change of
+skin, the active, slim larva changes into a white, fleshy grub, so
+organized as to float on the surface of the honey, with the mouth
+beneath, and the spiracles above the surface: “grâce à l’embonpoint du
+ventre,” says M. Fabre, “la larve est à l’abri de l’asphyxie.” In this
+state it remains until the honey is consumed; then the animal
+contracts, and detaches itself from its skin, within which the further
+transformations take place. In the next stage, which M. Fabre calls the
+pseudo-chrysalis (Fig. 11), the larva has a solid corneous envelope and
+an oval shape; and in its colour, consistency, and immobility reminds
+one of a Dipterous pupa. The time passed in this condition varies much.
+When it has elapsed, the animal moults again, again changes its form,
+and assumes that shown in Fig. 12; after this it becomes a pupa (Fig.
+13) without any remarkable peculiarities. Finally, after these wonderful
+changes and adventures, in the month of August the perfect _Sitaris_ (Pl.
+III., Fig. 4) makes its appearance.
+
+On the other hand, there are cases in which larvæ diverge remarkably
+from the ordinary type of the group to which they belong, without, as it
+seems in our present imperfect state of information, any sufficient
+reason.
+
+Thus the ordinary type of Hymenopterous larva, as we have already seen,
+is a fleshy apod grub; although those of the leaf-eating and wood-boring
+groups, Tenthredinidæ and Siricidæ (Fig. 14), are caterpillars, more or
+less closely resembling those of Lepidoptera. There is, however, a group
+of minute Hymenoptera, the larvæ of which reside within the eggs or
+larvæ of other insects. It is difficult to understand why these larvæ
+should differ from those of Ichneumons, which are also parasitic
+Hymenoptera, and should be, as will be seen by the accompanying figures,
+of such remarkable and grotesque forms. The first known of these curious
+larvæ was observed by De Filippi,[13] who, having collected some of the
+transparent eggs of a small Beetle (_Rhynchites betuleti_), to his great
+surprise found more than half of them attacked by a parasite, which
+proved to be the larva of a minute Hymenopterous insect belonging to the
+Pteromalidæ. Fig. 15 shows the egg of the Beetle, with the parasitic
+larva, which is represented on a larger scale in Fig. 16.
+
+[Illustration: FIG. 14, Larva of _Sirex_ (Westwood, loc. cit.). 15, Egg of
+_Rhynchites_, showing the parasitic Larva in the interior. 16, the
+parasitic Larva more magnified.]
+
+More recently this group has been studied by M. Ganin,[14] who thus
+describes the development of _Platygaster_. The egg, as in allied
+Hymenopterous families, for instance in _Cynips_, is elongated and
+club-shaped (Fig. 17). After a while a large nucleated cell appears in
+the centre (Fig. 18). This nucleated cell divides (Fig. 19) and
+subdivides. The outermost cells continue the same process, thus forming
+an outer investing layer. The central, on the contrary, enlarges
+considerably, and develops within itself a number of daughter cells
+(Figs. 20 and 21), which gradually form a mulberry-like mass, thus
+giving rise to the embryo (Fig. 22).
+
+[Illustration: FIG. 17, Egg of _Platygaster_ (after Ganin). 18, Egg of
+_Platygaster_ showing the central cell. 19, Egg of _Platygaster_ after the
+division of the central wall. 20, Egg of Platygaster more advanced. 21,
+Egg of _Platygaster_ more advanced. 22, Egg of Platygaster showing the
+rudiment of the embryo.]
+
+Ganin met with the larvæ of _Platygaster_ in those of a small gnat,
+_Cecidomyia_. Sometimes as many as fifteen parasites occurred in one gnat,
+but as a rule only one of these attained maturity. The three species of
+_Platygaster _differ considerably in form, as shown in Figs. 23-25. They
+creep about within the larva of _Cecidomyia_ by means of the strong hooked
+feet, _kf_, somewhat aided by movements of the tail. They possess a
+mouth, stomach, and muscles, but the nervous, vascular, and respiratory
+systems do not make their appearance until later. After some time the
+larva (Fig. 23) changes its skin, assuming the form represented in Fig.
+26. In this moult the last abdominal segment of the first larva is
+entirely thrown off: not merely the outer skin, as in the case of the
+other segments, but also the hypodermis and the muscles. This larva, as
+will be seen by the figure, resembles a barrel or egg in form, and is
+.870 mm. in length, the external appendages having disappeared, and the
+segments being indicated only by the arrangement of the muscles. _slkf_
+is the œsophagus leading into a wide stomach which occupies nearly
+the whole body, _gsae_ is the rudiment of the supra-œsophageal
+ganglia, _bsm_ the ventral nervous cords. The ventral nervous mass has
+the form of a broad band, with straight sides; it consists of embryonal
+cells, and remains in this undeveloped condition during the whole larval
+state.
+
+[Illustration: FIG. 23, Larva of _Platygaster_ (after Ganin)—_mo_, mouth;
+_a_, antenna; _kf_, hooked feet; _z_, toothed process; _lfg_, lateral
+process; _f_, branches of the tail. 24, Larva of another species of
+_Platygaster_. The letters indicate the same parts as in the preceding
+figure. 25, Larva of a third species of _Platygaster_. The letters
+indicate the same parts as in the preceding figures. 26, Larva of
+_Platygaster_ in the second stage—_mo_, mouth; _slkf_, œsophagus;
+_gsae_, supra-œsophageal ganglion; _lm_, muscles; _bsm_, nervous
+system; _ga_, _gh_, rudiments of the reproductive glands. 27, Larva of
+_Platygaster_ in the third stage—_mo_, mouth; _md_, mandibles; _gsae_,
+supra-œsophageal ganglion; _slk_, œsophagus; _ag_, ducts of the
+salivary glands; _bnm_, ventral nervous system; _sp_, salivary glands;
+_msl_, stomach; _im_, imaginal discs; _tr_, tracheæ; _fk_, fatty tissue;
+_ed_, intestine; _ga_, rudiments of reproductive organs; _ew_, wider
+portion of intestine; _ao_, posterior opening.]
+
+At the next moult the larva enters its third state, which, as far as the
+external form (Fig. 27) is concerned, differs from the second only in
+being somewhat more elongated. The internal organs, however, are much
+more complex and complete. The tracheæ have made their appearance, and
+the mouth is provided with a pair of mandibles. From this point the
+metamorphoses of _Platygaster_ do not appear to differ materially from
+those of other parasitic Hymenoptera.
+
+An allied genus, _Polynema_, has also very curious larvæ. The perfect
+insect is aquatic in its habits, swimming by means of its wings; flying,
+if we may say so, under water.[15] It lays its eggs inside those of
+Dragon-flies; and the embryo, as shown in Fig. 28, has the form of a
+bottle-shaped mass of undifferentiated embryonal cells, covered by a
+thin cuticle, but without any trace of further organization. Protected
+by the egg-shell of the Dragon-fly, and bathed in the nourishing fluid
+of the Dragon-fly’s egg, the young _Polynema_ imbibes nourishment through
+its whole surface, and increases rapidly in size. The digestive canal
+gradually makes its appearance; the cellular mass forms a new skin
+beneath the original cuticle, distinctly divided into segments, and
+provided with certain appendages. After a while the old cuticle is
+thrown off, and the larva gradually assumes the form shown in Fig. 29.
+The subsequent metamorphoses of _Polynema_ offer no special peculiarities.
+
+[Illustration: FIG. 28, Embryo of _Polynema_ (after Ganin). 29, Larva of
+_Polynema_—_asch_, rudiments of the antenna; _flsch_, rudiments of the
+wings; _bsch_, rudiments of the legs; _vfg_. lateral projections;
+_gsch_, rudiments of the ovipositor; _fk_, fatty tissue.]
+
+From these facts—and, if necessary, many more of the same nature might
+have been brought forward—it seems to me evident that while the form of
+any given larva depends to a certain extent on the group of insects to
+which it belongs, it is also greatly influenced by the external
+conditions to which it is subjected; that it is a function of the life
+which the larva leads and of the group to which it belongs.
+
+The larvæ of insects are generally regarded as being nothing more than
+immature states—as stages in the development of the egg into the
+imago; and this might more especially appear to be the case with those
+insects in which the larvæ offer a general resemblance in form and
+structure (excepting of course so far as relates to the wings) to the
+perfect insect. Nevertheless we see that this would be a very incomplete
+view of the case. The larva and pupa undergo changes which have no
+relation to the form which the insect will ultimately assume. With a
+general tendency to this goal, as regards size and the development of
+the wings, there are coincident other changes having reference only to
+existing wants and condition. Nor is there in this, I think, anything
+which need surprise us. External circumstances act on the insect in its
+preparatory states, as well as in its perfect condition. Those who
+believe that animals are susceptible of great, though gradual, change
+through the influence of external conditions, whether acting, as Mr.
+Darwin has suggested, through natural selection, or in any other manner,
+will see no reason why these changes should be confined to the mature
+animal. And it is evident that creatures which, like the majority of
+insects, live during the successive periods of their existence in very
+different circumstances, may undergo considerable changes in their
+larval organization, in consequence of forces acting on them while in
+that condition; not, indeed, without affecting, but certainly without
+affecting to any corresponding extent, their ultimate form.
+
+I conclude, therefore, that the form of the larva in insects, whenever
+it departs from the hexapod _Campodea_ type, has been modified by the
+conditions under which it lives. The external forces acting upon it are
+different from those which affect the mature form; and thus changes are
+produced in the young which have reference to its immediate wants,
+rather than to its final form.
+
+And, lastly, as a consequence, that metamorphoses may be divided into
+two kinds, developmental and adaptional or adaptive.
+
+
+
+
+CHAPTER III.
+
+_ON THE NATURE OF METAMORPHOSES._
+
+
+In the preceding chapters we have considered the life history of insects
+after they have quitted the egg; but it is obvious that to treat the
+subject in a satisfactory manner we must take the development as a
+whole, from the commencement of the changes in the egg, up to the
+maturity of the animal, and not suffer ourselves to be confused by the
+fact that insects leave the egg in very different stages of embryonal
+development. For though all young insects when they quit the egg are
+termed “larvæ,” whatever their form may be (the case of the so-called
+Pupipara not constituting a true exception), still it must be remembered
+that some of these larvæ are much more advanced than others. It is
+evident that the larva of a fly, as regards its stage of development,
+corresponds in reality neither with that of a moth nor with that of a
+grasshopper. The maggots of flies, in which the appendages of the head
+are rudimentary, belong to a lower grade than the grubs of bees, &c.,
+which have antennæ, mandibles, maxillæ, labrum, labium, and, in fact,
+all the mouth parts of a perfect insect.
+
+The caterpillars of Lepidoptera are generally classed with the vermiform
+larva of Diptera and Hymenoptera, and contrasted with those of
+Orthoptera, Hemiptera, &c.; but, in truth, the possession of thoracic
+legs places them, together with the similar larvæ of the Tenthredinidæ,
+on a decidedly higher level. Thus, then, the period of growth (that in
+which the animal eats and increases in size) occupies sometimes one
+stage in the development of an insect, sometimes another; sometimes, as
+for instance in the case of _Chloëon_, it continues through more than
+one; or, in other words, growth is accompanied by development. But, in
+fact, the question is even more complicated than this. It is not only
+that the larvæ of insects at their birth offer the most various grades
+of development, from the grub of a fly to the young of a grasshopper or
+a cricket; but that, if we were to classify larvæ according to their
+development, we should have to deal, not with a simple case of
+gradations only, but with a series of gradations, which would be
+different according to the organ which we took as our test.
+
+Apart, however, from the adaptive changes to which special reference was
+made in the previous chapter, the differences which larvæ present are
+those of gradation, not of direction. The development of a grasshopper
+does not pursue a different course from that of a butterfly, but the
+embryo attains a higher state before quitting the egg in the former than
+in the latter: while in most Hymenoptera, as for instance in Bees,
+Wasps, Ants, &c., the young are hatched without thoracic appendages; in
+the Orthoptera, on the contrary, the legs are fully developed before the
+young animal quits the egg.
+
+Prof. Owen,[16] indeed, goes so far as to say that the Orthoptera and
+other Homomorphous insects are, “at one stage of their development,
+apodal and acephalous larvæ, like the maggot of the fly; but instead of
+quitting the egg in this stage, they are quickly transformed into
+another, in which the head and rudimental thoracic feet are developed to
+the degree which characterizes the hexapod larvæ of the _Carabi_ and
+_Petalocera_.”
+
+[Illustration: FIG. 30, Egg of _Phryganea_ (Mystacides)—_A_¹,
+mandibular segment; _C_¹ to _C_⁵, maxillary, labial, and three
+thoracic segments; _D_, abdomen (after Zaddach). 31, Egg of _Phryganea_
+somewhat more advanced—_b_, mandibles; _c_, maxillæ; _cfs_, rudiments
+of the three pairs of legs.]
+
+I quite believe that this may have been true of such larvæ at an early
+geological period, but the fact now appears to be, so far at least as
+can be judged from the observations yet recorded, that the legs of those
+larvæ which leave the egg with these appendages generally make their
+appearance before the body-walls have closed, or the internal organs
+have approached to completion. Indeed, when the legs first appear, they
+are merely short projections, which it is not always easy to distinguish
+from the segments themselves. It must, however, be admitted, that the
+observations are neither so numerous, nor in most cases so full, as
+could be wished.
+
+Fig. 30 represents an egg of a May-fly (_Phryganea_), as represented by
+Zaddach in his excellent memoir,[17] just before the appearance of the
+appendages. It will be seen that a great part of the yolk is still
+undifferentiated, that the side walls are incomplete, the back quite
+open, and the segments merely indicated by undulations. This stage is
+rapidly passed through, and Zaddach only once met with an egg in this
+condition; in every other specimen which had indications of segments,
+the rudiments of the legs had also made their appearance, as in Fig. 31,
+which, however, as will be seen, does not in other respects show much
+advance on Fig. 30.
+
+Again in _Aphis_, the embryology of which has been so well worked out by
+Huxley,[18] the case is very similar, although the legs are somewhat
+later in making their appearance. When the young was 1/140th of an inch
+in length, he found the cephalic portion of the embryo beginning, he
+says, “to extend upwards again over the anterior face of the germ, so as
+to constitute its anterior and a small part of its superior wall. This
+portion is divided by a median fissure into two lobes, which play an
+important part in the development of the head, and will be termed the
+‘procephalic lobes.’ I have already made use of this term for the
+corresponding parts in the embryos of Crustacea. The rudimentary thorax
+presents traces of a division into three segments; and the dorso-lateral
+margins of the cephalic blastoderm, behind the procephalic lobes, have a
+sinuous margin. It is in embryos between this and 1/100th of an inch in
+length, that the rudiments of the appendages make their appearance; and
+by the growth of the cephalic, thoracic, and abdominal blastoderm,
+curious changes are effected in the relative position of those regions.”
+
+In _Chrysopa oculata_, one of the Hemerobiidæ, Packard has described[19]
+and figured a stage in which the body segments have made their
+appearance, but in which he says “there are no indications of limbs. The
+primitive band is fully formed, the protozorites being distinctly
+marked, the transverse impressed lines indicating the primitive segments
+being distinct, and the median furrow easily discerned.” Here also,
+again, the dorsal walls are incomplete, and the internal organs as yet
+unformed.
+
+In certain Dragon-flies (_Calepteryx_), and _Hemiptera_ (_Hydrometra_), the
+legs, according to Brandt,[20] appear at a still earlier stage.
+
+According to the observations of Kölliker,[21] it would appear that in
+the Coleopterous genus _Donacia_ the segments and appendages appear
+simultaneously.
+
+Kölliker himself, however, frankly admits that “meæ de hoc insecto
+observationes satis sunt manca,” and it is possible that he may never
+have met with an embryo in the state immediately preceding the
+appearance of the legs; especially as it appears from the observations
+of Kowalevski that in _Hydrophilus_ the appendages do not make their
+appearance until after the segments.[22]
+
+On the whole, as far as we can judge from the observations as yet
+recorded, it seems that in Homomorphous insects the ventral wall is
+developed and divided into segments, before the appearance of the legs;
+but that the latter are formed almost simultaneously with the cephalic
+appendages, and before either the dorsal walls of the body or the
+internal organs.
+
+[Illustration: FIG. 32.—Egg of _Pholcus opilionides_ (after Claparède).]
+
+As it is interesting, from this point of view, to compare the
+development of other Articulata with that of insects, I give a figure
+(Fig. 32), representing an early stage in the development of a spider
+(_Pholcus_) after Claparède,[23] who says, “C’est à ce moment qu’a lieu
+la formation des _protozonites_ ou segments primordiaux du corps de
+l’embryon. Le rudiment ventral s’épaissit suivant six zônes disposées
+transversalement entre le capuchon anal et le capuchon céphalique.”
+
+[Illustration: FIG. 33.—Embryo of _Julus_ (after Newport).]
+
+Among Centipedes the development of _Julus_ has been described by
+Newport.[24] The first period, from the deposition of the egg to the
+gradual bursting of the shell, and exposure of the embryo within it,
+which, however, remains for some time longer in connection with the
+shell, lasts for twenty-five days. The segments of the body, originally
+six in number, make their appearance on the twentieth day after the
+deposition of the egg, at which time there were no traces of legs. The
+larva, when it leaves the egg, is a soft, white, legless grub (Fig. 33),
+consisting of a head and seven segments, the head being somewhat firmer
+in texture than the rest of the body. It exhibits rudimentary antennæ,
+but the legs are still only represented by very slight papilliform
+processes on the undersides of the segments to which they belong.
+
+As already mentioned, it is possible that at one time the vermiform
+state of the Homomorphous insects—which, as we have seen, is now so
+short, and passed through at so early a stage of development—was more
+important, more prolonged, and accompanied by a more complete condition
+of the internal organs. The compression, and even disappearance of those
+embryonal stages which are no longer adapted to the mode of life—which
+do not benefit the animal—is a phenomenon not without a parallel in
+other parts of the animal or even of the vegetable kingdom. Just as in
+language long compound words have a tendency to concision, and single
+letters sometimes linger on, indicating the history of a word, like the
+“l” in “alms,” or the “b” in “debt,” long after they have ceased to
+influence the sound; so in embryology useless stages, interesting as
+illustrations of past history, but without direct advantage under
+present conditions, are rapidly passed through, and even, as it would
+appear, in some cases altogether omitted.
+
+[Illustration: FIG. 34.—Colony of _Bougainvillea fruticosa_, natural
+size, to the underside of a piece of floating timber (after Allman).]
+
+For instance, among the Hydroida, in the great majority of cases, the
+egg produces a body more or less resembling the common _Hydra_ of our
+ponds, and known technically as the “trophosome,” which develops into
+the well-known Medusæ or jelly-fishes. The group, however, for which
+Prof. Allman has proposed the term Monopsea,[25] and of which the genus
+_Ægina_ may be taken as the type, is, as he says, distinguished by the
+absence of a hydriform stage, “the ovum becoming developed through
+direct metamorphosis into a medusiform body, just as in the other orders
+it is developed into a hydriform body.” Fig. 34 represents, after
+Allman, a colony of _Bougainvillea fruticosa_ of the natural size. It is
+a British species, which is found growing on buoys, floating timber,
+&c., and, says Allman,[26] “when in health and vigour, offers a
+spectacle unsurpassed in interest by any other species—every branchlet
+crowned by its graceful hydranth and budding with Medusæ in all stages
+of development (Fig. 35), some still in the condition of minute buds, in
+which no trace of the definite Medusa-form can yet be detected; others,
+in which the outlines of the Medusa can be distinctly traced within the
+transparent _ectothèque_ (external layer); others, again, just casting
+off this thin outer pellicle, and others completely freed from it,
+struggling with convulsive efforts to break loose from the colony, and
+finally launched forth in the full enjoyment of their freedom into the
+surrounding water. I know of no form in which so many of the
+characteristic features of a typical hydroid are more finely expressed
+than in this beautiful species.”
+
+[Illustration: FIG. 35.—Portion of colony of _Bougainvillea fruticosa_,
+more magnified.]
+
+[Illustration: FIG. 36.—The Medusa form of the same species.]
+
+Fig. 36 represents the Medusa form of this species, and the development
+thus described may be regarded as typical of the Hydroida; yet, as
+already mentioned, the Æginidæ do not present us with any stage
+corresponding to the fixed condition of _Bougainvillea_, but, on the
+contrary, are developed into Medusæ direct from the egg.
+
+On the other hand, there are groups in which the Medusiform stage
+becomes less and less important.
+
+[Illustration: FIG. 37, Larva of Prawn, Nauplius stage (after F.
+Müller). 38, Larva of Prawn, more advanced, Zoëa stage.]
+
+The great majority of the higher Crustacea go through well-marked
+metamorphoses. Figs. 37 and 38 represent two stages in the development
+of the prawn. In the first (Fig. 37), representing the young animal as
+it quits the egg, the body is more or less oval and unsegmented; there
+is a median frontal eye, and three pairs of natatory feet, the first
+pair simple, while the two posterior are two-branched. Very similar
+larvæ occur in various other groups of Crustacea. They were at first
+regarded as mature forms, and O. F. Müller gave them the name of
+Nauplius. So also, the second or Zoëa form (Fig. 38) was at first
+supposed to be a mature animal, until its true nature was discovered by
+Vaughan Thompson.
+
+The Zoëa form of larva differs from the perfect prawn or crab in the
+absence of the middle portion of the body and its appendages. The
+mandibles have no palpi, the maxillipeds or foot-jaws are used as feet,
+whereas in the mature form they serve as jaws. Branchiæ are either
+wanting or rudimentary, respiration being principally effected through
+the walls of the carapace. The abdomen and tail are destitute of
+articulate appendages. The development of Zoëa into the perfect animal
+has been well described by Mr. Spence Bate[27] in the case of the common
+crab (_Carcinus mænas_).
+
+All crabs, as far as we know, with the exception of a species of land
+crab (_Gegarcinus_), described by Westwood, pass through a stage more or
+less resembling that shown in Fig. 38. On the other hand, the great
+group of Edriopthalma, comprising Amphipoda (shore-hoppers, &c.) and
+Isopoda (wood-lice, &c.) pass through no such metamorphosis; the
+development is direct, as in the Orthoptera. It is true that one
+species, _Tanais Dulongii_, though a typical Isopod in form and general
+character, is said to retain in some points, and especially in the mode
+of respiration, some peculiarities of the Zoëa type; but this is quite
+an exceptional case. In _Mysis_, says F. Müller,[28] “there is still a
+trace of the Nauplius stage; being transferred back to a period when it
+had not to provide for itself, the Nauplius has become degraded into a
+mere skin; in _Ligia_ this larva-skin has lost the traces of limbs, and
+in _Philoscia_ it is scarcely demonstrable.”
+
+The Echinodermata in most cases “go through a very well-marked
+metamorphosis, which often has more than one larval stage.... The mass
+of more or less differentiated sarcode, of which the larva, or
+pseud-embryo, as opposed to the Echinoderm within it, is made up, always
+carries upon its exterior certain bilaterally-arranged ciliated bands,
+by the action of which the whole organism is moved from place to place;
+and it may be strengthened by the super-addition to it of a framework
+of calcareous rods.”[29] Müller considered that the mouth and pharynx of
+the larva were either absorbed or cast off with the calcareous rods, but
+were never converted into the corresponding organs of the perfect
+Echinoderm. According to A. Agassiz, however, this is not the case, but
+on the contrary “the whole larva and all its appendages are gradually
+drawn into the body, and appropriated.”[30]
+
+Fig. 39 represents the larva of a sea-egg (_Echino cidaris_) after
+Müller.[31] The body is transparent, shaped somewhat like a double
+easel, but with two long horns in front, which, as well as the posterior
+processes, are supported by calcareous rods. This larva swims by means
+of minute vibratile hairs, or ciliæ. It has a mouth, stomach, and in
+fact a well-defined alimentary canal; but no nerves or other internal
+organs have yet been discovered in it. After swimming about in this
+condition for a while, it begins to show signs of change. An involution
+of the integument takes place on one side of the back, and continues to
+deepen till it reaches a mass or store of what is called blastema, or
+the raw material of the animal body. This blastema then begins to
+change, and gradually assumes the form of the perfect Echinoderm.[32]
+
+[Illustration: FIG. 39.—Larva of _Echino cidaris_, seen from above × 6/10
+(after Müller).]
+
+[Illustration: FIG. 40, Larva of _Echinus_, × 100. _A_, front arm; _F_,
+arms of the mouth process; _B_, posterior side arm; _E_₁, accessory
+arm of the mouth process; _a_, mouth; _a´_, œsophagus; _b_, stomach;
+_b´_, intestine; _o_, posterior orifice; _d_, ciliated bands; _f_,
+ciliated epaulets; _c_, disc of future _Echinus_ (after Müller).]
+
+Fig. 40 represents a larva, probably of another sea-egg (_Echinus
+lividus_), from the Mediterranean, and shows the commencement of the
+sea-egg within the body of the larva. The capital letters denote the
+different arms: _a_ is the mouth, _a´_ the œsophagus, _b_ the
+stomach, _b´_ the intestine, _f_ the ciliated lobes or epaulets, _c_ the
+young sea-egg.
+
+The development of the beautiful _Comatula rosacea_ (Fig. 41) has been
+described in the “Philosophical Transactions,” by Prof. Wyville Thomson
+and Dr. Carpenter.[33] The larva quits the egg, as shown in Fig. 42, in
+the form of an oval body about 1/30 inch in length, something like a
+barrel, surrounded by four bands or hoops of long vibratile hairs or
+ciliæ. There is also a tuft of still longer hairs at the narrower
+posterior end of the body. Gradually a number of minute calcareous
+spines and plates make their appearance (Fig. 43) in the body of this
+larva, and at length arrange themselves in a definite order, so as to
+form a bent calcareous club or rod with an enlarged head.
+
+[Illustration: FIG. 41.—_Comatula rosacea_ (after Forbes).]
+
+[Illustration: FIG. 42, Larva of Comatula rosacea (after Thomson). 43,
+Larva of _Comatula rosacea_, more advanced. 44, Larva of Comatula rosacea,
+in the Pentacrinus state.]
+
+As this process continues, the little creature gradually loses its power
+of swimming, and, sinking to the bottom, looses the bands of ciliæ, and
+attaches itself by its base to some stone or other solid substance, the
+knob of the club being free. The calcareous framework increases in size,
+and the expanded head forms itself into a cup, round which from five to
+fifteen delicate tentacles, as shown in Fig. 44, make their appearance.
+
+In this stage the young animal resembles one of the stalked Crinoids, a
+family of Echinoderms very abundant in earlier geological periods, but
+which has almost disappeared, being, as we see, now represented by the
+young states of existing more advanced, free, species. This attached,
+plant-like condition of _Comatula_ was indeed at first supposed to be a
+mature form, and was named Pentacrinus; but we now know that it is only
+a stage in the development of _Comatula_. The so-called Pentacrinus
+increases considerably in size, and after various gradual changes, which
+time does not now permit me to describe, quits the stalk, and becomes a
+free _Comatula_.
+
+The metamorphoses of the Starfishes are also very remarkable. Sars
+discovered, in the year 1835, a curious little creature about an inch in
+length, which he named _Bipinnaria asterigera_ (Figs. 45-47), and which
+he then supposed to be allied to the ciliograde Medusæ. Subsequent
+observations, however, made in 1844, suggested to him that it was the
+larva of a Starfish, and in 1847 MM. Koren and Danielssen satisfied
+themselves that this was the case.
+
+Figs. 45 and 46 represent the front and side view of a Bipinnaria found
+by Müller[34] near Marseilles. _a_ is the mouth, _b_ the œsophagus,
+_c_ the stomach, _c_´ the intestine. Fig. 47 represents a somewhat older
+specimen, in which the Starfish (_k_) is already beginning to make its
+appearance.
+
+[Illustration: FIG. 45, Larva of Starfish (Bipinnaria), × 100 (after
+Müller). 46, Larva of Starfish (Bipinnaria), × 100, seen from the
+side—_a_, mouth; _b_, œsophagus; _c_, stomach; _c´_, intestine. 47,
+Larva of another Bipinnaria, showing the commencement of the
+Starfish—_g_, canal of the ciliated sac; _i_, rudiments of tentacles;
+_d_, ciliated band.]
+
+But while certain Starfishes thus go through metamorphoses similar in
+character, and not less remarkable than those of sea-eggs, there are
+others—as, for instance, the genus _Asteracanthion_—in which development
+may be said to be direct—the organs and appendages special to the
+Pseud-embryo being in abeyance; while in another genus, _Pteraster_, they
+are reduced to a mere investing membrane.[35]
+
+Among the Ophiurans also we find two well-marked types of development.
+Some passing through metamorphoses, while others, as for instance
+_Ophiopholis bellis_, “is developed very much after the method of
+_Asteracanthion Mülleri_, without passing through the Plutean
+stage.”[36]
+
+Even in the same species of Echinoderm the degree of development
+attained by the larva differs to a certain extent according to the
+temperature, the supply of food, &c. Thus in _Comatula_, specimens which
+are liberally supplied with sea-water, and kept warm, hurry as it were
+through their early stages, and the free larva becomes distorted by the
+growing Pentacrinus (see Fig. 43), almost before it has attained its
+perfect form. On the other hand, under less favourable conditions, if
+the temperature is low and food less abundant, the early stages are
+prolonged, the larva is longer lived, and reaches a much higher degree
+of independent development. Similar differences occur in the development
+of other animals, as for instance, in the Hydroids,[37] and among the
+insects themselves, in Flies;[38] and it is obvious that these facts
+throw much light on the nature and origin of the metamorphoses of
+insects, which subject we shall now proceed to consider.
+
+
+
+
+CHAPTER IV.
+
+_ON THE ORIGIN OF METAMORPHOSES._
+
+
+The question still remains, Why do insects pass through metamorphoses?
+Messrs. Kirby and Spence tell us they “can only answer that such is the
+will of the Creator;”[39] this, however, is a general confession of
+faith, not an explanation of metamorphoses. So indeed they themselves
+appear to have felt; for they immediately proceed to make a suggestion.
+“Yet one reason,” they say, “for this conformation may be hazarded. A
+very important part assigned to insects in the economy of nature, as we
+shall hereafter show, is that of speedily removing superabundant and
+decaying animal and vegetable matter. For such agents an insatiable
+voracity is an indispensable qualification, and not less so unusual
+powers of multiplication. But these faculties are in a great degree
+incompatible; an insect occupied in the work of reproduction could not
+continue its voracious feeding. Its life, therefore, after leaving the
+egg, is divided into three stages.”
+
+But there are some insects—as, for instance, the Aphides—which
+certainly are not among the least voracious, and which grow and breed at
+the same time. There are also many scavengers among other groups of
+animals—such, for instance, as the dog, the pig, and the vulture—which
+undergo no metamorphosis.
+
+It is certainly true that, as a general rule, growth and reproduction do
+not occur together; and it follows, almost as a necessary consequence,
+that in such cases the first must precede the second. But this has no
+immediate connection with the occurrence of metamorphoses. The question
+is not, why an insect does not generally begin to breed until it has
+ceased to grow, but why, in attaining to its perfect form, it passes
+through such remarkable changes; why these changes are so sudden and
+apparently violent; and why they are so often closed by a state of
+immobility—that of the chrysalis or pupa; for undoubtedly the quiescent
+and death-like condition of the pupa is one of the most remarkable
+phenomena of insect-metamorphoses.
+
+In the first place, it must be observed that many animals which differ
+considerably in their mature state, resemble one another more nearly
+when young. Thus birds of the same genus, or of closely allied genera,
+which, when mature, differ much in colour, are often very similarly
+coloured when young. The young of the lion and the puma are often
+striped, and the fœtal Black whale has teeth, like its ally the Sperm
+whale.
+
+In fact, the great majority of animals do go through well-marked
+metamorphoses, though in many cases they are passed through within the
+egg, and thus do not come within the popular ken. “La larve,” says,
+Quatrefages, “n’est qu’un embryon à vie indépendante.”[40] Those
+naturalists who accept in any form the theory of evolution, consider
+that “the embryonal state of each species reproduces more or less
+completely the form and structure of its less modified progenitors.”[41]
+“Each organism,” says Herbert Spencer,[42] “exhibits within a short
+space of time a series of changes which, when supposed to occupy a
+period indefinitely great, and to go on in various ways instead of one
+way, give us a tolerably clear conception of organic evolution in
+general.”
+
+The naturalists of the older school do not, as Darwin and Fritz Müller
+have already pointed out, dispute these facts, though they explain them
+in a different manner—generally by the existence of a supposed tendency
+to diverge from an original type. Thus Johannes Müller says, “The idea
+of development is not that of mere increase of size, but that of
+progress from what is not yet distinguished, but which potentially
+contains the distinction in itself, to the actually distinct. It is
+clear that the less an organ is developed, so much the more does it
+approach the type, and that during its development it acquires more and
+more peculiarities. The types discovered by comparative anatomy and
+developmental history must therefore agree.” And again, “What is true in
+this idea is, that every embryo at first bears only the type of its
+section, from which the type of the class, order, &c., is only
+afterwards developed.” Agassiz also observes that “the embryos of
+different animals resemble each other the more the younger they are.”
+
+There are, no doubt, cases in which the earlier states are rapidly
+passed through, or but obscurely indicated; yet we may almost state it
+as a general proposition, that either before or after birth animals
+undergo metamorphoses. The state of development of the young animal at
+birth varies immensely. The kangaroo (_Macropus major_), which attains a
+height of seven feet ten inches, does not when born exceed one inch and
+two lines in length; the chick leaves the egg in a much more advanced
+condition than the thrush; and so, among insects, the young cricket is
+much more highly developed, when it leaves the egg, than the larva of
+the fly or of the bee; and, as I have already mentioned, differences
+occur even within the limit of one species, though not of course to
+anything like the same extent.
+
+In oviparous animals the condition of the young at birth depends much on
+the size of the egg: where the egg is large, the abundant supply of
+nourishment enables the embryo to attain a high stage of development;
+where the egg is small, and the yolk consequently scanty, the embryo
+requires an additional supply of food before it can do so. In the former
+case the embryo is more likely to survive; but when the eggs are large,
+they cannot be numerous, and a multiplicity of germs may be therefore in
+some circumstances a great advantage. Even in the same species the
+development of the egg presents certain differences.[43]
+
+The metamorphoses of insects depend then primarily on the fact that the
+young quit the egg at a more or less early stage of development; and
+that consequently the external forces, acting upon them in this state,
+are very different from those by which they are affected when they
+arrive at maturity.
+
+Hence it follows that, while in many instances mature forms, differing
+greatly from one another, arise from very similar larvæ, in other cases,
+as we have seen, among some the parasitic Hymenoptera, insects agreeing
+closely with one another, are produced from larvæ which are very unlike.
+The same phenomenon occurs in other groups. Thus, while in many cases
+very dissimilar jelly-fishes arise from almost identical Hydroids, we
+have also the reverse of the proposition in the fact that in some
+species, Hydroids of an entirely distinct character produce very similar
+Medusæ.[44]
+
+We may now pass to the second part of our subject: the apparent
+suddenness and abruptness of the changes which insects undergo during
+metamorphosis. But before doing so I must repeat that these changes are
+not always, even apparently, sudden and great. The development of an
+Orthopterous insect, say a grasshopper, from its leaving the egg to
+maturity, is so gradual that the ordinary nomenclature of entomological
+works (larva state and pupa state) does not apply to it; and even in the
+case of Lepidoptera, the change from the caterpillar to the chrysalis
+and from this to the butterfly is in reality less rapid than might at
+first sight be supposed; the internal organs are metamorphosed very
+gradually, and even the sudden and striking change in external form is
+very deceptive, consisting merely of a throwing off of the outer
+skin—the drawing aside, as it were of a curtain and the revelation of a
+form which, far from being new, has been in preparation for days;
+sometimes even for months.
+
+Swammerdam, indeed, supposed (and his view was adopted by Kirby and
+Spence) that the larva contained within itself “the germ of the future
+butterfly, enclosed in what will be the case of the pupa, which is
+itself included in three or more skins, one over the other, that will
+successively cover the larva.” This was a mistake; but it is true that,
+if a larva be examined shortly before it is full grown, the future pupa
+may be traced within it. In the same manner, if we examine a pupa which
+is about to disclose the butterfly, we find the future insect, soft
+indeed and imperfect, but still easily recognizable, lying more or less
+loosely within the pupa-skin.
+
+One important difference between an insect and a vertebrate animal is,
+that whereas in the latter—as, for instance, in ourselves—the muscles
+are attached to an internal bony skeleton, in insects no such skeleton
+exists. They have no bones, and their muscles are attached to the skin;
+whence the necessity for the hard and horny dermal investment of
+insects, so different from the softness and suppleness of our own skin.
+The chitine, or horny substance, of which the outside of an insect
+consists, is formed by a layer of cells lying beneath it, and, once
+secreted, cannot be altered. From this the result is, that without a
+change of skin, a change of form is impossible. In some cases, as for
+instance in _Chloëon_, each change of skin is accompanied by a change of
+form, and thus the perfect insect is gradually evolved. In others, as in
+caterpillars, several changes of skin take place without any material
+alteration of form, and the change, instead of being spread over many,
+is confined to the last two moults.
+
+One explanation of this difference between the larvæ which change their
+form with every change of skin, and those which do not, is, I believe,
+to be found in the structure of the mouth. That of the caterpillar is
+provided with a pair of strong jaws, fitted to eat leaves; and the
+digestive organs are adapted for this kind of food. On the contrary, the
+mouth of the butterfly is suctorial; it has a long proboscis,
+beautifully adapted to suck the nectar from flowers, but which would be
+quite useless, and indeed only an embarrassment to the larva. The
+digestive organs also of the butterfly are adapted for the assimilation,
+not of leaves, but of honey. Now it is evident that if the mouth-parts
+of the larva were slowly metamorphosed into those of the perfect insect,
+through a number of small changes, the insect would in the meantime be
+unable to feed, and liable to perish of starvation in the midst of
+plenty. In the Orthoptera, and among those insects in which the changes
+are gradual, the mouth of the so-called larva resembles that of the
+perfect insect, and the principal difference consists in the presence of
+wings.
+
+Similar considerations throw much light on the nature of the chrysalis
+or pupa state—that remarkable period of death-like quiescence which is
+one of the most striking characteristics of insect metamorphosis. The
+quiescence of the pupa is mainly owing to the rapidity of the changes
+going on in it. In that of a butterfly, not only (as has been already
+mentioned) are the mouth and the digestive organs undergoing change, but
+the muscles are in a similar state of transition. The powerful ones
+which move the wings are in process of formation; and even the nervous
+system, by which the movements are set on foot and regulated, is in a
+state of rapid change.[45]
+
+It must not be forgotten that all insects are inactive for a longer or
+shorter space of time after each moult. The slighter the change, as a
+general rule, the shorter is the period of inaction. Thus, after the
+ordinary moult of a caterpillar, the insect only requires a short rest
+until the new skin is hardened. When, however, the change is great, the
+period of inaction is correspondingly prolonged. Most pupæ indeed have
+some slight powers of motion; those which assume the chrysalis state in
+wood or beneath the ground usually come to the surface when about to
+assume the perfect state, and the aquatic pupæ of certain Diptera swim
+about with much activity. Among the Neuroptera, certain families have
+pupæ as quiescent as those of the Lepidoptera: others—as, for
+instance, _Raphidia_—are quiescent at first, but at length acquire
+sufficient strength to walk, though still enclosed within the pupa-skin:
+a power dependent partly on the fact that this skin is very thin. Others
+again—as, for instance, dragon-flies—are not quiescent on assuming the
+so-called pupa state for any longer time than at their other changes of
+skin. The inactivity of the pupa is therefore not a new condition
+peculiar to this stage, but a prolongation of the inaction which has
+accompanied every previous change of skin.
+
+Nevertheless the metamorphoses of insects have always seemed to me one
+of the greatest difficulties of the Darwinian theory. In most cases, the
+development of the individual reproduces to a certain extent that of the
+race; but the motionless, imbecile pupa cannot represent a mature form.
+No one, so far as I know, has yet attempted to explain, in accordance
+with Mr. Darwin’s views, a life-history in which the mouth is first
+mandibulate and then suctorial, as, for example, in a butterfly. A clue
+to the difficulty may, I think, be found in the distinction between
+developmental and adaptive changes; to which I have called attention in
+a previous chapter. The larva of an insect is by no means a mere stage
+in the development of the perfect animal. On the contrary, it is subject
+to the influence of natural selection, and undergoes changes which have
+reference entirely to its own requirements and condition. It is evident,
+then, that while the embryonic development of an animal in the egg may
+be an epitome of its specific history, this is by no means the case
+with species in which the immature forms have a separate and
+independent existence. If an animal which, when young, pursues one mode
+of life, and lives on one kind of food, subsequently, either from its
+own growth in size and strength, or from any change of season, alters
+its habits or food, however slightly, it immediately becomes subject to
+the action of new forces: natural selection affects it in two different,
+and, it may be, very distinct manners, gradually tending to changes
+which may become so great as to involve an intermediate period of change
+and quiescence.
+
+There are, however, peculiar difficulties in those cases in which, as
+among the Lepidoptera, the same species is mandibulate as a larva, and
+suctorial as an imago. From this point of view _Campodea_ and the
+Collembola (_Podura_, &c.) are peculiarly interesting. There are in
+insects three principal types of mouth:—
+
+First, the mandibulate;
+
+Secondly, the suctorial; and
+
+Thirdly, that of _Campodea_ and the Collembola generally,
+
+in which the mandibles and maxillæ are retracted, but have some freedom
+of motion, and can be used for biting and chewing soft substances. This
+type is, in some respects, intermediate between the other two. Assuming
+that certain representatives of such a type were placed under conditions
+which made a suctorial mouth advantageous, those individuals in which
+the mandibles and maxillæ were best calculated to pierce or prick would
+be favoured by natural selection, and their power of lateral motion
+would tend to fall into abeyance; while, on the other hand, if
+masticatory jaws were an advantage, the opposite process would take
+place.
+
+There is yet a third possibility—namely, that during the first portion
+of life, the power of mastication should be an advantage, and during the
+second that of suction, or _vice versâ_. A certain kind of food might
+abound at one season and fail at another; might be suitable for the
+animal at one age and not at another. Now in such cases we should have
+two forces acting successively on each individual, and tending to modify
+the organization of the mouth in different directions. It cannot be
+denied that the innumerable variations in the mouth-parts of insects
+have special reference to their mode of life, and are of some advantage
+to the species in which they occur. Hence, no believer in natural
+selection can doubt the possibility of the three cases above suggested,
+the last of which seems to throw some light on the possible origin of
+species which are mandibulate in one period of life and not in another.
+Granting then the transition from the one condition to the other, this
+would no doubt take place contemporaneously with a change of skin. At
+such times we know that, even when there is no change in form, the
+softness of the organs temporarily precludes the insect from feeding for
+a time, as, for instance, in the case of caterpillars. If, however, any
+considerable change were involved, this period of fasting must be
+prolonged, and would lead to the existence of a third condition, that of
+the pupa, intermediate between the other two. Since the acquisition of
+wings is a more conspicuous change than any relating to the mouth, we
+are apt to associate with it the existence of a pupa-state: but the case
+of the Orthoptera (grasshoppers, &c.) is sufficient proof that the
+development of wings is perfectly compatible with permanent activity;
+the necessity for prolonged rest is in reality much more intimately
+connected with the change in the constitution of the mouth, although in
+many cases, no doubt, this is accompanied by changes in the legs, and in
+the internal organization. An originally mandibulate mouth, however,
+like that of a beetle, could not, I think, have been directly modified
+into a suctorial organ like that of a butterfly or a gnat, because the
+intermediate stages would necessarily be injurious. Neither, on the
+other hand, for the same reasons, could the mouth of the Hemiptera be
+modified into a mandibulate type like that of the Coleoptera. But in
+_Campodea_ and the _Collembola_ we have a type of animal closely
+resembling certain larvæ which occur both in the mandibulate and
+suctorial series of insects, possessing a mouth neither distinctly
+mandibulate nor distinctly suctorial, but constituted on a peculiar
+type, capable of modification in either direction by gradual change,
+without loss of utility.
+
+In discussing this subject, it is necessary also to take into
+consideration the nature and origin of wings. Whence are they derived?
+why are there normally two pairs? and why are they attached to the
+meso-and meta-thorax? These questions are as difficult as they are
+interesting. It has been suggested, and I think with justice, that the
+wings of insects originally served for aquatic and respiratory
+purposes.
+
+In the larva of _Chloëon_ (Pl. IV., Fig. 1), for instance, which in
+other respects so singularly resembles _Campodea_ (Pl. III., Fig. 5),
+several of the segments are provided with foliaceous expansions which
+serve as respiratory organs. These so-called branchiæ are in constant
+agitation, and the muscles which move them in several points resemble
+those of true wings. It is true that in _Chloëon_ the vibration of the
+branchiæ is scarcely, if at all, utilized for the purpose of locomotion;
+the branchiæ are, in fact, placed too far back to act efficiently. The
+situation of these branchiæ differs in different groups; indeed, it
+seems probable that originally there were a pair on each segment. In
+such a case, those branchiæ situated near the centre of the body,
+neither too much in front nor too far back, would serve the most
+efficiently as propellers: the same causes which determined the position
+of the legs would also affect the wings. Thus a division of labour would
+be effected; the branchiæ on the thorax would be devoted to locomotion;
+those on the abdomen to respiration. This would tend to increase the
+development of the thoracic segments, already somewhat enlarged, in
+order to receive the muscles of the legs.
+
+That wings may be of use to insects under water is proved by the very
+interesting case of _Polynema natans_,[46] which uses its wings for
+swimming. This, however, is a rare case, and it is possible that the
+principal use of the wings was, primordially, to enable the mature forms
+to pass from pond to pond, thus securing fresh habitats and avoiding
+in-and-in breeding. If this were so, the development of wings would
+gradually have been relegated to a late period of life; and by the
+tendency to the inheritance of characters at corresponding ages, which
+Mr. Darwin has pointed out,[47] the development of wings would have thus
+become associated with the maturity of the insect. Thus the late
+acquisition of wings in the Insecta generally seems to be itself an
+indication of their descent from a stock which was at one period, if not
+originally, aquatic, and which probably resembled the present larvæ of
+_Chloëon_ in form, but had thoracic as well as abdominal branchiæ.
+
+Finally, from the subject of metamorphosis we pass naturally to that
+most remarkable phenomenon which is known as the “Alternation of
+Generations:” for the first systematic view of which we are indebted to
+my eminent friend Prof Steenstrup.[48]
+
+I have always felt it very difficult to understand why any species
+should have been created in this double character; nor, so far as I am
+aware, has any explanation of the fact yet been attempted. Nevertheless
+insects offer, in their metamorphoses, a phenomenon not altogether
+dissimilar, and give a clue to the manner in which alternation of
+generations may have originated.
+
+The caterpillar owes its difference from the butterfly to the
+undeveloped state in which it leaves the egg; but its actual form is
+mainly due to the influence of the conditions under which it lives. If
+the caterpillar, instead of changing into one butterfly, produced
+several, we should have an instance of alternation of generations. Until
+lately, however, we knew of no such case among insects; each larva
+produced one imago, and that not by generation, but by development. It
+has long been known, indeed, that there are species in which certain
+individuals remain always apterous, while others acquire wings. Many
+entomologists, however, regard these abnormal individuals as perfect,
+though wingless insects; and therefore I shall found no argument upon
+these cases, although they appear to me deserving of more attention than
+they have yet received.
+
+Recently, however, Prof. Wagner[49] has discovered that, among certain
+small gnats, the larvæ do not directly produce in all cases perfect
+insects, but give birth to other larvæ, which undergo metamorphoses of
+the usual character, and eventually become gnats. His observations have
+been confirmed, as regards this main fact, by other naturalists; and
+Grimm has met with a species of _Chironomus_ in which the pupæ lay
+eggs.[50]
+
+Here, then, we have a distinct case of alternation of generations, as
+characterized by Steenstrup. Probably other cases will be discovered in
+which insects undeniably in the larval state will be found fertile. Nay,
+it seems to me possible, if not probable, that some larvæ which do not
+now breed may, in the course of ages, acquire the power of doing so. If
+this idea is correct, it shows how the remarkable phenomenon, known as
+alternation of generations, may have originated.
+
+Summing up, then, the preceding argument, we find among insects various
+modes of development; from simple growth on the one hand, to well-marked
+instances of the so-called alternation of generation on the other. In
+the wingless species of Orthoptera there is little external difference,
+excepting in size, between the young larva and the perfect insect. The
+growth is gradual, and there is nothing which would, in ordinary
+language, be called a metamorphosis. In the majority of Orthoptera,
+though the presence of wings produces a marked difference between the
+larva and the imago, the habits are nearly the same throughout life, and
+consequently the action of external circumstances affects the larva in
+the same manner as it does the perfect insect.
+
+This is not the case with the Neuroptera. The larvæ do not live under
+the same conditions as the perfect insects: external forces accordingly
+affect them in a different manner; and we have seen that they pass
+through some changes which bear no reference to the form of the perfect
+insect: these changes, however, are for the most part very gradual. The
+caterpillars of Lepidoptera have even more extensive modifications to
+undergo; the mouth of the larva, for instance, being remarkably unlike
+that of the perfect insect. A change in this organ, however, could
+hardly take place while the insect was growing fast, and consequently
+feeding voraciously; nor, even if the change could be thus effected,
+would the mouth, in its intermediate stages, be in any way fitted for
+biting and chewing leaves. The same reasoning applies also to the
+digestive organs. Hence the caterpillar undergoes little, if any,
+change, except in size, and the metamorphosis is concentrated, so to
+say, into the last two moults. The changes then become so rapid and
+extensive, that the intermediate period is necessarily one of
+quiescence. In some exceptional cases, as in _Sitaris_ (_ante_, p. 30) we
+even find that, the conditions of life not being uniform throughout the
+larval period, the larva itself undergoes metamorphoses.
+
+Owing to the fact that the organs connected with the reproduction of the
+species come to maturity at a late period, larvæ are generally incapable
+of breeding. There are, however, some flies which have viviparous larvæ,
+and thus offer a typical case of alternation of generations.
+
+Thus, then, we find among insects every gradation, from simple growth to
+alternation of generations; and see how, from the single fact of the
+very early period of development at which certain animals quit the egg,
+we can throw some light on their metamorphoses, and for the still more
+remarkable phenomenon that, among many of the lower animals, the species
+is represented by two very different forms. We may even conclude, from
+the same considerations, that this phenomenon may in the course of ages
+become still more common than it is at present. As long, however, as the
+external organs arrive at their mature form before the internal
+generative organs are fully developed, we have metamorphosis; but if the
+reverse is the case, then alternation of generations often results.
+
+The same considerations throw much light on the remarkable circumstance,
+that in alternation of generations the reproduction is, as a general
+rule, agamic in one form. This results from the fact that reproduction
+by distinct sexes requires the perfection both of the external and
+internal organs; and if the phenomenon arise, as has just been
+suggested, from the fact that the internal organs arrive at maturity
+before the external ones, reproduction will result in those species only
+which have the power of agamic multiplication.
+
+Moreover, it is evident that we have in the animal kingdom two kinds of
+dimorphism.
+
+This term has usually been applied to those cases in which animals or
+plants present themselves at maturity under two forms. Ants and Bees
+afford us familiar instances among animals; and among plants the
+interesting case of the genus _Primula_ has recently been described by
+Mr. Darwin. Even more recently he has made known to us the still more
+remarkable phenomenon afforded by the genus _Lythrum_, in which there
+are three distinct forms, and which therefore offers an instance of
+polymorphism.[51]
+
+The other kind of dimorphism or polymorphism differs from the first in
+being the result of the differentiating action of external
+circumstances, not on the mature, but on the young individual. Such
+different forms, therefore, stand towards one another in the relation of
+succession. In the first kind the chain of being divides at the
+extremity; in the other it is composed of dissimilar links. Many
+instances of this second form of dimorphism have been described under
+the name of alternation of generations.
+
+The term, however, has met with much opposition, and is clearly
+inapplicable to the differences exhibited by insects in various periods
+of their life. Strictly speaking, the phenomena are frequently not
+alternate, and in the opinion of some eminent naturalists they are not,
+strictly speaking, cases of generation at all.[52]
+
+In order, then, to have some name for these remarkable phenomena, and to
+distinguish them from those cases in which the _mature_ animal or plant
+is represented by two or more different forms, I think it would be
+convenient to retain exclusively for these latter the terms dimorphism
+and polymorphism; and those cases in which animals or plants pass
+through a succession of different forms might be distinguished by the
+name of dieidism or polyeidism.
+
+The conclusions, then, which I think we may draw from the preceding
+considerations, are:—
+
+1. That the occurrence of metamorphoses arises from the immaturity of
+the condition in which some animals quit the egg.
+
+2. That the form of the insect larva depends in great measure on the
+conditions in which it lives. The external forces acting upon it are
+different from those which affect the mature form; and thus changes are
+produced in the young, having reference to its immediate wants, rather
+than to its final form.
+
+3. That metamorphoses may therefore be divided into two kinds,
+developmental and adaptional or adaptive.
+
+4. That the apparent abruptness of the changes which insects undergo,
+arises in great measure from the hardness of their skin, which admits of
+no gradual alteration of form, and which is itself necessary in order to
+afford sufficient support to the muscles.
+
+5. The immobility of the pupa or chrysalis depends on the rapidity of
+the changes going on in it.
+
+6. Although the majority of insects go through three well-marked stages
+after leaving the egg, still a large number arrive at maturity through a
+greater or smaller number of slight changes.
+
+7. When the external organs arrive at this final form before the organs
+of reproduction are matured, these changes are known as metamorphoses;
+when, on the contrary, the organs of reproduction are functionally
+perfect before the external organs, or when the creature has the power
+of budding, then the phenomenon is known as alternation of generations.
+
+
+
+
+CHAPTER V.
+
+_ON THE ORIGIN OF INSECTS._
+
+
+“Personne,” says Carl Vogt, “en Europe au moins, n’ose plus soutenir la
+Création indépendante et de toutes pièces des espèces,” and though this
+statement is perhaps not strictly correct, still it is no doubt true,
+that the Doctrine of Evolution, in some form or other, is accepted by
+most, if not by all, the greatest naturalists of Europe. Yet it is
+surprising how much, in spite of all that has been written, Mr. Darwin’s
+views are still misunderstood. Thus Browning, in one of his recent
+poems, says:—
+
+  “That mass man sprang from was a jelly lump
+   Once on a time; he kept an after course
+   Through fish and insect, reptile, bird, and beast,
+   Till he attained to be an ape at last,
+   Or last but one.”[53]
+
+This theory, though it would be regarded by many as a fair statement of
+his views, is one which Mr. Darwin would entirely repudiate. Whether
+fish and insect, reptile, bird and beast, are derived from one original
+stock or not, they are certainly not links in one sequence. I do not,
+however, propose to discuss the question of Natural Selection, but may
+observe that it is one thing to acknowledge that in Natural Selection,
+or the survival of the fittest, Mr. Darwin has called attention to a
+_vera causa_, has pointed out the true explanation of certain phenomena;
+but it is quite another thing to maintain that all animals are descended
+from some primordial source.
+
+For my own part, I am satisfied that Natural Selection is a true cause,
+and, whatever may be the final result of our present inquiries—whether
+animated nature be derived from one ancestral source, or from many—the
+publication of the Origin of Species will none the less have constituted
+an epoch in the History of Biology. But, how far the present condition
+of living beings is due to that cause; how far, on the other hand, the
+action of Natural Selection has been modified and checked by other
+natural laws—by the unalterability of types, by atavism, &c.; how many
+types of life originally came into being; and whether they arose
+simultaneously or successively,—these and many other similar questions
+remain unsolved, even admitting the theory of Natural Selection. All
+this has indeed been clearly pointed out by Mr. Darwin himself, and
+would not need repetition but for the careless criticism by which in too
+many cases the true question has been obscured. Without, however,
+discussing the argument for and against Mr. Darwin’s conclusions, so
+often do we meet with travesties of it like that which I have just
+quoted, that it is well worth while to consider the stages through which
+some group, say for instance that of insects, have probably come to be
+what they are, assuming them to have developed under natural laws from
+simpler organisms. The question is one of great difficulty. It is hardly
+necessary to say that insects cannot have passed through all the lower
+forms of animal life, and naturalists do not at present agree as to the
+actual line of their development.
+
+In the case of insects, the gradual course of evolution through which
+the present condition of the group has probably been reached, has been
+discussed by Mr. Darwin, by Fritz Müller, Haeckel, Brauer, myself and
+others.
+
+In other instances Palæontology throws much light on this question.
+Leidy has shown that the milk-teeth of the genus _Equus_ resemble the
+permanent teeth of the ancient _Anchitherium_, while the milk-teeth of
+_Anchitherium_ again approximate to the dental system of the still
+earlier _Merychippus_. Rütimeyer, while calling attention to this
+interesting observation, adds that the milk-teeth of _Equus caballus_ in
+the same way, and still more those of _E. fossilis_, resemble the
+permanent teeth of _Hipparion_.
+
+“If we were not acquainted with the horse,” says Flower,[54] “we could
+scarcely conceive of an animal whose only support was the tip of a
+single toe on each extremity, to say nothing of the singular
+conformation of its teeth and other organs. So striking have these
+characters appeared to many zoologists, that the animals possessing them
+have been reckoned as an order apart, called Solidungula; but
+palæontology has revealed that in the structure of its skull, its teeth,
+its limbs, the horse is nothing more than a modified _Palæotherium_; and
+though still with gaps in certain places, many of the intermediate
+stages of these modifications are already known to us, being the
+_Palæotherium_, _Anchitherium_, _Merychippus_, and _Hipparion_.”
+
+“All Echinoids,” says A. Agassiz,[55] “pass, in their early stages,
+through a condition which recalls to us the first Echinoids which made
+their appearance in geological ages.” On embryological grounds, he
+observes, we should “place true Echini lowest, then the Clypeastroids,
+next the Echinolamps, and finally the Spatangoids.” Now among the
+Echinoids of the Trias there are no Clypeastroids, Echinolamps, or
+Spatangoids. The Clypeastroids make their appearance in the Lias, the
+Echinolamps in the Jurassic, while the Spatangoids commence in the
+Cretaceous period.
+
+Again[56] “in the Radiates, the Acalephs in their first stages of
+growth, that is, in their Hydroid condition, remind us of the adult
+forms among Polyps, showing the structural rank of the Acalephs to be
+the highest, since they pass beyond a stage which is permanent with the
+Polyps; while the Adult forms of the Acalephs have in their turn a
+certain resemblance to the embryonic phases of the class next above
+them, the Echinoderms; within the limits of the classes, the same
+correspondence exists as between the different orders; the embryonic
+forms of the highest Polyps recall the adult forms of the lower ones,
+and the same is true of the Acalephs as far as these phenomena have been
+followed and compared among them.” Indeed, the accomplished authors from
+whom I have taken the above quotation, do not hesitate to say[57] that
+“whenever such comparisons have been successfully carried out, the
+result is always the same; the present representatives of the fossil
+types recall in their embryonic condition the ancient forms, and often
+explain their true position in the animal kingdom.”
+
+Fossil insects are unfortunately rare, there being but few strata in
+which the remains of this group are well preserved. Moreover,
+well-characterized Orthoptera and Neuroptera occur as early as the
+Devonian strata; Coleoptera and Hemiptera in the Coal-measures;
+Hymenoptera and Diptera in the Jurassic; Lepidoptera, on the contrary,
+not until the Tertiary. But although it appears from these facts that,
+as far as our present information goes, the Orthoptera and Neuroptera
+are the most ancient orders, it is not, I think, conceivable that the
+latter should have been derived from any known species of the former; on
+the other hand, the earliest known Neuroptera and Orthoptera, though in
+some respects less specialized than existing forms, are as truly, and as
+well characterized, Insects, as any now existing; nor are we acquainted
+with any earlier forms, which in any way tend to bridge over the gap
+between them and lower groups, though, as we shall see, there are types
+yet existing which throw much light on the subject.
+
+In the consideration then of this question, we must rely principally on
+Embryology and Development. I have already referred to the cases in
+which species, very unlike in their mature condition, are very
+similar one to another when young. Haeckel, in his “Naturliche
+Schöpfungsgeschichte,” gives a diagram which illustrates this very well
+as regards Crustacea. Pls. 1-4 show the same to be the case with
+Insects.
+
+The Stag-beetle, the Dragon-fly, the Moth, the Bee, the Ant, the Gnat,
+the Grasshopper,—these and other less familiar types seem at first to
+have little in common. They differ in size, in form, in colour, in
+habits, and modes of life. Yet the researches of entomologists,
+following the clue supplied by the illustrious Savigny, have proved, not
+only that while differing greatly in details, they are constructed on
+one common plan; but also that other groups, as for instance, Crustacea
+(Lobsters, Crabs, &c.) and Arachnida (Spiders and Mites), can be shown
+to be fundamentally similar. In Pl. 4 I have figured the larvæ of an
+_Ephemera_ (Fig. 1), of a _Meloë_ (Fig. 2), of a Dragon-fly (Fig. 3), of a
+Sitaris (Fig. 4), of a _Campodea_ (Fig. 5), of a _Dyticus_ (Fig. 6), of a
+Termite (Fig. 7), of a _Stylops_ (Fig. 8), and of a _Thrips_ (Fig. 9). All
+these larvæ possess many characters in common. The mature forms are
+represented in the corresponding figures of Plate 3, and it will at once
+be seen how considerably they differ from one another. The same fact is
+also illustrated in Figs. 48-55, where Figs. 48-51 represent the larval
+states of the mature forms represented in Figs. 52-55. Fig. 48 is the
+larva of a moth, _Agrotis suffusa_ (Fig. 52); Fig. 49 of a beetle,
+_Haltica_ (Fig. 53); Fig. 50 of a Saw-fly, _Cimbex_ (Fig. 54); and Fig.
+51 of a Centipede, _Julus_ (Fig. 55).
+
+[Illustration: FIG. 48, Larva of Moth (_Agrotis suffusa_), after
+Packard. 49, Larva of Beetle (_Haltica_), after Westwood. 50, Larva of
+Saw-fly (_Cimbex_), Brischke and Zaddach. Beob. ub d. arten. der Blatt
+und Holzwespen, Fig. 8. 51, Larva of _Julus_. Newport, Philos.
+Transactions, 1841.]
+
+Thus, then, although it can be demonstrated that perfect insects,
+however much they differ in appearance, are yet reducible to one type,
+the fact becomes much more evident if we compare the larvæ. M.
+Brauer[58] and I[59] have pointed out that two types of larvæ, which I
+have proposed to call _Campodea_-form and _Lindia_-form, and which Packard
+has named Leptiform and Eruciform, run through the principal groups of
+insects. This is obviously a fact of great importance: as all individual
+_Meloës_ are derived from a form resembling Pl. 2, Fig. 2, it is surely no
+rash hypothesis to suggest that the genus itself may have been so.
+
+[Illustration: FIG. 52, _Agrotis suffusa_ (after Packard). 53, _Haltica_
+(after Westwood).]
+
+[Illustration: FIG. 54, _Cimbex_, Brischae and Zaddach. l.c. T. 2, Fig.
+9.]
+
+[Illustration: FIG. 55. _Julus_ (after Gervais).]
+
+Firstly, however, let me say a word as to the general Insect type. It
+may be described shortly as consisting of animals possessing a head,
+with mouth parts, eyes and antennæ; a many segmented body, with three
+pairs of legs on the segments immediately following the head; with, when
+mature, either one or two pairs of wings, generally with caudal
+appendages I will not now enter into a description of their internal
+anatomy. It will be seen that, except as regards the wings, Pl. 4, Fig.
+4, representing the larva of a small beetle named _Sitaris_, answers very
+well to this description. Many other Beetles are developed from larvæ
+closely resembling those of _Meloë_ (Pl. 4, Fig. 2), and Sitaris (Pl. 4,
+Fig. 4); in fact—except those species the larvæ of which, as, for
+instance of the Weevils (Pl. 2, Fig. 6), are internal feeders, and do
+not require legs—we may say that the Coleoptera generally are derived
+from larvæ of this type.
+
+I will now pass to a second order, the Neuroptera. Pl. 4, Fig. 1,
+represents the larva of _Chloëon_, a species the metamorphoses of which I
+described some years ago in the Linnean Transactions,[60] and it is
+obvious that in essential points it closely resembles the form to which
+I have just alluded.
+
+The Orthoptera, again, the order to which Grasshoppers, Crickets,
+Locusts, &c. belong, commence life in a similar condition; and the same
+may also be said of the Trichoptera.
+
+The larvæ of Bees when they quit the egg are entirely legless, but in an
+earlier stage they possess well-marked rudiments of thoracic legs,
+showing, as it seems to me, that their apodal condition is an adaptation
+to their circumstances. Other Hymenopterous larvæ, those for example of
+_Sirex_ (Fig. 9), and of the Saw-flies (Fig. 50) have well-developed
+thoracic legs.
+
+From the difference in external form, and especially from the large
+comparative size of the abdomen, these larvæ, as well as those of
+Lepidoptera (Fig. 48), have generally been classed with the maggots of
+Flies, Weevils, &c., rather than with the more active form of larva just
+adverted to. This seems to me, as I have already pointed out,[61] to be
+a mistake. The caterpillar type differs, no doubt, in its general
+appearance, owing to its greater clumsiness, but still essentially
+agrees with that already described.
+
+No Dipterous larva, so far as I know, belongs truly to this type; in
+fact, the early stages of the pupa in the Diptera seem in some respects
+to correspond to the larvæ of other Insect orders. The Development of
+the Diptera is, however, as Weissman[62] has shown, very abnormal in
+other respects.
+
+Thus, then, we find in many of the principal groups of insects that,
+greatly as they differ from one another in their mature condition, when
+they leave the egg they more nearly resemble the typical insect type;
+consisting of a head; a three-segmented thorax, with three pairs of
+legs; and a many-jointed abdomen, often with anal appendages. Now, is
+there any mature animal which answers to this description? We need not
+have been surprised if this type, through which it would appear that
+insects must have passed so many ages since (for winged Neuroptera have
+been found in the carboniferous strata) had long ago become extinct. Yet
+it is not so. The interesting genus _Campodea_ (Pl. 3, Fig. 5) still
+lives; it inhabits damp earth, and closely resembles the larva of
+_Chloëon_ (Pl. 2, Fig. 1), constituting, indeed, a type which, as shown in
+Pl. 4, occurs in many orders of insects. It is true that the
+mouth-parts of _Campodea_ do not resemble either the strongly mandibulate
+form which prevails among the larvæ of Coleoptera, Orthoptera,
+Neuroptera, Hymenoptera, Lepidoptera; or the suctorial type of the
+Homoptera and Heteroptera. It is, however, not the less interesting or
+significant on that account, since, as I have elsewhere[63] pointed out,
+its mouth-parts are intermediate between the mandibulate and haustellate
+types; a fact which seems to me most suggestive.
+
+It appears, then, that there are good grounds for considering that the
+various types of insects are descended from ancestors more or less
+resembling the genus _Campodea_, with a body divided into head, thorax,
+and abdomen: the head provided with mouth-parts, eyes, and one pair of
+antennæ; the thorax with three pairs of legs; and the abdomen, in all
+probability, with caudal appendages.
+
+If these views are correct, the genus _Campodea_ must be regarded as a
+form of remarkable interest since it is the living representative of a
+primæval type, from which not only the Collembola and Thysanura, but the
+other great orders of insects have derived their origin.
+
+From what lower group the _Campodea_ type was itself derived is a question
+of great difficulty. Fritz Müller indeed says,[64] “if all the classes
+of Arthropoda (Crustacea, Insecta, Myriopoda, and Arachnida) are indeed
+all branches of a common stem (and of this there can scarcely be a
+doubt), it is evident that the water-inhabiting and water-breathing
+Crustacea must be regarded as the original stem from which the other
+terrestrial classes, with their tracheal respiration, have branched
+off.” Haeckel, moreover, is of the opinion that the Tracheata are
+developed from the Crustacea, and probably from the Zoëpoda. For my own
+part, though I feel very great diffidence in expressing an opinion at
+variance with that of such high authorities, I am rather disposed to
+suggest that the _Campodea_ type may possibly have been derived from a
+less highly developed one, resembling the modern Tardigrade,[65] a (Fig.
+56) smaller and much less highly organized being than _Campodea_. It
+possesses two eyes, three anterior pairs of legs, and one at the
+posterior end of the body, giving it a curious resemblance to some
+Lepidopterous larvæ.
+
+[Illustration: FIG. 56, Tardigrade (after Dujardin).]
+
+These legs, however, as will be seen, are reduced to mere projections.
+But for them, the Tardigrada would closely resemble the vermiform larva
+so common among insects. Among Trichoptera the larva early acquires
+three pairs of legs, but as Zaddach has shown,[66] there is a stage,
+though it is quickly passed through, in which the divisions of the body
+are indicated, but no trace of legs is yet present. Indeed, there appear
+to be reasons for considering that while among Crustacea the appendages
+appear before the segments, in Insects the segments precede the
+appendages, although this stage of development is very transitory, and
+apparently, in some cases, altogether suppressed. I say “apparently,”
+because, as I have already mentioned, I am not yet satisfied that it
+will not eventually be found to be so in all cases. Zaddach, in his
+careful observations of the embryology of _Phryganea_, only once found a
+specimen in this stage, which also, according to the researches of
+Huxley,[67] seems to be little more than indicated in _Aphis_. It is
+therefore possible that in other cases, when no such stage has been
+observed, it not really may be absent, but, from its transitoriness, may
+have hitherto escaped attention.
+
+Fritz Müller has expressed the opinion[68] that this vermiform type is
+of comparatively recent origin. He says: “The ancient insects approached
+more nearly to the existing Orthoptera, and perhaps to the wingless
+Blattidæ, than to any other order, and the complete metamorphosis of the
+Beetles, Lepidoptera, &c., is of later origin.” “There were,” he adds,
+“perfect insects before larvæ and pupæ.” This opinion has been adopted
+by Mr. Packard[69] in his “Embryological Studies on Hexapodous Insects.”
+
+M. Brauer[70] also considers that the vermiform larva is a more recent
+type than the Hexapod form, and is to be regarded not as a developmental
+form, but as an adaptational modification of the earlier active hexapod
+type. In proof of this he quotes the case of _Sitaris_.
+
+Considering, however, the peculiar habits of this genus, to which I have
+already referred, and also that the vermiform type is altogether lower
+in organization and less differentiated than the _Campodea_ form, I cannot
+but regard this case as exceptional; one in which the development has
+been, as it were, to use an expression of Fritz Müller’s, “falsified” by
+the struggle for existence, and which therefore does not truly indicate
+the successive stages of evolution. On the whole, the facts seem to me
+to point to the conclusion that, though the grub-like larvæ of Coleoptera
+and some other insects, owe their present form mainly to the influence
+of external circumstances, and partially also to atavism, still the
+_Campodea_ type is itself derived from earlier vermiform ancestors.
+Nicolas Wagner has shown in the case of a small gnat, allied to
+_Cecidomyia_, that even now, in some instances, the vermiform larvæ
+possess the power of reproduction. Such a larva (as, for instance, Fig.
+57) very closely resembles some of the Rotatoria, such for instance as
+_Albertia_ or _Notommata_, which however possess vibratile cilia. There is,
+indeed, one genus—_Lindia_ (Fig. 58)—in which these ciliæ are altogether
+absent, and which, though resembling _Macrobiotus_ in many respects,
+differs from that genus in being entirely destitute of legs. I have
+never met with it myself, but it is described by Dujardin, who found it
+in a ditch near Paris, as being oblong, vermiform, divided into rings,
+and terminating posteriorly in two short conical appendages. The jaws
+are not unlike those of the larvæ of Flies, and indeed many naturalists
+meeting with such a creature would, I am sure, regard it as a small
+Dipterous larva; yet Dujardin figures a specimen containing an egg, and
+seems to have no doubt that it is a mature form.[71]
+
+For the next descending stage we must, I think, look among the
+Infusoria, through such genera as _Chætonotus_ or _Ichthydium_. Other
+forms of the Rotatoria, such for instance as _Rattulus_, and still more
+the very remarkable species discovered in 1871 by Mr. Hudson,[72] and
+described under the name of _Pedalion mira_, seem to lead to the
+Crustacea through the Nauplius form. Dr. Cobbold tells me that he
+regards the _Gordii_ as the lowest of the Scolecida; Mr. E. Ray
+Lankester considers some of the Turbellaria, such genera as
+_Mesostomum_, _Vortex_, &c., to be the lowest of existing worms;
+excluding the parasitic groups. Haeckel[73] also regards the Turbellaria
+as forming the nearest approach to the Infusoria. The true worms seem,
+however, to constitute a separate branch of the animal kingdom.
+
+We may take, as an illustration of the lower worms, the genus
+Prorhynchus (Fig. 59), which consists of a hollow cylindrical body,
+containing a straight simple tube, the digestive organ.
+
+But however simple such a creature as this may be, there are others
+which are far less complex, far less differentiated; which therefore, on
+Mr. Darwin’s principles, may be considered still more closely to
+represent the primæval ancestor from which these more highly-developed
+types have been derived, and which, in spite of their great
+antiquity—in spite of, or perhaps in consequence of, their simplicity,
+still maintain themselves almost unaltered.
+
+Thus the form which Haeckel has described[74] under the name
+_Protamœba primitiva_, Pl. 5, Fig. 1-5, consists of a homogeneous and
+structureless substance, which continually alters its form; putting out
+and drawing in again more or less elongated processes, and creeping
+about like a true _Amœba_, from which, however, _Protamœba_ differs,
+in the absence of a nucleus. It seems difficult to imagine anything
+simpler; indeed, as described, it appears to be an illustration of
+properties without structure. It takes into itself any suitable particle
+with which it comes in contact, absorbs that which is nutritious, and
+rejects the rest. From time to time a constriction appears at the centre
+(Pl. 5, Fig. 2), its form approximates more and more to that of an
+hour-glass (Pl. 5, Fig. 3), and at length the two halves separate, and
+each commences an independent existence (Pl. 5, Fig. 5).
+
+[Illustration: FIG. 59, _Prorhynchus stagnaus_.[75]]
+
+[Illustration: PLATE V.
+
+FIGS. 1-5, _Protamœba_; 6-9, _Protamyxa Aurantiaca_,
+Haeckel, Beit. zur Monog. der Moneren, pl. 1; 10-18, _Magosphæra planula_,
+Haeckel, loc. cit. pl. 5.]
+
+In the true _Amœbas_, on the contrary, we find a differentiation
+between the exterior and the interior: the body being more or less
+distinctly divisible into an outer layer and an inner parenchyme. In the
+_Amœbas_, as in _Protamœba_, multiplication takes place by
+self-division, and nothing corresponding to sexual reproduction has yet
+been discovered.
+
+Somewhat more advanced, but still of great simplicity, is the _Protomyxa
+aurantiaca_ (Pl. 5, Fig. 8), discovered by Haeckel[76] on dead shells of
+_Spirula_, where it appears as a minute orange speck, which shows well
+against the clear white of the _Spirula_. Examined with a microscope, the
+speck is seen to be a spherical mass of orange-coloured, homogeneous,
+albuminous matter, surrounded by a delicate, structureless membrane. It
+is obvious from this description that these bodies closely resemble
+eggs, for which indeed Haeckel at first mistook them. Gradually,
+however, the yellow sphere broke itself up into smaller spherules (Pl.
+5, Fig. 9), after which the containing membrane burst, and the separate
+spherules, losing their globular form, crept out as small _Amœbæ_ (Pl.
+5, Fig. 6), or amœboid bodies. These little bodies moved about,
+assimilated the minute particles of organic matter, with which they came
+in contact, and gradually increased in size (Pl. 5, Fig. 7) with more or
+less rapidity according to the amount of nourishment they were able to
+obtain. They threw out arms in various directions, and if divided each
+section maintained its individual existence. After a while their
+movements ceased, they contracted into a ball, and again secreted round
+themselves a clear structureless envelope.
+
+This completes their life history as observed by Haeckel, who found it
+easy to retain them in his glasses in perfect health, and who watched
+them closely.
+
+As another illustration I may take the _Magosphæra planula_, discovered
+by Haeckel on the coast of Norway.
+
+In one stage of its existence (Pl. 5, Fig. 10) it is a minute mass of
+gelatinous matter, which continually alters its form, moves about,
+feeds, and in fact behaves altogether like the _Amœba_ just described.
+It does not, however, remain always in this condition. After a while it
+contracts into a spherical form (Pl. 5, Fig. ii), and secretes round
+itself a structureless envelope, which, with the nucleus, gives it a
+very close resemblance to a minute egg.
+
+Gradually the nucleus divides, and the protoplasm also separates into
+two spherules (Pl. 5, Fig. 12); these two subdivide into four (Pl. 5,
+Fig. 13), and so on (Pl. 5, Fig 14), until at length thirty-two are
+present, compressed into a more or less polygonal form (Pl. 5, Fig. 15).
+Here this process ends. The separate spherules now begin to lose their
+smooth outline, to throw out processes, and to show amœboid movements
+like those of the creatures just described. The processes or pseudopods
+grow gradually longer, thinner, and more pointed. Their movements become
+more active, until at length they take the form of ciliæ. The spherical
+_Magosphæra_, the upper surface of which has thus become covered with
+ciliæ, now begins to rotate within the cyst or envelope, which at length
+gives way and sets free the contained sphere, which then swims about
+freely in the water (Pl. 5, Fig. 16), thus closely resembling _Synura_, or
+one of the Volvocineæ. After swimming about in this condition for a
+certain time, the sphere breaks up into the separate cells of which it
+is composed (Pl. 5, Fig. 17). As long as the individual cells remained
+together, they had undergone no changes of form, but after separating
+they show considerable contractility, and gradually alter their form,
+until they become undistinguishable from true _Amœbæ_ (Pl. 5, Fig. 18).
+Finally, according to Haeckel, these amœboid bodies, after living for
+a certain time in this condition, return to a state of rest, again
+contract into a spherical form, and secrete round themselves a
+structureless envelope. The life history of some other low organisms, as
+for instance _Gregarina_, is of a similar character.
+
+It may be said, and said truly, that the difference between such beings
+as these and the _Campodea_, or Tardigrade, is immense. But if it be
+considered incredible that even during the long lapse of geological time
+such great changes should have taken place as are implied in the belief
+that there is genetic connection between them and these lower groups,
+let us consider what happens under our eyes in the development of each
+one of these little creatures in the proverbially short space of their
+individual life.
+
+I will take for instance the first stages, and for the sake of brevity
+only the first stages, of the life-history of a Tardigrade.[77] As shown
+in Fig. 60, the egg is at first a round body or cell, with a clear
+central nucleus—the germinal vesicle; it increases in size, and after
+a while the yolk and the germinal vesicle divide into two (Fig. 61),
+then into four (Fig. 62), and so on, just as we have seen to be the case
+in _Magosphæra_. From the minute cells (Fig. 63) arising through this
+process of yolk-segmentation, the body of the Tardigrade is then built
+up.[78]
+
+[Illustration: FIG. 60, Egg of Tardigrade, Kaufmann, Zeit f. Wiss.
+Zool. 1851, Pl. 1. 61, Egg of Tardigrade after the yolk has subdivided.
+62, Egg of Tardigrade in the next stage. 63, Egg of Tardigrade more
+advanced.]
+
+Though I will not now attempt to point out the full bearing of these
+facts on the study of embryology generally, yet I cannot resist calling
+attention to the similarity of the development of _Magosphæra_ with the
+first stages of development of other animals, because it appears to me
+to possess a significance, the importance of which it would be difficult
+to overestimate.
+
+Among the Zoophytes Prof. Allman thus describes[79] the process in
+_Laomedea_, as representing the Hydroids (Pl. 6, Fig. 1, represents the
+young egg):—“The first step observable in the segmentation-process is
+the cleavage of the yolk into two segments (Pl. 6, Fig. 2), immediately
+followed by the cleavage of these into other two, so that the vitellus
+is now composed of four cleavage spheres (Pl. 6, Fig. 3).” These spheres
+again divide (Pl. 6, Fig. 4) and subdivide, thus at length forming
+minute cells, of which the body of the embryo is built up.
+
+In Pl. 6, Figs. 5-9 represent the corresponding stages in the
+development of a small parasitic worm—the _Filaria mustelarum_—as
+given by Van Beneden.[80] The first process is that within the egg,
+which represents, so to say, the encysted condition of _Magosphæra_, the
+yolk divides itself into two balls (Pl. 6, Fig. 6), then into four,
+eight, and so on, the cells thus constituted finally forming the young
+worm. I have myself observed the same stages in the eggs of the very
+remarkable and abnormal _Sphærularia bombi_.[81]
+
+Among the Echinoderms M. Derbès thus describes the first stages (Pl. 6,
+Figs. 10-13) in the development of the egg of an _Echinus_ (_Echinus
+esculentus_):—“Le jaune commence à se segmenter, d’abord en deux, puis
+en quatre et ainsi de suite, chacune des nouvelles cellules se
+partageant à son tour en deux.”[82] Sars has observed the same thing in
+the starfish.[83]
+
+[Illustration: PLATE. 6.]
+
+In the Rotatoria, as shown by Huxley in _Lacinularia_,[84] and by
+Williamson in _Melicerta_,[85] the yolk is at first a single globular
+mass, the first changes which take place in it being as follows:—“The
+central nucleus becomes drawn out and subdivides into two, this division
+being followed by a corresponding segmentation of the yolk. The same
+process is repeated again and again, until at length the entire yolk is
+converted into a mass of minute cells.” Among the Crustacea the total
+segmentation of the yolk occurs among the Copepoda, Rhizocephala, and
+Cirripedia. Sars has described the same process in one of the
+nudibranchiate mollusca[86] (_Tritonia_), Müller in Entochocha,[87]
+Haeckel in Ascidia,[88] Lacaze Duthiers in _Dentalium_.[89] Figures 18 to
+21, Pl. 6, are taken from Koren and Danielssen’s[90] memoir on the
+development of _Purpura lapillus_.
+
+Figs. 22-24 show the same stages in a fish (_Amphioxus_) as given by
+Haeckel, and it is unnecessary to point out the great similarity.
+
+Lastly, figures 25 to 29, Pl. 6, are given by Dr. Allen Thomson,[91] as
+illustrating the first stages in the development of the vertebrata.
+
+I might have given many other examples, but the above are probably
+sufficient, and will show that the processes which constitute the
+life-history of the lowest organized beings very closely resemble the
+first stages in the development of more advanced groups; that as Allen
+Thomson has truly observed,[92] “the occurrence of segmentation and the
+regularity of its phenomena are so constant that we may regard it as one
+of the best established series of facts in organic nature.”
+
+It is true that normal yolk-segmentation is not universal in the animal
+kingdom; that there are great groups in which the yolk does not divide
+in this manner,—perhaps owing to some difference in its relation to the
+germinal vesicle, or perhaps because one of the suppressed stages in
+embryological development, many examples might be given, not only in
+zoology, but, as I may state on the authority of Dr. Hooker, in botany
+also. But, however, this may be, it is surely not uninteresting, nor
+without significance, to find that changes which constitute the
+life-history of the lowest creatures for the initial stages even of the
+highest.
+
+Returning, in conclusion, to the immediate subject of this work, I have
+pointed out that many beetles and other insects are derived from larvæ
+closely resembling _Campodea_.
+
+Since, then, individual insects are certainly in many cases developed
+from larvæ closely resembling the genus _Campodea_, why should it be
+regarded as incredible that insects as a group have gone through similar
+stages? That the ancestors of beetles under the influence of varying
+external conditions, and in the lapse of geological ages, should have
+undergone changes which the individual beetle passes through under our
+own eyes and in the space of a few days, is surely no wild or
+extravagant hypothesis. Again, other insects come from vermiform larvæ
+much resembling the genus _Lindia_, and it has been also repeatedly shown
+that in many particulars the embryo of the more specialized forms
+resembles the full-grown representatives of lower types. I conclude,
+therefore, that the Insecta generally are descended from ancestors
+resembling the existing genus _Campodea_, and that these again have arisen
+from others belonging to a type represented more or less closely by the
+existing genus _Lindia_.
+
+Of course it may be argued that these facts have not really the
+significance which they seem to me to possess. It may be said that when
+Divine power created insects, they were created with these remarkable
+developmental processes. By such arguments the conclusions of geologists
+were long disputed. When God made the rocks, it was tersely said, He
+made the fossils in them. No one, I suppose, would now be found to
+maintain such a theory; and I believe the time will come when it will be
+generally admitted that the structure of the embryo, and its
+developmental changes, indicate as truly the course of organic
+development in ancient times as the contents of rocks and their sequence
+teach us the past history of the earth itself.
+
+
+FOOTNOTES:
+
+[1] Darwin’s “Researches into the Geology and Natural History of the
+Countries visited by H.M.S. _Beagle_,” p. 326.
+
+[2] Introduction to Entomology, vi. p. 50.
+
+[3] Manual of Entomology, p. 30.
+
+[4] Linnean Journal, vol. xi.
+
+[5] Introduction to the Modern Classification of Insects, p. 17.
+
+[6] Linnean Transactions, 1863—“On the Development of _Chloëon_.”
+
+[7] The figures on the first four plates are principally borrowed from
+Mr. Westwood’s excellent “Introduction to the Modern Classification of
+Insects.”
+
+[8] “Sur la Domestication des _Clavigers_ par les Fourmis.” Bull. de la
+Soc. d’Anthropologie de Paris, 1868, p. 315.
+
+[9] Westwood’s Introduction, vol. i. p. 36.
+
+[10] Westwood’s Introduction, vol. ii. p. 52.
+
+[11] Die Fortpflanzung und Entwickelung der Pupiparen. Von Dr. R.
+Leuckart. Halle. 1848.
+
+[12] Ann. des Sci. Nat., sér. 4, tome vii. See also _Natural History
+Review_, April 1862.
+
+[13] Ann. and Mag. of Nat. Hist. 1852.
+
+[14] Zeits. für Wiss. Zool. 1869.
+
+[15] Transactions of the Linnean Society, 1863.
+
+[16] Lectures on the Anatomy, &c. of the Invertebrate Animals.
+
+[17] Untersuchungen über die Entwickelung und den Bau der Gliederthiere,
+1854.
+
+[18] Linnean Transactions, vol. xxii. 1858.
+
+[19] “Embryological Studies on Hexapodous Insects.” Peabody Academy of
+Science. Third Memoir.
+
+[20] Mém. de l’Acad. Imp. des Sci. de St. Pétersbourg. 1869.
+
+[21] Observationes de Prima Insectorum Genesi, p. 14.
+
+[22] Mém. de l’Acad. Imp. des Sci. de St. Pétersbourg. tome xvi. 1871,
+p. 35.
+
+[23] Recherches sur l’Evolution des Araignées.
+
+[24] Philosophical Transactions, 1841.
+
+[25] Monog. of the Gymnoblastic or Tubularian Hydroids. See also Hincks,
+British Hydroid Zoophytes. Pl. x.
+
+[26] Loc. cit. p. 315.
+
+[27] Philosophical Transactions, 1859, p. 589.
+
+[28] “Facts for Darwin,” Eng. Trans. p. 127.
+
+[29] Rolleston, “Forms of Animal Life,” p. 146.
+
+[30] A. Agassiz, “Embryology of the Starfish,” p. 25; “Embryology of
+Echinoderms.” Mem. of Am. Ac. of Arts and Sciences N.S. vol. ix. p. 9.
+
+[31] Ueber die Gattungen der Seeigellarven. Siebente Abhandlung. Kön.
+Akad. d. Wiss. zu Berlin. Von Joh. Müller, 1855, Pl. iii. fig. 3.
+
+[32] Huxley, Introduction to the Classification of Animals, p. 45.
+
+[33] Philosophical Transactions, 1865 and 1866.
+
+[34] Loc. cit. Zweit. Abh. Pl. i., figs. 8 and 9.
+
+[35] Thomson, on the Embryology of the Echinodermata, _Natural History
+Review_, 1863, p. 415. See also Agassiz, “Embryology of the Starfish,”
+p. 62.
+
+[36] A. Agassiz, Embryology of Echinoderms, p. 18.
+
+[37] Hincks. British Hydroid Zoophytes, pp. 120-147.
+
+[38] Zeits. für Wiss. Zool. 1864, p. 228.
+
+[39] Introduction to Entomology, 6th ed. vol. i. p. 61.
+
+[40] Métamorphoses de l’Homme et des Animaux, p. 133. See also
+Carpenter, Principles of Physiology. 1851, p. 389.
+
+[41] Darwin, Origin of Species, 4th ed. p. 532.
+
+[42] Principles of Biology, vi. p. 349.
+
+[43] For differences in larva consequent on variation in the external
+condition, see _ante_, p. 61.
+
+[44] See Hincks. British Hydroid Zoophytes, P. lxii. Agassiz, Sea-side
+Studies, p. 43.
+
+[45] See Newport, Phil. Trans., 1832.
+
+[46] Linnean Transactions, 1862.
+
+[47] Origin of Species, 4th ed., pp. 14 and 97.
+
+[48] On the Alternation of Generations. By J. J. Steenstrup. Trans. by
+C. Busk, Esq. Ray Society. 1842.
+
+[49] Zeit. für Wiss. Zool. 1863.
+
+[50] Mém. de l’Acad. Imp. de St. Pétersbourg. vol. xv. 1870.
+
+[51] Of course all animals in which the sexes are distinct are in one
+sense dimorphic.
+
+[52] “There is no such thing as a true case of ‘alternation of
+generations in the animal kingdom;’ there is only an alternation of true
+generation with the totally distinct process of gemmation or
+fission.”—HUXLEY _on Animal Individuality_, Ann. and Mag. of Nat. Hist.
+June 1852.
+
+[53] Prince Hohenstiel Schwangau, p. 68.
+
+[54] Journal of the Royal Institution. April 1873.
+
+[55] “Embryology of Echinoderms,” l. c. p. 15.
+
+[56] Mr. and Mrs. Agassiz: “Sea-side Studies,” p. 139.
+
+[57] l. c. p. 138.
+
+[58] Wien. Zool. Bot. Gesells, 1869.
+
+[59] Linnean Transactions, 1863.
+
+[60] Linnean Transactions, 1866, vol. xxv.
+
+[61] Linnean Transactions, vol. xxiv. p. 65.
+
+[62] Siebold und Kolliker’s Zeitschr. f. Wiss. Zool., 1864.
+
+[63] Linnean Journal, vol. xi.
+
+[64] Facts for Darwin, p. 120.
+
+[65] A still nearer approach is afforded by the genus _Peripatus_, which
+since the above was written has been carefully described, especially by
+Moseley and Hutton. There are several species, scattered over the
+southern hemisphere. In general appearance they look like a link between
+a caterpillar and a centipede. They have a pair of antennæ, two pairs of
+jaws, and (according to the species) from fourteen to thirty-three pairs
+of legs. They breathe by means of tracheæ, which open diffusely all over
+the body.
+
+[66] Unters. üb. die Entwick, und den Bau der Gliederthiere, p. 73.
+
+[67] Linnean Transactions, v. xxii.
+
+[68] Facts for Darwin, trans. by Dallas, p. 118. See also Darwin,
+“Origin of Species,” p. 530. 4th ed.
+
+[69] Mem. Peabody Academy of Science, v. I. No, 3.
+
+[70] Wien. Zool. Bott. Gesells. 1869, p. 310.
+
+[71] See also the descriptions given by Dujardin (Ann. des Sci. Nat.
+1851, v. xv.) and Claparède (Anat. und Entwickl. der Wirbel osen Thiere)
+of the interesting genus _Echinoderes_, which these two eminent
+naturalists unite in regarding as intermediate between the Annelides and
+the Crustacea.
+
+[72] “On a New Rotifer.” _Monthly Microscopical Journal_, Sept. 1871.
+
+[73] Generelle Morphologie, vol. ii. p. 79.
+
+[74] Monographie der Moneren, p. 43.
+
+[75] Gegenbaur. Grund. d. Vergleich. Anat. p. 210. See also Dr. M. S.
+Schultze, Beiträge zur Naturg. der. Turbellarien. 1851. Pl. vi. fig. 1.
+
+[76] Monographieder Moneren, p. 10.
+
+[77] See Kauffmann, Ueber die Entwickelung and systematische Stellung
+der Tardigraden. Zeits. f. Wiss. Zool. 1851, p. 220.
+
+[78] It is true that among the Insecta generally the first stages of
+development differ in appearance considerably from those above
+described; those of _Platygaster_, as figured by Ganin (ante Figs. 17-22),
+being very exceptional.
+
+[79] Monograph of the Gymnoblastic or Tubularian Hydroids, by G. J.
+Allman, Ray Soc. 1871, p. 86.
+
+[80] Mém. sur les Vers Intestinaux, 1858.
+
+[81] Natural History Review, 1861, p. 44.
+
+[82] Ann. des Sci. Nat. 1847, p. 90.
+
+[83] Fauna littoralis Norvegiæ, pl. viii.
+
+[84] Trans. of the Microsc. Soc. of London, 1851.
+
+[85] Quarterly Journal of Microsc. Science, 1853.
+
+[86] Wiegmann’s Archiv., 1840, p. 196.
+
+[87] Ueber die Erzeugung von Schnecken in Holothurier. Berlin, Bericht,
+1851. Ann. Nat. Hist. 1852, v. ix. Müller’s Archiv., 1852.
+
+[88] Natürliche Schöpfungsgeschichte, pl. x.
+
+[89] Ann. des Sci. Nat. 1853, p. 89.
+
+[90] Ann. des Sci. Nat. 1857, pl. vi.
+
+[91] Cyclopædia of Anatomy and Physiology. Art. Ovum, p. 4.
+
+[92] Thomson, loc. cit. Article, Ovum, p. 139.
+
+
+   THE END.
+
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diff --git a/38207-0.zip b/38207-0.zip
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+The Project Gutenberg eBook, On the Origin and Metamorphoses of Insects,
+by Sir John Lubbock
+
+
+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
+
+
+
+
+
+Title: On the Origin and Metamorphoses of Insects
+
+
+Author: Sir John Lubbock
+
+
+
+Release Date: December 3, 2011  [eBook #38207]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+
+***START OF THE PROJECT GUTENBERG EBOOK ON THE ORIGIN AND METAMORPHOSES OF
+INSECTS***
+
+
+E-text prepared by Bryan Ness, Turgut Dincer, and the Online Distributed
+Proofreading Team (http://www.pgdp.net) from page images generously made
+available by Internet Archive/American Libraries
+(http://www.archive.org/details/americana)
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+Note: Project Gutenberg also has an HTML version of this
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+      See 38207-h.htm or 38207-h.zip:
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+      or
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+      Images of the original pages are available through
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+
+
+      +--------------------------------------------------------------+
+      | Transcriber's note:                                          |
+      |                                                              |
+      | All non-italic genus names in the text have been italicized. |
+      +--------------------------------------------------------------+
+
+
+
+
+
+[Illustration: NATURE SERIES]
+
+
+
+
+ORIGIN AND METAMORPHOSES OF INSECTS.
+
+[Illustration]
+
+Nature Series
+
+ON THE ORIGIN AND METAMORPHOSES OF INSECTS
+
+BY
+
+Sir John Lubbock, Bart., M.P., F.R.S., D.C.L., LL.D.
+
+Principal of the London Working Men's College; President of the London
+Chamber of Commerce; and Vice-Chairman of the London County Council
+
+With Numerous Illustrations
+
+
+
+
+
+
+
+London Macmillan and Co. and New York 1890
+
+The Right of Translation and Reproduction is Reserved
+
+Richard Clay and Sons, Limited, London and Bungay.
+
+First Edition 1873. Reprinted 1874. New Edition 1890.
+
+
+
+
+PREFACE.
+
+
+For some years, much of my leisure time has been devoted to the study of
+the anatomy, development, and habits of the Annulosa, and especially of
+Insects, on which subjects I have published various memoirs, chiefly in
+the Transactions of the Royal, Linn�an, and Entomological Societies: of
+these papers I subjoin a list. Although the details, of which these
+memoirs necessarily for the most part consist, offer little interest,
+excepting to those persons who are specially devoted to Entomology,
+still there are portions which, having reference to the nature of
+metamorphoses and to the origin of insects, are of a more general
+character. I have also briefly referred to these questions in a
+Monograph of the Collembola and Thysanura, recently published by the Ray
+Society, and in the Opening Address to the Biological Section of the
+British Association at Brighton in 1872. Under these circumstances, it
+has been suggested to me that a small volume, containing, at somewhat
+greater length, in a more accessible form, and with the advantage of
+illustrations, the conclusions to which I have been led on this
+interesting subject, might not be altogether without interest to the
+general reader. The result, which has already appeared in the pages of
+_Nature_, is now submitted to the public, with some additions. I am well
+aware that it has no pretence to be in any sense a complete treatise;
+that the subject itself is one as to which our knowledge is still very
+incomplete, and on which the highest authorities are much divided in
+opinion. Whatever differences of opinion, however, there may be as to
+the views here put forward, the facts on which they are based will, I
+believe, be found correct. On this point I speak with the more
+confidence, on account of the valuable assistance I have received from
+many friends: to Mr. and Mrs. Busk and Dr. Hooker I am especially
+indebted.
+
+The papers above referred to are as follows:--
+
+   1. _On Labidocera._--Annals and Magazine of Natural History,
+        vol. xi., 1853.
+
+   2. On Two New Sub-genera of Calanid�.--Annals and Magazine of
+        Natural History, vol. xii., 1853.
+
+   3. On Two New Species of Calanid�.--Annals and Magazine of
+        Natural History, vol. xii., No. lxvii., 1853.
+
+   4. On Two New Species of Calanid�.--Annals and Magazine of
+        Natural History, vol. xii., No. lxix., 1853.
+
+   5. On some Arctic Calanid�.--Annals and Magazine of Natural
+        History, 1854.
+
+   6. On the Freshwater Entomostraca of South
+        America.--Transactions of the Entomological Society, vol.
+        iii., 1855.
+
+   7. On some New Entomostraca.--Transactions of the
+        Entomological Society, vol. iv., 1856.
+
+   8. On some Marine Entomostraca found at Weymouth.--Annals and
+        Magazine of Natural History, vol. xx., 1857.
+
+   9. On the Respiration of Insects.--Entomological Annual, 1857.
+
+  10. An Account of the Two Methods of Reproduction in
+         _Daphnia_.--Transactions of the Royal Society, 1857.
+
+  11. On the Ova and Pseudova of Insects.--Transactions of the
+        Royal Society, 1858.
+
+  12. On the Arrangement of the Cutaneous Muscles of _Pyg�ra
+        Bucephala_.--Linnean Society's Transactions, vol. xxii., 1858.
+
+  13. On the Freshwater Entomostraca of South
+        America.--Entomological Society's Transactions, 1858.
+
+  14. On _Coccus Hesperidum_.--Royal Society Proceedings, vol.
+        ix., 1858.
+
+  15. On the Distribution of Trache� in Insects.--Linnean
+        Society's Transactions, vol. xxiii., 1860.
+
+  16. On the Generative Organs and on the Formation of the Egg
+        in Annulosa. Transactions of the Royal Society, 1861.
+
+  17. On _Sph�rularia Bombi._--Natural History Review, 1861.
+
+  18. On some Oceanic Entomostraca.--Linnean Society's
+        Transactions, vol. xxiii., 1860.
+
+  19. On the Thysanura. Part 1.--Linnean Society's Transactions,
+        1862.
+
+  20. On the Development of Lonchoptera.--Entomological
+        Society's Transactions, 1862.
+
+  21. On the Thysanura. Part 2.--Linnean Society's Transactions,
+        1862.
+
+  22. On the Development of Chlo�on. Part 1.--Linnean Society's
+        Transactions, 1863.
+
+  23. On Two Aquatic Hymenoptera.--Linnean Society's
+        Transactions, 1863.
+
+  24. On some little-known Species of Freshwater
+        Entomostraca.--Linnean Society's Transactions, vol. xxiv.,
+        1863.
+
+  25. On _Sph�rularia Bombi_.--Natural History Review, 1864.
+
+  26. On the Development of Chlo�on. Part 2.--Linnean Society's
+        Transactions, 1865.
+
+  27. Metamorphoses of Insects.--Journal of the Royal
+        Institution, 1866.
+
+  28. On _Pauropus_.--Linnean Society's Transactions, 1866.
+
+  29. On the Thysanura. Part 3.--Linnean Society's Transactions,
+        1867.
+
+  30. Address to the Entomological Society.--Entomological
+        Society's Transactions, 1867.
+
+  31. On the Larva of Micropeplus Staphilinoides.--Entomological
+        Society's Transactions, 1868.
+
+  32. On the Thysanura. Part 4.--Linnean Society's Transactions,
+        1869.
+
+  33. Addresses to the Entomological Society.--Entomological
+        Society's Transactions, 1867-1868.
+
+  34. On the Origin of Insects.--Journal of the Linnean Society,
+        vol. xi.
+
+  35. Opening Address to the Biological Section of the British
+        Association.--British Association Report, 1872.
+
+  36. Observations on Ants, Bees, and Wasps. Part 1.--Journal of
+        the Linnean Society, 1873.
+
+  37. On British Wild Flowers considered in relation to Insects,
+        1874.
+
+  38. Observations on Ants, Bees, and Wasps. Part 2.--Journal of
+        the Linnean Society, 1874.
+
+  39. Observations on Ants, Bees, and Wasps. Part 3.--Journal of
+        the Linnean Society, 1875.
+
+  40. Observations on Ants, Bees, and Wasps. Part 4.--Journal of
+        the Linnean Society, 1877.
+
+  41. On some Points in the Anatomy of Ants.--Quekett Lecture,
+        1877.--Microscopical Journal.
+
+  42. On the Colors of Caterpillars.--Entomological Society's
+        Transactions, 1878.
+
+  43. Observations on Ants, Bees, and Wasps. Part 5.--Journal of
+        the Linnean Society, 1878.
+
+  44. Observations on Ants, Bees, and Wasps. Part 6.--Journal of
+        the Linnean Society, 1879.
+
+  45. On the Anatomy of Ants.--Linnean Society's Transactions,
+        1880.
+
+  46. Observations on Ants, Bees, and Wasps. Part 7.--Journal of
+        the Linnean Society, 1880.
+
+  47. Observations on Ants, Bees, and Wasps. Part 8.--Journal of
+        the Linnean Society, 1881.
+
+  48. On Fruits and Seeds.--Journal of the Royal Institution,
+        1881.
+
+  49. Observations on Ants, Bees, and Wasps. Part 9.--Journal of
+        the Linnean Society, 1881.
+
+  50. On the Limits of Vision among some of the lower
+        Animals.--Journal of the Linnean Society, 1881.
+
+  51. Observations on Ants, Bees, and Wasps. Part 10.--Journal
+        of the Linnean Society, 1882.
+
+
+
+
+CONTENTS.
+
+
+  CHAPTER I.
+
+  THE CLASSIFICATION OF INSECTS.
+
+  Introduction.--Stages in the Life of an Insect.--Classification
+    of Insects.--Characters derived from the Wings; from the parts
+    of the Mouth; from the Metamorphoses.--The Classes of Insects:
+    Hymenoptera, Strepsiptera, Coleoptera, Euplexoptera,
+    Orthoptera, Thysanoptera, Neuroptera, Trichoptera, Diptera,
+    Aphaniptera, Heteroptera, Homoptera, Lepidoptera          _page_ 1-26
+
+
+  CHAPTER II.
+
+  THE INFLUENCE OF EXTERNAL CONDITIONS ON THE FORM AND STRUCTURE
+  OF LARV�.
+
+  Larv� depend partly on the group to which they
+    belong.--Wood-eating Larv�.--Larv� of Lamellicorns.--Larv�
+    depend also in part on mode of life.--Larv� of Hymenoptera, of
+    _Sirex_; of _Tenthredo_; of Ichneumons; of Bees.--Rudimentary
+    legs of Bee Embryo.--Beetles, _Weevils_, _Scolytus_,
+    _Crioceris_, _Sitaris_, Metamorphoses of Pteromalid�.
+    _Platygaster_, _Polynema_.--Influence of external
+    conditions.--Developmental and adaptive Metamorphoses    _page_ 27-41
+
+
+  CHAPTER III.
+
+  THE NATURE OF METAMORPHOSES.
+
+  The life history of an Insect must be considered as a
+    whole.--Vagueness of the term Larva.--Some larv� much more
+    advanced than others.--Organs develope in different order, in
+    different groups.--Suppressed stages.--Apod condition of
+    _Phryganea_; of _Aphis_; of
+    _Chrysopa_.--Libellulid�.--_Donacia_.--Spiders.--Myriapods.--Apod
+    stage of Homomorphous Insects once probably longer than
+    now.--Suppression of embryonic stages.--Metamorphoses of
+    Hydroida, Crustacea, Isopods, and
+    Amphipods.--Echinoderms.--Variations in development induced by
+    the influence of external conditions.                    _page_ 41-62
+
+
+  CHAPTER IV.
+
+  THE ORIGIN OF METAMORPHOSES.
+
+  Origin of Metamorphoses.--Views of Messrs. Kirby and
+    Spence.--Nature of the question.--Young animals often more
+    similar than mature.--Views of Darwin, Herbert Spencer,
+    Johannes M�ller, Fritz M�ller, and Agassiz.--Effect of size of
+    egg.--Insects leave the egg in a more or less developed
+    condition.--Consideration of pupal condition.--Quiescence of
+    pupa.--Period of quiescence at each moult.--Changes not so
+    abrupt as generally supposed.--Change in
+    mouth-parts.--Difficulty in reference to Darwinian
+    theory.--Mouth-parts of _Campodea_ and Collembola, as
+    intermediate between the mandibulate and haustellate
+    types.--Change in mouth-parts as connected with pupal
+    conditions.--Origin of wings.--Use of wings under
+    water.--Connection of metamorphoses with alternation of
+    generations.--Parthenogenetic larv� of _Cecidomyia_.--In
+    alternation of generations one form always agamic.--Dimorphism
+    and Dieidism.--Summary and Conclusions                   _page_ 62-81
+
+
+  CHAPTER V.
+
+  THE ORIGIN OF INSECTS.
+
+  The Origin of Insects.--Mistaken views of Darwinian
+    theory.--Natural selection a _vera causa_.--Application of
+    Darwin's views to Insects.--Similarity of young Crustacea as
+    compared with mature forms; ditto in Insects.--Type of
+    Insecta.--Two principal types of larv�: Hexapod and
+    Apod.--Conclusions to be drawn from them.--_Campodea_ the modern
+    representative of the Insect-stock.--_Campodea_, perhaps
+    derived from Tardigrade.--Vermiform or Apod type of
+    larva.--Views of Fritz M�ller, Brauer, and Packard.--Represents
+    a still earlier ancestor.--Modern representatives.--_Notommata_,
+    _Albertia_, _Lindia_.--Earlier forms difficult to trace.--Lowest
+    forms of animal life.--Yolk-segmentation.--Embryology and
+    Evolution.--Light thrown by the evolution of the individual on
+    that of the species                                     _page_ 82-108
+
+  DESCRIPTION OF THE PLATES.
+
+
+  PLATE I. p. 7.
+
+  FIG.
+
+  1. Cricket. Westwood, Intro. to the Modern Classification of
+       Insects, vol. i. p. 440.
+
+  2. Earwig. Westwood, loc. cit. vol. i. p. 399.
+
+  3. _Aphis_. Packard, Guide to the Study of Insects, pp. 521, 522.
+
+  4. _Scolytus_. Westwood, loc. cit. vol. i. p. 350.
+
+  5. _Anthrax_. Westwood, loc. cit. vol. ii. p. 538.
+
+  6. _Balaninus_.
+
+  7. _Cynips_. Westwood, loc. cit. vol. ii. p. 121.
+
+  8. Ant (_Formica_). Westwood, loc. cit. vol. ii. p. 218.
+
+  9. Wasp. Ormerod, Nat. Hist. of Wasps, pl. i. fig. 1.
+
+
+  PLATE II. p. 8.
+
+  FIG.
+
+  1. Larva of Cricket. Westwood, loc. cit. vol. i. p. 440.
+
+  2. Larva of _Aphis_. Packard, loc. cit. pp. 521, 522.
+
+  3. Larva of Earwig. Westwood, loc. cit. vol. i. p. 399.
+
+  4. Larva of _Scolytus_. Westwood, loc. cit. vol. i. p. 350.
+
+  5. Larva of _Anthrax_. Westwood, loc. cit. vol. ii. p. 546.
+
+  6. Larva of _Balaninus_.
+
+  7. Larva of _Cynips_. Westwood, loc. cit. vol. ii. p. 121.
+
+  8. Larva of Ant (_Formica_). Westwood, loc. cit. vol. ii. p. 226.
+
+  9. Larva of Wasp. Newport, Art. Insecta, Todd's Cycl. Anat. and
+       Phys., p. 871.
+
+
+  PLATE III. p. 14.
+
+  FIG.
+
+  1. _Chlo�on_. Linn. Trans. 1866.
+
+  2. _Melo�_. Spry and Shuckard, Coleoptera Delineated, pl. 56.
+
+  3. _Calepteryx_.
+
+  4. _Sitaris_. Spry and Shuckard, loc. cit. pl. 56.
+
+  5. _Campodea_. Suites � Buffon. Apt�res.
+
+  6. _Acilius_. Westwood, loc. cit. vol. i. p. 100.
+
+  7. _Termes_. Westwood, loc. cit. vol. ii. p. 12.
+
+  8. _Stylops_. Duncan, Met. of Insects, p. 387; Packard, p. 482.
+
+  9. _Thrips_. Westwood, loc. cit. vol. ii. p. 1.
+
+
+  PLATE IV. p. 15.
+
+  FIG.
+
+  1. Larva of _Chlo�on_. Linn. Trans. 1863.
+
+  2. Larva of _Melo�_. Chapuis and Cand�ze, Mem. Soc. Roy. Li�ge,
+       1853, pp. 1, 7.
+
+  3. Larva of _Calepteryx_. Dufour, Ann. Sci. Nat. 1852.
+
+  4. Larva of _Sitaris_. Duncan, Met. of Insects, p. 309.
+
+  5. Larva of _Campodea_. Gervais' Suites � Buffon. Apt�res.
+
+  6. Larva of _Acilius_. Westwood, loc. cit. vol. i. p. 100.
+
+  7. Larva of _Termes_. Duncan, loc. cit. p. 348.
+
+  8. Larva of _Stylops_. Westwood, Trans. Ent. Soc. 1839, vol. ii.
+       pl. xv. fig. 13a.
+
+  9. Larva of _Thrips_. Westwood, loc. cit. vol. ii. p. i.
+
+
+  PLATE V. p. 99.
+
+  FIG.
+
+  1-5. _Protamoeba_.
+
+  6-9. _Protamyxa aurantiaca_. Haeckel Beit. zur. Monog. der
+         Moneren, pl. 1.
+
+  10-18. _Magosphoera planula_. Haeckel, loc. cit. pl. v.
+
+
+  PLATE VI. p. 105.
+
+  FIG.
+
+  1-4. Yolk-segmentation in _Laomedea_. After Allman. Mon. of
+         Tubularian Hydroids. Ray Society.
+
+  5-9. Yolk-segmentation in _Filaria_. After Van Beneden. Mem. sur
+         les Vers Intestinaux.
+
+  10-13. Yolk-segmentation in _Echinus_. After Derb�s. Ann. des.
+           Sci. Nat. 1847.
+
+  14-17. Yolk-segmentation in _Lacinularia_. After Huxley. J. of
+           Mic. Sci. 1853.
+
+  18-21. Yolk-segmentation in _Purpura_. After Koren and
+           Danielssen. Ann. des. Sci. Nat. 1853.
+
+  22-24. Yolk-segmentation in _Amphioxus_. After Haeckel.
+           Naturliche Sch�pfungsgeschichte, pl. x.
+
+  25-29. Yolk-segmentation in Vertebrate. After Allen Thompson.
+           Art. Ovum. Cyclop. of Anatomy and Physiology.
+
+
+  DESCRIPTION OF THE FIGURES.
+
+
+  FIG. 1. Larva of the Cockchafer (_Melolontha_)
+
+   2. Larva of _Cetonia_.
+
+   3. Larva of _Trox_.
+
+   4. Larva of _Oryctes_.
+
+   5. Larva of _Aphodius_.
+
+   6. Larva of _Lucanus_.
+
+   7. Larva of _Brachytarsus_.
+
+   8. Larva of _Crioceris_.
+
+   9. Larva of _Sitaris humeralis_.
+
+  10. Larva of _Sitaris humeralis_, in the second stage.
+
+  11. Larva of _Sitaris humeralis_, in the third stage.
+
+  12. Larva of _Sitaris humeralis_, in the fourth stage.
+
+  13. Pupa of _Sitaris_.
+
+  14. Larva of _Sirex_.
+
+  15. Egg of _Rhynchites_, showing the parasitic larva.
+
+  16. The parasitic larva, more magnified.
+
+  17. Egg of _Platygaster_.
+
+  18. Egg of _Platygaster_, showing the central cell.
+
+  19. Egg of _Platygaster_, after the division of the central cell.
+
+  20. Egg of _Platygaster_, more advanced.
+
+  21. Egg of _Platygaster_, more advanced.
+
+  22. Egg of _Platygaster_, showing the rudiment of the embryo.
+
+  23. Larva of _Platygaster_.--_mo_, mouth; _a_, antenna; _kf_,
+        hooked feet; _r_, toothed process; _lfg_, lateral
+        process; _f_, branches of the tail.
+
+  24. Larva of another species of _Platygaster_. (The letters
+        indicate the same parts as in the preceding figure.)
+
+  25. Larva of a third species of _Platygaster_. (The letters
+        indicate the same parts as in the preceding figure.)
+
+  26. Larva of _Platygaster_ in the second stage.--_mo_, mouth;
+        _slkf_, oesophagus; _gsae_, supra-oesophagal ganglion;
+        _lm_, muscles; _bsm_, nervous system; _gagh_, rudiments
+        of the reproductive glands.
+
+  27. Larva of _Platygaster_ in the third stage.--_mo_, mouth;
+        _ma_, mandibles; _gsae_, supra-oesophagal ganglion; _slk_,
+        oesophagus; _ag_, ducts of the salivary glands; _bnm_,
+        ventral nervous system; _sp_, salivary glands; _msl_,
+        stomach; _im_, imaginal discs; _tr_, trache�; _fk_, fatty
+        tissue; _ed_, intestine; _ga_, rudiments of reproductive
+        organs; _ew_, wider portion of intestine; _ao_, posterior
+        opening.
+
+  28. Embryo of _Polynema_.
+
+  29. Larva of _Polynema_.--_asch_, rudiments of the antenn�;
+        _flsch_, of the wings; _bsch_, of the legs; _vfg_,
+        lateral projections; _gsch_, rudiments of the ovipositor;
+        _fk_, fatty tissue.
+
+  30. Egg of _Phryganea_ (Mystacides).--_A_^1, mandibular segment;
+        _C_^1-_C_^5, maxillary, labial, and three thoracic
+        segments; _D_, abdomen.
+
+  31. Egg of _Phryganea_ somewhat more advanced.--_b_, mandibles;
+        _c_, maxill�; _cfs_, rudiments of the three pairs of
+        legs.
+
+  32. Egg of _Pholcus opilionides_, showing the Protozonites.
+
+  33. Embryo of _Julus_.
+
+  34. Colony of _Bougainvillea fruticosa_, natural size, attached
+        to the underside of a piece of floating timber.
+
+  35. Portion of the same, more magnified.
+
+  36. The Medusa from the same species.
+
+  37. Larva of Prawn, Nauplius stage.
+
+  38. Larva of Prawn, more advanced, Zo�a stage.
+
+  39. Larva of Echino-cidaris oequituberculata seen from above �6/10.
+
+  40. Larva of _Echinus_ � 100.--_A_, front arm; _F_, arms of the
+        mouth-process; _B_, posterior side arm; _E_^1, accessory
+        arm of the mouth-process; _a_, mouth; _a_^1, oesophagus;
+        _b_, stomach; _b_^1, intestine; _o_, posterior orifice;
+        _d_, ciliated bands; _f_, ciliated epaulets; _c_, disc of
+        future _Echinus_.
+
+  41. _Comatula rosacea_.
+
+  42. Larva of _Comatula rosacea_.
+
+  43. Larva of _Comatula rosacea_, more advanced.
+
+  44. Larva of _Comatula rosacea_, in the Pentacrinus state.
+
+  45. Larva of Starfish (Bipinnaria), � 100.
+
+  46. Larva of Starfish (Bipinnaria), � 100, seen from the
+  side.--_a_, mouth; _b_, oesophagus; _c_, stomach; _c_^1,
+  intestine.
+
+  47. Larva of another Bipinnaria, showing the commencement of
+  the Starfish.--_g_, canal of the ciliated sac; _i_, rudiments
+  of tentacles; _d_, ciliated band.
+
+  48. Larva of Moth (_Agrotis_).
+
+  49. Larva of Beetle (_Haltica_).
+
+  50. Larva of Saw-fly (_Cimbex_).
+
+  51. Larva of _Julus_.
+
+  52. _Agrotis suffusa_.
+
+  53. _Haltica_.
+
+  54. _Cimbex_.
+
+  55. _Julus_.
+
+  56. Tardigrade.
+
+  57. Larva of _Cecidomyia_.
+
+  58. _Lindia torulosa_.
+
+  59. _Prorhynchus stagnalis_.
+
+  60. Egg of Tardigrade.
+
+  61. Egg of Tardigrade, after the yolk has subdivided.
+
+  62. Egg of Tardigrade, in the next stage.
+
+  63. Egg of Tardigrade, more advanced.
+
+
+
+
+
+ON THE ORIGIN AND METAMORPHOSES OF INSECTS.
+
+
+
+
+CHAPTER I.
+
+  _THE CLASSIFICATION OF INSECTS._
+
+
+About forty years ago the civil and ecclesiastical authorities of St.
+Fernando in Chili arrested a certain M. Renous on a charge of
+witchcraft, because he kept some caterpillars which turned into
+butterflies.[1] This was no doubt an extreme case of ignorance; it is
+now almost universally known that the great majority of insects quit the
+egg in a state very different from that which they ultimately assume;
+and the general statement in works on entomology has been that the life
+of an insect may be divided into four periods.
+
+Thus, according to Kirby and Spence,[2] "The states through which
+insects pass are four: the _egg_, the _larva_, the _pupa_, and the
+_imago_." Burmeister,[3] also, says that, excluding certain very rare
+anomalies, "we may observe four distinct periods of existence in every
+insect,--namely, those of the egg, the larva, the pupa, and the imago,
+or perfect insect." In fact, however, the various groups of insects
+differ widely from one another in the metamorphoses they pass through:
+in some, as in the grasshoppers and crickets, the changes consist
+principally in a gradual increase of size, and in the acquisition of
+wings; while others, as for instance the common fly, acquire their full
+bulk in a form very different from that which they ultimately assume,
+and pass through a period of inaction in which not only is the whole
+form of the body altered, not only are legs and wings acquired, but even
+the internal organs themselves are almost entirely disintegrated and
+re-formed. It will be my object, after having briefly described these
+changes, to throw some light on the causes to which they are due, and on
+the indications they afford of the stages through which insects have
+been evolved.
+
+The following list gives the orders or principal groups into which the
+Class Insecta may be divided. I will not, indeed, here enter upon my own
+views, but will adopt the system given by Mr. Westwood in his excellent
+"Introduction to the Modern Classification of Insects," from which also,
+as a standard authority, most of the figures on Plates I. to IV., when
+not otherwise acknowledged, have been taken. He divides insects into
+thirteen groups, and with reference to eight of them it may be said that
+there is little difference of opinion among entomologists. These orders
+are by far the most numerous, and I have placed them in capital
+letters. As regards the other five there is still much difference of
+opinion. It must also be observed that Prof. Westwood omits the
+parasitic Anoplura, as well as the Thysanura and Collembola.
+
+
+ORDERS OF INSECTS ACCORDING TO WESTWOOD.
+
+   1. HYMENOPTERA   Bees, Wasps, Ants, &c.
+   2. STREPSIPTERA  _Stylops_, _Zenos_, &c.
+   3. COLEOPTERA    Beetles.
+   4. EUPLEXOPTERA  Earwigs.
+   5. ORTHOPTERA    Grasshoppers, Crickets, Cockroaches, &c.
+   6. THYSANOPTERA  _Thrips_.
+   7. NEUROPTERA    _Ephemeras_, &c.
+   8. TRICHOPTERA   _Phryganea_.
+   9. DIPTERA       Flies and Gnats.
+  10. APHANIPTERA   Fleas.
+  11. HETEROPTERA   Bugs.
+  12. HOMOPTERA     _Aphis_, _Coccus_, &c.
+  13. LEPIDOPTERA   Butterflies and Moths.
+
+Of these thirteen orders, the eight which I have placed in capital
+letters--namely the first, third, fifth, seventh, ninth, eleventh,
+twelfth, and thirteenth, are much the most important in the number and
+variety of their species; the other five form comparatively small
+groups. The Strepsiptera are minute insects, parasitic on Hymenoptera:
+Rossi, by whom they were discovered, regarded them as Hymenopterous;
+Lamarck placed them among the Diptera; by others they have been
+considered to be most closely allied to the Coleoptera, but they are now
+generally treated as an independent order.
+
+The Euplexoptera or Earwigs are only too familiar to most of us. Linn�us
+classed them among the Coleoptera, from which, however, they differ in
+their transformations. Fabricius, Olivier, and Latreille regarded them
+as Orthoptera; but Dr. Leach, on account of the structure of their
+wings, considered them as forming the type of a distinct order, in which
+view he has been followed by Westwood, Kirby, and many other
+entomologists.
+
+The Thysanoptera, consisting of the Linn�an genus _Thrips_, are minute
+insects well known to gardeners, differing from the Coleoptera in the
+nature of their metamorphoses, in which they resemble the Orthoptera and
+Hemiptera. The structure of the wings and mouth-parts, however, are
+considered to exclude them from these two orders.
+
+The Trichoptera, or Caddis worms, offer many points of resemblance to
+the Neuroptera, while in others they approach more nearly to the
+Lepidoptera. According to Westwood, the genus _Phryganea_ "forms the
+connecting link between the Neuroptera and Lepidoptera."
+
+The last of these small aberrant orders is that of the Aphaniptera,
+constituted for the family Pulicid�. In their transformations, as in
+many other respects, they closely resemble the Diptera. Strauss
+Durckheim indeed said that "_la puce est un dipt�re sans ailes_."
+Westwood, however, regards it as constituting a separate order.
+
+As indicated by the names of these orders, the structure of the wings
+affords extremely natural and convenient characters by which the various
+groups may be distinguished from one another. The mouth-parts also are
+very important; and, regarded from this point of view, the Insecta have
+been divided into two series--the Mandibulata and Haustellata, or
+mandibulate and suctorial groups, between which, as I have elsewhere
+shown,[4] the Collembola (_Podura_, _Smynthurus_, &c.) occupy an
+intermediate position. These two series are:--
+
+MANDIBULATA.
+
+  Hymenoptera.
+  Strepsiptera.
+  Coleoptera.
+  Euplexoptera.
+  Orthoptera.
+  Trichoptera?
+  Thysanoptera?
+
+HAUSTELLATA.
+
+  Lepidoptera.
+  Diptera.
+  Aphaniptera.
+  Hemiptera.
+  Homoptera.
+
+Again--and this is the most important from my present point of
+view--insects have sometimes been divided into two other series,
+according to the nature of their metamorphoses: "Heteromorpha," to use
+the terminology of Prof. Westwood,[5] "or those in which there is no
+resemblance between the parent and the offspring; and Homomorpha, or
+those in which the larva resembles the imago, except in the absence of
+wings. In the former the larva is generally worm-like, of a soft and
+fleshy consistence, and furnished with a mouth, and often with six short
+legs attached in pairs to the three segments succeeding the head. In the
+Homomorpha, including the Orthoptera, Hemiptera, Homoptera, and certain
+Neuroptera, the body, legs, and antenn� are nearly similar in their form
+to those of the perfect insect, but the wings are wanting."
+
+HETEROMORPHA.
+
+  Hymenoptera.
+  Strepsiptera.
+  Coleoptera.
+  Trichoptera.
+  Diptera.
+  Aphaniptera.
+  Lepidoptera.
+
+HOMOMORPHA.
+
+  Euplexoptera.
+  Orthoptera.
+  Hemiptera.
+  Homoptera.
+  Thysanoptera.
+  Neuroptera.
+
+But though the Homomorphic insects do not pass through such striking
+changes of form as the Heteromorphic, and are active throughout life,
+still it was until within the last few years generally (though
+erroneously) considered, that in them, as in the Heteromorpha, the life
+fell into four distinct periods; those of (1) the egg, (2) the larva,
+characterized by the absence of wings, (3) the pupa with imperfect
+wings, and (4) the imago, or perfect insect.
+
+I have, however, elsewhere[6] shown that there are not, as a matter of
+fact, four well-marked stages, and four only, but that in many cases the
+process is much more gradual.
+
+The species belonging to the order Hymenoptera are among the most
+interesting of insects. To this order belong the gallflies, the
+sawflies, the ichneumons, and, above all, the ants and bees. We are
+accustomed to class the Anthropoid apes next to man in the scale of
+creation, but if we were to judge animals by their works, the chimpanzee
+and the gorilla must certainly give place to the bee and the ant. The
+larv� of the sawflies, which live on leaves, and of the Siricid� or
+long-tailed wasps, which feed on wood, are very much like caterpillars,
+having three pairs of legs, and in the former case abdominal pro-legs
+as well: but in the great majority of Hymenoptera the larv� are legless,
+fleshy grubs (Plate II., Figs. 7-9); and the various modes by which the
+females provide for, or secure to, them a sufficient supply of
+appropriate nourishment constitutes one of the most interesting pages of
+Natural History.
+
+The species of Hymenoptera are very numerous; in this country alone
+there are about 3,000 kinds, most of which are very small. In the pupa
+state they are inactive, and show distinctly all the limbs of the
+perfect insect, encased in distinct sheaths, and folded on the breast.
+In the perfect state they are highly organized and very active. The
+working ants and some few species are wingless, but the great majority
+have four strong membranous wings, a character distinguishing them at
+once from the true flies, which have only one pair of wings.
+
+The saw-flies are so called because they possess at the end of the body a
+curious organ, corresponding to the sting of a wasp, but which is in the
+form of a fine-toothed saw. With this instrument the female sawfly cuts
+a slit in the stem or leaf of a plant, into which she introduces her
+egg. The larva much resembles a caterpillar, both in form and habits. To
+this group belongs the nigger, or black caterpillar of the turnip, which
+is often in sufficient numbers to do much mischief. Some species make
+galls, but the greater number of galls are formed by insects of another
+family, the Cynipid�.
+
+[Illustration: PLATE I.[7]--MATURE INSECTS.
+
+Fig. 1, Cricket; 2, Earwig; 3, _Aphis_; 4, _Scolytus_; 5, Anthrax;
+6, _Balaninus_; 7, _Cynips_; 8, Ant; 9, Wasp.]
+
+[Illustration: PLATE II.--LARV� OF THE INSECTS REPRESENTED ON PLATE I.
+
+Fig. 1, Larva of Cricket; 2, Larva of Aphis; 3, Larva of Earwig; 4,
+Larva of _Scolytus_ (Beetle); 5, Larva of _Anthrax_ (Fly); 6, Larva of
+_Balaninus_ (Nut Weevil); 7, Larva of _Cynips_; 8, Larva of Ant;
+9, Larva of Wasp.]
+
+In the Cynipid� (Plate I., Fig. 7) the female is provided with an organ
+corresponding to the saw of the sawfly, but resembling a needle. With
+this she stings or punctures the surface of leaves, buds, stalks, or
+even roots of various plants. In the wound thus produced she lays one or
+more eggs. The effects of this proceeding, and particularly of the
+irritating fluid which she injects into the wound, is to produce a
+tumour or gall, within which the egg hatches, and on which the larva, a
+thick fleshy grub (Plate II., Fig. 7), feeds. In some species each gall
+contains a single larva; in others, several live together.
+
+The oak supports several kinds of gallflies: one produces the well-known
+oak-apple, one a small swelling on the leaf resembling a currant,
+another a gall somewhat like an acorn, another attacks the root; the
+species making the bullet-like galls, which are now so common, has only
+existed for a few years in this country; the beautiful little spangles
+so common in autumn on the under side of oak leaves are the work of
+another species, the _Cynus longipennis_. One curious point about this
+group is, that in some of the commonest species the females alone are
+known, no one yet having ever succeeded in finding a male.
+
+Another great family of the Hymenoptera is that of the ichneumons; the
+females lay their eggs either in or on other insects, within the bodies
+of which the larv� live. These larv� are thick, fleshy, legless grubs,
+and feed on the fatty tissues of their hosts, but do not attack the
+vital organs. When full-grown, the grubs eat their way through the skin
+of the insect, and turn into chrysalides. Almost every kind of insect
+is subject to the attacks of these little creatures, which are no doubt
+useful in preventing the too great multiplication of insects, and
+especially of caterpillars. Some species are so minute that they
+actually lay their eggs within those of other insects (Figs. 15, 16).
+These parasites assume very curious forms in their larval state.
+
+But of all the Hymenoptera, the group containing the ant, the bee, and
+the wasp is the most interesting. This is especially the case with the
+social species, though the solitary ones also are extremely remarkable.
+The solitary bee or wasp, for instance, forms a cell generally in the
+ground, places in it a sufficient amount of food, lays an egg, and
+closes the cell. In the case of bees, the food consists of honey; in
+that of wasps, the larva requires animal food, and the mother therefore
+places a certain number of insects in the cell, each species having its
+own special prey, some selecting small caterpillars, some beetles, some
+spiders. _Cerceris bupresticida_, as its name denotes, attacks beetles
+belonging to the genus _Buprestis_. Now if the Cerceris were to kill the
+beetle before placing it in the cell, it would decay, and the young
+larva, when hatched, would find only a mass of corruption. On the other
+hand, if the beetle were buried uninjured, in its struggles to escape it
+would be almost certain to destroy the egg. The wasp has, however, the
+instinct of stinging its prey in the centre of the nervous system, thus
+depriving it of motion, and let us hope of suffering, but not of life;
+consequently, when the young larva leaves the egg, it finds ready a
+sufficient store of wholesome food.
+
+Other wasps are social, and, like the bees and ants, dwell together in
+communities. They live for one season, dying in autumn, except some of
+the females, which hibernate, awake in the spring, and form new
+colonies. These, however, do not, under ordinary circumstances, live
+through a second winter. One specimen which I kept tame through last
+spring and summer, lived until the end of February, but then died. The
+larv� of wasps (Plate II., Fig. 9) are fat, fleshy, legless grubs. When
+full-grown they spin for themselves a silken covering, within which they
+turn into chrysalides. The oval bodies which are so numerous in ants'
+nests, and which are generally called ants' eggs, are really not eggs
+but cocoons. Ants are very fond of the honey-dew which is formed by the
+Aphides, and have been seen to tap the Aphides with their antenn�, as if
+to induce them to emit some of the sweet secretion. There is a species
+of _Aphis_ which lives on the roots of grass, and some ants collect these
+into their nests, keeping them, in fact, just as we do cows. Moreover
+they collect the eggs in the autumn and tend them through the winter
+(when they are of no use) with the same care as their own, so as to have
+a supply of young Aphides in the spring. This is one of the most
+remarkable facts I know in the whole history of animal life. One species
+of red ant does no work for itself, but makes slaves of a black kind,
+which then do everything for their masters. The slave makers will not
+even put food into their own mouths, but would starve in the midst of
+plenty, if they had not a slave to feed them. I found, however, that I
+could keep them in life and health for months if I gave them a slave for
+an hour or two in a week to clean and feed them.
+
+Ants also keep a variety of beetles and other insects in their nests.
+That they have some reason for this seems clear, because they readily
+attack any unwelcome intruder; but what that reason is, we do not yet
+know. If these insects are to be regarded as the domestic animals of the
+ants, then we must admit that the ants possess more domestic animals
+than we do.
+
+Some indeed of these beetles produce a secretion which is licked by the
+ants like the honey-dew; there are others, however, which have not yet
+been shown to be of any use to the ants, and yet are rarely, if ever,
+found, excepting in ants' nests.
+
+M. Lesp�s, who regards these insects as true domestic animals, has
+recorded[8] some interesting observations on the relations between one
+of them (_Claviger Duvalii_) and the ants (_Lasius niger_) with which it
+lives. This species of _Claviger_ is never met with except in ants'
+nests, though on the other hand there are many communities of _Lasius_
+which possess none of these beetles; and M. Lesp�s found that when he
+placed _Clavigers_ in a nest of ants which had none of their own, the
+beetles were immediately killed and eaten, the ants themselves being on
+the other hand kindly received by other communities of the same species.
+He concludes from these observations that some communities of ants are
+more advanced in civilization than others; the suggestion is no doubt
+ingenious, and the fact curiously resembles the experience of navigators
+who have endeavoured to introduce domestic animals among barbarous
+tribes; but M. Lesp�s has not yet, so far as I am aware, published the
+details of his observations, without which it is impossible to form a
+decided opinion. I have sometimes wondered whether the ants have any
+feeling of reverence for these beetles; but the whole subject is as yet
+very obscure, and would well repay careful study.
+
+[Illustration: PLATE III.--MATURE INSECTS.
+
+Fig. 1, _Chlo�on_; 2, _Melo�_ (after Shuckard); 3, _Calepteryx_;
+4, _Sitaris_ (after Shuckard); 5, _Campodea_ (after Gervais);
+6, _Acilius_; 7, _Termes_; 8, _Stylops_ (female); 9, _Thrips_.]
+
+[Illustration: PLATE IV. YOUNG FORMS OF THE INSECTS REPRESENTED ON PLATE
+III.--Fig. 1, Larva of _Chlo�on_; 2, Larva of _Melo�_ (after Chapuis and
+Cand�ze); 3, Larva of _Calepteryx_ (after L�on Dufour); 4, Larva of
+_Sitaris_; 5, Larva of _Campodea_; 6, Larva of _Acilius_;
+7, Larva of Termes (after Blanchard); 8, Larva of _Stylops_; 9, Larva
+of _Thrips_.]
+
+The order Strepsiptera are a small, but very remarkable group of
+insects, parasitic on bees and wasps. The larva (Pl. IV., Fig. 8) is
+minute, six-legged, and very active; it passes through its
+transformations within the body of the bee or wasp. The male and female
+are very dissimilar. The males are minute, very active, short-lived, and
+excitable, with one pair of large membranous wings. The females (Pl.
+III., Fig. 8), on the contrary, are almost motionless, and shaped very
+much like a bottle; they never quit the body of the bee, but only thrust
+out the top of the bottle between the abdominal rings of the bee.
+
+In the order Coleoptera, the larv� differ very much in form. The
+majority are elongated, active, hexapod, and more or less depressed; but
+those of the Weevils (Pl. II., Fig. 6), of _Scolytus_ (Pl. II., Fig. 4),
+&c., which are vegetable feeders, and live surrounded by their
+food,--as, for instance, in grain, nuts, &c.,--are apod, white, fleshy
+grubs, not unlike those of bees and ants. The larv� of the Longicorns,
+which live inside trees, are long, soft, and fleshy, with six short
+legs. The Geodephaga, corresponding with the Linn�an genera _Cicindela_
+and _Carabus_, have six-legged, slender, carnivorous larv�; those of
+_Cicindela_, which waylay their prey, being less active than the hunting
+larv� of the Carabid�. The Hydradephaga, or water-beetles (Dyticid� and
+Gyrinid�), have long and narrow larv� (Pl. IV., Fig. 6), with strong
+sickle-shaped jaws, short antenn�, four palpi, and six small eyes on
+each side of the head; they are very voracious. The larv� of the
+Staphylinid� are by no means unlike the perfect insect, and are found in
+similar situations; their jaws are powerful, and their legs moderately
+strong. The larv� of the Lamellicorn beetles (Figs. 1-6)--cockchafers,
+stag-beetles, &c.--feed on vegetable substances or on dead animal
+matter. They are long, soft, fleshy grubs, with the abdomen somewhat
+curved, and generally lie on their side. The larv� of the Elaterid�,
+known as wireworms, are long and slender, with short legs. That of the
+glowworm (Lampyrid�) is not unlike the apterous female. The male
+glowworm, on the contrary, is very different. It has long, thin, brown
+wing-cases, and often flies into rooms at night, attracted by the light,
+which it probably mistakes for that of its mate.
+
+The metamorphoses of the Cantharid� are very remarkable, and will be
+described subsequently. The larv� are active and hexapod. The Phytophaga
+(_Crioceris_, _Galeruca_, _Haltica_, _Chrysomela_, &c.) are vegetable
+feeders, both as larv� and in the perfect state. The larv� are furnished
+with legs, and are not unlike the caterpillars of certain Lepidoptera.
+
+The larva of _Coccinella_ (the Ladybird) is somewhat depressed, of an
+elongated ovate form, with a small head, and moderately strong legs. It
+feeds on Aphides.
+
+Thus, then, we see that there are among the Coleoptera many different
+forms of larv�. Macleay considered that there were five principal types.
+
+1. Carnivorous hexapod larv�, with an elongated, more or less flattened
+body, six eyes on each side of the head, and sharp falciform mandibles
+(_Carabus_, _Dyticus_, &c.).
+
+2. Herbivorous hexapod larv�, with fleshy, cylindrical bodies, somewhat
+curved, so that they lie on their side.
+
+3. Apod grub-like larv�, with scarcely the rudiments of antenn�
+(_Curculio_).
+
+4. Hexapod antenniferous larv�, with a subovate body, the second segment
+being somewhat larger than the others (_Chrysomela_, _Coccinella_).
+
+5. Hexapod antenniferous larv�, of oblong form, somewhat resembling the
+former, but with caudal appendages (_Melo�_, _Sitaris_).
+
+The pupa of the Coleoptera is quiescent, and "the parts of the future
+beetle are plainly perceivable, being encased in distinct sheaths; the
+head is applied against the breast; the antenn� lie along the sides of
+the thorax; the elytra and wings are short and folded at the sides of
+the body, meeting on the under side of the abdomen; the two anterior
+pairs of legs are entirely exposed, but the hind pair are covered by
+wing-cases, the extremity of the thigh only appearing beyond the sides
+of the body."[9]
+
+In the next three orders--namely, the Orthoptera (grasshoppers, locusts,
+crickets, walking-stick insects, cockroaches, &c.), Euplexoptera
+(earwigs), and Thysanoptera, a small group of insects well known to
+gardeners under the name of _Thrips_ (Pl. I. and II., Figs. 1 and 2)--the
+larv� when they quit the egg already much resemble the mature form,
+differing, in fact, principally in the absence of wings, which are more
+or less gradually acquired, as the insect increases in size. They are
+active throughout life. Those specimens which have rudimentary wings
+are, however, usually called pup�.
+
+The Neuroptera present, perhaps, more differences in the character of
+their metamorphoses than any other order of insects. Their larv� are
+generally active, hexapod little creatures, and do not vary from one
+another in appearance so much, for instance, as those of the Coleoptera,
+but their pup� differ essentially; some groups, namely, the Psocid�,
+Termitid�, Libellulid�, Ephemerid�, and Perlid�, remaining active
+throughout life, like the Orthoptera; while a second division, including
+the Myrmeleonid�, Hemerobiid�, Sialid�, Panorpid�, Raphidiid�, and
+Mantispid�, have quiescent pup�, which, however, in some cases, acquire
+more or less power of locomotion shortly before they assume the mature
+state; thus that of _Raphidia_, though motionless at first, at length
+acquires strength enough to walk, even while still enclosed in the pupa
+skin, which is very thin.[10]
+
+One of the most remarkable families belonging to this order is that of
+the Termites, or white ants. They abound in the tropics, where they are
+a perfect pest, and a serious impediment to human development. Their
+colonies are extremely numerous, and they attack woodwork and furniture
+of all kinds, generally working from within, so that their presence is
+often unsuspected, until it is suddenly found that they have completely
+eaten away the interior of some post or table, leaving nothing but a
+thin outer shell. Their nests, which are made of earth, are sometimes
+ten or twelve feet high, and strong enough to bear a man. One species,
+_Termes lucifugus_, is found in the South of France, where it has been
+carefully studied by Latreille. He found in these communities five kinds
+of individuals--(1) males; (2) females, which grow to a very large size,
+their bodies being distended with eggs, of which they sometimes lay as
+many as 80,000 in a day; (3) a form described by some observers as Pup�,
+but by others as neuters. These differ very much from the others, having
+a long, soft body without wings, but with an immense head, and very
+large, strong jaws. These individuals act as soldiers, doing apparently
+no work, but keeping watch over the nest and attacking intruders with
+great boldness. (4) Apterous, eyeless individuals, somewhat resembling
+the winged ones, but with a larger and more rounded head; these
+constitute the greater part of the community, and, like the workers of
+ants and bees, perform all the labour, building the nest and collecting
+food. (5) Latreille mentions another kind of individual which he regards
+as the pupa, and which resembles the workers, but has four white
+tubercles on the back, where the wings afterwards make their appearance.
+There is still, however, much difference of opinion among entomologists,
+with reference to the true nature of these different classes of
+individuals. M. Lesp�s, who has recently studied the same species,
+describes a second kind of male and a second kind of female, and the
+subject, indeed, is one which offers a most promising field for future
+study.
+
+Another interesting family of Neuroptera is that of the Ephemer�, or
+Mayflies (Pl. III., Fig. 1), so well known to fishermen. The larv� (Pl.
+IV., Fig. 1) are semi-transparent, active, six-legged little creatures,
+which live in water; having at first no gills, they respire through the
+general surface of the body. They grow rapidly and change their skin
+every few days. After one or two moults they acquire seven pairs of
+branchi�, or gills, which are generally in the form of leaves, one pair
+to the segment. When the larv� are about half grown, the posterior
+angles of the two posterior thoracic segments begin to elongate. These
+elongations become more and more marked with every change of skin. One
+morning, in the month of June, some years ago, I observed a full-grown
+larva, which had a glistening appearance, owing to the presence of a
+film of air under the skin. I put it under the microscope, and, having
+added a drop of water with a pipette, looked through the glass. To my
+astonishment, the insect was gone, and an empty skin only remained. I
+then caught a second specimen, in a similar condition, and put it under
+the microscope, hoping to see it come out. Nor was I disappointed. Very
+few moments had elapsed, when I had the satisfaction of seeing the
+thorax open along the middle of the back; the two sides turned over; the
+insect literally walked out of itself, unfolded its wings, and in an
+instant flew up to the window. Several times since, I have had the
+pleasure of witnessing this marvellous change, and it is really
+wonderful how rapidly it takes place: from the moment when the skin
+first cracks, not ten seconds are over before the insect has flown away.
+
+Another family of Neuroptera, the Dragon-flies, or Horse-stingers, as
+they are sometimes called, from a mistaken idea that they sting severely
+enough to hurt a horse, though in fact they are quite harmless, also
+spend their early days in the water. The larv� are brown, sluggish, ugly
+creatures, with six legs. They feed on small water-animals, for which
+they wait very patiently, either at the bottom of the water, or on some
+aquatic plant. The lower jaws are attached to a long folding rod; and
+when any unwary little creature approaches too near the larva, this
+apparatus is shot out with such velocity that the prey which comes
+within its reach seldom escapes. In their perfect condition, also,
+Dragon-flies feed on other insects, and may often be seen hawking round
+ponds. The so-called Ant-lions in many respects resemble the
+Dragon-flies, but the habits of the larv� are very dissimilar. They do
+not live in the water, but prefer dry places, where they bury themselves
+in the loose sand, and seize with their long jaws any small insect which
+may pass. The true Ant-lion makes itself a round, shallow pit in loose
+ground or sand, and buries itself at the bottom. Any inattentive little
+insect which steps over the edge of this pit immediately falls to the
+bottom, and is instantaneously seized by the Ant-lion. Should the insect
+escape, and attempt to climb up the side of the pit, the Ant-lion is
+said to throw sand at it, knocking it down again.
+
+One other family of Neuroptera which I must mention, is the
+Hemerobiid�. The perfect insect is a beautiful, lace-winged, very
+delicate, green creature, something like a tender Dragon-fly, and with
+bright, green, touching eyes. The female deposits her eggs on leaves,
+not directly on the plant itself, but attached to it by a long white
+slender footstalk. The larva has six legs and powerful jaws, and makes
+itself very useful in destroying the Hop-fly.
+
+The insects forming the order Trichoptera are well known in their larval
+condition, under the name of caddis worms. These larv� are not
+altogether unlike caterpillars in form, but they live in water--which is
+the case with very few lepidopterous larv�--and form for themselves
+cylindrical cases or tubes, built up of sand, little stones, bits of
+stick, leaves, or even shells. They generally feed on vegetable
+substances, but will also attack minute freshwater animals. When full
+grown, the larva fastens its case to a stone, the stem of a plant, or
+some other fixed substance, and closes the two ends with an open grating
+of silken threads, so as to admit the free access of water, while
+excluding enemies. It then turns into a pupa which bears some
+resemblance to the perfect insect, "except that the antenn�, palpi,
+wings, and legs are shorter, enclosed in separate sheaths, and arranged
+upon the breast." The pupa remains quiet in the tube until nearly ready
+to emerge, when it comes to the surface, and in some cases creeps out of
+the water. It is not therefore so completely motionless as the pup� of
+Lepidoptera.
+
+The Diptera, or Flies, comprise insects with two wings only, the hinder
+pair being represented by minute club-shaped organs called "halt�res."
+Flies quit the egg generally in the form of fat, fleshy, legless grubs.
+They feed principally on decaying animal or vegetable matter, and are no
+doubt useful as scavengers. Other species, as the gadflies, deposit
+their eggs on the bodies of animals, within which the grubs feed, when
+hatched. The mouth is generally furnished with two hooks which serve
+instead of jaws. The pup� of Diptera are of two kinds. In the true
+flies, the outer skin of the full-grown larva is not shed, but contracts
+and hardens, thus assuming the appearance of an oval brownish shell or
+case, within which the insect changes into a chrysalis. The pup� of the
+gnats, on the contrary, have the limbs distinct and enclosed in sheaths.
+They are generally inactive, but some of the aquatic species continue to
+swim about.
+
+One group of Flies, which is parasitic on horses, sheep, bats, and other
+animals, has been called the Pupipara, because it was supposed that they
+were not born until they had arrived at the condition of pup�. They come
+into the world in the form of smooth, ovate bodies, much resembling
+ordinary dipterous pup�, but as Leuckart has shown,[11] they are true,
+though abnormal, larv�.
+
+The next order, that of the Aphaniptera, is very small in number,
+containing only the different species of Flea. The larva is long,
+cylindrical, and legless; the chrysalis is motionless, and the perfect
+insect is too well known, at least, as regards its habits, to need any
+description.
+
+The Heteroptera, unlike the preceding orders of insects, quit the egg in
+a form differing from that of the perfect insect principally in the
+absence of wings, which are gradually acquired. In their metamorphoses
+they resemble the Orthoptera, and are active through life. The majority
+are dull in colour, though some few are very beautiful. The species
+constituting this group, though very numerous, are generally small, and
+not so familiarly known to us as those of the other large orders, with
+indeed one exception, the well-known Bug. This is not, apparently, an
+indigenous insect, but seems to have been introduced. The word is indeed
+used by old writers, but either as meaning a bugbear, or in a general
+sense, and not with reference to this particular insect. In this country
+it never acquires wings, but is stated to do so sometimes in warmer
+climates. The Heteroptera cannot exactly be said either to sting or
+bite. The jaws, of which, as usual among insects, there are two pairs,
+are like needles, which are driven into the flesh, and the blood is then
+sucked up the lower lip, which has the form of a tube. This peculiar
+structure of the mouth prevails throughout the whole order; consequently
+their nutriment consists almost entirely of the juices of animals or
+plants. The Homoptera agree with the Heteroptera in the structure of the
+mouth, and in the metamorphoses. They differ principally in the front
+wings, which in Homoptera are membranous throughout, while in the
+Heteroptera, the front part is thickened and leathery. As in the
+Heteroptera, however, so also in the Homoptera, some species do not
+acquire wings. The Cicada, celebrated for its chirp, and the lanthorn
+fly, belong to this group. So also does the so-called Cuckoo-spit, so
+common in our gardens, which has the curious faculty of secreting round
+itself a quantity of frothy fluid which serves to protect it from its
+enemies. But the best known insects of this group are the Aphides or
+Plant-lice; while the most useful belong to the Coccid�, or scale
+insects, from one species of which we obtain the substance called lac,
+so extensively used in the manufacture of sealing-wax and varnish.
+Several species also have been used in dyeing, especially the Cochineal
+insect of Mexico, a species which lives on the cactus. The male _Coccus_
+is a minute, active insect, with four large wings; while the female, on
+the contrary, never acquires wings, but is very sluggish, broad, more or
+less flattened, and in fact, when full grown, looks like a small brown,
+red, or white scale.
+
+The larva of the order Lepidoptera are familiar to us all, under the
+name of caterpillars. The insects of this order in their larval
+condition are almost all phytophagous, and are very uniform both in
+structure and in habits. The body is long and cylindrical, consisting of
+thirteen segments; the head is armed with powerful jaws; the three
+following segments, the future prothorax, mesothorax, and meta-thorax,
+each bears a pair of simple articulated legs. Of the posterior segments,
+five also bear false or pro-legs, which are short, unjointed, and
+provided with a number of hooklets. A caterpillar leads a dull and
+uneventful life; it eats ravenously, and grows rapidly, casting its skin
+several times during the process, which generally lasts only a few
+weeks; though in some cases, as for instance that of the goat-moth, it
+extends over a period of two or three years, after which the larva
+changes into a quiescent pupa or chrysalis.
+
+
+
+
+CHAPTER II.
+
+_THE INFLUENCE OF EXTERNAL CONDITIONS ON THE FORM AND STRUCTURE OF
+LARV�._
+
+
+The facts recapitulated briefly in the preceding chapter show, that the
+forms of insect larv� depend greatly on the group to which they belong.
+Thus the same tree may harbour larv� of Diptera, Hymenoptera,
+Coleoptera, and Lepidoptera; each presenting the form typical of the
+family to which it belongs.
+
+If, again, we take a group, such, for instance, as the Lamellicorn
+beetles, we shall find larv� extremely similar in form, yet very
+different in habits. Those, for instance, of the common cockchafer (Fig.
+1) feed on the roots of grass; those of _Cetonia aurata_ (Fig. 2)
+inhabit ants' nests; the larv� of the genus _Trox_ (Fig. 3) are found on
+dry animal substances; of _Oryctes_ (Fig. 4) in tan-pits; of _Aphodius_
+(Fig. 5) in dung; of _Lucanus_ (the stag-beetle, Fig. 6) in wood.
+
+[Illustration: FIG. 1, Larva of the Cockchafer (_Melolontha_).
+(Westwood, Int. to the Modern Classification of Insects, vol. i. p.
+194.). 2, Larva of _Cetonia_. 3, Larva of _Trox_. 4, Larva of _Oryctes_.
+5, Larva of _Aphodius_ (Chapuis and Cand�ze, M�m. Soc. Roy. Li�ge,
+1853). 6, Larva of _Lucanus_. (Packard, Guide to the Study of Insects,
+Fig. 403).]
+
+On the other hand, in the present chapter it will be my object to show
+that the form of the larva depends very much on the conditions of its
+life. Thus, those larv� which are internal parasites, whether in
+animals or plants, are vermiform, as are those which live in cells, and
+depend on their parents for food. On the other hand, larv� which burrow
+in wood have strong jaws and generally somewhat weak thoracic legs;
+whilst those which feed on leaves have the thoracic legs more developed,
+but less so than the carnivorous species. Now, the Hymenoptera, as a
+general rule, belong to the first category: the larv� of the Ichneumons,
+&c., which live in animals,--those of the Cynipid�, inhabiting
+galls,--and those of ants, bees, wasps, &c., which are fed by their
+parents, are fleshy, apodal grubs; though the remarkable fact that the
+embryos of bees in one stage of their development possess rudiments of
+thoracic legs which subsequently disappear, seems to show, not indeed
+that the larv� of bees were ever hexapod, but that bees are descended
+from ancestors which had hexapod larv�, and that the present apod
+condition of these larv� is not original, but results from their mode of
+life.
+
+On the other hand, the larv� of _Sirex_ (Fig. 14) being wood-burrowers,
+possess well-developed thoracic legs. Again, the larv� of the
+Tenthredinid�, which feed upon leaves, closely resemble the caterpillars
+of Lepidoptera, even to the presence of abdominal pro-legs.
+
+[Illustration: FIG. 7, Larva of _Brachytarsus_ (Ratzeburg, Forst.
+Insecten). 8, Larva of _Crioceris_ (Westwood, loc. cit.).]
+
+The larv� of most Coleoptera (Beetles) are active, hexapod, and more or
+less flattened: but those which live inside vegetable tissues, such as
+the weevils, are apod fleshy grubs, like those of Hymenoptera. Pl. II.,
+Fig. 6, represents the larva of the nut-weevil, _Balaninus_ (Pl. I., Fig.
+6), and it will be seen that it closely resembles Pl. II., Fig. 5, which
+represents that of a fly (_Anthrax_), Pl. I., Fig. 5, and Pl. II., Figs.
+7, 8, and 9, which represent respectively those of a _Cynips_ or gall-fly
+(Pl. I., Fig. 7), an ant (Pl. I., Fig. 8), and wasp (Pl. I., Fig. 9).
+Nor is _Balaninus_ the only genus of Coleoptera which affords us examples
+of this fact. Thus in the genus _Scolytus_ (Pl. I., Fig. 4), the larv�
+(Pl. II., Fig. 4), which, as already mentioned, feed on the bark of the
+elm, closely resemble those just described, as also do those of
+_Brachytarsus_ (Fig. 7). On the other hand, the larv� of certain beetles
+feed on leaves, like the caterpillars of Lepidoptera; thus that of
+_Crioceris Asparagi_ (Fig. 8)--which, as its name denotes, feeds on the
+asparagus--closely resembles the larv� of certain Lepidoptera, as for
+instance of _Thecla spini_. From this point of view the transformations
+of the genus _Sitaris_ (Pl. III., Fig. 4), which have been very carefully
+investigated by M. Fabre, are peculiarly interesting.[12]
+
+[Illustration: FIG. 9, Larva of _Sitaris numeralis_ (Fabre, Ann. des Sci.
+Nat., s�r. 4, tome vii.). 10, Larva of _Sitaris humeralis_, in the second
+stage. 11, Larva of _Sitaris humeralis_, in the third stage. 12, Larva of
+_Sitaris humeralis_, in the fourth stage. 13, Pupa of _Sitaris_.]
+
+The genus _Sitaris_ (a small beetle allied to Cantharis, the blister-fly,
+and to _Melo�_, the oil-beetle) is parasitic on a kind of Bee
+(Anthophora), which excavates subterranean galleries, each leading to a
+cell. The eggs of the _Sitaris_, which are deposited at the entrance of
+these galleries, are hatched at the end of September or beginning of
+October; and M. Fabre not unnaturally expected that the young larv�,
+which are active little creatures with six serviceable legs (Fig. 9),
+would at once eat their way into the cells of the Anthophora. No such
+thing: till the month of April following they remain without leaving
+their birthplace, and consequently without food; nor do they in this
+long time change either in form or size. M. Fabre ascertained this, not
+only by examining the burrows of the _Anthophoras_, but also by direct
+observation of some young larv� kept in captivity. In April, however,
+his captives at last awoke from their long lethargy, and hurried
+anxiously about their prisons. Naturally inferring that they were in
+search of food, M. Fabre supposed that this would consist either of the
+larv� or pup� of the Anthophora, or of the honey with which it stores
+its cell. All three were tried without success. The first two were
+neglected, and the larv�, when placed on the latter, either hurried
+away, or perished in the attempt, being evidently unable to deal with
+the sticky substance. M. Fabre was in despair: "Jamais exp�rience," he
+says, "n'a �prouv� pareille d�confiture. Larves, nymphes, cellules,
+miel, je vous ai tous offert; que voulez-vous donc, bestioles maudites?"
+The first ray of light came to him from our countryman, Newport, who
+ascertained that a small parasite found by L�on Dufour on one of the
+wild bees, and named by him Triungulinus, was, in fact, the larva of
+_Melo�_. The larv� of _Sitaris_ much resembled Dufour's Triungulinus;
+and acting on this hint, M. Fabre examined many specimens of Anthophora,
+and found on them at last the larv� of his _Sitaris_. The males of
+Anthophora emerge from the pup� sooner than the females, and M. Fabre
+ascertained that, as they come out of their galleries, the little
+_Sitaris_ larv� fasten upon them. Not, however, for long: instinct
+teaches them that they are not yet in the straight path of development;
+and, watching their opportunity, they pass from the male to the female
+bee. Guided by these indications, M. Fabre examined several cells of the
+Anthophora: in some, the egg of the Anthophora floated by itself on the
+surface of the honey; in others, on the egg, as on a raft, sat the still
+more minute larva of the _Sitaris_. The mystery was solved. At the
+moment when the egg is laid the _Sitaris_ larva springs upon it. Even
+while the poor mother is carefully fastening up her cell, her mortal
+enemy is beginning to devour her offspring: for the egg of the
+Anthophora serves not only as a raft, but as a repast. The honey which
+is enough for either, would be too little for both; and the _Sitaris_,
+therefore, at its first meal, relieves itself from its only rival. After
+eight days the egg is consumed, and on the empty shell the _Sitaris_
+undergoes its first transformation, and makes its appearance in a very
+different form, as shown in Fig. 10.
+
+The honey which was fatal before is now necessary; the activity which
+before was necessary is now useless; consequently, with the change of
+skin, the active, slim larva changes into a white, fleshy grub, so
+organized as to float on the surface of the honey, with the mouth
+beneath, and the spiracles above the surface: "gr�ce � l'embonpoint du
+ventre," says M. Fabre, "la larve est � l'abri de l'asphyxie." In this
+state it remains until the honey is consumed; then the animal
+contracts, and detaches itself from its skin, within which the further
+transformations take place. In the next stage, which M. Fabre calls the
+pseudo-chrysalis (Fig. 11), the larva has a solid corneous envelope and
+an oval shape; and in its colour, consistency, and immobility reminds
+one of a Dipterous pupa. The time passed in this condition varies much.
+When it has elapsed, the animal moults again, again changes its form,
+and assumes that shown in Fig. 12; after this it becomes a pupa (Fig.
+13) without any remarkable peculiarities. Finally, after these wonderful
+changes and adventures, in the month of August the perfect _Sitaris_ (Pl.
+III., Fig. 4) makes its appearance.
+
+On the other hand, there are cases in which larv� diverge remarkably
+from the ordinary type of the group to which they belong, without, as it
+seems in our present imperfect state of information, any sufficient
+reason.
+
+Thus the ordinary type of Hymenopterous larva, as we have already seen,
+is a fleshy apod grub; although those of the leaf-eating and wood-boring
+groups, Tenthredinid� and Siricid� (Fig. 14), are caterpillars, more or
+less closely resembling those of Lepidoptera. There is, however, a group
+of minute Hymenoptera, the larv� of which reside within the eggs or
+larv� of other insects. It is difficult to understand why these larv�
+should differ from those of Ichneumons, which are also parasitic
+Hymenoptera, and should be, as will be seen by the accompanying figures,
+of such remarkable and grotesque forms. The first known of these curious
+larv� was observed by De Filippi,[13] who, having collected some of the
+transparent eggs of a small Beetle (_Rhynchites betuleti_), to his great
+surprise found more than half of them attacked by a parasite, which
+proved to be the larva of a minute Hymenopterous insect belonging to the
+Pteromalid�. Fig. 15 shows the egg of the Beetle, with the parasitic
+larva, which is represented on a larger scale in Fig. 16.
+
+[Illustration: FIG. 14, Larva of _Sirex_ (Westwood, loc. cit.). 15, Egg of
+_Rhynchites_, showing the parasitic Larva in the interior. 16, the
+parasitic Larva more magnified.]
+
+More recently this group has been studied by M. Ganin,[14] who thus
+describes the development of _Platygaster_. The egg, as in allied
+Hymenopterous families, for instance in _Cynips_, is elongated and
+club-shaped (Fig. 17). After a while a large nucleated cell appears in
+the centre (Fig. 18). This nucleated cell divides (Fig. 19) and
+subdivides. The outermost cells continue the same process, thus forming
+an outer investing layer. The central, on the contrary, enlarges
+considerably, and develops within itself a number of daughter cells
+(Figs. 20 and 21), which gradually form a mulberry-like mass, thus
+giving rise to the embryo (Fig. 22).
+
+[Illustration: FIG. 17, Egg of _Platygaster_ (after Ganin). 18, Egg of
+_Platygaster_ showing the central cell. 19, Egg of _Platygaster_ after the
+division of the central wall. 20, Egg of Platygaster more advanced. 21,
+Egg of _Platygaster_ more advanced. 22, Egg of Platygaster showing the
+rudiment of the embryo.]
+
+Ganin met with the larv� of _Platygaster_ in those of a small gnat,
+_Cecidomyia_. Sometimes as many as fifteen parasites occurred in one gnat,
+but as a rule only one of these attained maturity. The three species of
+_Platygaster _differ considerably in form, as shown in Figs. 23-25. They
+creep about within the larva of _Cecidomyia_ by means of the strong hooked
+feet, _kf_, somewhat aided by movements of the tail. They possess a
+mouth, stomach, and muscles, but the nervous, vascular, and respiratory
+systems do not make their appearance until later. After some time the
+larva (Fig. 23) changes its skin, assuming the form represented in Fig.
+26. In this moult the last abdominal segment of the first larva is
+entirely thrown off: not merely the outer skin, as in the case of the
+other segments, but also the hypodermis and the muscles. This larva, as
+will be seen by the figure, resembles a barrel or egg in form, and is
+.870 mm. in length, the external appendages having disappeared, and the
+segments being indicated only by the arrangement of the muscles. _slkf_
+is the oesophagus leading into a wide stomach which occupies nearly
+the whole body, _gsae_ is the rudiment of the supra-oesophageal
+ganglia, _bsm_ the ventral nervous cords. The ventral nervous mass has
+the form of a broad band, with straight sides; it consists of embryonal
+cells, and remains in this undeveloped condition during the whole larval
+state.
+
+[Illustration: FIG. 23, Larva of _Platygaster_ (after Ganin)--_mo_, mouth;
+_a_, antenna; _kf_, hooked feet; _z_, toothed process; _lfg_, lateral
+process; _f_, branches of the tail. 24, Larva of another species of
+_Platygaster_. The letters indicate the same parts as in the preceding
+figure. 25, Larva of a third species of _Platygaster_. The letters
+indicate the same parts as in the preceding figures. 26, Larva of
+_Platygaster_ in the second stage--_mo_, mouth; _slkf_, oesophagus;
+_gsae_, supra-oesophageal ganglion; _lm_, muscles; _bsm_, nervous
+system; _ga_, _gh_, rudiments of the reproductive glands. 27, Larva of
+_Platygaster_ in the third stage--_mo_, mouth; _md_, mandibles; _gsae_,
+supra-oesophageal ganglion; _slk_, oesophagus; _ag_, ducts of the
+salivary glands; _bnm_, ventral nervous system; _sp_, salivary glands;
+_msl_, stomach; _im_, imaginal discs; _tr_, trache�; _fk_, fatty tissue;
+_ed_, intestine; _ga_, rudiments of reproductive organs; _ew_, wider
+portion of intestine; _ao_, posterior opening.]
+
+At the next moult the larva enters its third state, which, as far as the
+external form (Fig. 27) is concerned, differs from the second only in
+being somewhat more elongated. The internal organs, however, are much
+more complex and complete. The trache� have made their appearance, and
+the mouth is provided with a pair of mandibles. From this point the
+metamorphoses of _Platygaster_ do not appear to differ materially from
+those of other parasitic Hymenoptera.
+
+An allied genus, _Polynema_, has also very curious larv�. The perfect
+insect is aquatic in its habits, swimming by means of its wings; flying,
+if we may say so, under water.[15] It lays its eggs inside those of
+Dragon-flies; and the embryo, as shown in Fig. 28, has the form of a
+bottle-shaped mass of undifferentiated embryonal cells, covered by a
+thin cuticle, but without any trace of further organization. Protected
+by the egg-shell of the Dragon-fly, and bathed in the nourishing fluid
+of the Dragon-fly's egg, the young _Polynema_ imbibes nourishment through
+its whole surface, and increases rapidly in size. The digestive canal
+gradually makes its appearance; the cellular mass forms a new skin
+beneath the original cuticle, distinctly divided into segments, and
+provided with certain appendages. After a while the old cuticle is
+thrown off, and the larva gradually assumes the form shown in Fig. 29.
+The subsequent metamorphoses of _Polynema_ offer no special peculiarities.
+
+[Illustration: FIG. 28, Embryo of _Polynema_ (after Ganin). 29, Larva of
+_Polynema_--_asch_, rudiments of the antenna; _flsch_, rudiments of the
+wings; _bsch_, rudiments of the legs; _vfg_. lateral projections;
+_gsch_, rudiments of the ovipositor; _fk_, fatty tissue.]
+
+From these facts--and, if necessary, many more of the same nature might
+have been brought forward--it seems to me evident that while the form of
+any given larva depends to a certain extent on the group of insects to
+which it belongs, it is also greatly influenced by the external
+conditions to which it is subjected; that it is a function of the life
+which the larva leads and of the group to which it belongs.
+
+The larv� of insects are generally regarded as being nothing more than
+immature states--as stages in the development of the egg into the
+imago; and this might more especially appear to be the case with those
+insects in which the larv� offer a general resemblance in form and
+structure (excepting of course so far as relates to the wings) to the
+perfect insect. Nevertheless we see that this would be a very incomplete
+view of the case. The larva and pupa undergo changes which have no
+relation to the form which the insect will ultimately assume. With a
+general tendency to this goal, as regards size and the development of
+the wings, there are coincident other changes having reference only to
+existing wants and condition. Nor is there in this, I think, anything
+which need surprise us. External circumstances act on the insect in its
+preparatory states, as well as in its perfect condition. Those who
+believe that animals are susceptible of great, though gradual, change
+through the influence of external conditions, whether acting, as Mr.
+Darwin has suggested, through natural selection, or in any other manner,
+will see no reason why these changes should be confined to the mature
+animal. And it is evident that creatures which, like the majority of
+insects, live during the successive periods of their existence in very
+different circumstances, may undergo considerable changes in their
+larval organization, in consequence of forces acting on them while in
+that condition; not, indeed, without affecting, but certainly without
+affecting to any corresponding extent, their ultimate form.
+
+I conclude, therefore, that the form of the larva in insects, whenever
+it departs from the hexapod _Campodea_ type, has been modified by the
+conditions under which it lives. The external forces acting upon it are
+different from those which affect the mature form; and thus changes are
+produced in the young which have reference to its immediate wants,
+rather than to its final form.
+
+And, lastly, as a consequence, that metamorphoses may be divided into
+two kinds, developmental and adaptional or adaptive.
+
+
+
+
+CHAPTER III.
+
+_ON THE NATURE OF METAMORPHOSES._
+
+
+In the preceding chapters we have considered the life history of insects
+after they have quitted the egg; but it is obvious that to treat the
+subject in a satisfactory manner we must take the development as a
+whole, from the commencement of the changes in the egg, up to the
+maturity of the animal, and not suffer ourselves to be confused by the
+fact that insects leave the egg in very different stages of embryonal
+development. For though all young insects when they quit the egg are
+termed "larv�," whatever their form may be (the case of the so-called
+Pupipara not constituting a true exception), still it must be remembered
+that some of these larv� are much more advanced than others. It is
+evident that the larva of a fly, as regards its stage of development,
+corresponds in reality neither with that of a moth nor with that of a
+grasshopper. The maggots of flies, in which the appendages of the head
+are rudimentary, belong to a lower grade than the grubs of bees, &c.,
+which have antenn�, mandibles, maxill�, labrum, labium, and, in fact,
+all the mouth parts of a perfect insect.
+
+The caterpillars of Lepidoptera are generally classed with the vermiform
+larva of Diptera and Hymenoptera, and contrasted with those of
+Orthoptera, Hemiptera, &c.; but, in truth, the possession of thoracic
+legs places them, together with the similar larv� of the Tenthredinid�,
+on a decidedly higher level. Thus, then, the period of growth (that in
+which the animal eats and increases in size) occupies sometimes one
+stage in the development of an insect, sometimes another; sometimes, as
+for instance in the case of _Chlo�on_, it continues through more than
+one; or, in other words, growth is accompanied by development. But, in
+fact, the question is even more complicated than this. It is not only
+that the larv� of insects at their birth offer the most various grades
+of development, from the grub of a fly to the young of a grasshopper or
+a cricket; but that, if we were to classify larv� according to their
+development, we should have to deal, not with a simple case of
+gradations only, but with a series of gradations, which would be
+different according to the organ which we took as our test.
+
+Apart, however, from the adaptive changes to which special reference was
+made in the previous chapter, the differences which larv� present are
+those of gradation, not of direction. The development of a grasshopper
+does not pursue a different course from that of a butterfly, but the
+embryo attains a higher state before quitting the egg in the former than
+in the latter: while in most Hymenoptera, as for instance in Bees,
+Wasps, Ants, &c., the young are hatched without thoracic appendages; in
+the Orthoptera, on the contrary, the legs are fully developed before the
+young animal quits the egg.
+
+Prof. Owen,[16] indeed, goes so far as to say that the Orthoptera and
+other Homomorphous insects are, "at one stage of their development,
+apodal and acephalous larv�, like the maggot of the fly; but instead of
+quitting the egg in this stage, they are quickly transformed into
+another, in which the head and rudimental thoracic feet are developed to
+the degree which characterizes the hexapod larv� of the _Carabi_ and
+_Petalocera_."
+
+[Illustration: FIG. 30, Egg of _Phryganea_ (Mystacides)--_A_^1,
+mandibular segment; _C_^1 to _C_^5, maxillary, labial, and three
+thoracic segments; _D_, abdomen (after Zaddach). 31, Egg of _Phryganea_
+somewhat more advanced--_b_, mandibles; _c_, maxill�; _cfs_, rudiments
+of the three pairs of legs.]
+
+I quite believe that this may have been true of such larv� at an early
+geological period, but the fact now appears to be, so far at least as
+can be judged from the observations yet recorded, that the legs of those
+larv� which leave the egg with these appendages generally make their
+appearance before the body-walls have closed, or the internal organs
+have approached to completion. Indeed, when the legs first appear, they
+are merely short projections, which it is not always easy to distinguish
+from the segments themselves. It must, however, be admitted, that the
+observations are neither so numerous, nor in most cases so full, as
+could be wished.
+
+Fig. 30 represents an egg of a May-fly (_Phryganea_), as represented by
+Zaddach in his excellent memoir,[17] just before the appearance of the
+appendages. It will be seen that a great part of the yolk is still
+undifferentiated, that the side walls are incomplete, the back quite
+open, and the segments merely indicated by undulations. This stage is
+rapidly passed through, and Zaddach only once met with an egg in this
+condition; in every other specimen which had indications of segments,
+the rudiments of the legs had also made their appearance, as in Fig. 31,
+which, however, as will be seen, does not in other respects show much
+advance on Fig. 30.
+
+Again in _Aphis_, the embryology of which has been so well worked out by
+Huxley,[18] the case is very similar, although the legs are somewhat
+later in making their appearance. When the young was 1/140th of an inch
+in length, he found the cephalic portion of the embryo beginning, he
+says, "to extend upwards again over the anterior face of the germ, so as
+to constitute its anterior and a small part of its superior wall. This
+portion is divided by a median fissure into two lobes, which play an
+important part in the development of the head, and will be termed the
+'procephalic lobes.' I have already made use of this term for the
+corresponding parts in the embryos of Crustacea. The rudimentary thorax
+presents traces of a division into three segments; and the dorso-lateral
+margins of the cephalic blastoderm, behind the procephalic lobes, have a
+sinuous margin. It is in embryos between this and 1/100th of an inch in
+length, that the rudiments of the appendages make their appearance; and
+by the growth of the cephalic, thoracic, and abdominal blastoderm,
+curious changes are effected in the relative position of those regions."
+
+In _Chrysopa oculata_, one of the Hemerobiid�, Packard has described[19]
+and figured a stage in which the body segments have made their
+appearance, but in which he says "there are no indications of limbs. The
+primitive band is fully formed, the protozorites being distinctly
+marked, the transverse impressed lines indicating the primitive segments
+being distinct, and the median furrow easily discerned." Here also,
+again, the dorsal walls are incomplete, and the internal organs as yet
+unformed.
+
+In certain Dragon-flies (_Calepteryx_), and _Hemiptera_ (_Hydrometra_), the
+legs, according to Brandt,[20] appear at a still earlier stage.
+
+According to the observations of K�lliker,[21] it would appear that in
+the Coleopterous genus _Donacia_ the segments and appendages appear
+simultaneously.
+
+K�lliker himself, however, frankly admits that "me� de hoc insecto
+observationes satis sunt manca," and it is possible that he may never
+have met with an embryo in the state immediately preceding the
+appearance of the legs; especially as it appears from the observations
+of Kowalevski that in _Hydrophilus_ the appendages do not make their
+appearance until after the segments.[22]
+
+On the whole, as far as we can judge from the observations as yet
+recorded, it seems that in Homomorphous insects the ventral wall is
+developed and divided into segments, before the appearance of the legs;
+but that the latter are formed almost simultaneously with the cephalic
+appendages, and before either the dorsal walls of the body or the
+internal organs.
+
+[Illustration: FIG. 32.--Egg of _Pholcus opilionides_ (after Clapar�de).]
+
+As it is interesting, from this point of view, to compare the
+development of other Articulata with that of insects, I give a figure
+(Fig. 32), representing an early stage in the development of a spider
+(_Pholcus_) after Clapar�de,[23] who says, "C'est � ce moment qu'a lieu
+la formation des _protozonites_ ou segments primordiaux du corps de
+l'embryon. Le rudiment ventral s'�paissit suivant six z�nes dispos�es
+transversalement entre le capuchon anal et le capuchon c�phalique."
+
+[Illustration: FIG. 33.--Embryo of _Julus_ (after Newport).]
+
+Among Centipedes the development of _Julus_ has been described by
+Newport.[24] The first period, from the deposition of the egg to the
+gradual bursting of the shell, and exposure of the embryo within it,
+which, however, remains for some time longer in connection with the
+shell, lasts for twenty-five days. The segments of the body, originally
+six in number, make their appearance on the twentieth day after the
+deposition of the egg, at which time there were no traces of legs. The
+larva, when it leaves the egg, is a soft, white, legless grub (Fig. 33),
+consisting of a head and seven segments, the head being somewhat firmer
+in texture than the rest of the body. It exhibits rudimentary antenn�,
+but the legs are still only represented by very slight papilliform
+processes on the undersides of the segments to which they belong.
+
+As already mentioned, it is possible that at one time the vermiform
+state of the Homomorphous insects--which, as we have seen, is now so
+short, and passed through at so early a stage of development--was more
+important, more prolonged, and accompanied by a more complete condition
+of the internal organs. The compression, and even disappearance of those
+embryonal stages which are no longer adapted to the mode of life--which
+do not benefit the animal--is a phenomenon not without a parallel in
+other parts of the animal or even of the vegetable kingdom. Just as in
+language long compound words have a tendency to concision, and single
+letters sometimes linger on, indicating the history of a word, like the
+"l" in "alms," or the "b" in "debt," long after they have ceased to
+influence the sound; so in embryology useless stages, interesting as
+illustrations of past history, but without direct advantage under
+present conditions, are rapidly passed through, and even, as it would
+appear, in some cases altogether omitted.
+
+[Illustration: FIG. 34.--Colony of _Bougainvillea fruticosa_, natural
+size, to the underside of a piece of floating timber (after Allman).]
+
+For instance, among the Hydroida, in the great majority of cases, the
+egg produces a body more or less resembling the common _Hydra_ of our
+ponds, and known technically as the "trophosome," which develops into
+the well-known Medus� or jelly-fishes. The group, however, for which
+Prof. Allman has proposed the term Monopsea,[25] and of which the genus
+_�gina_ may be taken as the type, is, as he says, distinguished by the
+absence of a hydriform stage, "the ovum becoming developed through
+direct metamorphosis into a medusiform body, just as in the other orders
+it is developed into a hydriform body." Fig. 34 represents, after
+Allman, a colony of _Bougainvillea fruticosa_ of the natural size. It is
+a British species, which is found growing on buoys, floating timber,
+&c., and, says Allman,[26] "when in health and vigour, offers a
+spectacle unsurpassed in interest by any other species--every branchlet
+crowned by its graceful hydranth and budding with Medus� in all stages
+of development (Fig. 35), some still in the condition of minute buds, in
+which no trace of the definite Medusa-form can yet be detected; others,
+in which the outlines of the Medusa can be distinctly traced within the
+transparent _ectoth�que_ (external layer); others, again, just casting
+off this thin outer pellicle, and others completely freed from it,
+struggling with convulsive efforts to break loose from the colony, and
+finally launched forth in the full enjoyment of their freedom into the
+surrounding water. I know of no form in which so many of the
+characteristic features of a typical hydroid are more finely expressed
+than in this beautiful species."
+
+[Illustration: FIG. 35.--Portion of colony of _Bougainvillea fruticosa_,
+more magnified.]
+
+[Illustration: FIG. 36.--The Medusa form of the same species.]
+
+Fig. 36 represents the Medusa form of this species, and the development
+thus described may be regarded as typical of the Hydroida; yet, as
+already mentioned, the �ginid� do not present us with any stage
+corresponding to the fixed condition of _Bougainvillea_, but, on the
+contrary, are developed into Medus� direct from the egg.
+
+On the other hand, there are groups in which the Medusiform stage
+becomes less and less important.
+
+[Illustration: FIG. 37, Larva of Prawn, Nauplius stage (after F.
+M�ller). 38, Larva of Prawn, more advanced, Zo�a stage.]
+
+The great majority of the higher Crustacea go through well-marked
+metamorphoses. Figs. 37 and 38 represent two stages in the development
+of the prawn. In the first (Fig. 37), representing the young animal as
+it quits the egg, the body is more or less oval and unsegmented; there
+is a median frontal eye, and three pairs of natatory feet, the first
+pair simple, while the two posterior are two-branched. Very similar
+larv� occur in various other groups of Crustacea. They were at first
+regarded as mature forms, and O. F. M�ller gave them the name of
+Nauplius. So also, the second or Zo�a form (Fig. 38) was at first
+supposed to be a mature animal, until its true nature was discovered by
+Vaughan Thompson.
+
+The Zo�a form of larva differs from the perfect prawn or crab in the
+absence of the middle portion of the body and its appendages. The
+mandibles have no palpi, the maxillipeds or foot-jaws are used as feet,
+whereas in the mature form they serve as jaws. Branchi� are either
+wanting or rudimentary, respiration being principally effected through
+the walls of the carapace. The abdomen and tail are destitute of
+articulate appendages. The development of Zo�a into the perfect animal
+has been well described by Mr. Spence Bate[27] in the case of the common
+crab (_Carcinus m�nas_).
+
+All crabs, as far as we know, with the exception of a species of land
+crab (_Gegarcinus_), described by Westwood, pass through a stage more or
+less resembling that shown in Fig. 38. On the other hand, the great
+group of Edriopthalma, comprising Amphipoda (shore-hoppers, &c.) and
+Isopoda (wood-lice, &c.) pass through no such metamorphosis; the
+development is direct, as in the Orthoptera. It is true that one
+species, _Tanais Dulongii_, though a typical Isopod in form and general
+character, is said to retain in some points, and especially in the mode
+of respiration, some peculiarities of the Zo�a type; but this is quite
+an exceptional case. In _Mysis_, says F. M�ller,[28] "there is still a
+trace of the Nauplius stage; being transferred back to a period when it
+had not to provide for itself, the Nauplius has become degraded into a
+mere skin; in _Ligia_ this larva-skin has lost the traces of limbs, and
+in _Philoscia_ it is scarcely demonstrable."
+
+The Echinodermata in most cases "go through a very well-marked
+metamorphosis, which often has more than one larval stage.... The mass
+of more or less differentiated sarcode, of which the larva, or
+pseud-embryo, as opposed to the Echinoderm within it, is made up, always
+carries upon its exterior certain bilaterally-arranged ciliated bands,
+by the action of which the whole organism is moved from place to place;
+and it may be strengthened by the super-addition to it of a framework
+of calcareous rods."[29] M�ller considered that the mouth and pharynx of
+the larva were either absorbed or cast off with the calcareous rods, but
+were never converted into the corresponding organs of the perfect
+Echinoderm. According to A. Agassiz, however, this is not the case, but
+on the contrary "the whole larva and all its appendages are gradually
+drawn into the body, and appropriated."[30]
+
+Fig. 39 represents the larva of a sea-egg (_Echino cidaris_) after
+M�ller.[31] The body is transparent, shaped somewhat like a double
+easel, but with two long horns in front, which, as well as the posterior
+processes, are supported by calcareous rods. This larva swims by means
+of minute vibratile hairs, or cili�. It has a mouth, stomach, and in
+fact a well-defined alimentary canal; but no nerves or other internal
+organs have yet been discovered in it. After swimming about in this
+condition for a while, it begins to show signs of change. An involution
+of the integument takes place on one side of the back, and continues to
+deepen till it reaches a mass or store of what is called blastema, or
+the raw material of the animal body. This blastema then begins to
+change, and gradually assumes the form of the perfect Echinoderm.[32]
+
+[Illustration: FIG. 39.--Larva of _Echino cidaris_, seen from above � 6/10
+(after M�ller).]
+
+[Illustration: FIG. 40, Larva of _Echinus_, � 100. _A_, front arm; _F_,
+arms of the mouth process; _B_, posterior side arm; _E_(1), accessory
+arm of the mouth process; _a_, mouth; _a'_, oesophagus; _b_, stomach;
+_b'_, intestine; _o_, posterior orifice; _d_, ciliated bands; _f_,
+ciliated epaulets; _c_, disc of future _Echinus_ (after M�ller).]
+
+Fig. 40 represents a larva, probably of another sea-egg (_Echinus
+lividus_), from the Mediterranean, and shows the commencement of the
+sea-egg within the body of the larva. The capital letters denote the
+different arms: _a_ is the mouth, _a'_ the oesophagus, _b_ the
+stomach, _b'_ the intestine, _f_ the ciliated lobes or epaulets, _c_ the
+young sea-egg.
+
+The development of the beautiful _Comatula rosacea_ (Fig. 41) has been
+described in the "Philosophical Transactions," by Prof. Wyville Thomson
+and Dr. Carpenter.[33] The larva quits the egg, as shown in Fig. 42, in
+the form of an oval body about 1/30 inch in length, something like a
+barrel, surrounded by four bands or hoops of long vibratile hairs or
+cili�. There is also a tuft of still longer hairs at the narrower
+posterior end of the body. Gradually a number of minute calcareous
+spines and plates make their appearance (Fig. 43) in the body of this
+larva, and at length arrange themselves in a definite order, so as to
+form a bent calcareous club or rod with an enlarged head.
+
+[Illustration: FIG. 41.--_Comatula rosacea_ (after Forbes).]
+
+[Illustration: FIG. 42, Larva of Comatula rosacea (after Thomson). 43,
+Larva of _Comatula rosacea_, more advanced. 44, Larva of Comatula rosacea,
+in the Pentacrinus state.]
+
+As this process continues, the little creature gradually loses its power
+of swimming, and, sinking to the bottom, looses the bands of cili�, and
+attaches itself by its base to some stone or other solid substance, the
+knob of the club being free. The calcareous framework increases in size,
+and the expanded head forms itself into a cup, round which from five to
+fifteen delicate tentacles, as shown in Fig. 44, make their appearance.
+
+In this stage the young animal resembles one of the stalked Crinoids, a
+family of Echinoderms very abundant in earlier geological periods, but
+which has almost disappeared, being, as we see, now represented by the
+young states of existing more advanced, free, species. This attached,
+plant-like condition of _Comatula_ was indeed at first supposed to be a
+mature form, and was named Pentacrinus; but we now know that it is only
+a stage in the development of _Comatula_. The so-called Pentacrinus
+increases considerably in size, and after various gradual changes, which
+time does not now permit me to describe, quits the stalk, and becomes a
+free _Comatula_.
+
+The metamorphoses of the Starfishes are also very remarkable. Sars
+discovered, in the year 1835, a curious little creature about an inch in
+length, which he named _Bipinnaria asterigera_ (Figs. 45-47), and which
+he then supposed to be allied to the ciliograde Medus�. Subsequent
+observations, however, made in 1844, suggested to him that it was the
+larva of a Starfish, and in 1847 MM. Koren and Danielssen satisfied
+themselves that this was the case.
+
+Figs. 45 and 46 represent the front and side view of a Bipinnaria found
+by M�ller[34] near Marseilles. _a_ is the mouth, _b_ the oesophagus,
+_c_ the stomach, _c_' the intestine. Fig. 47 represents a somewhat older
+specimen, in which the Starfish (_k_) is already beginning to make its
+appearance.
+
+[Illustration: FIG. 45, Larva of Starfish (Bipinnaria), � 100 (after
+M�ller). 46, Larva of Starfish (Bipinnaria), � 100, seen from the
+side--_a_, mouth; _b_, oesophagus; _c_, stomach; _c'_, intestine. 47,
+Larva of another Bipinnaria, showing the commencement of the
+Starfish--_g_, canal of the ciliated sac; _i_, rudiments of tentacles;
+_d_, ciliated band.]
+
+But while certain Starfishes thus go through metamorphoses similar in
+character, and not less remarkable than those of sea-eggs, there are
+others--as, for instance, the genus _Asteracanthion_--in which development
+may be said to be direct--the organs and appendages special to the
+Pseud-embryo being in abeyance; while in another genus, _Pteraster_, they
+are reduced to a mere investing membrane.[35]
+
+Among the Ophiurans also we find two well-marked types of development.
+Some passing through metamorphoses, while others, as for instance
+_Ophiopholis bellis_, "is developed very much after the method of
+_Asteracanthion M�lleri_, without passing through the Plutean
+stage."[36]
+
+Even in the same species of Echinoderm the degree of development
+attained by the larva differs to a certain extent according to the
+temperature, the supply of food, &c. Thus in _Comatula_, specimens which
+are liberally supplied with sea-water, and kept warm, hurry as it were
+through their early stages, and the free larva becomes distorted by the
+growing Pentacrinus (see Fig. 43), almost before it has attained its
+perfect form. On the other hand, under less favourable conditions, if
+the temperature is low and food less abundant, the early stages are
+prolonged, the larva is longer lived, and reaches a much higher degree
+of independent development. Similar differences occur in the development
+of other animals, as for instance, in the Hydroids,[37] and among the
+insects themselves, in Flies;[38] and it is obvious that these facts
+throw much light on the nature and origin of the metamorphoses of
+insects, which subject we shall now proceed to consider.
+
+
+
+
+CHAPTER IV.
+
+_ON THE ORIGIN OF METAMORPHOSES._
+
+
+The question still remains, Why do insects pass through metamorphoses?
+Messrs. Kirby and Spence tell us they "can only answer that such is the
+will of the Creator;"[39] this, however, is a general confession of
+faith, not an explanation of metamorphoses. So indeed they themselves
+appear to have felt; for they immediately proceed to make a suggestion.
+"Yet one reason," they say, "for this conformation may be hazarded. A
+very important part assigned to insects in the economy of nature, as we
+shall hereafter show, is that of speedily removing superabundant and
+decaying animal and vegetable matter. For such agents an insatiable
+voracity is an indispensable qualification, and not less so unusual
+powers of multiplication. But these faculties are in a great degree
+incompatible; an insect occupied in the work of reproduction could not
+continue its voracious feeding. Its life, therefore, after leaving the
+egg, is divided into three stages."
+
+But there are some insects--as, for instance, the Aphides--which
+certainly are not among the least voracious, and which grow and breed at
+the same time. There are also many scavengers among other groups of
+animals--such, for instance, as the dog, the pig, and the vulture--which
+undergo no metamorphosis.
+
+It is certainly true that, as a general rule, growth and reproduction do
+not occur together; and it follows, almost as a necessary consequence,
+that in such cases the first must precede the second. But this has no
+immediate connection with the occurrence of metamorphoses. The question
+is not, why an insect does not generally begin to breed until it has
+ceased to grow, but why, in attaining to its perfect form, it passes
+through such remarkable changes; why these changes are so sudden and
+apparently violent; and why they are so often closed by a state of
+immobility--that of the chrysalis or pupa; for undoubtedly the quiescent
+and death-like condition of the pupa is one of the most remarkable
+phenomena of insect-metamorphoses.
+
+In the first place, it must be observed that many animals which differ
+considerably in their mature state, resemble one another more nearly
+when young. Thus birds of the same genus, or of closely allied genera,
+which, when mature, differ much in colour, are often very similarly
+coloured when young. The young of the lion and the puma are often
+striped, and the foetal Black whale has teeth, like its ally the Sperm
+whale.
+
+In fact, the great majority of animals do go through well-marked
+metamorphoses, though in many cases they are passed through within the
+egg, and thus do not come within the popular ken. "La larve," says,
+Quatrefages, "n'est qu'un embryon � vie ind�pendante."[40] Those
+naturalists who accept in any form the theory of evolution, consider
+that "the embryonal state of each species reproduces more or less
+completely the form and structure of its less modified progenitors."[41]
+"Each organism," says Herbert Spencer,[42] "exhibits within a short
+space of time a series of changes which, when supposed to occupy a
+period indefinitely great, and to go on in various ways instead of one
+way, give us a tolerably clear conception of organic evolution in
+general."
+
+The naturalists of the older school do not, as Darwin and Fritz M�ller
+have already pointed out, dispute these facts, though they explain them
+in a different manner--generally by the existence of a supposed tendency
+to diverge from an original type. Thus Johannes M�ller says, "The idea
+of development is not that of mere increase of size, but that of
+progress from what is not yet distinguished, but which potentially
+contains the distinction in itself, to the actually distinct. It is
+clear that the less an organ is developed, so much the more does it
+approach the type, and that during its development it acquires more and
+more peculiarities. The types discovered by comparative anatomy and
+developmental history must therefore agree." And again, "What is true in
+this idea is, that every embryo at first bears only the type of its
+section, from which the type of the class, order, &c., is only
+afterwards developed." Agassiz also observes that "the embryos of
+different animals resemble each other the more the younger they are."
+
+There are, no doubt, cases in which the earlier states are rapidly
+passed through, or but obscurely indicated; yet we may almost state it
+as a general proposition, that either before or after birth animals
+undergo metamorphoses. The state of development of the young animal at
+birth varies immensely. The kangaroo (_Macropus major_), which attains a
+height of seven feet ten inches, does not when born exceed one inch and
+two lines in length; the chick leaves the egg in a much more advanced
+condition than the thrush; and so, among insects, the young cricket is
+much more highly developed, when it leaves the egg, than the larva of
+the fly or of the bee; and, as I have already mentioned, differences
+occur even within the limit of one species, though not of course to
+anything like the same extent.
+
+In oviparous animals the condition of the young at birth depends much on
+the size of the egg: where the egg is large, the abundant supply of
+nourishment enables the embryo to attain a high stage of development;
+where the egg is small, and the yolk consequently scanty, the embryo
+requires an additional supply of food before it can do so. In the former
+case the embryo is more likely to survive; but when the eggs are large,
+they cannot be numerous, and a multiplicity of germs may be therefore in
+some circumstances a great advantage. Even in the same species the
+development of the egg presents certain differences.[43]
+
+The metamorphoses of insects depend then primarily on the fact that the
+young quit the egg at a more or less early stage of development; and
+that consequently the external forces, acting upon them in this state,
+are very different from those by which they are affected when they
+arrive at maturity.
+
+Hence it follows that, while in many instances mature forms, differing
+greatly from one another, arise from very similar larv�, in other cases,
+as we have seen, among some the parasitic Hymenoptera, insects agreeing
+closely with one another, are produced from larv� which are very unlike.
+The same phenomenon occurs in other groups. Thus, while in many cases
+very dissimilar jelly-fishes arise from almost identical Hydroids, we
+have also the reverse of the proposition in the fact that in some
+species, Hydroids of an entirely distinct character produce very similar
+Medus�.[44]
+
+We may now pass to the second part of our subject: the apparent
+suddenness and abruptness of the changes which insects undergo during
+metamorphosis. But before doing so I must repeat that these changes are
+not always, even apparently, sudden and great. The development of an
+Orthopterous insect, say a grasshopper, from its leaving the egg to
+maturity, is so gradual that the ordinary nomenclature of entomological
+works (larva state and pupa state) does not apply to it; and even in the
+case of Lepidoptera, the change from the caterpillar to the chrysalis
+and from this to the butterfly is in reality less rapid than might at
+first sight be supposed; the internal organs are metamorphosed very
+gradually, and even the sudden and striking change in external form is
+very deceptive, consisting merely of a throwing off of the outer
+skin--the drawing aside, as it were of a curtain and the revelation of a
+form which, far from being new, has been in preparation for days;
+sometimes even for months.
+
+Swammerdam, indeed, supposed (and his view was adopted by Kirby and
+Spence) that the larva contained within itself "the germ of the future
+butterfly, enclosed in what will be the case of the pupa, which is
+itself included in three or more skins, one over the other, that will
+successively cover the larva." This was a mistake; but it is true that,
+if a larva be examined shortly before it is full grown, the future pupa
+may be traced within it. In the same manner, if we examine a pupa which
+is about to disclose the butterfly, we find the future insect, soft
+indeed and imperfect, but still easily recognizable, lying more or less
+loosely within the pupa-skin.
+
+One important difference between an insect and a vertebrate animal is,
+that whereas in the latter--as, for instance, in ourselves--the muscles
+are attached to an internal bony skeleton, in insects no such skeleton
+exists. They have no bones, and their muscles are attached to the skin;
+whence the necessity for the hard and horny dermal investment of
+insects, so different from the softness and suppleness of our own skin.
+The chitine, or horny substance, of which the outside of an insect
+consists, is formed by a layer of cells lying beneath it, and, once
+secreted, cannot be altered. From this the result is, that without a
+change of skin, a change of form is impossible. In some cases, as for
+instance in _Chlo�on_, each change of skin is accompanied by a change of
+form, and thus the perfect insect is gradually evolved. In others, as in
+caterpillars, several changes of skin take place without any material
+alteration of form, and the change, instead of being spread over many,
+is confined to the last two moults.
+
+One explanation of this difference between the larv� which change their
+form with every change of skin, and those which do not, is, I believe,
+to be found in the structure of the mouth. That of the caterpillar is
+provided with a pair of strong jaws, fitted to eat leaves; and the
+digestive organs are adapted for this kind of food. On the contrary, the
+mouth of the butterfly is suctorial; it has a long proboscis,
+beautifully adapted to suck the nectar from flowers, but which would be
+quite useless, and indeed only an embarrassment to the larva. The
+digestive organs also of the butterfly are adapted for the assimilation,
+not of leaves, but of honey. Now it is evident that if the mouth-parts
+of the larva were slowly metamorphosed into those of the perfect insect,
+through a number of small changes, the insect would in the meantime be
+unable to feed, and liable to perish of starvation in the midst of
+plenty. In the Orthoptera, and among those insects in which the changes
+are gradual, the mouth of the so-called larva resembles that of the
+perfect insect, and the principal difference consists in the presence of
+wings.
+
+Similar considerations throw much light on the nature of the chrysalis
+or pupa state--that remarkable period of death-like quiescence which is
+one of the most striking characteristics of insect metamorphosis. The
+quiescence of the pupa is mainly owing to the rapidity of the changes
+going on in it. In that of a butterfly, not only (as has been already
+mentioned) are the mouth and the digestive organs undergoing change, but
+the muscles are in a similar state of transition. The powerful ones
+which move the wings are in process of formation; and even the nervous
+system, by which the movements are set on foot and regulated, is in a
+state of rapid change.[45]
+
+It must not be forgotten that all insects are inactive for a longer or
+shorter space of time after each moult. The slighter the change, as a
+general rule, the shorter is the period of inaction. Thus, after the
+ordinary moult of a caterpillar, the insect only requires a short rest
+until the new skin is hardened. When, however, the change is great, the
+period of inaction is correspondingly prolonged. Most pup� indeed have
+some slight powers of motion; those which assume the chrysalis state in
+wood or beneath the ground usually come to the surface when about to
+assume the perfect state, and the aquatic pup� of certain Diptera swim
+about with much activity. Among the Neuroptera, certain families have
+pup� as quiescent as those of the Lepidoptera: others--as, for
+instance, _Raphidia_--are quiescent at first, but at length acquire
+sufficient strength to walk, though still enclosed within the pupa-skin:
+a power dependent partly on the fact that this skin is very thin. Others
+again--as, for instance, dragon-flies--are not quiescent on assuming the
+so-called pupa state for any longer time than at their other changes of
+skin. The inactivity of the pupa is therefore not a new condition
+peculiar to this stage, but a prolongation of the inaction which has
+accompanied every previous change of skin.
+
+Nevertheless the metamorphoses of insects have always seemed to me one
+of the greatest difficulties of the Darwinian theory. In most cases, the
+development of the individual reproduces to a certain extent that of the
+race; but the motionless, imbecile pupa cannot represent a mature form.
+No one, so far as I know, has yet attempted to explain, in accordance
+with Mr. Darwin's views, a life-history in which the mouth is first
+mandibulate and then suctorial, as, for example, in a butterfly. A clue
+to the difficulty may, I think, be found in the distinction between
+developmental and adaptive changes; to which I have called attention in
+a previous chapter. The larva of an insect is by no means a mere stage
+in the development of the perfect animal. On the contrary, it is subject
+to the influence of natural selection, and undergoes changes which have
+reference entirely to its own requirements and condition. It is evident,
+then, that while the embryonic development of an animal in the egg may
+be an epitome of its specific history, this is by no means the case
+with species in which the immature forms have a separate and
+independent existence. If an animal which, when young, pursues one mode
+of life, and lives on one kind of food, subsequently, either from its
+own growth in size and strength, or from any change of season, alters
+its habits or food, however slightly, it immediately becomes subject to
+the action of new forces: natural selection affects it in two different,
+and, it may be, very distinct manners, gradually tending to changes
+which may become so great as to involve an intermediate period of change
+and quiescence.
+
+There are, however, peculiar difficulties in those cases in which, as
+among the Lepidoptera, the same species is mandibulate as a larva, and
+suctorial as an imago. From this point of view _Campodea_ and the
+Collembola (_Podura_, &c.) are peculiarly interesting. There are in
+insects three principal types of mouth:--
+
+First, the mandibulate;
+
+Secondly, the suctorial; and
+
+Thirdly, that of _Campodea_ and the Collembola generally,
+
+in which the mandibles and maxill� are retracted, but have some freedom
+of motion, and can be used for biting and chewing soft substances. This
+type is, in some respects, intermediate between the other two. Assuming
+that certain representatives of such a type were placed under conditions
+which made a suctorial mouth advantageous, those individuals in which
+the mandibles and maxill� were best calculated to pierce or prick would
+be favoured by natural selection, and their power of lateral motion
+would tend to fall into abeyance; while, on the other hand, if
+masticatory jaws were an advantage, the opposite process would take
+place.
+
+There is yet a third possibility--namely, that during the first portion
+of life, the power of mastication should be an advantage, and during the
+second that of suction, or _vice vers�_. A certain kind of food might
+abound at one season and fail at another; might be suitable for the
+animal at one age and not at another. Now in such cases we should have
+two forces acting successively on each individual, and tending to modify
+the organization of the mouth in different directions. It cannot be
+denied that the innumerable variations in the mouth-parts of insects
+have special reference to their mode of life, and are of some advantage
+to the species in which they occur. Hence, no believer in natural
+selection can doubt the possibility of the three cases above suggested,
+the last of which seems to throw some light on the possible origin of
+species which are mandibulate in one period of life and not in another.
+Granting then the transition from the one condition to the other, this
+would no doubt take place contemporaneously with a change of skin. At
+such times we know that, even when there is no change in form, the
+softness of the organs temporarily precludes the insect from feeding for
+a time, as, for instance, in the case of caterpillars. If, however, any
+considerable change were involved, this period of fasting must be
+prolonged, and would lead to the existence of a third condition, that of
+the pupa, intermediate between the other two. Since the acquisition of
+wings is a more conspicuous change than any relating to the mouth, we
+are apt to associate with it the existence of a pupa-state: but the case
+of the Orthoptera (grasshoppers, &c.) is sufficient proof that the
+development of wings is perfectly compatible with permanent activity;
+the necessity for prolonged rest is in reality much more intimately
+connected with the change in the constitution of the mouth, although in
+many cases, no doubt, this is accompanied by changes in the legs, and in
+the internal organization. An originally mandibulate mouth, however,
+like that of a beetle, could not, I think, have been directly modified
+into a suctorial organ like that of a butterfly or a gnat, because the
+intermediate stages would necessarily be injurious. Neither, on the
+other hand, for the same reasons, could the mouth of the Hemiptera be
+modified into a mandibulate type like that of the Coleoptera. But in
+_Campodea_ and the _Collembola_ we have a type of animal closely
+resembling certain larv� which occur both in the mandibulate and
+suctorial series of insects, possessing a mouth neither distinctly
+mandibulate nor distinctly suctorial, but constituted on a peculiar
+type, capable of modification in either direction by gradual change,
+without loss of utility.
+
+In discussing this subject, it is necessary also to take into
+consideration the nature and origin of wings. Whence are they derived?
+why are there normally two pairs? and why are they attached to the
+meso-and meta-thorax? These questions are as difficult as they are
+interesting. It has been suggested, and I think with justice, that the
+wings of insects originally served for aquatic and respiratory
+purposes.
+
+In the larva of _Chlo�on_ (Pl. IV., Fig. 1), for instance, which in
+other respects so singularly resembles _Campodea_ (Pl. III., Fig. 5),
+several of the segments are provided with foliaceous expansions which
+serve as respiratory organs. These so-called branchi� are in constant
+agitation, and the muscles which move them in several points resemble
+those of true wings. It is true that in _Chlo�on_ the vibration of the
+branchi� is scarcely, if at all, utilized for the purpose of locomotion;
+the branchi� are, in fact, placed too far back to act efficiently. The
+situation of these branchi� differs in different groups; indeed, it
+seems probable that originally there were a pair on each segment. In
+such a case, those branchi� situated near the centre of the body,
+neither too much in front nor too far back, would serve the most
+efficiently as propellers: the same causes which determined the position
+of the legs would also affect the wings. Thus a division of labour would
+be effected; the branchi� on the thorax would be devoted to locomotion;
+those on the abdomen to respiration. This would tend to increase the
+development of the thoracic segments, already somewhat enlarged, in
+order to receive the muscles of the legs.
+
+That wings may be of use to insects under water is proved by the very
+interesting case of _Polynema natans_,[46] which uses its wings for
+swimming. This, however, is a rare case, and it is possible that the
+principal use of the wings was, primordially, to enable the mature forms
+to pass from pond to pond, thus securing fresh habitats and avoiding
+in-and-in breeding. If this were so, the development of wings would
+gradually have been relegated to a late period of life; and by the
+tendency to the inheritance of characters at corresponding ages, which
+Mr. Darwin has pointed out,[47] the development of wings would have thus
+become associated with the maturity of the insect. Thus the late
+acquisition of wings in the Insecta generally seems to be itself an
+indication of their descent from a stock which was at one period, if not
+originally, aquatic, and which probably resembled the present larv� of
+_Chlo�on_ in form, but had thoracic as well as abdominal branchi�.
+
+Finally, from the subject of metamorphosis we pass naturally to that
+most remarkable phenomenon which is known as the "Alternation of
+Generations:" for the first systematic view of which we are indebted to
+my eminent friend Prof Steenstrup.[48]
+
+I have always felt it very difficult to understand why any species
+should have been created in this double character; nor, so far as I am
+aware, has any explanation of the fact yet been attempted. Nevertheless
+insects offer, in their metamorphoses, a phenomenon not altogether
+dissimilar, and give a clue to the manner in which alternation of
+generations may have originated.
+
+The caterpillar owes its difference from the butterfly to the
+undeveloped state in which it leaves the egg; but its actual form is
+mainly due to the influence of the conditions under which it lives. If
+the caterpillar, instead of changing into one butterfly, produced
+several, we should have an instance of alternation of generations. Until
+lately, however, we knew of no such case among insects; each larva
+produced one imago, and that not by generation, but by development. It
+has long been known, indeed, that there are species in which certain
+individuals remain always apterous, while others acquire wings. Many
+entomologists, however, regard these abnormal individuals as perfect,
+though wingless insects; and therefore I shall found no argument upon
+these cases, although they appear to me deserving of more attention than
+they have yet received.
+
+Recently, however, Prof. Wagner[49] has discovered that, among certain
+small gnats, the larv� do not directly produce in all cases perfect
+insects, but give birth to other larv�, which undergo metamorphoses of
+the usual character, and eventually become gnats. His observations have
+been confirmed, as regards this main fact, by other naturalists; and
+Grimm has met with a species of _Chironomus_ in which the pup� lay
+eggs.[50]
+
+Here, then, we have a distinct case of alternation of generations, as
+characterized by Steenstrup. Probably other cases will be discovered in
+which insects undeniably in the larval state will be found fertile. Nay,
+it seems to me possible, if not probable, that some larv� which do not
+now breed may, in the course of ages, acquire the power of doing so. If
+this idea is correct, it shows how the remarkable phenomenon, known as
+alternation of generations, may have originated.
+
+Summing up, then, the preceding argument, we find among insects various
+modes of development; from simple growth on the one hand, to well-marked
+instances of the so-called alternation of generation on the other. In
+the wingless species of Orthoptera there is little external difference,
+excepting in size, between the young larva and the perfect insect. The
+growth is gradual, and there is nothing which would, in ordinary
+language, be called a metamorphosis. In the majority of Orthoptera,
+though the presence of wings produces a marked difference between the
+larva and the imago, the habits are nearly the same throughout life, and
+consequently the action of external circumstances affects the larva in
+the same manner as it does the perfect insect.
+
+This is not the case with the Neuroptera. The larv� do not live under
+the same conditions as the perfect insects: external forces accordingly
+affect them in a different manner; and we have seen that they pass
+through some changes which bear no reference to the form of the perfect
+insect: these changes, however, are for the most part very gradual. The
+caterpillars of Lepidoptera have even more extensive modifications to
+undergo; the mouth of the larva, for instance, being remarkably unlike
+that of the perfect insect. A change in this organ, however, could
+hardly take place while the insect was growing fast, and consequently
+feeding voraciously; nor, even if the change could be thus effected,
+would the mouth, in its intermediate stages, be in any way fitted for
+biting and chewing leaves. The same reasoning applies also to the
+digestive organs. Hence the caterpillar undergoes little, if any,
+change, except in size, and the metamorphosis is concentrated, so to
+say, into the last two moults. The changes then become so rapid and
+extensive, that the intermediate period is necessarily one of
+quiescence. In some exceptional cases, as in _Sitaris_ (_ante_, p. 30) we
+even find that, the conditions of life not being uniform throughout the
+larval period, the larva itself undergoes metamorphoses.
+
+Owing to the fact that the organs connected with the reproduction of the
+species come to maturity at a late period, larv� are generally incapable
+of breeding. There are, however, some flies which have viviparous larv�,
+and thus offer a typical case of alternation of generations.
+
+Thus, then, we find among insects every gradation, from simple growth to
+alternation of generations; and see how, from the single fact of the
+very early period of development at which certain animals quit the egg,
+we can throw some light on their metamorphoses, and for the still more
+remarkable phenomenon that, among many of the lower animals, the species
+is represented by two very different forms. We may even conclude, from
+the same considerations, that this phenomenon may in the course of ages
+become still more common than it is at present. As long, however, as the
+external organs arrive at their mature form before the internal
+generative organs are fully developed, we have metamorphosis; but if the
+reverse is the case, then alternation of generations often results.
+
+The same considerations throw much light on the remarkable circumstance,
+that in alternation of generations the reproduction is, as a general
+rule, agamic in one form. This results from the fact that reproduction
+by distinct sexes requires the perfection both of the external and
+internal organs; and if the phenomenon arise, as has just been
+suggested, from the fact that the internal organs arrive at maturity
+before the external ones, reproduction will result in those species only
+which have the power of agamic multiplication.
+
+Moreover, it is evident that we have in the animal kingdom two kinds of
+dimorphism.
+
+This term has usually been applied to those cases in which animals or
+plants present themselves at maturity under two forms. Ants and Bees
+afford us familiar instances among animals; and among plants the
+interesting case of the genus _Primula_ has recently been described by
+Mr. Darwin. Even more recently he has made known to us the still more
+remarkable phenomenon afforded by the genus _Lythrum_, in which there
+are three distinct forms, and which therefore offers an instance of
+polymorphism.[51]
+
+The other kind of dimorphism or polymorphism differs from the first in
+being the result of the differentiating action of external
+circumstances, not on the mature, but on the young individual. Such
+different forms, therefore, stand towards one another in the relation of
+succession. In the first kind the chain of being divides at the
+extremity; in the other it is composed of dissimilar links. Many
+instances of this second form of dimorphism have been described under
+the name of alternation of generations.
+
+The term, however, has met with much opposition, and is clearly
+inapplicable to the differences exhibited by insects in various periods
+of their life. Strictly speaking, the phenomena are frequently not
+alternate, and in the opinion of some eminent naturalists they are not,
+strictly speaking, cases of generation at all.[52]
+
+In order, then, to have some name for these remarkable phenomena, and to
+distinguish them from those cases in which the _mature_ animal or plant
+is represented by two or more different forms, I think it would be
+convenient to retain exclusively for these latter the terms dimorphism
+and polymorphism; and those cases in which animals or plants pass
+through a succession of different forms might be distinguished by the
+name of dieidism or polyeidism.
+
+The conclusions, then, which I think we may draw from the preceding
+considerations, are:--
+
+1. That the occurrence of metamorphoses arises from the immaturity of
+the condition in which some animals quit the egg.
+
+2. That the form of the insect larva depends in great measure on the
+conditions in which it lives. The external forces acting upon it are
+different from those which affect the mature form; and thus changes are
+produced in the young, having reference to its immediate wants, rather
+than to its final form.
+
+3. That metamorphoses may therefore be divided into two kinds,
+developmental and adaptional or adaptive.
+
+4. That the apparent abruptness of the changes which insects undergo,
+arises in great measure from the hardness of their skin, which admits of
+no gradual alteration of form, and which is itself necessary in order to
+afford sufficient support to the muscles.
+
+5. The immobility of the pupa or chrysalis depends on the rapidity of
+the changes going on in it.
+
+6. Although the majority of insects go through three well-marked stages
+after leaving the egg, still a large number arrive at maturity through a
+greater or smaller number of slight changes.
+
+7. When the external organs arrive at this final form before the organs
+of reproduction are matured, these changes are known as metamorphoses;
+when, on the contrary, the organs of reproduction are functionally
+perfect before the external organs, or when the creature has the power
+of budding, then the phenomenon is known as alternation of generations.
+
+
+
+
+CHAPTER V.
+
+_ON THE ORIGIN OF INSECTS._
+
+
+"Personne," says Carl Vogt, "en Europe au moins, n'ose plus soutenir la
+Cr�ation ind�pendante et de toutes pi�ces des esp�ces," and though this
+statement is perhaps not strictly correct, still it is no doubt true,
+that the Doctrine of Evolution, in some form or other, is accepted by
+most, if not by all, the greatest naturalists of Europe. Yet it is
+surprising how much, in spite of all that has been written, Mr. Darwin's
+views are still misunderstood. Thus Browning, in one of his recent
+poems, says:--
+
+  "That mass man sprang from was a jelly lump
+   Once on a time; he kept an after course
+   Through fish and insect, reptile, bird, and beast,
+   Till he attained to be an ape at last,
+   Or last but one."[53]
+
+This theory, though it would be regarded by many as a fair statement of
+his views, is one which Mr. Darwin would entirely repudiate. Whether
+fish and insect, reptile, bird and beast, are derived from one original
+stock or not, they are certainly not links in one sequence. I do not,
+however, propose to discuss the question of Natural Selection, but may
+observe that it is one thing to acknowledge that in Natural Selection,
+or the survival of the fittest, Mr. Darwin has called attention to a
+_vera causa_, has pointed out the true explanation of certain phenomena;
+but it is quite another thing to maintain that all animals are descended
+from some primordial source.
+
+For my own part, I am satisfied that Natural Selection is a true cause,
+and, whatever may be the final result of our present inquiries--whether
+animated nature be derived from one ancestral source, or from many--the
+publication of the Origin of Species will none the less have constituted
+an epoch in the History of Biology. But, how far the present condition
+of living beings is due to that cause; how far, on the other hand, the
+action of Natural Selection has been modified and checked by other
+natural laws--by the unalterability of types, by atavism, &c.; how many
+types of life originally came into being; and whether they arose
+simultaneously or successively,--these and many other similar questions
+remain unsolved, even admitting the theory of Natural Selection. All
+this has indeed been clearly pointed out by Mr. Darwin himself, and
+would not need repetition but for the careless criticism by which in too
+many cases the true question has been obscured. Without, however,
+discussing the argument for and against Mr. Darwin's conclusions, so
+often do we meet with travesties of it like that which I have just
+quoted, that it is well worth while to consider the stages through which
+some group, say for instance that of insects, have probably come to be
+what they are, assuming them to have developed under natural laws from
+simpler organisms. The question is one of great difficulty. It is hardly
+necessary to say that insects cannot have passed through all the lower
+forms of animal life, and naturalists do not at present agree as to the
+actual line of their development.
+
+In the case of insects, the gradual course of evolution through which
+the present condition of the group has probably been reached, has been
+discussed by Mr. Darwin, by Fritz M�ller, Haeckel, Brauer, myself and
+others.
+
+In other instances Pal�ontology throws much light on this question.
+Leidy has shown that the milk-teeth of the genus _Equus_ resemble the
+permanent teeth of the ancient _Anchitherium_, while the milk-teeth of
+_Anchitherium_ again approximate to the dental system of the still
+earlier _Merychippus_. R�timeyer, while calling attention to this
+interesting observation, adds that the milk-teeth of _Equus caballus_ in
+the same way, and still more those of _E. fossilis_, resemble the
+permanent teeth of _Hipparion_.
+
+"If we were not acquainted with the horse," says Flower,[54] "we could
+scarcely conceive of an animal whose only support was the tip of a
+single toe on each extremity, to say nothing of the singular
+conformation of its teeth and other organs. So striking have these
+characters appeared to many zoologists, that the animals possessing them
+have been reckoned as an order apart, called Solidungula; but
+pal�ontology has revealed that in the structure of its skull, its teeth,
+its limbs, the horse is nothing more than a modified _Pal�otherium_; and
+though still with gaps in certain places, many of the intermediate
+stages of these modifications are already known to us, being the
+_Pal�otherium_, _Anchitherium_, _Merychippus_, and _Hipparion_."
+
+"All Echinoids," says A. Agassiz,[55] "pass, in their early stages,
+through a condition which recalls to us the first Echinoids which made
+their appearance in geological ages." On embryological grounds, he
+observes, we should "place true Echini lowest, then the Clypeastroids,
+next the Echinolamps, and finally the Spatangoids." Now among the
+Echinoids of the Trias there are no Clypeastroids, Echinolamps, or
+Spatangoids. The Clypeastroids make their appearance in the Lias, the
+Echinolamps in the Jurassic, while the Spatangoids commence in the
+Cretaceous period.
+
+Again[56] "in the Radiates, the Acalephs in their first stages of
+growth, that is, in their Hydroid condition, remind us of the adult
+forms among Polyps, showing the structural rank of the Acalephs to be
+the highest, since they pass beyond a stage which is permanent with the
+Polyps; while the Adult forms of the Acalephs have in their turn a
+certain resemblance to the embryonic phases of the class next above
+them, the Echinoderms; within the limits of the classes, the same
+correspondence exists as between the different orders; the embryonic
+forms of the highest Polyps recall the adult forms of the lower ones,
+and the same is true of the Acalephs as far as these phenomena have been
+followed and compared among them." Indeed, the accomplished authors from
+whom I have taken the above quotation, do not hesitate to say[57] that
+"whenever such comparisons have been successfully carried out, the
+result is always the same; the present representatives of the fossil
+types recall in their embryonic condition the ancient forms, and often
+explain their true position in the animal kingdom."
+
+Fossil insects are unfortunately rare, there being but few strata in
+which the remains of this group are well preserved. Moreover,
+well-characterized Orthoptera and Neuroptera occur as early as the
+Devonian strata; Coleoptera and Hemiptera in the Coal-measures;
+Hymenoptera and Diptera in the Jurassic; Lepidoptera, on the contrary,
+not until the Tertiary. But although it appears from these facts that,
+as far as our present information goes, the Orthoptera and Neuroptera
+are the most ancient orders, it is not, I think, conceivable that the
+latter should have been derived from any known species of the former; on
+the other hand, the earliest known Neuroptera and Orthoptera, though in
+some respects less specialized than existing forms, are as truly, and as
+well characterized, Insects, as any now existing; nor are we acquainted
+with any earlier forms, which in any way tend to bridge over the gap
+between them and lower groups, though, as we shall see, there are types
+yet existing which throw much light on the subject.
+
+In the consideration then of this question, we must rely principally on
+Embryology and Development. I have already referred to the cases in
+which species, very unlike in their mature condition, are very
+similar one to another when young. Haeckel, in his "Naturliche
+Sch�pfungsgeschichte," gives a diagram which illustrates this very well
+as regards Crustacea. Pls. 1-4 show the same to be the case with
+Insects.
+
+The Stag-beetle, the Dragon-fly, the Moth, the Bee, the Ant, the Gnat,
+the Grasshopper,--these and other less familiar types seem at first to
+have little in common. They differ in size, in form, in colour, in
+habits, and modes of life. Yet the researches of entomologists,
+following the clue supplied by the illustrious Savigny, have proved, not
+only that while differing greatly in details, they are constructed on
+one common plan; but also that other groups, as for instance, Crustacea
+(Lobsters, Crabs, &c.) and Arachnida (Spiders and Mites), can be shown
+to be fundamentally similar. In Pl. 4 I have figured the larv� of an
+_Ephemera_ (Fig. 1), of a _Melo�_ (Fig. 2), of a Dragon-fly (Fig. 3), of a
+Sitaris (Fig. 4), of a _Campodea_ (Fig. 5), of a _Dyticus_ (Fig. 6), of a
+Termite (Fig. 7), of a _Stylops_ (Fig. 8), and of a _Thrips_ (Fig. 9). All
+these larv� possess many characters in common. The mature forms are
+represented in the corresponding figures of Plate 3, and it will at once
+be seen how considerably they differ from one another. The same fact is
+also illustrated in Figs. 48-55, where Figs. 48-51 represent the larval
+states of the mature forms represented in Figs. 52-55. Fig. 48 is the
+larva of a moth, _Agrotis suffusa_ (Fig. 52); Fig. 49 of a beetle,
+_Haltica_ (Fig. 53); Fig. 50 of a Saw-fly, _Cimbex_ (Fig. 54); and Fig.
+51 of a Centipede, _Julus_ (Fig. 55).
+
+[Illustration: FIG. 48, Larva of Moth (_Agrotis suffusa_), after
+Packard. 49, Larva of Beetle (_Haltica_), after Westwood. 50, Larva of
+Saw-fly (_Cimbex_), Brischke and Zaddach. Beob. ub d. arten. der Blatt
+und Holzwespen, Fig. 8. 51, Larva of _Julus_. Newport, Philos.
+Transactions, 1841.]
+
+Thus, then, although it can be demonstrated that perfect insects,
+however much they differ in appearance, are yet reducible to one type,
+the fact becomes much more evident if we compare the larv�. M.
+Brauer[58] and I[59] have pointed out that two types of larv�, which I
+have proposed to call _Campodea_-form and _Lindia_-form, and which Packard
+has named Leptiform and Eruciform, run through the principal groups of
+insects. This is obviously a fact of great importance: as all individual
+_Melo�s_ are derived from a form resembling Pl. 2, Fig. 2, it is surely no
+rash hypothesis to suggest that the genus itself may have been so.
+
+[Illustration: FIG. 52, _Agrotis suffusa_ (after Packard). 53, _Haltica_
+(after Westwood).]
+
+[Illustration: FIG. 54, _Cimbex_, Brischae and Zaddach. l.c. T. 2, Fig.
+9.]
+
+[Illustration: FIG. 55. _Julus_ (after Gervais).]
+
+Firstly, however, let me say a word as to the general Insect type. It
+may be described shortly as consisting of animals possessing a head,
+with mouth parts, eyes and antenn�; a many segmented body, with three
+pairs of legs on the segments immediately following the head; with, when
+mature, either one or two pairs of wings, generally with caudal
+appendages I will not now enter into a description of their internal
+anatomy. It will be seen that, except as regards the wings, Pl. 4, Fig.
+4, representing the larva of a small beetle named _Sitaris_, answers very
+well to this description. Many other Beetles are developed from larv�
+closely resembling those of _Melo�_ (Pl. 4, Fig. 2), and Sitaris (Pl. 4,
+Fig. 4); in fact--except those species the larv� of which, as, for
+instance of the Weevils (Pl. 2, Fig. 6), are internal feeders, and do
+not require legs--we may say that the Coleoptera generally are derived
+from larv� of this type.
+
+I will now pass to a second order, the Neuroptera. Pl. 4, Fig. 1,
+represents the larva of _Chlo�on_, a species the metamorphoses of which I
+described some years ago in the Linnean Transactions,[60] and it is
+obvious that in essential points it closely resembles the form to which
+I have just alluded.
+
+The Orthoptera, again, the order to which Grasshoppers, Crickets,
+Locusts, &c. belong, commence life in a similar condition; and the same
+may also be said of the Trichoptera.
+
+The larv� of Bees when they quit the egg are entirely legless, but in an
+earlier stage they possess well-marked rudiments of thoracic legs,
+showing, as it seems to me, that their apodal condition is an adaptation
+to their circumstances. Other Hymenopterous larv�, those for example of
+_Sirex_ (Fig. 9), and of the Saw-flies (Fig. 50) have well-developed
+thoracic legs.
+
+From the difference in external form, and especially from the large
+comparative size of the abdomen, these larv�, as well as those of
+Lepidoptera (Fig. 48), have generally been classed with the maggots of
+Flies, Weevils, &c., rather than with the more active form of larva just
+adverted to. This seems to me, as I have already pointed out,[61] to be
+a mistake. The caterpillar type differs, no doubt, in its general
+appearance, owing to its greater clumsiness, but still essentially
+agrees with that already described.
+
+No Dipterous larva, so far as I know, belongs truly to this type; in
+fact, the early stages of the pupa in the Diptera seem in some respects
+to correspond to the larv� of other Insect orders. The Development of
+the Diptera is, however, as Weissman[62] has shown, very abnormal in
+other respects.
+
+Thus, then, we find in many of the principal groups of insects that,
+greatly as they differ from one another in their mature condition, when
+they leave the egg they more nearly resemble the typical insect type;
+consisting of a head; a three-segmented thorax, with three pairs of
+legs; and a many-jointed abdomen, often with anal appendages. Now, is
+there any mature animal which answers to this description? We need not
+have been surprised if this type, through which it would appear that
+insects must have passed so many ages since (for winged Neuroptera have
+been found in the carboniferous strata) had long ago become extinct. Yet
+it is not so. The interesting genus _Campodea_ (Pl. 3, Fig. 5) still
+lives; it inhabits damp earth, and closely resembles the larva of
+_Chlo�on_ (Pl. 2, Fig. 1), constituting, indeed, a type which, as shown in
+Pl. 4, occurs in many orders of insects. It is true that the
+mouth-parts of _Campodea_ do not resemble either the strongly mandibulate
+form which prevails among the larv� of Coleoptera, Orthoptera,
+Neuroptera, Hymenoptera, Lepidoptera; or the suctorial type of the
+Homoptera and Heteroptera. It is, however, not the less interesting or
+significant on that account, since, as I have elsewhere[63] pointed out,
+its mouth-parts are intermediate between the mandibulate and haustellate
+types; a fact which seems to me most suggestive.
+
+It appears, then, that there are good grounds for considering that the
+various types of insects are descended from ancestors more or less
+resembling the genus _Campodea_, with a body divided into head, thorax,
+and abdomen: the head provided with mouth-parts, eyes, and one pair of
+antenn�; the thorax with three pairs of legs; and the abdomen, in all
+probability, with caudal appendages.
+
+If these views are correct, the genus _Campodea_ must be regarded as a
+form of remarkable interest since it is the living representative of a
+prim�val type, from which not only the Collembola and Thysanura, but the
+other great orders of insects have derived their origin.
+
+From what lower group the _Campodea_ type was itself derived is a question
+of great difficulty. Fritz M�ller indeed says,[64] "if all the classes
+of Arthropoda (Crustacea, Insecta, Myriopoda, and Arachnida) are indeed
+all branches of a common stem (and of this there can scarcely be a
+doubt), it is evident that the water-inhabiting and water-breathing
+Crustacea must be regarded as the original stem from which the other
+terrestrial classes, with their tracheal respiration, have branched
+off." Haeckel, moreover, is of the opinion that the Tracheata are
+developed from the Crustacea, and probably from the Zo�poda. For my own
+part, though I feel very great diffidence in expressing an opinion at
+variance with that of such high authorities, I am rather disposed to
+suggest that the _Campodea_ type may possibly have been derived from a
+less highly developed one, resembling the modern Tardigrade,[65] a (Fig.
+56) smaller and much less highly organized being than _Campodea_. It
+possesses two eyes, three anterior pairs of legs, and one at the
+posterior end of the body, giving it a curious resemblance to some
+Lepidopterous larv�.
+
+[Illustration: FIG. 56, Tardigrade (after Dujardin).]
+
+These legs, however, as will be seen, are reduced to mere projections.
+But for them, the Tardigrada would closely resemble the vermiform larva
+so common among insects. Among Trichoptera the larva early acquires
+three pairs of legs, but as Zaddach has shown,[66] there is a stage,
+though it is quickly passed through, in which the divisions of the body
+are indicated, but no trace of legs is yet present. Indeed, there appear
+to be reasons for considering that while among Crustacea the appendages
+appear before the segments, in Insects the segments precede the
+appendages, although this stage of development is very transitory, and
+apparently, in some cases, altogether suppressed. I say "apparently,"
+because, as I have already mentioned, I am not yet satisfied that it
+will not eventually be found to be so in all cases. Zaddach, in his
+careful observations of the embryology of _Phryganea_, only once found a
+specimen in this stage, which also, according to the researches of
+Huxley,[67] seems to be little more than indicated in _Aphis_. It is
+therefore possible that in other cases, when no such stage has been
+observed, it not really may be absent, but, from its transitoriness, may
+have hitherto escaped attention.
+
+Fritz M�ller has expressed the opinion[68] that this vermiform type is
+of comparatively recent origin. He says: "The ancient insects approached
+more nearly to the existing Orthoptera, and perhaps to the wingless
+Blattid�, than to any other order, and the complete metamorphosis of the
+Beetles, Lepidoptera, &c., is of later origin." "There were," he adds,
+"perfect insects before larv� and pup�." This opinion has been adopted
+by Mr. Packard[69] in his "Embryological Studies on Hexapodous Insects."
+
+M. Brauer[70] also considers that the vermiform larva is a more recent
+type than the Hexapod form, and is to be regarded not as a developmental
+form, but as an adaptational modification of the earlier active hexapod
+type. In proof of this he quotes the case of _Sitaris_.
+
+Considering, however, the peculiar habits of this genus, to which I have
+already referred, and also that the vermiform type is altogether lower
+in organization and less differentiated than the _Campodea_ form, I cannot
+but regard this case as exceptional; one in which the development has
+been, as it were, to use an expression of Fritz M�ller's, "falsified" by
+the struggle for existence, and which therefore does not truly indicate
+the successive stages of evolution. On the whole, the facts seem to me
+to point to the conclusion that, though the grub-like larv� of Coleoptera
+and some other insects, owe their present form mainly to the influence
+of external circumstances, and partially also to atavism, still the
+_Campodea_ type is itself derived from earlier vermiform ancestors.
+Nicolas Wagner has shown in the case of a small gnat, allied to
+_Cecidomyia_, that even now, in some instances, the vermiform larv�
+possess the power of reproduction. Such a larva (as, for instance, Fig.
+57) very closely resembles some of the Rotatoria, such for instance as
+_Albertia_ or _Notommata_, which however possess vibratile cilia. There is,
+indeed, one genus--_Lindia_ (Fig. 58)--in which these cili� are altogether
+absent, and which, though resembling _Macrobiotus_ in many respects,
+differs from that genus in being entirely destitute of legs. I have
+never met with it myself, but it is described by Dujardin, who found it
+in a ditch near Paris, as being oblong, vermiform, divided into rings,
+and terminating posteriorly in two short conical appendages. The jaws
+are not unlike those of the larv� of Flies, and indeed many naturalists
+meeting with such a creature would, I am sure, regard it as a small
+Dipterous larva; yet Dujardin figures a specimen containing an egg, and
+seems to have no doubt that it is a mature form.[71]
+
+For the next descending stage we must, I think, look among the
+Infusoria, through such genera as _Ch�tonotus_ or _Ichthydium_. Other
+forms of the Rotatoria, such for instance as _Rattulus_, and still more
+the very remarkable species discovered in 1871 by Mr. Hudson,[72] and
+described under the name of _Pedalion mira_, seem to lead to the
+Crustacea through the Nauplius form. Dr. Cobbold tells me that he
+regards the _Gordii_ as the lowest of the Scolecida; Mr. E. Ray
+Lankester considers some of the Turbellaria, such genera as
+_Mesostomum_, _Vortex_, &c., to be the lowest of existing worms;
+excluding the parasitic groups. Haeckel[73] also regards the Turbellaria
+as forming the nearest approach to the Infusoria. The true worms seem,
+however, to constitute a separate branch of the animal kingdom.
+
+We may take, as an illustration of the lower worms, the genus
+Prorhynchus (Fig. 59), which consists of a hollow cylindrical body,
+containing a straight simple tube, the digestive organ.
+
+But however simple such a creature as this may be, there are others
+which are far less complex, far less differentiated; which therefore, on
+Mr. Darwin's principles, may be considered still more closely to
+represent the prim�val ancestor from which these more highly-developed
+types have been derived, and which, in spite of their great
+antiquity--in spite of, or perhaps in consequence of, their simplicity,
+still maintain themselves almost unaltered.
+
+Thus the form which Haeckel has described[74] under the name
+_Protamoeba primitiva_, Pl. 5, Fig. 1-5, consists of a homogeneous and
+structureless substance, which continually alters its form; putting out
+and drawing in again more or less elongated processes, and creeping
+about like a true _Amoeba_, from which, however, _Protamoeba_ differs,
+in the absence of a nucleus. It seems difficult to imagine anything
+simpler; indeed, as described, it appears to be an illustration of
+properties without structure. It takes into itself any suitable particle
+with which it comes in contact, absorbs that which is nutritious, and
+rejects the rest. From time to time a constriction appears at the centre
+(Pl. 5, Fig. 2), its form approximates more and more to that of an
+hour-glass (Pl. 5, Fig. 3), and at length the two halves separate, and
+each commences an independent existence (Pl. 5, Fig. 5).
+
+[Illustration: FIG. 59, _Prorhynchus stagnaus_.[75]]
+
+[Illustration: PLATE V.
+
+FIGS. 1-5, _Protamoeba_; 6-9, _Protamyxa Aurantiaca_,
+Haeckel, Beit. zur Monog. der Moneren, pl. 1; 10-18, _Magosph�ra planula_,
+Haeckel, loc. cit. pl. 5.]
+
+In the true _Amoebas_, on the contrary, we find a differentiation
+between the exterior and the interior: the body being more or less
+distinctly divisible into an outer layer and an inner parenchyme. In the
+_Amoebas_, as in _Protamoeba_, multiplication takes place by
+self-division, and nothing corresponding to sexual reproduction has yet
+been discovered.
+
+Somewhat more advanced, but still of great simplicity, is the _Protomyxa
+aurantiaca_ (Pl. 5, Fig. 8), discovered by Haeckel[76] on dead shells of
+_Spirula_, where it appears as a minute orange speck, which shows well
+against the clear white of the _Spirula_. Examined with a microscope, the
+speck is seen to be a spherical mass of orange-coloured, homogeneous,
+albuminous matter, surrounded by a delicate, structureless membrane. It
+is obvious from this description that these bodies closely resemble
+eggs, for which indeed Haeckel at first mistook them. Gradually,
+however, the yellow sphere broke itself up into smaller spherules (Pl.
+5, Fig. 9), after which the containing membrane burst, and the separate
+spherules, losing their globular form, crept out as small _Amoeb�_ (Pl.
+5, Fig. 6), or amoeboid bodies. These little bodies moved about,
+assimilated the minute particles of organic matter, with which they came
+in contact, and gradually increased in size (Pl. 5, Fig. 7) with more or
+less rapidity according to the amount of nourishment they were able to
+obtain. They threw out arms in various directions, and if divided each
+section maintained its individual existence. After a while their
+movements ceased, they contracted into a ball, and again secreted round
+themselves a clear structureless envelope.
+
+This completes their life history as observed by Haeckel, who found it
+easy to retain them in his glasses in perfect health, and who watched
+them closely.
+
+As another illustration I may take the _Magosph�ra planula_, discovered
+by Haeckel on the coast of Norway.
+
+In one stage of its existence (Pl. 5, Fig. 10) it is a minute mass of
+gelatinous matter, which continually alters its form, moves about,
+feeds, and in fact behaves altogether like the _Amoeba_ just described.
+It does not, however, remain always in this condition. After a while it
+contracts into a spherical form (Pl. 5, Fig. ii), and secretes round
+itself a structureless envelope, which, with the nucleus, gives it a
+very close resemblance to a minute egg.
+
+Gradually the nucleus divides, and the protoplasm also separates into
+two spherules (Pl. 5, Fig. 12); these two subdivide into four (Pl. 5,
+Fig. 13), and so on (Pl. 5, Fig 14), until at length thirty-two are
+present, compressed into a more or less polygonal form (Pl. 5, Fig. 15).
+Here this process ends. The separate spherules now begin to lose their
+smooth outline, to throw out processes, and to show amoeboid movements
+like those of the creatures just described. The processes or pseudopods
+grow gradually longer, thinner, and more pointed. Their movements become
+more active, until at length they take the form of cili�. The spherical
+_Magosph�ra_, the upper surface of which has thus become covered with
+cili�, now begins to rotate within the cyst or envelope, which at length
+gives way and sets free the contained sphere, which then swims about
+freely in the water (Pl. 5, Fig. 16), thus closely resembling _Synura_, or
+one of the Volvocine�. After swimming about in this condition for a
+certain time, the sphere breaks up into the separate cells of which it
+is composed (Pl. 5, Fig. 17). As long as the individual cells remained
+together, they had undergone no changes of form, but after separating
+they show considerable contractility, and gradually alter their form,
+until they become undistinguishable from true _Amoeb�_ (Pl. 5, Fig. 18).
+Finally, according to Haeckel, these amoeboid bodies, after living for
+a certain time in this condition, return to a state of rest, again
+contract into a spherical form, and secrete round themselves a
+structureless envelope. The life history of some other low organisms, as
+for instance _Gregarina_, is of a similar character.
+
+It may be said, and said truly, that the difference between such beings
+as these and the _Campodea_, or Tardigrade, is immense. But if it be
+considered incredible that even during the long lapse of geological time
+such great changes should have taken place as are implied in the belief
+that there is genetic connection between them and these lower groups,
+let us consider what happens under our eyes in the development of each
+one of these little creatures in the proverbially short space of their
+individual life.
+
+I will take for instance the first stages, and for the sake of brevity
+only the first stages, of the life-history of a Tardigrade.[77] As shown
+in Fig. 60, the egg is at first a round body or cell, with a clear
+central nucleus--the germinal vesicle; it increases in size, and after
+a while the yolk and the germinal vesicle divide into two (Fig. 61),
+then into four (Fig. 62), and so on, just as we have seen to be the case
+in _Magosph�ra_. From the minute cells (Fig. 63) arising through this
+process of yolk-segmentation, the body of the Tardigrade is then built
+up.[78]
+
+[Illustration: FIG. 60, Egg of Tardigrade, Kaufmann, Zeit f. Wiss.
+Zool. 1851, Pl. 1. 61, Egg of Tardigrade after the yolk has subdivided.
+62, Egg of Tardigrade in the next stage. 63, Egg of Tardigrade more
+advanced.]
+
+Though I will not now attempt to point out the full bearing of these
+facts on the study of embryology generally, yet I cannot resist calling
+attention to the similarity of the development of _Magosph�ra_ with the
+first stages of development of other animals, because it appears to me
+to possess a significance, the importance of which it would be difficult
+to overestimate.
+
+Among the Zoophytes Prof. Allman thus describes[79] the process in
+_Laomedea_, as representing the Hydroids (Pl. 6, Fig. 1, represents the
+young egg):--"The first step observable in the segmentation-process is
+the cleavage of the yolk into two segments (Pl. 6, Fig. 2), immediately
+followed by the cleavage of these into other two, so that the vitellus
+is now composed of four cleavage spheres (Pl. 6, Fig. 3)." These spheres
+again divide (Pl. 6, Fig. 4) and subdivide, thus at length forming
+minute cells, of which the body of the embryo is built up.
+
+In Pl. 6, Figs. 5-9 represent the corresponding stages in the
+development of a small parasitic worm--the _Filaria mustelarum_--as
+given by Van Beneden.[80] The first process is that within the egg,
+which represents, so to say, the encysted condition of _Magosph�ra_, the
+yolk divides itself into two balls (Pl. 6, Fig. 6), then into four,
+eight, and so on, the cells thus constituted finally forming the young
+worm. I have myself observed the same stages in the eggs of the very
+remarkable and abnormal _Sph�rularia bombi_.[81]
+
+Among the Echinoderms M. Derb�s thus describes the first stages (Pl. 6,
+Figs. 10-13) in the development of the egg of an _Echinus_ (_Echinus
+esculentus_):--"Le jaune commence � se segmenter, d'abord en deux, puis
+en quatre et ainsi de suite, chacune des nouvelles cellules se
+partageant � son tour en deux."[82] Sars has observed the same thing in
+the starfish.[83]
+
+[Illustration: PLATE. 6.]
+
+In the Rotatoria, as shown by Huxley in _Lacinularia_,[84] and by
+Williamson in _Melicerta_,[85] the yolk is at first a single globular
+mass, the first changes which take place in it being as follows:--"The
+central nucleus becomes drawn out and subdivides into two, this division
+being followed by a corresponding segmentation of the yolk. The same
+process is repeated again and again, until at length the entire yolk is
+converted into a mass of minute cells." Among the Crustacea the total
+segmentation of the yolk occurs among the Copepoda, Rhizocephala, and
+Cirripedia. Sars has described the same process in one of the
+nudibranchiate mollusca[86] (_Tritonia_), M�ller in Entochocha,[87]
+Haeckel in Ascidia,[88] Lacaze Duthiers in _Dentalium_.[89] Figures 18 to
+21, Pl. 6, are taken from Koren and Danielssen's[90] memoir on the
+development of _Purpura lapillus_.
+
+Figs. 22-24 show the same stages in a fish (_Amphioxus_) as given by
+Haeckel, and it is unnecessary to point out the great similarity.
+
+Lastly, figures 25 to 29, Pl. 6, are given by Dr. Allen Thomson,[91] as
+illustrating the first stages in the development of the vertebrata.
+
+I might have given many other examples, but the above are probably
+sufficient, and will show that the processes which constitute the
+life-history of the lowest organized beings very closely resemble the
+first stages in the development of more advanced groups; that as Allen
+Thomson has truly observed,[92] "the occurrence of segmentation and the
+regularity of its phenomena are so constant that we may regard it as one
+of the best established series of facts in organic nature."
+
+It is true that normal yolk-segmentation is not universal in the animal
+kingdom; that there are great groups in which the yolk does not divide
+in this manner,--perhaps owing to some difference in its relation to the
+germinal vesicle, or perhaps because one of the suppressed stages in
+embryological development, many examples might be given, not only in
+zoology, but, as I may state on the authority of Dr. Hooker, in botany
+also. But, however, this may be, it is surely not uninteresting, nor
+without significance, to find that changes which constitute the
+life-history of the lowest creatures for the initial stages even of the
+highest.
+
+Returning, in conclusion, to the immediate subject of this work, I have
+pointed out that many beetles and other insects are derived from larv�
+closely resembling _Campodea_.
+
+Since, then, individual insects are certainly in many cases developed
+from larv� closely resembling the genus _Campodea_, why should it be
+regarded as incredible that insects as a group have gone through similar
+stages? That the ancestors of beetles under the influence of varying
+external conditions, and in the lapse of geological ages, should have
+undergone changes which the individual beetle passes through under our
+own eyes and in the space of a few days, is surely no wild or
+extravagant hypothesis. Again, other insects come from vermiform larv�
+much resembling the genus _Lindia_, and it has been also repeatedly shown
+that in many particulars the embryo of the more specialized forms
+resembles the full-grown representatives of lower types. I conclude,
+therefore, that the Insecta generally are descended from ancestors
+resembling the existing genus _Campodea_, and that these again have arisen
+from others belonging to a type represented more or less closely by the
+existing genus _Lindia_.
+
+Of course it may be argued that these facts have not really the
+significance which they seem to me to possess. It may be said that when
+Divine power created insects, they were created with these remarkable
+developmental processes. By such arguments the conclusions of geologists
+were long disputed. When God made the rocks, it was tersely said, He
+made the fossils in them. No one, I suppose, would now be found to
+maintain such a theory; and I believe the time will come when it will be
+generally admitted that the structure of the embryo, and its
+developmental changes, indicate as truly the course of organic
+development in ancient times as the contents of rocks and their sequence
+teach us the past history of the earth itself.
+
+
+FOOTNOTES:
+
+[1] Darwin's "Researches into the Geology and Natural History of the
+Countries visited by H.M.S. _Beagle_," p. 326.
+
+[2] Introduction to Entomology, vi. p. 50.
+
+[3] Manual of Entomology, p. 30.
+
+[4] Linnean Journal, vol. xi.
+
+[5] Introduction to the Modern Classification of Insects, p. 17.
+
+[6] Linnean Transactions, 1863--"On the Development of _Chlo�on_."
+
+[7] The figures on the first four plates are principally borrowed from
+Mr. Westwood's excellent "Introduction to the Modern Classification of
+Insects."
+
+[8] "Sur la Domestication des _Clavigers_ par les Fourmis." Bull. de la
+Soc. d'Anthropologie de Paris, 1868, p. 315.
+
+[9] Westwood's Introduction, vol. i. p. 36.
+
+[10] Westwood's Introduction, vol. ii. p. 52.
+
+[11] Die Fortpflanzung und Entwickelung der Pupiparen. Von Dr. R.
+Leuckart. Halle. 1848.
+
+[12] Ann. des Sci. Nat., s�r. 4, tome vii. See also _Natural History
+Review_, April 1862.
+
+[13] Ann. and Mag. of Nat. Hist. 1852.
+
+[14] Zeits. f�r Wiss. Zool. 1869.
+
+[15] Transactions of the Linnean Society, 1863.
+
+[16] Lectures on the Anatomy, &c. of the Invertebrate Animals.
+
+[17] Untersuchungen �ber die Entwickelung und den Bau der Gliederthiere,
+1854.
+
+[18] Linnean Transactions, vol. xxii. 1858.
+
+[19] "Embryological Studies on Hexapodous Insects." Peabody Academy of
+Science. Third Memoir.
+
+[20] M�m. de l'Acad. Imp. des Sci. de St. P�tersbourg. 1869.
+
+[21] Observationes de Prima Insectorum Genesi, p. 14.
+
+[22] M�m. de l'Acad. Imp. des Sci. de St. P�tersbourg. tome xvi. 1871,
+p. 35.
+
+[23] Recherches sur l'Evolution des Araign�es.
+
+[24] Philosophical Transactions, 1841.
+
+[25] Monog. of the Gymnoblastic or Tubularian Hydroids. See also Hincks,
+British Hydroid Zoophytes. Pl. x.
+
+[26] Loc. cit. p. 315.
+
+[27] Philosophical Transactions, 1859, p. 589.
+
+[28] "Facts for Darwin," Eng. Trans. p. 127.
+
+[29] Rolleston, "Forms of Animal Life," p. 146.
+
+[30] A. Agassiz, "Embryology of the Starfish," p. 25; "Embryology of
+Echinoderms." Mem. of Am. Ac. of Arts and Sciences N.S. vol. ix. p. 9.
+
+[31] Ueber die Gattungen der Seeigellarven. Siebente Abhandlung. K�n.
+Akad. d. Wiss. zu Berlin. Von Joh. M�ller, 1855, Pl. iii. fig. 3.
+
+[32] Huxley, Introduction to the Classification of Animals, p. 45.
+
+[33] Philosophical Transactions, 1865 and 1866.
+
+[34] Loc. cit. Zweit. Abh. Pl. i., figs. 8 and 9.
+
+[35] Thomson, on the Embryology of the Echinodermata, _Natural History
+Review_, 1863, p. 415. See also Agassiz, "Embryology of the Starfish,"
+p. 62.
+
+[36] A. Agassiz, Embryology of Echinoderms, p. 18.
+
+[37] Hincks. British Hydroid Zoophytes, pp. 120-147.
+
+[38] Zeits. f�r Wiss. Zool. 1864, p. 228.
+
+[39] Introduction to Entomology, 6th ed. vol. i. p. 61.
+
+[40] M�tamorphoses de l'Homme et des Animaux, p. 133. See also
+Carpenter, Principles of Physiology. 1851, p. 389.
+
+[41] Darwin, Origin of Species, 4th ed. p. 532.
+
+[42] Principles of Biology, vi. p. 349.
+
+[43] For differences in larva consequent on variation in the external
+condition, see _ante_, p. 61.
+
+[44] See Hincks. British Hydroid Zoophytes, P. lxii. Agassiz, Sea-side
+Studies, p. 43.
+
+[45] See Newport, Phil. Trans., 1832.
+
+[46] Linnean Transactions, 1862.
+
+[47] Origin of Species, 4th ed., pp. 14 and 97.
+
+[48] On the Alternation of Generations. By J. J. Steenstrup. Trans. by
+C. Busk, Esq. Ray Society. 1842.
+
+[49] Zeit. f�r Wiss. Zool. 1863.
+
+[50] M�m. de l'Acad. Imp. de St. P�tersbourg. vol. xv. 1870.
+
+[51] Of course all animals in which the sexes are distinct are in one
+sense dimorphic.
+
+[52] "There is no such thing as a true case of 'alternation of
+generations in the animal kingdom;' there is only an alternation of true
+generation with the totally distinct process of gemmation or
+fission."--HUXLEY _on Animal Individuality_, Ann. and Mag. of Nat. Hist.
+June 1852.
+
+[53] Prince Hohenstiel Schwangau, p. 68.
+
+[54] Journal of the Royal Institution. April 1873.
+
+[55] "Embryology of Echinoderms," l. c. p. 15.
+
+[56] Mr. and Mrs. Agassiz: "Sea-side Studies," p. 139.
+
+[57] l. c. p. 138.
+
+[58] Wien. Zool. Bot. Gesells, 1869.
+
+[59] Linnean Transactions, 1863.
+
+[60] Linnean Transactions, 1866, vol. xxv.
+
+[61] Linnean Transactions, vol. xxiv. p. 65.
+
+[62] Siebold und Kolliker's Zeitschr. f. Wiss. Zool., 1864.
+
+[63] Linnean Journal, vol. xi.
+
+[64] Facts for Darwin, p. 120.
+
+[65] A still nearer approach is afforded by the genus _Peripatus_, which
+since the above was written has been carefully described, especially by
+Moseley and Hutton. There are several species, scattered over the
+southern hemisphere. In general appearance they look like a link between
+a caterpillar and a centipede. They have a pair of antenn�, two pairs of
+jaws, and (according to the species) from fourteen to thirty-three pairs
+of legs. They breathe by means of trache�, which open diffusely all over
+the body.
+
+[66] Unters. �b. die Entwick, und den Bau der Gliederthiere, p. 73.
+
+[67] Linnean Transactions, v. xxii.
+
+[68] Facts for Darwin, trans. by Dallas, p. 118. See also Darwin,
+"Origin of Species," p. 530. 4th ed.
+
+[69] Mem. Peabody Academy of Science, v. I. No, 3.
+
+[70] Wien. Zool. Bott. Gesells. 1869, p. 310.
+
+[71] See also the descriptions given by Dujardin (Ann. des Sci. Nat.
+1851, v. xv.) and Clapar�de (Anat. und Entwickl. der Wirbel osen Thiere)
+of the interesting genus _Echinoderes_, which these two eminent
+naturalists unite in regarding as intermediate between the Annelides and
+the Crustacea.
+
+[72] "On a New Rotifer." _Monthly Microscopical Journal_, Sept. 1871.
+
+[73] Generelle Morphologie, vol. ii. p. 79.
+
+[74] Monographie der Moneren, p. 43.
+
+[75] Gegenbaur. Grund. d. Vergleich. Anat. p. 210. See also Dr. M. S.
+Schultze, Beitr�ge zur Naturg. der. Turbellarien. 1851. Pl. vi. fig. 1.
+
+[76] Monographieder Moneren, p. 10.
+
+[77] See Kauffmann, Ueber die Entwickelung and systematische Stellung
+der Tardigraden. Zeits. f. Wiss. Zool. 1851, p. 220.
+
+[78] It is true that among the Insecta generally the first stages of
+development differ in appearance considerably from those above
+described; those of _Platygaster_, as figured by Ganin (ante Figs. 17-22),
+being very exceptional.
+
+[79] Monograph of the Gymnoblastic or Tubularian Hydroids, by G. J.
+Allman, Ray Soc. 1871, p. 86.
+
+[80] M�m. sur les Vers Intestinaux, 1858.
+
+[81] Natural History Review, 1861, p. 44.
+
+[82] Ann. des Sci. Nat. 1847, p. 90.
+
+[83] Fauna littoralis Norvegi�, pl. viii.
+
+[84] Trans. of the Microsc. Soc. of London, 1851.
+
+[85] Quarterly Journal of Microsc. Science, 1853.
+
+[86] Wiegmann's Archiv., 1840, p. 196.
+
+[87] Ueber die Erzeugung von Schnecken in Holothurier. Berlin, Bericht,
+1851. Ann. Nat. Hist. 1852, v. ix. M�ller's Archiv., 1852.
+
+[88] Nat�rliche Sch�pfungsgeschichte, pl. x.
+
+[89] Ann. des Sci. Nat. 1853, p. 89.
+
+[90] Ann. des Sci. Nat. 1857, pl. vi.
+
+[91] Cyclop�dia of Anatomy and Physiology. Art. Ovum, p. 4.
+
+[92] Thomson, loc. cit. Article, Ovum, p. 139.
+
+
+   THE END.
+
+
+RICHARD CLAY AND SONS, LIMITED, LONDON AND BUNGAY.
+
+BY THE SAME AUTHOR.
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+     5_s._ (Kegan Paul, Trench & Co.)
+
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+     60th thousand. Paper Covers. 1_s._ _Library Edition._ Cloth,
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+     Third Edition. Globe 8vo. 3_s._ 6_d._ (Macmillan & Co.)
+
+
+NATURE SERIES.
+
+   POPULAR LECTURES AND ADDRESSES ON VARIOUS SUBJECTS IN PHYSICAL
+     SCIENCE. By Sir WILLIAM THOMSON, D.C.L., LL. D., F.R.S.E.,
+     Fellow of St. Peter's College, Cambridge, and Professor of
+     Natural Philosophy in the University of Glasgow. With
+     Illustrations. 3 vols. Crown 8vo. Vol. I. CONSTITUTION OF
+     MATTER. 6_s._
+
+   ON THE ORIGIN AND METAMORPHOSES OF INSECTS. By Sir JOHN
+     LUBBOCK, Bart., F.R.S., M.P., D.C.L., LL.D. With numerous
+     Illustrations. Fifth Edition. Crown 8vo. 3_s._ 6_d._
+
+   ON BRITISH WILD FLOWERS CONSIDERED IN RELATION TO INSECTS. By
+     Sir JOHN LUBBOCK, Bart., F.R.S., M.P., D.C.L., LL.D. With
+     Illustrations. Fifth Edition. Crown 8vo. 4_s._ 6_d._
+
+   FLOWERS, FRUITS, AND LEAVES. By Sir JOHN LUBBOCK, F.R.S., &c.
+     Second Edition. Crown 8vo. 4_s._ 6_d._
+
+   THE TRANSIT OF VENUS. By G. FORBES, M.A., Professor of Natural
+     Philosophy in the Andersonian University, Glasgow.
+     Illustrated. Crown 8vo. 3_s._ 6_d._
+
+   THE COMMON FROG. By ST. GEORGE MIVART, F.R.S., Lecturer in
+     Comparative Anatomy at St. Mary's Hospital. With numerous
+     Illustrations. Crown 8vo. 3_s._ 6_d._
+
+   POLARISATION OF LIGHT. By W. SPOTTISWOODE, F.R.S. With
+     Illustrations. Fourth Edition. Crown 8vo. 3_s._ 6_d._
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+     MEASURE AND WEIGHT. By H. W. CHISHOLM, Warden of the
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+   HOW TO DRAW A STRAIGHT LINE: a Lecture on Linkages. By A. B.
+     KEMPE. With Illustrations. Crown 8vo. 1_s._ 6_d._
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+     Diagrams. Crown 8vo. 3_s._ 6_d._
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+   DEGENERATION. By Professor E. RAY LANKESTER, F.R.S. With
+     Illustrations. Crown 8vo. 2_s._ 6_d._
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+   FASHION IN DEFORMITY, as Illustrated in the Customs of
+     Barbarous and Civilized Races. By Professor FLOWER. With
+     Illustrations. Crown 8vo. 2_s._ 6_d._
+
+   CHARLES DARWIN. Memorial Notices reprinted from _Nature_. By
+     THOMAS HENRY HUXLEY, F.R.S.; G. J. ROMANES, F.R.S.; ARCHIBALD
+     GEIKIE, F.R.S.; and W. T. THISELTON DYER, F.R.S. With a
+     Portrait engraved by C. H. JEENS. Crown 8vo. 2_s._ 6_d._
+
+   ON THE COLOURS OF FLOWERS. As Illustrated in the British
+     Flora. By GRANT ALLEN. With Illustrations. Crown 8vo. 3_s._
+     6_d._
+
+   THE SCIENTIFIC EVIDENCES OF ORGANIC EVOLUTION. By GEORGE J.
+     ROMANES, M.A., LL.D., F.R.S., Zoological Secretary of the
+     Linnean Society. 2_s._ 6_d._
+
+   A CENTURY OF ELECTRICITY. By T. C. MENDENHALL. Crown 8vo.
+     4_s._ 6_d._
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+   THE CHEMISTRY OF THE SECONDARY BATTERIES OF PLANT� AND FAURE.
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+     F.Inst.C.E., Lecturer on Chemistry at Dulwich College. Crown
+     8vo. 2_s._ 6_d._
+
+   ON LIGHT. The Burnett Lectures. By Sir GEORGE GABRIEL STOKES,
+     M.A., P.R.S., &c., Fellow of Pembroke College, and Lucasian
+     Professor of Mathematics in the University of Cambridge. Three
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+     F.R.S., Professor of Experimental Physics in University
+     College, Liverpool. With Illustrations. Crown 8vo. 6_s._ 6_d._
+
+   TIMBER AND SOME OF ITS DISEASES. By H. MARSHALL WARD, F.R.S,
+     Fellow of Christ's College, Cambridge, Professor of Botany at
+     the Royal Indian Engineering College, Cooper's Hill. With
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+   FIRST LESSONS IN PRACTICAL BOTANY. By G. T. BETTANY, M.A.,
+     F.L.S., formerly Lecturer in Botany at Guy's Hospital Medical
+     School. 18mo. 1_s._
+
+   A COURSE OF PRACTICAL INSTRUCTION IN BOTANY. By F. O. BOWER.
+     D.Sc., F.L.S., Regius Professor of Botany in the University of
+     Glasgow. Crown 8vo, 10_s._ 6_d._
+
+   STRUCTURAL BOTANY, OR ORGANOGRAPHY ON THE BASIS OF MORPHOLOGY.
+     To which are added the Principles of Taxonomy and Phytography,
+     and a Glossary of Botanical Terms. By Professor ASA GRAY,
+     LL.D. 8vo. 10_s._ 6_d._
+
+   Works by SIR J. D. HOOKER, K.C.S.I., C.B., M.D., F.R.S.,
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+     18mo. 1_s._ (_Science Primers._)
+
+   THE STUDENT'S FLORA OF THE BRITISH ISLANDS. Third Edition,
+     revised. Globe 8vo. 10_s._ 6_d._
+
+   THE FERTILISATION OF FLOWERS. By Professor HERMANN M�LLER.
+     Translated and Edited by D'Arcy W. THOMPSON, B.A., Professor
+     of Biology in University College, Dundee. With a Preface by
+     CHARLES DARWIN, F.R.S. With numerous Illustrations. Medium
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+   Works by DANIEL OLIVER, F.R.S., &c., Professor of Botany in
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+     Extra fcap 8vo. 6_s._ 6_d._
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+
+   DISEASES OF FIELD AND GARDEN CROPS, CHIEFLY SUCH AS ARE CAUSED
+     BY FUNGI. By WORTHINGTON G. SMITH, F.L.S., M.A.I., Member of
+     the Scientific Committee R.H.S. With 143 New Illustrations
+     drawn and engraved from Nature by the Author. Fcap 8vo. 4_s._
+     6_d._
+
+   DARWINISM. An Exposition of the Theory of Natural Selection
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+<h1 class="pg">The Project Gutenberg eBook, On the Origin and Metamorphoses of Insects,
+by Sir John Lubbock</h1>
+<pre>
+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 <a href = "http://www.gutenberg.org">www.gutenberg.org</a></pre>
+<p>Title: On the Origin and Metamorphoses of Insects</p>
+<p>Author: Sir John Lubbock</p>
+<p>Release Date: December 3, 2011  [eBook #38207]</p>
+<p>Language: English</p>
+<p>Character set encoding: ISO-8859-1</p>
+<p>***START OF THE PROJECT GUTENBERG EBOOK ON THE ORIGIN AND METAMORPHOSES OF INSECTS***</p>
+<p>&nbsp;</p>
+<h4 class="pg">E-text prepared by Bryan Ness, Turgut Dincer,<br />
+    and the Online Distributed Proofreading Team<br />
+    (<a href="http://www.pgdp.net">http://www.pgdp.net</a>)<br />
+    from page images generously made available by<br />
+    Internet Archive/American Libraries<br />
+    (<a href="http://www.archive.org/details/americana">http://www.archive.org/details/americana</a>)</h4>
+<p>&nbsp;</p>
+<table border="0" style="background-color: #ccccff;margin: 0 auto;" cellpadding="10">
+  <tr>
+    <td valign="top">
+      Note:
+    </td>
+    <td>
+      Images of the original pages are available through
+      Internet Archive/American Libraries. See
+      <a href="http://www.archive.org/details/onoriginmetamorp00lubb">
+      http://www.archive.org/details/onoriginmetamorp00lubb</a>
+   </td>
+  </tr>
+</table>
+<p>&nbsp;</p>
+<div class="box">
+<p>Transcriber's note:<br /><br />
+All non-italic genus names in the text have been italicized.</p>
+</div>
+<p>&nbsp;</p>
+<hr class="full" />
+<p>&nbsp;</p>
+
+<div class="figcenter" style="width: 350px;"><a name="logo" id="logo"></a>
+<img src="images/logo_001.png" width="350" height="155"
+alt="NATURE SERIES" title="" /></div>
+
+<h1>ORIGIN AND METAMORPHOSES</h1>
+
+<p class="right"><i>OF INSECTS.</i></p>
+<p>&nbsp;</p>
+<div class="figcenter" style="width: 500px;"><a name="frontispiece" id="frontispiece"></a>
+<img src="images/frontispiece.png" width="500" height="727"
+alt="frontispiece" title="" /></div>
+
+<div class="u"><i>NATURE SERIES</i></div>
+<h3>ON THE</h3>
+<h1>ORIGIN AND METAMORPHOSES</h1>
+<h1>OF INSECTS</h1>
+
+<h4>BY</h4>
+
+<h3><span class="smcap">SIR JOHN LUBBOCK, Bart.</span>, M.P., F.R.S., D.C.L., LL.D.</h3>
+<h6>PRINCIPAL OF THE LONDON WORKING MEN&#8217;S COLLEGE; PRESIDENT OF THE LONDON<br />
+CHAMBER OF COMMERCE; AND VICE-CHAIRMAN OF THE LONDON COUNTY COUNCIL</h6>
+
+<h3><i>WITH NUMEROUS ILLUSTRATIONS</i><br /></h3>
+<p>&nbsp;</p>
+<p>&nbsp;</p>
+<p>&nbsp;</p>
+
+<h4><span class="oldtype">London</span></h4>
+<h4>MACMILLAN AND CO.</h4>
+<h5>AND NEW YORK</h5>
+<h5>1890</h5>
+<h6><i>The Right of Translation and Reproduction is Reserved</i></h6>
+
+<h6><span class="smcap">Richard Clay and Sons, Limited,<br />
+london and bungay.</span></h6>
+
+<h6><i>First Edition 1873. Reprinted 1874.<br />
+New Edition 1890.</i></h6>
+<p><span class='pagenum'><a name="Page_vii" id="Page_vii">vii</a></span></p>
+
+<hr />
+
+<h3>PREFACE.</h3>
+
+<p>For some years, much of my leisure time has
+been devoted to the study of the anatomy, development,
+and habits of the Annulosa, and especially of
+Insects, on which subjects I have published various
+memoirs, chiefly in the Transactions of the Royal,
+Linn&aelig;an, and Entomological Societies: of these
+papers I subjoin a list. Although the details, of
+which these memoirs necessarily for the most part
+consist, offer little interest, excepting to those persons
+who are specially devoted to Entomology,
+still there are portions which, having reference to
+the nature of metamorphoses and to the origin of
+insects, are of a more general character. I have
+also briefly referred to these questions in a Monograph
+of the Collembola and Thysanura, recently
+published by the Ray Society, and in the Opening
+Address to the Biological Section of the British
+Association at Brighton in 1872. Under these<span class='pagenum'><a name="Page_viii" id="Page_viii">viii</a></span>
+circumstances, it has been suggested to me that a
+small volume, containing, at somewhat greater length,
+in a more accessible form, and with the advantage
+of illustrations, the conclusions to which I have been
+led on this interesting subject, might not be altogether
+without interest to the general reader. The
+result, which has already appeared in the pages of
+<i>Nature</i>, is now submitted to the public, with some
+additions. I am well aware that it has no pretence
+to be in any sense a complete treatise; that the
+subject itself is one as to which our knowledge
+is still very incomplete, and on which the highest
+authorities are much divided in opinion. Whatever
+differences of opinion, however, there may be as to
+the views here put forward, the facts on which they
+are based will, I believe, be found correct. On
+this point I speak with the more confidence, on
+account of the valuable assistance I have received
+from many friends: to Mr. and Mrs. Busk and Dr.
+Hooker I am especially indebted.</p>
+
+<p>The papers above referred to are as follows:&mdash;</p>
+
+<p class="indent">1. On <i>Labidocera</i>.&mdash;Annals and Magazine of Natural History, vol.
+xi., 1853.</p>
+
+<p class="indent">2. On Two New Sub-genera of Calanid&aelig;.&mdash;Annals and Magazine of
+Natural History, vol. xii., 1853.</p>
+<p><span class='pagenum'><a name="Page_ix" id="Page_ix">ix</a></span></p>
+<p class="indent">3. On Two New Species of Calanid&aelig;.&mdash;Annals and Magazine of
+Natural History, vol. xii., No. lxvii., 1853.</p>
+
+<p class="indent">4. On Two New Species of Calanid&aelig;.&mdash;Annals and Magazine of
+Natural History, vol. xii., No. lxix., 1853.</p>
+
+<p class="indent">5. On some Arctic Calanid&aelig;.&mdash;Annals and Magazine of Natural
+History, 1854.</p>
+
+<p class="indent">6. On the Freshwater Entomostraca of South America.&mdash;Transactions
+of the Entomological Society, vol. iii., 1855.</p>
+
+<p class="indent">7. On some New Entomostraca.&mdash;Transactions of the Entomological
+Society, vol. iv., 1856.</p>
+
+<p class="indent">8. On some Marine Entomostraca found at Weymouth.&mdash;Annals and
+Magazine of Natural History, vol. xx., 1857.</p>
+
+<p class="indent">9. On the Respiration of Insects.&mdash;Entomological Annual, 1857.</p>
+
+<p class="indent">10. An Account of the Two Methods of Reproduction in <i>Daphnia</i>.&mdash;Transactions
+of the Royal Society, 1857.</p>
+
+<p class="indent">11. On the Ova and Pseudova of Insects.&mdash;Transactions of the Royal
+Society, 1858.</p>
+
+<p class="indent">12. On the Arrangement of the Cutaneous Muscles of <i>Pyg&aelig;ra Bucephala</i>.&mdash;Linnean
+Society&#8217;s Transactions, vol. xxii., 1858.</p>
+
+<p class="indent">13. On the Freshwater Entomostraca of South America.&mdash;Entomological
+Society&#8217;s Transactions, 1858.</p>
+
+<p class="indent">14. On <i>Coccus Hesperidum</i>.&mdash;Royal Society Proceedings, vol. ix.,
+1858.</p>
+
+<p class="indent">15. On the Distribution of Trache&aelig; in Insects.&mdash;Linnean Society&#8217;s
+Transactions, vol. xxiii., 1860.</p>
+
+<p class="indent">16. On the Generative Organs and on the Formation of the Egg in
+Annulosa. Transactions of the Royal Society, 1861.</p>
+
+<p class="indent">17. On <i>Sph&aelig;rularia Bombi</i>.&mdash;Natural History Review, 1861.</p>
+
+<p class="indent">18. On some Oceanic Entomostraca.&mdash;Linnean Society&#8217;s Transactions,
+vol. xxiii., 1860.</p>
+
+<p class="indent">19. On the Thysanura. Part 1.&mdash;Linnean Society&#8217;s Transactions, 1862.</p>
+
+<p class="indent">20. On the Development of <i>Lonchoptera</i>.&mdash;Entomological Society&#8217;s
+Transactions, 1862.</p>
+
+<p class="indent">21. On the Thysanura. Part 2.&mdash;Linnean Society&#8217;s Transactions, 1862.</p>
+
+<p class="indent">22. On the Development of <i>Chlo&euml;on</i>. Part 1.&mdash;Linnean Society&#8217;s
+Transactions, 1863.</p>
+
+<p class="indent">23. On Two Aquatic Hymenoptera.&mdash;Linnean Society&#8217;s Transactions,
+1863.</p>
+
+<p class="indent">24. On some little-known Species of Freshwater Entomostraca.&mdash;Linnean
+Society&#8217;s Transactions, vol. xxiv., 1863.</p>
+
+<p class="indent">25. On <i>Sph&aelig;rularia Bombi</i>.&mdash;Natural History Review, 1864.</p>
+
+<p><span class='pagenum'><a name="Page_x" id="Page_x">x</a></span></p>
+
+<p class="indent">26. On the Development of <i>Chlo&euml;on</i>. Part 2.&mdash;Linnean Society&#8217;s
+Transactions, 1865.</p>
+
+<p class="indent">27. Metamorphoses of Insects.&mdash;Journal of the Royal Institution, 1866.</p>
+
+<p class="indent">28. On <i>Pauropus</i>.&mdash;Linnean Society&#8217;s Transactions, 1866.</p>
+
+<p class="indent">29. On the Thysanura. Part 3.&mdash;Linnean Society&#8217;s Transactions, 1867.</p>
+
+<p class="indent">30. Address to the Entomological Society.&mdash;Entomological Society&#8217;s
+Transactions, 1867.</p>
+
+<p class="indent">31. On the Larva of <i>Micropeplus Staphilinoides</i>.&mdash;Entomological
+Society&#8217;s Transactions, 1868.</p>
+
+<p class="indent">32. On the Thysanura. Part 4.&mdash;Linnean Society&#8217;s Transactions, 1869.</p>
+
+<p class="indent">33. Addresses to the Entomological Society.&mdash;Entomological Society&#8217;s
+Transactions, 1867-1868.</p>
+
+<p class="indent">34. On the Origin of Insects.&mdash;Journal of the Linnean Society, vol. xi.</p>
+
+<p class="indent">35. Opening Address to the Biological Section of the British Association.&mdash;British
+Association Report, 1872.</p>
+
+<p class="indent">36. Observations on Ants, Bees, and Wasps. Part 1.&mdash;Journal of the
+Linnean Society, 1873.</p>
+
+<p class="indent">37. On British Wild Flowers considered in relation to Insects, 1874.</p>
+
+<p class="indent">38. Observations on Ants, Bees, and Wasps. Part 2.&mdash;Journal of the
+Linnean Society, 1874.</p>
+
+<p class="indent">39. Observations on Ants, Bees, and Wasps. Part 3.&mdash;Journal of the
+Linnean Society, 1875.</p>
+
+<p class="indent">40. Observations on Ants, Bees, and Wasps. Part 4.&mdash;Journal of the
+Linnean Society, 1877.</p>
+
+<p class="indent">41. On some Points in the Anatomy of Ants.&mdash;Quekett Lecture,
+1877.&mdash;Microscopical Journal.</p>
+
+<p class="indent">42. On the Colors of Caterpillars.&mdash;Entomological Society&#8217;s Transactions,
+1878.</p>
+
+<p class="indent">43. Observations on Ants, Bees, and Wasps. Part 5.&mdash;Journal of the
+Linnean Society, 1878.</p>
+
+<p class="indent">44. Observations on Ants, Bees, and Wasps. Part 6.&mdash;Journal of the
+Linnean Society, 1879.</p>
+
+<p class="indent">45. On the Anatomy of Ants.&mdash;Linnean Society&#8217;s Transactions, 1880.</p>
+
+<p class="indent">46. Observations on Ants, Bees, and Wasps. Part 7.&mdash;Journal of the
+Linnean Society, 1880.</p>
+
+<p class="indent">47. Observations on Ants, Bees, and Wasps. Part 8.&mdash;Journal of the
+Linnean Society, 1881.</p>
+
+<p class="indent">48. On Fruits and Seeds.&mdash;Journal of the Royal Institution, 1881.</p>
+
+<p class="indent">49. Observations on Ants, Bees, and Wasps. Part 9.&mdash;Journal of the
+Linnean Society, 1881.</p>
+
+<p class="indent">50. On the Limits of Vision among some of the lower Animals.&mdash;Journal
+of the Linnean Society, 1881.</p>
+
+<p class="indent">51. Observations on Ants, Bees, and Wasps. Part 10.&mdash;Journal of the
+Linnean Society, 1882.</p>
+
+<p><span class='pagenum'><a name="Page_xi" id="Page_xi">xi</a></span></p>
+
+<hr />
+<h3>CONTENTS.<br /><br /></h3>
+
+<table width="100%" summary="contents" border="0">
+<tr>
+<td class="t100" colspan="2">CHAPTER I.</td>
+</tr><tr>
+<td class="t100s" colspan="2">THE CLASSIFICATION OF INSECTS.</td>
+</tr><tr>
+<td class="t85">Introduction.&mdash;Stages in the Life of an Insect.&mdash;Classification of
+Insects.&mdash;Characters derived from the Wings; from the parts of
+the Mouth; from the Metamorphoses.&mdash;The Classes of Insects:
+Hymenoptera, Strepsiptera, Coleoptera, Euplexoptera, Orthoptera,
+Thysanoptera, Neuroptera, Trichoptera, Diptera, Aphaniptera,
+Heteroptera, Homoptera, Lepidoptera</td>
+<td class="t15"><i>page </i><a href="#Page_1">1-26</a></td>
+</tr>
+<tr>
+<td class="t100" colspan="2">CHAPTER II.</td>
+</tr><tr>
+<td class="t100s" colspan="2">THE INFLUENCE OF EXTERNAL CONDITIONS ON THE FORM AND
+STRUCTURE OF LARV&AElig;.</td>
+</tr><tr>
+<td class="t85">Larv&aelig; depend partly on the group to which they belong.&mdash;Wood-eating
+Larv&aelig;.&mdash;Larv&aelig; of Lamellicorns.&mdash;Larv&aelig; depend also in part on
+mode of life.&mdash;Larv&aelig; of Hymenoptera, of <i>Sirex</i>; of <i>Tenthredo</i>; of
+Ichneumons; of Bees.&mdash;Rudimentary legs of Bee Embryo.&mdash;Beetles,
+<i>Weevils</i>, <i>Scolytus</i>, <i>Crioceris</i>, <i>Sitaris</i>, Metamorphoses of Pteromalid&aelig;.
+<i>Platygaster</i>, <i>Polynema</i>.&mdash;Influence of external conditions.&mdash;Developmental
+and adaptive Metamorphoses</td>
+<td class="t15"><i>page </i><a href="#Page_27">27-41</a></td>
+</tr>
+<tr>
+<td class="t100" colspan="2">CHAPTER III.</td>
+</tr><tr>
+<td class="t100s" colspan="2">THE NATURE OF METAMORPHOSES.</td>
+</tr><tr>
+<td class="t85">The life history of an Insect must be considered as a whole.&mdash;Vagueness
+of the term Larva.&mdash;Some larv&aelig; much more advanced than others.&mdash;Organs
+develope in different order, in different groups.&mdash;Suppressed
+stages.&mdash;Apod condition of <i>Phryganea</i>; of <i>Aphis</i>; of
+<span class='pagenum'><a name="Page_xii" id="Page_xii">xii</a></span><i>Chrysopa</i>.&mdash;Libellulid&aelig;.&mdash;<i>Donacia</i>.&mdash;Spiders.&mdash;Myriapods.&mdash;Apod
+stage of Homomorphous Insects once probably longer than now.&mdash;Suppression
+of embryonic stages.&mdash;Metamorphoses of Hydroida,
+Crustacea, Isopods, and Amphipods.&mdash;Echinoderms.&mdash;Variations
+in development induced by the influence of external conditions.</td>
+<td class="t15"><i>page </i><a href="#Page_41">41-62</a></td>
+</tr>
+<tr>
+<td class="t100" colspan="2">CHAPTER IV</td>
+</tr><tr>
+<td class="t100s" colspan="2">THE ORIGIN OF METAMORPHOSES.</td>
+</tr><tr>
+<td class="t85">Origin of Metamorphoses.&mdash;Views of Messrs. Kirby and Spence.&mdash;Nature
+of the question.&mdash;Young animals often more similar than
+mature.&mdash;Views of Darwin, Herbert Spencer, Johannes M&uuml;ller,
+Fritz M&uuml;ller, and Agassiz.&mdash;Effect of size of egg.&mdash;Insects leave the
+egg in a more or less developed condition.&mdash;Consideration of pupal
+condition.&mdash;Quiescence of pupa.&mdash;Period of quiescence at each
+moult.&mdash;Changes not so abrupt as generally supposed.&mdash;Change in
+mouth-parts.&mdash;Difficulty in reference to Darwinian theory.&mdash;Mouth-parts
+of <i>Campodea</i> and Collembola, as intermediate between the
+mandibulate and haustellate types.&mdash;Change in mouth-parts as connected
+with pupal conditions.&mdash;Origin of wings.&mdash;Use of wings
+under water.&mdash;Connection of metamorphoses with alternation of
+generations.&mdash;Parthenogenetic larv&aelig; of <i>Cecidomyia</i>.&mdash;In alternation
+of generations one form always agamic.&mdash;Dimorphism and Dieidism.&mdash;Summary
+and Conclusions</td>
+<td class="t15"><i>page </i><a href="#Page_62">62-81</a></td>
+</tr>
+<tr>
+<td class="t100" colspan="2">CHAPTER V</td>
+</tr><tr>
+<td class="t100s" colspan="2">THE ORIGIN OF INSECTS.</td>
+</tr><tr>
+<td class="t85">The Origin of Insects.&mdash;Mistaken views of Darwinian theory.&mdash;Natural
+selection a <i>vera causa</i>.&mdash;Application of Darwin&#8217;s views to Insects.&mdash;Similarity
+of young Crustacea as compared with mature forms;
+ditto in Insects.&mdash;Type of Insecta.&mdash;Two principal types of larv&aelig;:
+Hexapod and Apod.&mdash;Conclusions to be drawn from them.&mdash;<i>Campodea</i>
+the modern representative of the Insect-stock.&mdash;<i>Campodea</i>,
+perhaps derived from Tardigrade.&mdash;Vermiform or Apod type of
+larva.&mdash;Views of Fritz M&uuml;ller, Brauer, and Packard.&mdash;Represents
+a still earlier ancestor.&mdash;Modern representatives.&mdash;<i>Notommata</i>,
+<i>Albertia</i>, <i>Lindia.</i>&mdash;Earlier forms difficult to trace.&mdash;Lowest forms
+of animal life.&mdash;Yolk-segmentation.&mdash;Embryology and Evolution.&mdash;Light
+thrown by the evolution of the individual on that of the
+species</td>
+<td class="t15"><i>page </i><a href="#Page_82">82-108</a></td>
+</tr>
+</table>
+
+<hr />
+
+<p><span class='pagenum'><a name="Page_xiii" id="Page_xiii">xiii</a></span></p>
+
+<h3>DESCRIPTION OF THE PLATES.</h3>
+
+<h4><a href="#Page_8">PLATE I. p. 7.</a></h4>
+
+<p class="small">FIG.</p>
+
+<p class="indent">1. Cricket. Westwood, Intro. to the Modern Classification of Insects,
+vol. i. p. 440.</p>
+
+<p class="indent">2. Earwig. Westwood, loc. cit. vol. i. p. 399.</p>
+
+<p class="indent">3. <i>Aphis</i>. Packard, Guide to the Study of Insects, pp. 521, 522.</p>
+
+<p class="indent">4. <i>Scolytus</i>. Westwood, loc. cit. vol. i. p. 350.</p>
+
+<p class="indent">5. <i>Anthrax</i>. Westwood, loc. cit. vol. ii. p. 538.</p>
+
+<p class="indent">6. <i>Balaninus</i>.</p>
+
+<p class="indent">7. <i>Cynips</i>. Westwood, loc. cit. vol. ii. p. 121.</p>
+
+<p class="indent">8. Ant (<i>Formica</i>). Westwood, loc. cit. vol. ii. p. 218.</p>
+
+<p class="indent">9. Wasp. Ormerod, Nat. Hist. of Wasps, pl. i. fig. 1.</p>
+
+<h4><a href="#Page_9">PLATE II. p. 8.</a></h4>
+
+<p class="small">FIG.</p>
+
+<p class="indent">1. Larva of Cricket. Westwood, loc. cit. vol. i. p. 440.</p>
+
+<p class="indent">2. Larva of <i>Aphis</i>. Packard, loc. cit. pp. 521, 522.</p>
+
+<p class="indent">3. Larva of Earwig. Westwood, loc. cit. vol. i. p. 399.</p>
+
+<p class="indent">4. Larva of <i>Scolytus</i>. Westwood, loc. cit. vol. i. p. 350.</p>
+
+<p class="indent">5. Larva of <i>Anthrax</i>. Westwood, loc. cit. vol. ii. p. 546.</p>
+
+<p class="indent">6. Larva of <i>Balaninus</i>.</p>
+
+<p class="indent">7. Larva of <i>Cynips</i>. Westwood, loc. cit. vol. ii. p. 121.</p>
+
+<p class="indent">8. Larva of Ant (<i>Formica</i>). Westwood, loc. cit. vol. ii. p. 226.</p>
+
+<p class="indent">9. Larva of Wasp. Newport, Art. Insecta, Todd&#8217;s Cycl. Anat. and
+Phys., p. 871.</p>
+
+<h4><a href="#Page_14">PLATE III. p. 14.</a></h4>
+
+<p class="small">FIG.</p>
+
+<p class="indent">1. <i>Chlo&euml;on</i>. Linn. Trans. 1866.</p>
+
+<p class="indent">2. <i>Melo&euml;</i>. Spry and Shuckard, Coleoptera Delineated, pl. 56.</p>
+
+<p class="indent">3. <i>Calepteryx</i>.</p>
+
+<p class="indent">4. <i>Sitaris</i>. Spry and Shuckard, loc. cit. pl. 56.</p>
+
+<p class="indent">5. <i>Campodea</i>. Suites &agrave; Buffon. Apt&eacute;res.</p>
+
+<p><span class='pagenum'><a name="Page_xiv" id="Page_xiv">xiv</a></span></p>
+
+<p class="indent">6. <i>Acilius</i>. Westwood, loc. cit. vol. i. p. 100.</p>
+
+<p class="indent">7. <i>Termes</i>. Westwood, loc. cit. vol. ii. p. 12.</p>
+
+<p class="indent">8. <i>Stylops</i>. Duncan, Met. of Insects, p. 387; Packard, p. 482.</p>
+
+<p class="indent">9. <i>Thrips</i>. Westwood, loc. cit. vol. ii. p. 1.</p>
+
+<h4><a href="#Page_15">PLATE IV. p. 15.</a></h4>
+
+<p class="small">FIG.</p>
+
+<p class="indent">1. Larva of <i>Chlo&euml;on</i>. Linn. Trans. 1863.</p>
+
+<p class="indent">2. Larva of <i>Melo&euml;</i>. Chapuis and Cand&egrave;ze, Mem. Soc. Roy. Li&eacute;ge,
+1853, pp. 1, 7.</p>
+
+<p class="indent">3. Larva of <i>Calepteryx</i>. Dufour, Ann. Sci. Nat. 1852.</p>
+
+<p class="indent">4. Larva of <i>Sitaris</i>. Duncan, Met. of Insects, p. 309.</p>
+
+<p class="indent">5. Larva of <i>Campodea</i>. Gervais' Suites &agrave; Buffon. Apt&eacute;res.</p>
+
+<p class="indent">6. Larva of <i>Acilius</i>. Westwood, loc. cit. vol. i. p. 100.</p>
+
+<p class="indent">7. Larva of <i>Termes</i>. Duncan, loc. cit. p. 348.</p>
+
+<p class="indent">8. Larva of <i>Stylops</i>. Westwood, Trans. Ent. Soc. 1839, vol. ii.
+pl. xv. fig. 13a.</p>
+
+<p class="indent">9. Larva of <i>Thrips</i>. Westwood, loc. cit. vol. ii. p. i.</p>
+
+<h4><a href="#Page_8">PLATE V. p. 99.</a></h4>
+
+<p class="small">FIG.</p>
+
+<p class="indent">1-5. <i>Protam&oelig;ba</i>.</p>
+
+<p class="indent">6-9. <i>Protamyxa aurantiaca</i>. Haeckel Beit. zur. Monog. der Moneren,
+pl. 1.</p>
+<p class="indent">10-18. <i>Magosph&oelig;ra planula</i>. Haeckel, loc. cit. pl. v.</p>
+
+<h4><a href="#Page_8">PLATE VI. p. 105.</a></h4>
+
+<p class="small">FIG.</p>
+
+<p class="indent">1-4. Yolk-segmentation in <i>Laomedea</i>. After Allman. Mon. of
+Tubularian Hydroids. Ray Society.</p>
+
+<p class="indent">5-9. Yolk-segmentation in <i>Filaria</i>. After Van Beneden. Mem.
+sur les Vers Intestinaux.</p>
+
+<p class="indent">10-13. Yolk-segmentation in <i>Echinus</i>. After Derbes. Ann. des. Sci.
+Nat. 1847.</p>
+
+<p class="indent">14-17. Yolk-segmentation in <i>Lacinularia</i>. After Huxley. J. of Mic.
+Sci. 1853.</p>
+
+<p class="indent">18-21. Yolk-segmentation in <i>Purpura</i>. After Koren and Danielssen.
+Ann. des. Sci. Nat. 1853.</p>
+
+<p class="indent">22-24. Yolk-segmentation in <i>Amphioxus</i>. After Haeckel. Naturliche
+Sch&ouml;pfungsgeschichte, pl. x.</p>
+
+<p class="indent">25-29. Yolk-segmentation in Vertebrate. After Allen Thompson.
+Art. Ovum. Cyclop. of Anatomy and Physiology.</p>
+
+<p><span class='pagenum'><a name="Page_xv" id="Page_xv">xv</a></span></p>
+
+<hr  />
+
+<h3>DESCRIPTION OF THE FIGURES.</h3>
+
+<p class="small">FIG.</p>
+
+<p class="indent">1. Larva of the Cockchafer (<i>Melolontha</i>)</p>
+
+<p class="indent">2. Larva of <i>Cetonia</i>.</p>
+
+<p class="indent">3. Larva of <i>Trox</i>.</p>
+
+<p class="indent">4. Larva of <i>Oryctes</i>.</p>
+
+<p class="indent">5. Larva of <i>Aphodius</i>.</p>
+
+<p class="indent">6. Larva of <i>Lucanus</i>.</p>
+
+<p class="indent">7. Larva of <i>Brachytarsus</i>.</p>
+
+<p class="indent">8. Larva of <i>Crioceris</i>.</p>
+
+<p class="indent">9. Larva of <i>Sitaris humeralis.</i></p>
+
+<p class="indent">10. Larva of <i>Sitaris humeralis</i>, in the second stage.</p>
+
+<p class="indent">11. Larva of <i>Sitaris humeralis</i>, in the third stage.</p>
+
+<p class="indent">12. Larva of <i>Sitaris humeralis</i>, in the fourth stage.</p>
+
+<p class="indent">13. Pupa of <i>Sitaris</i>.</p>
+
+<p class="indent">14. Larva of <i>Sirex</i>.</p>
+
+<p class="indent">15. Egg of <i>Rhynchites</i>, showing the parasitic larva.</p>
+
+<p class="indent">16. The parasitic larva, more magnified.</p>
+
+<p class="indent">17. Egg of <i>Platygaster</i>.</p>
+
+<p class="indent">18. Egg of <i>Platygaster</i>, showing the central cell.</p>
+
+<p class="indent">19. Egg of <i>Platygaster</i>, after the division of the central cell.</p>
+
+<p class="indent">20. Egg of <i>Platygaster</i>, more advanced.</p>
+
+<p class="indent">21. Egg of <i>Platygaster</i>, more advanced.</p>
+
+<p class="indent">22. Egg of <i>Platygaster</i>, showing the rudiment of the embryo.</p>
+
+<p class="indent">23. Larva of <i>Platygaster</i>.&mdash;<i>mo</i>, mouth; <i>a</i>, antenna; <i>kf</i>, hooked feet;
+<i>r</i>, toothed process; <i>lfg</i>, lateral process; <i>f</i>, branches of the tail.</p>
+
+<p class="indent">24. Larva of another species of <i>Platygaster</i>. (The letters indicate the
+same parts as in the preceding figure.)</p>
+
+<p class="indent">25. Larva of a third species of <i>Platygaster</i>. (The letters indicate the
+same parts as in the preceding figure.)</p>
+
+<p class="indent">26. Larva of <i>Platygaster</i> in the second stage.&mdash;<i>mo</i>, mouth; <i>slkf</i>,
+&oelig;sophagus; <i>gsae</i>, supra-&oelig;sophagal ganglion; <i>lm</i>, muscles;
+<i>bsm</i>, nervous system; <i>gagh</i>, rudiments of the reproductive glands.</p>
+
+<p class="indent">27. Larva of <i>Platygaster</i> in the third stage.&mdash;<i>mo</i>, mouth; <i>ma</i>, mandibles;
+<i>gsae</i>, supra-&oelig;sophagal ganglion; <i>slk</i>, &oelig;sophagus; <i>ag</i>,
+ducts of the salivary glands; <i>bnm</i>, ventral nervous system; <i>sp</i>,
+salivary glands; <i>msl</i>, stomach; <i>im</i>, imaginal discs; <i>tr</i>, trache&aelig;;
+<i>fk</i>, fatty tissue; <i>ed</i>, intestine; <i>ga</i>, rudiments of reproductive
+organs; <i>ew</i>, wider portion of intestine; <i>ao</i>, posterior opening.</p>
+
+<p class="indent">28. Embryo of <i>Polynema</i>.</p>
+
+<p class="indent">29. Larva of <i>Polynema</i>.&mdash;<i>asch</i>, rudiments of the antenn&aelig;; <i>flsch</i>, of
+the wings; <i>bsch</i>, of the legs; <i>vfg</i>, lateral projections; <i>gsch</i>,
+rudiments of the ovipositor; <i>fk</i>, fatty tissue.</p>
+
+<p class="indent"><span class='pagenum'><a name="Page_xvi" id="Page_xvi">xvi</a></span>
+30. Egg of <i>Phryganea</i> (Mystacides).&mdash;<i>A</i><sup>1</sup>, mandibular segment; <i>C</i><sup>1</sup>-<i>C</i><sup>5</sup>,
+maxillary, labial, and three thoracic segments; <i>D</i>, abdomen.</p>
+
+<p class="indent">31. Egg of <i>Phryganea</i> somewhat more advanced.&mdash;<i>b</i>, mandibles; <i>c</i>,
+maxill&aelig;; <i>cfs</i>, rudiments of the three pairs of legs.</p>
+
+<p class="indent">32. Egg of <i>Pholcus opilionides</i>, showing the Protozonites.</p>
+
+<p class="indent">33. Embryo of <i>Julus</i>.</p>
+
+<p class="indent">34. Colony of <i>Bougainvillea fruticosa</i>, natural size, attached to the underside
+of a piece of floating timber.</p>
+
+<p class="indent">35. Portion of the same, more magnified.</p>
+
+<p class="indent">36. The Medusa from the same species.</p>
+
+<p class="indent">37. Larva of Prawn, Nauplius stage.</p>
+
+<p class="indent">38. Larva of Prawn, more advanced, Zo&euml;a stage.</p>
+
+<p class="indent">39. Larva of <i>Echino-cidaris &oelig;quituberculata</i> seen from above &#10005; 6/10.</p>
+
+<p class="indent">40. Larva of <i>Echinus</i> &#10005; 100.&mdash;<i>A</i>, front arm; <i>F</i>, arms of the mouth-process;
+<i>B</i>, posterior side arm; <i>E</i><sup>1</sup>, accessory arm of the mouth-process;
+<i>a</i>, mouth; <i>a</i><sup>1</sup>, &oelig;sophagus; <i>b</i>, stomach; <i>b</i><sup>1</sup>, intestine;
+<i>o</i>, posterior orifice; <i>d</i>, ciliated bands; <i>f</i>, ciliated epaulets;
+<i>c</i>, disc of future <i>Echinus</i>.</p>
+
+<p class="indent">41. <i>Comatula rosacea</i>.</p>
+
+<p class="indent">42. Larva of <i>Comatula rosacea</i>.</p>
+
+<p class="indent">43. Larva of <i>Comatula rosacea</i>, more advanced.</p>
+
+<p class="indent">44. Larva of <i>Comatula rosacea</i>, in the Pentacrinus state.</p>
+
+<p class="indent">45. Larva of Starfish (Bipinnaria), &#10005; 100.</p>
+
+<p class="indent">46. Larva of Starfish (Bipinnaria), &#10005; 100, seen from the side.&mdash;<i>a</i>,
+mouth; <i>b</i>, &oelig;sophagus; <i>c</i>, stomach; <i>c</i><sup>1</sup>, intestine.</p>
+
+<p class="indent">47. Larva of another Bipinnaria, showing the commencement of the
+Starfish.&mdash;<i>g</i>, canal of the ciliated sac; <i>i</i>, rudiments of tentacles;
+<i>d</i>, ciliated band.</p>
+
+<p class="indent">48. Larva of Moth (<i>Agrotis</i>).</p>
+
+<p class="indent">49. Larva of Beetle (<i>Haltica</i>).</p>
+
+<p class="indent">50. Larva of Saw-fly (<i>Cimbex</i>).</p>
+
+<p class="indent">51. Larva of <i>Julus</i>.</p>
+
+<p class="indent">52. <i>Agrotis suffusa</i>.</p>
+
+<p class="indent">53. <i>Haltica</i>.</p>
+
+<p class="indent">54. <i>Cimbex</i>.</p>
+
+<p class="indent">55. <i>Julus</i>.</p>
+
+<p class="indent">56. Tardigrade.</p>
+
+<p class="indent">57. Larva of <i>Cecidomyia</i>.</p>
+
+<p class="indent">58. <i>Lindia torulosa</i>.</p>
+
+<p class="indent">59. <i>Prorhynchus stagnalis</i>.</p>
+
+<p class="indent">60. Egg of Tardigrade.</p>
+
+<p class="indent">61. Egg of Tardigrade, after the yolk has subdivided.</p>
+
+<p class="indent">62. Egg of Tardigrade, in the next stage.</p>
+
+<p class="indent">63. Egg of Tardigrade, more advanced.</p>
+
+<hr />
+
+<p><span class='pagenum'><a name="Page_1" id="Page_1">1</a></span></p>
+
+<h4>ON THE</h4>
+<h2>ORIGIN AND METAMORPHOSES<br />
+OF INSECTS.</h2>
+
+<h4>CHAPTER I.</h4>
+
+<h4><i>THE CLASSIFICATION OF INSECTS.</i></h4>
+
+<p>About forty years ago the civil and ecclesiastical
+authorities of St. Fernando in Chili arrested a certain
+M. Renous on a charge of witchcraft, because he kept
+some caterpillars which turned into butterflies.<a name="FNanchor_1" id="FNanchor_1"></a><a href="#Footnote_1" class="fnanchor">1</a> This
+was no doubt an extreme case of ignorance; it is now
+almost universally known that the great majority of
+insects quit the egg in a state very different from
+that which they ultimately assume; and the general
+statement in works on entomology has been that the
+life of an insect may be divided into four periods.</p>
+
+<p>Thus, according to Kirby and Spence,<a name="FNanchor_2" id="FNanchor_2"></a><a href="#Footnote_2" class="fnanchor">2</a> &#8220;The states
+through which insects pass are four: the <i>egg</i>, the
+<i>larva</i>, the <i>pupa</i>, and the <i>imago</i>.&#8221; Burmeister,<a name="FNanchor_3" id="FNanchor_3"></a><a href="#Footnote_3" class="fnanchor">3</a> also,
+<span class='pagenum'><a name="Page_2" id="Page_2">2</a></span>says that, excluding certain very rare anomalies,
+&#8220;we may observe four distinct periods of existence
+in every insect,&mdash;namely, those of the egg, the larva,
+the pupa, and the imago, or perfect insect.&#8221; In fact,
+however, the various groups of insects differ widely
+from one another in the metamorphoses they pass
+through: in some, as in the grasshoppers and crickets,
+the changes consist principally in a gradual increase
+of size, and in the acquisition of wings; while others,
+as for instance the common fly, acquire their full
+bulk in a form very different from that which they
+ultimately assume, and pass through a period of inaction
+in which not only is the whole form of the
+body altered, not only are legs and wings acquired,
+but even the internal organs themselves are almost
+entirely disintegrated and re-formed. It will be my
+object, after having briefly described these changes,
+to throw some light on the causes to which they are
+due, and on the indications they afford of the stages
+through which insects have been evolved.</p>
+
+<p>The following list gives the orders or principal
+groups into which the Class Insecta may be divided.
+I will not, indeed, here enter upon my own views, but
+will adopt the system given by Mr. Westwood in his
+excellent &#8220;Introduction to the Modern Classification
+of Insects,&#8221; from which also, as a standard authority,
+most of the figures on Plates I. to IV., when not otherwise
+acknowledged, have been taken. He divides
+insects into thirteen groups, and with reference to
+eight of them it may be said that there is little
+difference of opinion among entomologists. These
+orders are by far the most numerous, and I have<span class='pagenum'><a name="Page_3" id="Page_3">3</a></span>
+placed them in capital letters. As regards the other
+five there is still much difference of opinion. It must
+also be observed that Prof. Westwood omits the
+parasitic Anoplura, as well as the Thysanura and
+Collembola.</p>
+
+<h4>ORDERS OF INSECTS ACCORDING TO WESTWOOD.<br /><br /></h4>
+
+<table width="80%" summary="orders of insects">
+<tr>
+<td class="t30">&nbsp;&nbsp;&nbsp;1. <span class="smcap">Hymenoptera</span></td>
+<td class="t70">Bees, Wasps, Ants, &amp;c.</td>
+</tr><tr>
+<td class="t30">&nbsp;&nbsp;&nbsp;2. Strepsiptera</td>
+<td class="t70"><i>Stylops</i>, <i>Zenos</i>, &amp;c.</td>
+</tr><tr>
+<td class="t30">&nbsp;&nbsp;&nbsp;3. <span class="smcap">Coleoptera</span></td>
+<td class="t70">Beetles.</td>
+</tr><tr>
+<td class="t30">&nbsp;&nbsp;&nbsp;4. Euplexoptera</td>
+<td class="t70">Earwigs.</td>
+</tr><tr>
+<td class="t30">&nbsp;&nbsp;&nbsp;5. <span class="smcap">Orthoptera</span></td>
+<td class="t70">Grasshoppers, Crickets, Cockroaches, &amp;c.</td>
+</tr><tr>
+<td class="t30">&nbsp;&nbsp;&nbsp;6. Thysanoptera</td>
+<td class="t70"><i>Thrips</i>.</td>
+</tr><tr>
+<td class="t30">&nbsp;&nbsp;&nbsp;7. <span class="smcap">Neuroptera</span></td>
+<td class="t70"><i>Ephemeras</i>, &amp;c.</td>
+</tr><tr>
+<td class="t30">&nbsp;&nbsp;&nbsp;8. Trichoptera</td>
+<td class="t70"><i>Phryganea</i>.</td>
+</tr><tr>
+<td class="t30">&nbsp;&nbsp;&nbsp;9. <span class="smcap">Diptera</span></td>
+<td class="t70">Flies and Gnats.</td>
+</tr><tr>
+<td class="t30">10. Aphaniptera</td>
+<td class="t70">Fleas</td>
+</tr><tr>
+<td class="t30">11. <span class="smcap">Heteroptera</span></td>
+<td class="t70">Bugs.</td>
+</tr><tr>
+<td class="t30">12. <span class="smcap">Homoptera</span></td>
+<td class="t70"><i>Aphis</i>, <i>Coccus</i>, &amp;c.</td>
+</tr><tr>
+<td class="t30">13. <span class="smcap">Lepidoptera</span></td>
+<td class="t70">Butterflies and Moths.</td>
+</tr>
+</table>
+
+<p>Of these thirteen orders, the eight which I have
+placed in capital letters&mdash;namely the first, third, fifth,
+seventh, ninth, eleventh, twelfth, and thirteenth, are
+much the most important in the number and variety
+of their species; the other five form comparatively
+small groups. The Strepsiptera are minute insects,
+parasitic on Hymenoptera: Rossi, by whom they
+were discovered, regarded them as Hymenopterous;
+Lamarck placed them among the Diptera; by others
+they have been considered to be most closely allied
+to the Coleoptera, but they are now generally treated
+as an independent order.</p>
+
+<p>The Euplexoptera or Earwigs are only too familiar
+to most of us. Linn&aelig;us classed them among the<span class='pagenum'><a name="Page_4" id="Page_4">4</a></span>
+Coleoptera, from which, however, they differ in
+their transformations. Fabricius, Olivier, and Latreille
+regarded them as Orthoptera; but Dr. Leach, on
+account of the structure of their wings, considered
+them as forming the type of a distinct order, in which
+view he has been followed by Westwood, Kirby, and
+many other entomologists.</p>
+
+<p>The Thysanoptera, consisting of the Linn&aelig;an genus
+<i>Thrips</i>, are minute insects well known to gardeners,
+differing from the Coleoptera in the nature of their
+metamorphoses, in which they resemble the Orthoptera
+and Hemiptera. The structure of the wings and
+mouth-parts, however, are considered to exclude them
+from these two orders.</p>
+
+<p>The Trichoptera, or Caddis worms, offer many
+points of resemblance to the Neuroptera, while in
+others they approach more nearly to the Lepidoptera.
+According to Westwood, the genus <i>Phryganea</i> &#8220;forms
+the connecting link between the Neuroptera and Lepidoptera.&#8221;</p>
+
+<p>The last of these small aberrant orders is that of
+the Aphaniptera, constituted for the family Pulicid&aelig;.
+In their transformations, as in many other respects,
+they closely resemble the Diptera. Strauss Durckheim
+indeed said that &#8220;<i>la puce est un dipt&egrave;re sans
+ailes</i>.&#8221; Westwood, however, regards it as constituting
+a separate order.</p>
+
+<p>As indicated by the names of these orders, the
+structure of the wings affords extremely natural and
+convenient characters by which the various groups
+may be distinguished from one another. The mouth-parts
+also are very important; and, regarded from<span class='pagenum'><a name="Page_5" id="Page_5">5</a></span>
+this point of view, the Insecta have been divided
+into two series&mdash;the Mandibulata and Haustellata, or
+mandibulate and suctorial groups, between which,
+as I have elsewhere shown,<a name="FNanchor_4" id="FNanchor_4"></a><a href="#Footnote_4" class="fnanchor">4</a> the Collembola (<i>Podura</i>,
+<i>Smynthurus</i>, &amp;c.) occupy an intermediate position.
+These two series are:&mdash;</p>
+
+<table width="70%" summary="orders of insects">
+<tr>
+<td class="t50"><span class="smcap">Mandibulata.</span></td>
+<td class="t50"><span class="smcap">Haustellata.</span></td>
+</tr>
+<tr>
+<td class="t50">Hymenoptera.</td>
+<td class="t50">Lepidoptera.</td>
+</tr>
+<tr>
+<td class="t50">Strepsiptera.</td>
+<td class="t50">Diptera.</td>
+</tr>
+<tr>
+<td class="t50">Coleoptera.</td>
+<td class="t50">Aphaniptera.</td>
+</tr>
+<tr>
+<td class="t50">Euplexoptera.</td>
+<td class="t50">Hemiptera.</td>
+</tr>
+<tr>
+<td class="t50">Orthoptera.</td>
+<td class="t50">Homoptera.</td>
+</tr>
+<tr>
+<td class="t50">Trichoptera?</td>
+<td class="t50">&nbsp;</td>
+</tr>
+<tr>
+<td class="t50">Thysanoptera?</td>
+<td class="t50">&nbsp;</td>
+</tr>
+</table>
+
+<p>Again&mdash;and this is the most important from my
+present point of view&mdash;insects have sometimes been
+divided into two other series, according to the nature
+of their metamorphoses: &#8220;Heteromorpha,&#8221; to use the
+terminology of Prof. Westwood,<a name="FNanchor_5" id="FNanchor_5"></a><a href="#Footnote_5" class="fnanchor">5</a> &#8220;or those in which
+there is no resemblance between the parent and the
+offspring; and Homomorpha, or those in which the
+larva resembles the imago, except in the absence of
+wings. In the former the larva is generally worm-like,
+of a soft and fleshy consistence, and furnished
+with a mouth, and often with six short legs attached
+in pairs to the three segments succeeding the head.
+In the Homomorpha, including the Orthoptera,
+Hemiptera, Homoptera, and certain Neuroptera, the
+body, legs, and antenn&aelig; are nearly similar in their
+form to those of the perfect insect, but the wings
+are wanting.&#8221;</p>
+
+<p><span class='pagenum'><a name="Page_6" id="Page_6">6</a></span></p>
+
+<table width="70%" summary="orders of insects">
+<tr>
+<td class="t50"><span class="smcap">Heteromorpha.</span></td>
+<td class="t50"><span class="smcap">Haustellata.</span></td>
+</tr>
+<tr>
+<td class="t50">Hymenoptera.</td>
+<td class="t50">Euplexoptera.</td>
+</tr>
+<tr>
+<td class="t50">Strepsiptera.</td>
+<td class="t50">Orthoptera.</td>
+</tr>
+<tr>
+<td class="t50">Coleoptera.</td>
+<td class="t50">Hemiptera.</td>
+</tr>
+<tr>
+<td class="t50">Trichoptera.</td>
+<td class="t50">Homoptera.</td>
+</tr>
+<tr>
+<td class="t50">Diptera.</td>
+<td class="t50">Thysanoptera.</td>
+</tr>
+<tr>
+<td class="t50">Aphaniptera.</td>
+<td class="t50">&nbsp;</td>
+</tr>
+<tr>
+<td class="t50">Lepidoptera.</td>
+<td class="t50">&nbsp;</td>
+</tr>
+<tr>
+<td class="t100" colspan="2">Neuroptera.</td>
+
+</tr>
+</table>
+
+<p>But though the Homomorphic insects do not pass
+through such striking changes of form as the
+Heteromorphic, and are active throughout life, still
+it was until within the last few years generally
+(though erroneously) considered, that in them, as
+in the Heteromorpha, the life fell into four distinct
+periods; those of (1) the egg, (2) the larva, characterized
+by the absence of wings, (3) the pupa with
+imperfect wings, and (4) the imago, or perfect insect.</p>
+
+<p>I have, however, elsewhere<a name="FNanchor_6" id="FNanchor_6"></a><a href="#Footnote_6" class="fnanchor">6</a> shown that there are
+not, as a matter of fact, four well-marked stages, and
+four only, but that in many cases the process is much
+more gradual.</p>
+
+<p>The species belonging to the order Hymenoptera
+are among the most interesting of insects. To this
+order belong the gallflies, the sawflies, the ichneumons,
+and, above all, the ants and bees. We are
+accustomed to class the Anthropoid apes next to
+man in the scale of creation, but if we were to judge
+animals by their works, the chimpanzee and the
+gorilla must certainly give place to the bee and
+the ant. The larv&aelig; of the sawflies, which live on
+leaves, and of the Siricid&aelig; or long-tailed wasps,
+which feed on wood, are very much like caterpillars,
+<span class='pagenum'><a name="Page_7" id="Page_7">7</a></span>having three pairs of legs, and in the former case
+abdominal pro-legs as well: but in the great majority
+of Hymenoptera the larv&aelig; are legless, fleshy grubs
+(Plate <a href="#p2">II.</a>, Figs. 7-9); and the various modes by which
+the females provide for, or secure to, them a sufficient
+supply of appropriate nourishment constitutes one of
+the most interesting pages of Natural History.</p>
+
+<p>The species of Hymenoptera are very numerous;
+in this country alone there are about 3,000 kinds,
+most of which are very small. In the pupa state
+they are inactive, and show distinctly all the limbs of
+the perfect insect, encased in distinct sheaths, and
+folded on the breast. In the perfect state they are
+highly organized and very active. The working ants
+and some few species are wingless, but the great
+majority have four strong membranous wings, a character
+distinguishing them at once from the true flies,
+which have only one pair of wings.</p>
+
+<p>The sawflies are so called because they possess at
+the end of the body a curious organ, corresponding to
+the sting of a wasp, but which is in the form of a
+fine-toothed saw. With this instrument the female
+sawfly cuts a slit in the stem or leaf of a plant, into
+which she introduces her egg. The larva much resembles
+a caterpillar, both in form and habits. To
+this group belongs the nigger, or black caterpillar
+of the turnip, which is often in sufficient numbers to
+do much mischief. Some species make galls, but
+the greater number of galls are formed by insects
+of another family, the Cynipid&aelig;.</p>
+
+<p><span class='pagenum'><a name="Page_8" id="Page_8">8</a></span></p>
+
+<div class="figcenter" style="width: 500px;"><a name="p1" id="p1"></a>
+<img src="images/plate_001.png" width="500" height="712"
+alt="PLATE I." title="" />
+
+<p class="center">PLATE I.<a name="FNanchor_7" id="FNanchor_7"></a><a href="#Footnote_7" class="fnanchor">7</a>&mdash;MATURE INSECTS.<br /><br />
+
+Fig. 1, Cricket; 2, Earwig; 3, <i>Aphis</i>; 4, <i>Scolytus</i>; 5, <i>Anthrax</i>; 6, <i>Balaninus</i>;
+7, <i>Cynips</i>; 8, Ant; 9, Wasp.</p></div>
+
+<p><span class='pagenum'><a name="Page_9" id="Page_9">9</a></span></p>
+
+<div class="figcenter" style="width: 500px;"><a name="p2" id="p2"></a>
+<img src="images/plate_002.png" width="500" height="805"
+alt="PLATE II." title="" />
+
+<p class="center">PLATE II.&mdash;LARV&AElig; OF THE INSECTS REPRESENTED ON PLATE&nbsp;I.</p>
+
+<p class="caption">Fig. 1, Larva of Cricket; 2, Larva of <i>Aphis</i>; 3, Larva of Earwig; 4, Larva of
+<i>Scolytus</i> (Beetle); 5, Larva of <i>Anthrax</i> (Fly); 6, Larva of <i>Balaninus</i> (Nut
+Weevil); 7, Larva of <i>Cynips</i>; 8, Larva of Ant; 9, Larva of Wasp.</p></div>
+
+<p><span class='pagenum'><a name="Page_10" id="Page_10">10</a></span></p>
+
+<p>In the Cynipid&aelig; (Plate <a href="#p1">I.</a>, Fig. 7) the female is
+provided with an organ corresponding to the saw of
+the sawfly, but resembling a needle. With this she
+stings or punctures the surface of leaves, buds, stalks,
+or even roots of various plants. In the wound thus
+produced she lays one or more eggs. The effects of
+this proceeding, and particularly of the irritating fluid
+which she injects into the wound, is to produce a
+tumour or gall, within which the egg hatches, and on
+which the larva, a thick fleshy grub (Plate <a href="#p2">II.</a>, Fig. 7),
+feeds. In some species each gall contains a single
+larva; in others, several live together.</p>
+
+<p>The oak supports several kinds of gallflies:
+one produces the well-known oak-apple, one a
+small swelling on the leaf resembling a currant,
+another a gall somewhat like an acorn, another
+attacks the root; the species making the bullet-like
+galls, which are now so common, has only
+existed for a few years in this country; the
+beautiful little spangles so common in autumn
+on the under side of oak leaves are the work
+of another species, the <i>Cynus longipennis</i>. One
+curious point about this group is, that in some
+of the commonest species the females alone are
+known, no one yet having ever succeeded in
+finding a male.</p>
+
+<p>Another great family of the Hymenoptera is that
+of the ichneumons; the females lay their eggs either
+in or on other insects, within the bodies of which the
+larv&aelig; live. These larv&aelig; are thick, fleshy, legless
+grubs, and feed on the fatty tissues of their hosts,
+but do not attack the vital organs. When full-grown,
+the grubs eat their way through the skin of<span class='pagenum'><a name="Page_11" id="Page_11">11</a></span>
+the insect, and turn into chrysalides. Almost every
+kind of insect is subject to the attacks of these little
+creatures, which are no doubt useful in preventing
+the too great multiplication of insects, and especially
+of caterpillars. Some species are so minute that they
+actually lay their eggs within those of other insects
+Figs. (<a href="#f14">15, 16</a>). These parasites assume very curious
+forms in their larval state.</p>
+
+<p>But of all the Hymenoptera, the group containing
+the ant, the bee, and the wasp is the most interesting.
+This is especially the case with the social species,
+though the solitary ones also are extremely remarkable.
+The solitary bee or wasp, for instance, forms a
+cell generally in the ground, places in it a sufficient
+amount of food, lays an egg, and closes the cell. In
+the case of bees, the food consists of honey; in that
+of wasps, the larva requires animal food, and the
+mother therefore places a certain number of insects
+in the cell, each species having its own special
+prey, some selecting small caterpillars, some beetles,
+some spiders. <i>Cerceris bupresticida</i>, as its name
+denotes, attacks beetles belonging to the genus <i>Buprestis</i>.
+Now if the <i>Cerceris</i> were to kill the beetle
+before placing it in the cell, it would decay, and the
+young larva, when hatched, would find only a mass
+of corruption. On the other hand, if the beetle
+were buried uninjured, in its struggles to escape it
+would be almost certain to destroy the egg. The
+wasp has, however, the instinct of stinging its prey
+in the centre of the nervous system, thus depriving
+it of motion, and let us hope of suffering, but not
+of life; consequently, when the young larva leaves<span class='pagenum'><a name="Page_12" id="Page_12">12</a></span>
+the egg, it finds ready a sufficient store of wholesome
+food.</p>
+
+<p>Other wasps are social, and, like the bees and ants,
+dwell together in communities. They live for one
+season, dying in autumn, except some of the females,
+which hibernate, awake in the spring, and form new
+colonies. These, however, do not, under ordinary
+circumstances, live through a second winter. One
+specimen which I kept tame through last spring and
+summer, lived until the end of February, but then
+died. The larv&aelig; of wasps (Plate <a href="#p2">II.</a>, Fig. 9) are fat,
+fleshy, legless grubs. When full-grown they spin for
+themselves a silken covering, within which they turn
+into chrysalides. The oval bodies which are so numerous
+in ants' nests, and which are generally called
+ants' eggs, are really not eggs but cocoons. Ants are
+very fond of the honey-dew which is formed by the
+Aphides, and have been seen to tap the Aphides with
+their antenn&aelig;, as if to induce them to emit some
+of the sweet secretion. There is a species of <i>Aphis</i>
+which lives on the roots of grass, and some ants
+collect these into their nests, keeping them, in fact,
+just as we do cows. Moreover they collect the eggs in
+the autumn and tend them through the winter (when
+they are of no use) with the same care as their own,
+so as to have a supply of young Aphides in the spring.
+This is one of the most remarkable facts I know in the
+whole history of animal life. One species of red ant
+does no work for itself, but makes slaves of a black
+kind, which then do everything for their masters. The
+slave makers will not even put food into their own
+mouths, but would starve in the midst of plenty, if they<span class='pagenum'><a name="Page_13" id="Page_13">13</a></span>
+had not a slave to feed them. I found, however, that
+I could keep them in life and health for months if I
+gave them a slave for an hour or two in a week to clean
+and feed them.</p>
+
+<p><span class='pagenum'><a name="Page_14" id="Page_14">14</a></span></p>
+
+<div class="figcenter" style="width: 500px;"><a name="p3" id="p3"></a>
+<img src="images/plate_003.png" width="500" height="812"
+alt="PLATE III." title="" />
+
+<p class="center">PLATE III.--MATURE INSECTS.</p>
+
+<p class="caption">Fig. 1, <i>Chlo&euml;on;</i> 2, <i>Melo&euml;</i> (after Shuckard); 3, <i>Calepteryx</i>; 4, <i>Sitaris</i> (after Shuckard);
+5, <i>Campodea</i> (after Gervais); 6, <i>Acilius</i>; 7, <i>Termes</i>; 8, <i>Stylops</i> (female);
+9, <i>Thrips</i>.</p></div>
+
+
+<p><span class='pagenum'><a name="Page_15" id="Page_15">15</a></span></p>
+
+<div class="figcenter" style="width: 500px;"><a name="p4" id="p4"></a>
+<img src="images/plate_004.png" width="500" height="844"
+alt="PLATE IV." title="" />
+
+<p class="caption">PLATE IV. YOUNG FORMS OF THE INSECTS REPRESENTED ON
+<span class="smcap">PLATE III</span>.--Fig. 1, Larva of <i>Chlo&euml;on;</i> 2, Larva of <i>Melo&euml;</i> (after Chapuis and Cand&egrave;ze);
+3, Larva of <i>Calepteryx</i> (after L&eacute;on Dufour); 4, Larva of <i>Sitaris</i>; 5, Larva
+of <i>Campodea</i>; 6, Larva of <i>Acilius</i>; 7, Larva of <i>Termes</i> (after Blanchard); 8,
+Larva of <i>Stylops</i>; 9, Larva of <i>Thrips</i>.</p></div>
+
+<p>Ants also keep a variety of beetles and other insects
+in their nests. That they have some reason for this
+seems clear, because they readily attack any unwelcome
+intruder; but what that reason is, we do not yet
+know. If these insects are to be regarded as the
+domestic animals of the ants, then we must admit that
+the ants possess more domestic animals than we do.</p>
+
+<p>Some indeed of these beetles produce a secretion
+which is licked by the ants like the honeydew; there
+are others, however, which have not yet been shown
+to be of any use to the ants, and yet are rarely, if&#8216;
+ever, found, excepting in ants' nests.</p>
+
+<p>M. Lesp&egrave;s, who regards these insects as true
+domestic animals, has recorded<a name="FNanchor_8" id="FNanchor_8"></a><a href="#Footnote_8" class="fnanchor">8</a> some interesting
+observations on the relations between one of them
+(<i>Claviger Duvalii</i>) and the ants (<i>Lasius niger</i>) with
+which it lives. This species of <i>Claviger</i> is never met
+with except in ants' nests, though on the other hand
+there are many communities of <i>Lasius</i> which possess
+none of these beetles; and M. Lesp&egrave;s found that
+when he placed <i>Clavigers</i> in a nest of ants which
+had none of their own, the beetles were immediately
+killed and eaten, the ants themselves being on the
+other hand kindly received by other communities of
+the same species. He concludes from these observations
+that some communities of ants are more advanced
+in civilization than others; the suggestion is
+<span class='pagenum'><a name="Page_16" id="Page_16">16</a></span>
+no doubt ingenious, and the fact curiously resembles
+the experience of navigators who have endeavoured
+to introduce domestic animals among barbarous
+tribes; but M. Lep&egrave;s has not yet, so far as I am
+aware, published the details of his observations, without
+which it is impossible to form a decided opinion.
+I have sometimes wondered whether the ants have
+any feeling of reverence for these beetles; but the
+whole subject is as yet very obscure, and would well
+repay careful study.</p>
+
+<p>The order Strepsiptera are a small, but very remarkable
+group of insects, parasitic on bees and wasps.
+The larva (Pl. <a href="#p4">IV.</a>, Fig. 8) is minute, six-legged, and
+very active; it passes through its transformations
+within the body of the bee or wasp. The male and
+female are very dissimilar. The males are minute,
+very active, short-lived, and excitable, with one pair
+of large membranous wings. The females (Pl. <a href="#p3">III.</a>, Fig.
+8), on the contrary, are almost motionless, and shaped
+very much like a bottle; they never quit the body of
+the bee, but only thrust out the top of the bottle
+between the abdominal rings of the bee.</p>
+
+<p>In the order Coleoptera, the larv&aelig; differ very much
+in form. The majority are elongated, active, hexapod,
+and more or less depressed; but those of the <i>Weevils</i>
+(Pl. <a href="#p2">II.</a>, Fig. 6), of <i>Scolytus</i> (Pl. <a href="#p2">II.</a>, Fig. 4), &amp;c., which
+are vegetable feeders, and live surrounded by their
+food,&mdash;as, for instance, in grain, nuts, &amp;c.,&mdash;are apod,
+white, fleshy grubs, not unlike those of bees and ants.
+The larv&aelig; of the Longicorns, which live inside trees,
+are long, soft, and fleshy, with six short legs. The
+Geodephaga, corresponding with the Linn&aelig;an genera<span class='pagenum'><a name="Page_17" id="Page_17">17</a></span>
+<i>Cicindela</i> and <i>Carabus</i>, have six-legged, slender, carnivorous
+larv&aelig;; those of <i>Cicindela</i>, which waylay
+their prey, being less active than the hunting larv&aelig; of
+the Carabid&aelig;. The Hydradephaga, or water-beetles
+(Dyticid&aelig; and Gyrinid&aelig;), have long and narrow larv&aelig;
+(Pl. <a href="#p4">IV.</a>, Fig. 6), with strong sickle-shaped jaws, short
+antenn&aelig;, four palpi, and six small eyes on each side
+of the head; they are very voracious. The larv&aelig; of
+the Staphylinid&aelig; are by no means unlike the perfect
+insect, and are found in similar situations; their jaws
+are powerful, and their legs moderately strong. The
+larv&aelig; of the Lamellicorn beetles Figs. (<a href="#f1">1-6</a>)&mdash;cockchafers,
+stag-beetles, &amp;c.&mdash;feed on vegetable substances
+or on dead animal matter. They are long,
+soft, fleshy grubs, with the abdomen somewhat curved,
+and generally lie on their side. The larv&aelig; of the
+Elaterid&aelig;, known as wireworms, are long and slender,
+with short legs. That of the glowworm (Lampyrid&aelig;)
+is not unlike the apterous female. The male glowworm,
+on the contrary, is very different. It has long,
+thin, brown wing-cases, and often flies into rooms at
+night, attracted by the light, which it probably mistakes
+for that of its mate.</p>
+
+<p>The metamorphoses of the Cantharid&aelig; are very
+remarkable, and will be described subsequently.
+The larv&aelig; are active and hexapod. The Phytophaga
+(<i>Crioceris</i>, <i>Galeruca</i>, <i>Haltica</i>, <i>Chrysomela</i>,
+&amp;c.) are vegetable feeders, both as larv&aelig; and in
+the perfect state. The larv&aelig; are furnished with
+legs, and are not unlike the caterpillars of certain
+Lepidoptera.</p>
+
+<p>The larva of <i>Coccinella</i> (the Ladybird) is somewhat
+depressed, of an elongated ovate form, with a<span class='pagenum'><a name="Page_18" id="Page_18">18</a></span>
+small head, and moderately strong legs. It feeds
+on Aphides.</p>
+
+<p>Thus, then, we see that there are among the Coleoptera
+many different forms of larv&aelig;. Macleay considered
+that there were five principal types.</p>
+
+<p>1. Carnivorous hexapod larv&aelig;, with an elongated,
+more or less flattened body, six eyes on each side of
+the head, and sharp falciform mandibles (<i>Carabus</i>,
+<i>Dyticus</i>, &amp;c.).</p>
+
+<p>2. Herbivorous hexapod larv&aelig;, with fleshy, cylindrical
+bodies, somewhat curved, so that they lie on
+their side.</p>
+
+<p>3. Apod grub-like larv&aelig;, with scarcely the rudiments
+of antenn&aelig; (<i>Curculio</i>).</p>
+
+<p>4. Hexapod antenniferous larv&aelig;, with a subovate
+body, the second segment being somewhat larger
+than the others (<i>Chrysomela</i>, <i>Coccinella</i>).</p>
+
+<p>5. Hexapod antenniferous larv&aelig;, of oblong form,
+somewhat resembling the former, but with caudal
+appendages (<i>Melo&euml;</i>, <i>Sitaris</i>).</p>
+
+<p>The pupa of the Coleoptera is quiescent, and &#8220;the
+parts of the future beetle are plainly perceivable,
+being encased in distinct sheaths; the head is applied
+against the breast; the antenn&aelig; lie along the sides
+of the thorax; the elytra and wings are short and
+folded at the sides of the body, meeting on the under
+side of the abdomen; the two anterior pairs of legs
+are entirely exposed, but the hind pair are covered by
+wing-cases, the extremity of the thigh only appearing
+beyond the sides of the body.&#8221;<a name="FNanchor_9" id="FNanchor_9"></a><a href="#Footnote_9" class="fnanchor">9</a></p>
+
+<p>In the next three orders&mdash;namely, the Orthoptera
+(grasshoppers, locusts, crickets, walking-stick insects,
+<span class='pagenum'><a name="Page_19" id="Page_19">19</a></span>cockroaches, &amp;c.), Euplexoptera (earwigs), and Thysanoptera,
+a small group of insects well known to
+gardeners under the name of <i>Thrips</i> (Pl. <a href="#p1">I.</a> and <a href="#p2">II.</a>,
+Figs. <a href="#f1">1 and 2</a>)&mdash;the larv&aelig; when they quit the egg
+already much resemble the mature form, differing, in
+fact, principally in the absence of wings, which are
+more or less gradually acquired, as the insect increases
+in size. They are active throughout life.
+Those specimens which have rudimentary wings are,
+however, usually called pup&aelig;.</p>
+
+<p>The Neuroptera present, perhaps, more differences
+in the character of their metamorphoses than any
+other order of insects. Their larv&aelig; are generally
+active, hexapod little creatures, and do not vary
+from one another in appearance so much, for instance,
+as those of the Coleoptera, but their pup&aelig;
+differ essentially; some groups, namely, the Psocid&aelig;,
+Termitid&aelig;, Libellulid&aelig;, Ephemerid&aelig;, and Perlid&aelig;,
+remaining active throughout life, like the Orthoptera;
+while a second division, including the Myrmeleonid&aelig;,
+Hemerobiid&aelig;, Sialid&aelig;, Panorpid&aelig;, Raphidiid&aelig;, and
+Mantispid&aelig;, have quiescent pup&aelig;, which, however, in
+some cases, acquire more or less power of locomotion
+shortly before they assume the mature state; thus
+that of <i>Raphidia</i>, though motionless at first, at length
+acquires strength enough to walk, even while still
+enclosed in the pupa skin, which is very thin.<a name="FNanchor_10" id="FNanchor_10"></a><a href="#Footnote_10" class="fnanchor">10</a></p>
+
+<p>One of the most remarkable families belonging
+to this order is that of the Termites, or white ants.
+They abound in the tropics, where they are a perfect
+pest, and a serious impediment to human development.
+Their colonies are extremely numerous, and
+<span class='pagenum'><a name="Page_20" id="Page_20">20</a></span>they attack woodwork and furniture of all kinds,
+generally working from within, so that their presence
+is often unsuspected, until it is suddenly found that
+they have completely eaten away the interior of
+some post or table, leaving nothing but a thin outer
+shell. Their nests, which are made of earth, are
+sometimes ten or twelve feet high, and strong enough
+to bear a man. One species, <i>Termes lucifugus</i>, is
+found in the South of France, where it has been
+carefully studied by Latreille. He found in these
+communities five kinds of individuals&mdash;(1) males;
+(2) females, which grow to a very large size, their
+bodies being distended with eggs, of which they
+sometimes lay as many as 80,000 in a day; (3) a
+form described by some observers as Pup&aelig;, but by
+others as neuters. These differ very much from the
+others, having a long, soft body without wings, but
+with an immense head, and very large, strong jaws.
+These individuals act as soldiers, doing apparently
+no work, but keeping watch over the nest and attacking
+intruders with great boldness. (4) Apterous,
+eyeless individuals, somewhat resembling the winged
+ones, but with a larger and more rounded head;
+these constitute the greater part of the community,
+and, like the workers of ants and bees, perform all the
+labour, building the nest and collecting food. (5)
+Latreille mentions another kind of individual which
+he regards as the pupa, and which resembles the
+workers, but has four white tubercles on the back,
+where the wings afterwards make their appearance.
+There is still, however, much difference of opinion
+among entomologists, with reference to the true
+nature of these different classes of individuals. M.<span class='pagenum'><a name="Page_21" id="Page_21">21</a></span>
+Lesp&egrave;s, who has recently studied the same species,
+describes a second kind of male and a second kind of
+female, and the subject, indeed, is one which offers a
+most promising field for future study.</p>
+
+<p>Another interesting family of Neuroptera is that of
+the Ephemer&aelig;, or Mayflies (Pl. <a href="#p3">III.</a>, Fig. 1), so well
+known to fishermen. The larv&aelig; (Pl. <a href="#p4">IV.</a>, Fig. 1) are
+semi-transparent, active, six-legged little creatures,
+which live in water; having at first no gills, they respire
+through the general surface of the body. They
+grow rapidly and change their skin every few days.
+After one or two moults they acquire seven pairs
+of branchi&aelig;, or gills, which are generally in the form
+of leaves, one pair to the segment. When the larv&aelig;
+are about half grown, the posterior angles of the two
+posterior thoracic segments begin to elongate. These
+elongations become more and more marked with
+every change of skin. One morning, in the month
+of June, some years ago, I observed a full-grown
+larva, which had a glistening appearance, owing to
+the presence of a film of air under the skin. I put
+it under the microscope, and, having added a drop
+of water with a pipette, looked through the glass.
+To my astonishment, the insect was gone, and an
+empty skin only remained. I then caught a second
+specimen, in a similar condition, and put it under
+the microscope, hoping to see it come out. Nor
+was I disappointed. Very few moments had elapsed,
+when I had the satisfaction of seeing the thorax open
+along the middle of the back; the two sides turned
+over; the insect literally walked out of itself, unfolded
+its wings, and in an instant flew up to the window.
+Several times since, I have had the pleasure of<span class='pagenum'><a name="Page_22" id="Page_22">22</a></span>
+witnessing this marvellous change, and it is really wonderful
+how rapidly it takes place: from the moment
+when the skin first cracks, not ten seconds are over
+before the insect has flown away.</p>
+
+<p>Another family of Neuroptera, the Dragon-flies,
+or Horse-stingers, as they are sometimes called, from
+a mistaken idea that they sting severely enough to
+hurt a horse, though in fact they are quite harmless,
+also spend their early days in the water. The larv&aelig;
+are brown, sluggish, ugly creatures, with six legs.
+They feed on small water-animals, for which they
+wait very patiently, either at the bottom of the
+water, or on some aquatic plant. The lower jaws
+are attached to a long folding rod; and when any
+unwary little creature approaches too near the larva,
+this apparatus is shot out with such velocity that the
+prey which comes within its reach seldom escapes.
+In their perfect condition, also, Dragon-flies feed on
+other insects, and may often be seen hawking round
+ponds. The so-called Ant-lions in many respects
+resemble the Dragon-flies, but the habits of the
+larv&aelig; are very dissimilar. They do not live in the
+water, but prefer dry places, where they bury themselves
+in the loose sand, and seize with their long
+jaws any small insect which may pass. The true Ant-lion
+makes itself a round, shallow pit in loose ground
+or sand, and buries itself at the bottom. Any inattentive
+little insect which steps over the edge of this pit
+immediately falls to the bottom, and is instantaneously
+seized by the Ant-lion. Should the insect escape, and
+attempt to climb up the side of the pit, the Ant-lion
+is said to throw sand at it, knocking it down again.</p>
+
+<p>One other family of Neuroptera which I must<span class='pagenum'><a name="Page_23" id="Page_23">23</a></span>
+mention, is the Hemerobiid&aelig;. The perfect insect is
+a beautiful, lace-winged, very delicate, green creature,
+something like a tender Dragon-fly, and with bright,
+green, touching eyes. The female deposits her eggs
+on leaves, not directly on the plant itself, but attached
+to it by a long white slender footstalk. The larva
+has six legs and powerful jaws, and makes itself very
+useful in destroying the Hop-fly.</p>
+
+<p>The insects forming the order Trichoptera are well
+known in their larval condition, under the name of
+caddis worms. These larv&aelig; are not altogether unlike
+caterpillars in form, but they live in water&mdash;which is
+the case with very few lepidopterous larv&aelig;&mdash;and form
+for themselves cylindrical cases or tubes, built up of
+sand, little stones, bits of stick, leaves, or even shells.
+They generally feed on vegetable substances, but will
+also attack minute freshwater animals. When full
+grown, the larva fastens its case to a stone, the stem
+of a plant, or some other fixed substance, and closes
+the two ends with an open grating of silken threads,
+so as to admit the free access of water, while excluding
+enemies. It then turns into a pupa which bears some
+resemblance to the perfect insect, &#8220;except that the
+antenn&aelig;, palpi, wings, and legs are shorter, enclosed
+in separate sheaths, and arranged upon the breast.&#8221;
+The pupa remains quiet in the tube until nearly
+ready to emerge, when it comes to the surface, and
+in some cases creeps out of the water. It is not
+therefore so completely motionless as the pup&aelig; of
+Lepidoptera.</p>
+
+<p>The Diptera, or Flies, comprise insects with two
+wings only, the hinder pair being represented by
+minute club-shaped organs called &#8220;halt&egrave;res.&#8221; Flies<span class='pagenum'><a name="Page_24" id="Page_24">24</a></span>
+quit the egg generally in the form of fat, fleshy,
+legless grubs. They feed principally on decaying
+animal or vegetable matter, and are no doubt useful
+as scavengers. Other species, as the gadflies, deposit
+their eggs on the bodies of animals, within which the
+grubs feed, when hatched. The mouth is generally
+furnished with two hooks which serve instead of jaws.
+The pup&aelig; of Diptera are of two kinds. In the true
+flies, the outer skin of the full-grown larva is not shed,
+but contracts and hardens, thus assuming the appearance
+of an oval brownish shell or case, within which
+the insect changes into a chrysalis. The pup&aelig; of the
+gnats, on the contrary, have the limbs distinct and
+enclosed in sheaths. They are generally inactive, but
+some of the aquatic species continue to swim about.</p>
+
+<p>One group of Flies, which is parasitic on horses,
+sheep, bats, and other animals, has been called the
+Pupipara, because it was supposed that they were
+not born until they had arrived at the condition of
+pup&aelig;. They come into the world in the form of
+smooth, ovate bodies, much resembling ordinary dipterous
+pup&aelig;, but as Leuckart has shown,<a name="FNanchor_11" id="FNanchor_11"></a><a href="#Footnote_11" class="fnanchor">11</a> they are
+true, though abnormal, larv&aelig;.</p>
+
+<p>The next order, that of the Aphaniptera, is very
+small in number, containing only the different species
+of Flea. The larva is long, cylindrical, and legless;
+the chrysalis is motionless, and the perfect insect is
+too well known, at least, as regards its habits, to need
+any description.</p>
+
+<p>The Heteroptera, unlike the preceding orders of
+insects, quit the egg in a form differing from that of
+<span class='pagenum'><a name="Page_25" id="Page_25">25</a></span>the perfect insect principally in the absence of wings,
+which are gradually acquired. In their metamorphoses
+they resemble the Orthoptera, and are active
+through life. The majority are dull in colour, though
+some few are very beautiful. The species constituting
+this group, though very numerous, are generally small,
+and not so familiarly known to us as those of the
+other large orders, with indeed one exception, the
+well-known Bug. This is not, apparently, an indigenous
+insect, but seems to have been introduced.
+The word is indeed used by old writers, but either
+as meaning a bugbear, or in a general sense, and not
+with reference to this particular insect. In this country
+it never acquires wings, but is stated to do so sometimes
+in warmer climates. The Heteroptera cannot
+exactly be said either to sting or bite. The jaws, of
+which, as usual among insects, there are two pairs,
+are like needles, which are driven into the flesh, and
+the blood is then sucked up the lower lip, which has
+the form of a tube. This peculiar structure of the
+mouth prevails throughout the whole order; consequently
+their nutriment consists almost entirely of
+the juices of animals or plants. The Homoptera
+agree with the Heteroptera in the structure of the
+mouth, and in the metamorphoses. They differ principally
+in the front wings, which in Homoptera are
+membranous throughout, while in the Heteroptera,
+the front part is thickened and leathery. As in the
+Heteroptera, however, so also in the Homoptera,
+some species do not acquire wings. The Cicada,
+celebrated for its chirp, and the lanthorn fly, belong
+to this group. So also does the so-called Cuckoo-spit,
+so common in our gardens, which has the curious<span class='pagenum'><a name="Page_26" id="Page_26">26</a></span>
+faculty of secreting round itself a quantity of frothy
+fluid which serves to protect it from its enemies.
+But the best known insects of this group are the
+Aphides or Plant-lice; while the most useful belong
+to the Coccid&aelig;, or scale insects, from one species of
+which we obtain the substance called lac, so extensively
+used in the manufacture of sealing-wax and
+varnish. Several species also have been used in
+dyeing, especially the Cochineal insect of Mexico, a
+species which lives on the cactus. The male <i>Coccus</i>
+is a minute, active insect, with four large wings;
+while the female, on the contrary, never acquires
+wings, but is very sluggish, broad, more or less
+flattened, and in fact, when full grown, looks like a
+small brown, red, or white scale.</p>
+
+<p>The larva of the order Lepidoptera are familiar to
+us all, under the name of caterpillars. The insects
+of this order in their larval condition are almost all
+phytophagous, and are very uniform both in structure
+and in habits. The body is long and cylindrical, consisting
+of thirteen segments; the head is armed with
+powerful jaws; the three following segments, the
+future prothorax, mesothorax, and metathorax, each
+bears a pair of simple articulated legs. Of the posterior
+segments, five also bear false or pro-legs, which
+are short, unjointed, and provided with a number of
+hooklets. A caterpillar leads a dull and uneventful
+life; it eats ravenously, and grows rapidly, casting its
+skin several times during the process, which generally
+lasts only a few weeks; though in some cases, as for
+instance that of the goat-moth, it extends over a
+period of two or three years, after which the larva
+changes into a quiescent pupa or chrysalis.</p>
+
+<hr />
+
+<p><span class='pagenum'><a name="Page_27" id="Page_27">27</a></span></p>
+
+
+<h4>CHAPTER II.</h4>
+
+<h4><i>THE INFLUENCE OF EXTERNAL CONDITIONS
+ON THE FORM AND STRUCTURE OF LARV&AElig;.</i></h4>
+
+<p>The facts recapitulated briefly in the preceding
+chapter show, that the forms of insect larv&aelig; depend
+greatly on the group to which they belong. Thus
+the same tree may harbour larv&aelig; of Diptera,
+Hymenoptera, Coleoptera, and Lepidoptera; each
+presenting the form typical of the family to which
+it belongs.</p>
+
+<p>If, again, we take a group, such, for instance, as
+the Lamellicorn beetles, we shall find larv&aelig; extremely
+similar in form, yet very different in habits. Those,
+for instance, of the common cockchafer (Fig. <a href="#f1">1</a>) feed
+on the roots of grass; those of <i>Cetonia aurata</i> (Fig. <a href="#f1">2</a>)
+inhabit ants' nests; the larv&aelig; of the genus <i>Trox</i>
+(Fig. <a href="#f1">3</a>) are found on dry animal substances; of
+<i>Oryctes</i> (Fig. <a href="#f1">4</a>) in tan-pits; of <i>Aphodius</i> (Fig. <a href="#f1">5</a>) in
+dung; of <i>Lucanus</i> (the stag-beetle, Fig. <a href="#f1">6</a>) in wood.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f1" id="f1"></a>
+<img src="images/fig_001-6.png" width="500" height="303"
+alt="Figs. 1-6" title="" />
+
+<p class="caption"><span class="smcap">Fig. 1</span>, Larva of the Cockchafer (<i>Melolontha</i>). (Westwood, Int. to the
+Modern Classification of Insects, vol. i. p. 194.). 2, Larva of <i>Cetonia</i>.
+3, Larva of <i>Trox</i>. 4, Larva of <i>Oryctes</i>. 5, Larva of <i>Aphodius</i> (Chapuis
+and Cand&egrave;ze, M&eacute;m. Soc. Roy. Li&egrave;ge, 1853). 6, Larva of <i>Lucanus</i>.
+(Packard, Guide to the Study of Insects, Fig. 403).</p></div>
+
+<p>On the other hand, in the present chapter it will be
+my object to show that the form of the larva depends
+very much on the conditions of its life. Thus, those
+larv&aelig; which are internal parasites, whether in animals<span class='pagenum'><a name="Page_28" id="Page_28">28</a></span>
+or plants, are vermiform, as are those which live in
+cells, and depend on their parents for food. On the
+other hand, larv&aelig; which burrow in wood have strong
+jaws and generally somewhat weak thoracic legs;
+whilst those which feed on leaves have the thoracic
+legs more developed, but less so than the carnivorous
+species. Now, the Hymenoptera, as a general
+rule, belong to the first category: the larv&aelig; of the
+Ichneumons, &amp;c., which live in animals,&mdash;those of
+the Cynipid&aelig;, inhabiting galls,&mdash;and those of ants,
+bees, wasps, &amp;c., which are fed by their parents, are
+fleshy, apodal grubs; though the remarkable fact
+that the embryos of bees in one stage of their development
+possess rudiments of thoracic legs which
+subsequently disappear, seems to show, not indeed
+that the larv&aelig; of bees were ever hexapod, but that
+bees are descended from ancestors which had hex<span class='pagenum'><a name="Page_29" id="Page_29">29</a></span>apod
+larv&aelig;, and that the present apod condition of
+these larv&aelig; is not original, but results from their
+mode of life.</p>
+
+<p>On the other hand, the larv&aelig; of <i>Sirex</i> (Fig. <a href="#f14">14</a>)
+being wood-burrowers, possess well-developed thoracic
+legs. Again, the larv&aelig; of the Tenthredinid&aelig;,
+which feed upon leaves, closely resemble the caterpillars
+of Lepidoptera, even to the presence of
+abdominal pro-legs.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="f7" id="f7"></a>
+<img src="images/fig_007-8.png" width="400" height="125"
+alt="figs. 7-8" title="" />
+
+<p class="center"><span class="smcap">Fig. 7</span>, Larva of <i>Brachytarsus</i> (Ratzeburg, Forst. Insecten). 8, Larva of <i>Crioceris</i>
+(Westwood, loc. cit.).</p></div>
+
+<p>The larv&aelig; of most Coleoptera (Beetles) are active,
+hexapod, and more or less flattened: but those which
+live inside vegetable tissues, such as the weevils, are
+apod fleshy grubs, like those of Hymenoptera. Pl. <a href="#p2">II.</a>,
+Fig. 6, represents the larva of the nut-weevil, <i>Balaninus</i>
+(Pl. <a href="#p1">I.</a>, Fig. 6), and it will be seen that it closely
+resembles Pl. <a href="#p2">II.</a>, Fig. 5, which represents that of a fly
+(<i>Anthrax</i>), Pl. <a href="#p1">I.</a>, Fig. 5, and Pl. <a href="#p2">II.</a>, Figs. 7, 8, and 9,
+which represent respectively those of a <i>Cynips</i> or
+gall-fly (Pl. <a href="#p1">I.</a>, Fig. 7), an ant (Pl. <a href="#p1">I.</a>, Fig. 8), and wasp
+(Pl. <a href="#p1">I.</a>, Fig. 9). Nor is <i>Balaninus</i> the only genus of
+Coleoptera which affords us examples of this fact.
+Thus in the genus <i>Scolytus</i> (Pl. <a href="#p1">I.</a>, Fig. 4), the larv&aelig;
+(Pl. <a href="#p2">II.</a>, Fig. 4), which, as already mentioned, feed on
+the bark of the elm, closely resemble those just described,
+as also do those of <i>Brachytarsus</i> (Fig. <a href="#f7">7</a>). On
+the other hand, the larv&aelig; of certain beetles feed on<span class='pagenum'><a name="Page_30" id="Page_30">30</a></span>
+leaves, like the caterpillars of Lepidoptera; thus that
+of <i>Crioceris Asparagi</i> (Fig. <a href="#f7">8</a>)&mdash;which, as its name
+denotes, feeds on the asparagus&mdash;closely resembles
+the larv&aelig; of certain Lepidoptera, as for instance of
+<i>Thecla spini</i>. From this point of view the transformations
+of the genus <i>Sitaris</i> (Pl. <a href="#p3">III.</a>, Fig. 4), which
+have been very carefully investigated by M. Fabre,
+are peculiarly interesting.<a name="FNanchor_12" id="FNanchor_12"></a><a href="#Footnote_12" class="fnanchor">12</a></p>
+
+<div class="figcenter" style="width: 500px;"><a name="f9" id="f9"></a>
+<img src="images/fig_009-13.png" width="500" height="324"
+alt="Figs. 9-13" title="" />
+
+<p class="caption"><span class="smcap">Fig. 9</span>, Larva of <i>Sitaris humeralis</i> (Fabre, Ann. des Sci. Nat., s&eacute;r.
+4, tome vii.). 10, Larva of <i>Sitaris humeralis</i>, in the second stage.
+11, Larva of <i>Sitaris humeralis</i>, in the third stage. 12, Larva of <i>Sitaris humeralis</i>, in the fourth stage. 13, Pupa of <i>Sitaris</i>.</p></div>
+
+<p>The genus <i>Sitaris</i> (a small beetle allied to Cantharis,
+the blister-fly, and to <i>Melo&euml;</i>, the oil-beetle) is
+parasitic on a kind of Bee (Anthophora), which excavates
+subterranean galleries, each leading to a cell.
+The eggs of the <i>Sitaris</i>, which are deposited at the
+entrance of these galleries, are hatched at the end of
+September or beginning of October; and M. Fabre not
+<span class='pagenum'><a name="Page_31" id="Page_31">31</a></span>unnaturally expected that the young larv&aelig;, which are
+active little creatures with six serviceable legs (Fig. <a href="#f9">9</a>),
+would at once eat their way into the cells of the Anthophora.
+No such thing: till the month of April
+following they remain without leaving their birthplace,
+and consequently without food; nor do they in this
+long time change either in form or size. M. Fabre
+ascertained this, not only by examining the burrows
+of the <i>Anthophoras</i>, but also by direct observation of
+some young larv&aelig; kept in captivity. In April, however,
+his captives at last awoke from their long lethargy,
+and hurried anxiously about their prisons. Naturally
+inferring that they were in search of food, M. Fabre
+supposed that this would consist either of the larv&aelig;
+or pup&aelig; of the Anthophora, or of the honey with
+which it stores its cell. All three were tried without
+success. The first two were neglected, and the larv&aelig;,
+when placed on the latter, either hurried away, or
+perished in the attempt, being evidently unable to
+deal with the sticky substance. M. Fabre was in
+despair: &#8220;Jamais exp&eacute;rience,&#8221; he says, &#8220;n&#8217;a &eacute;prouv&eacute;
+pareille d&eacute;confiture. Larves, nymphes, cellules, miel,
+je vous ai tous offert; que voulez-vous donc, bestioles
+maudites?&#8221; The first ray of light came to him from
+our countryman, Newport, who ascertained that a
+small parasite found by L&eacute;on Dufour on one of the
+wild bees, and named by him Triungulinus, was, in
+fact, the larva of <i>Melo&euml;</i>;. The larv&aelig; of <i>Sitaris</i> much
+resembled Dufour&#8217;s Triungulinus; and acting on this
+hint, M. Fabre examined many specimens of Anthophora,
+and found on them at last the larv&aelig; of his
+<i>Sitaris</i>. The males of Anthophora emerge from the<span class='pagenum'><a name="Page_32" id="Page_32">32</a></span>
+pup&aelig; sooner than the females, and M. Fabre ascertained
+that, as they come out of their galleries, the
+little <i>Sitaris</i> larv&aelig; fasten upon them. Not, however,
+for long: instinct teaches them that they are not yet
+in the straight path of development; and, watching
+their opportunity, they pass from the male to the
+female bee. Guided by these indications, M. Fabre
+examined several cells of the Anthophora: in some,
+the egg of the Anthophora floated by itself on the
+surface of the honey; in others, on the egg, as on a
+raft, sat the still more minute larva of the <i>Sitaris</i>.
+The mystery was solved. At the moment when the
+egg is laid the <i>Sitaris</i> larva springs upon it. Even
+while the poor mother is carefully fastening up her
+cell, her mortal enemy is beginning to devour her
+offspring: for the egg of the Anthophora serves not
+only as a raft, but as a repast. The honey which is
+enough for either, would be too little for both; and
+the <i>Sitaris</i>, therefore, at its first meal, relieves itself
+from its only rival. After eight days the egg is consumed,
+and on the empty shell the <i>Sitaris</i> undergoes
+its first transformation, and makes its appearance
+in a very different form, as shown in Fig. <a href="#f9">10.</a></p>
+
+<p>The honey which was fatal before is now necessary;
+the activity which before was necessary is now useless;
+consequently, with the change of skin, the
+active, slim larva changes into a white, fleshy grub,
+so organized as to float on the surface of the honey,
+with the mouth beneath, and the spiracles above the
+surface: &#8220;gr&acirc;ce &agrave; l&#8217;embonpoint du ventre,&#8221; says M.
+Fabre, &#8220;la larve est &agrave; l&#8217;abri de l&#8217;asphyxie.&#8221; In this
+state it remains until the honey is consumed; then the<span class='pagenum'><a name="Page_33" id="Page_33">33</a></span>
+animal contracts, and detaches itself from its skin,
+within which the further transformations take place.
+In the next stage, which M. Fabre calls the pseudo-chrysalis
+(Fig. <a href="#f9">11</a>), the larva has a solid corneous
+envelope and an oval shape; and in its colour, consistency,
+and immobility reminds one of a Dipterous
+pupa. The time passed in this condition varies much.
+When it has elapsed, the animal moults again, again
+changes its form, and assumes that shown in Fig. <a href="#f9">12</a>;
+after this it becomes a pupa (Fig. <a href="#f9">13</a>) without any
+remarkable peculiarities. Finally, after these wonderful
+changes and adventures, in the month of August the
+perfect <i>Sitaris</i> (Pl. <a href="#p3">III.</a>, Fig. 4) makes its appearance.</p>
+
+<p>On the other hand, there are cases in which larv&aelig;
+diverge remarkably from the ordinary type of the
+group to which they belong, without, as it seems in
+our present imperfect state of information, any sufficient
+reason.</p>
+
+<p>Thus the ordinary type of Hymenopterous larva, as
+we have already seen, is a fleshy apod grub; although
+those of the leaf-eating and wood-boring groups,
+Tenthredinid&aelig; and Siricid&aelig; (Fig. <a href="#f14">14</a>), are caterpillars,
+more or less closely resembling those of Lepidoptera.
+There is, however, a group of minute Hymenoptera,
+the larv&aelig; of which reside within the eggs or larv&aelig;
+of other insects. It is difficult to understand why
+these larv&aelig; should differ from those of Ichneumons,
+which are also parasitic Hymenoptera, and should be,
+as will be seen by the accompanying figures, of such
+remarkable and grotesque forms. The first known of
+these curious larv&aelig; was observed by De Filippi,<a name="FNanchor_13" id="FNanchor_13"></a><a href="#Footnote_13" class="fnanchor">13</a> who,
+<span class='pagenum'><a name="Page_34" id="Page_34">34</a></span>having collected some of the transparent eggs of
+a small Beetle (<i>Rhynchites betuleti</i>), to his great
+surprise found more than half of them attacked by
+a parasite, which proved to be the larva of a minute
+Hymenopterous insect belonging to the Pteromalid&aelig;.
+Fig. <a href="#f14">15</a> shows the egg of the Beetle, with the parasitic
+larva, which is represented on a larger scale in
+Fig. <a href="#f14">16.</a></p>
+
+<div class="figcenter" style="width: 500px;"><a name="f14" id="f14"></a>
+<img src="images/fig_014-16.png" width="500" height="188"
+alt="Figs. 14-16" title="" />
+
+<p class="caption"><span class="smcap">Fig. 14</span>, Larva of <i>Sirex</i> (Westwood, loc. cit.). 15, Egg of <i>Rhynchites</i>, showing the
+parasitic Larva in the interior. 16, the parasitic Larva more magnified.</p></div>
+
+<p>More recently this group has been studied by M.
+Ganin,<a name="FNanchor_14" id="FNanchor_14"></a><a href="#Footnote_14" class="fnanchor">14</a> who thus describes the development of <i>Platygaster</i>.
+The egg, as in allied Hymenopterous families,
+for instance in <i>Cynips</i>, is elongated and club-shaped
+(Fig. <a href="#f17">17</a>). After a while a large nucleated cell appears
+in the centre (Fig. <a href="#f17">18</a>). This nucleated cell
+divides (Fig. <a href="#f17">19</a>) and subdivides. The outermost cells
+continue the same process, thus forming an outer
+investing layer. The central, on the contrary, enlarges
+considerably, and develops within itself a
+number of daughter cells (Figs. <a href="#f17">20 and 21</a>), which
+gradually form a mulberry-like mass, thus giving
+rise to the embryo (Fig. <a href="#f17">22</a>).</p>
+
+<p><span class='pagenum'><a name="Page_35" id="Page_35">35</a></span></p>
+
+<div class="figcenter" style="width: 500px;"><a name="f17" id="f17"></a>
+<img src="images/fig_017-22.png" width="500" height="345"
+alt="Figs. 17-22" title="" />
+
+<p class="caption"><span class="smcap">Fig. 17</span>, Egg of <i>Platygaster</i> (after Ganin). 18, Egg of <i>Platygaster</i>
+showing the central cell. 19, Egg of <i>Platygaster</i> after the division of
+the central wall. 20, Egg of <i>Platygaster</i> more advanced. 21, Egg of
+<i>Platygaster</i> more advanced. 22, Egg of <i>Platygaster</i> showing the rudiment
+of the embryo.</p></div>
+
+<p>Ganin met with the larv&aelig; of <i>Platygaster</i> in those
+of a small gnat, <i>Cecidomyia</i>. Sometimes as many as
+fifteen parasites occurred in one gnat, but as a rule
+only one of these attained maturity. The three
+species of <i>Platygaster</i> differ considerably in form, as
+shown in Figs. <a href="#f23">23-25</a>. They creep about within
+the larva of <i>Cecidomyia</i> by means of the strong
+hooked feet, <i>kf</i>, somewhat aided by movements
+of the tail. They possess a mouth, stomach, and
+muscles, but the nervous, vascular, and respiratory
+systems do not make their appearance until later.
+After some time the larva (Fig. <a href="#f23">23</a>) changes its
+skin, assuming the form represented in Fig. <a href="#f23">26</a>. In
+this moult the last abdominal segment of the first
+larva is entirely thrown off: not merely the outer
+skin, as in the case of the other segments, but also<span class='pagenum'><a name="Page_36" id="Page_36">36</a></span>
+the hypodermis and the muscles. This larva, as will
+be seen by the figure, resembles a barrel or egg in
+form, and is .870 mm. in length, the external appendages
+having disappeared, and the segments being<span class='pagenum'><a name="Page_37" id="Page_37">37</a></span>
+indicated only by the arrangement of the muscles.
+<i>slkf</i> is the &oelig;sophagus leading into a wide stomach
+which occupies nearly the whole body, <i>gsae</i> is the
+rudiment of the supra-&oelig;sophageal ganglia, <i>bsm</i> the
+ventral nervous cords. The ventral nervous mass has
+the form of a broad band, with straight sides; it
+consists of embryonal cells, and remains in this undeveloped
+condition during the whole larval state.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f23" id="f23"></a>
+<img src="images/fig_023-27.png" width="500" height="525"
+alt="Figs. 23-27" title="" />
+
+<p class="caption"><span class="smcap">Fig. 23</span>, Larva of <i>Platygaster</i> (after Ganin)&mdash;<i>mo</i>, mouth; <i>a</i>, antenna;
+<i>kf</i>, hooked feet; <i>z</i>, toothed process; <i>lfg</i>, lateral process; <i>f</i>, branches
+of the tail. 24, Larva of another species of <i>Platygaster</i>. The letters indicate
+the same parts as in the preceding figure. 25, Larva of a third
+species of <i>Platygaster</i>. The letters indicate the same parts as in the preceding
+figures. 26, Larva of <i>Platygaster</i> in the second stage&mdash;<i>mo</i>, mouth;
+<i>slkf</i>, &oelig;sophagus; <i>gsae</i>, supra-&oelig;sophageal ganglion; <i>lm</i>, muscles;
+<i>bsm</i>, nervous system; <i>ga</i>, <i>gh</i>, rudiments of the reproductive glands.
+27, Larva of <i>Platygaster</i> in the third stage&mdash;<i>mo</i>, mouth; <i>md</i>,
+mandibles; <i>gsae</i>, supra-&oelig;sophageal ganglion; <i>slk</i>, &oelig;sophagus; <i>ag</i>,
+ducts of the salivary glands; <i>bnm</i>, ventral nervous system; <i>sp</i>, salivary
+glands; <i>msl</i>, stomach; <i>im</i>, imaginal discs; <i>tr</i>, trache&aelig;; <i>fk</i>, fatty
+tissue; <i>ed</i>, intestine; <i>ga</i>, rudiments of reproductive organs; <i>ew</i>, wider
+portion of intestine; <i>ao</i>, posterior opening.</p></div>
+
+<p>At the next moult the larva enters its third state,
+which, as far as the external form (Fig. <a href="#f23">27</a>) is concerned,
+differs from the second only in being somewhat
+more elongated. The internal organs, however,
+are much more complex and complete. The trache&aelig;
+have made their appearance, and the mouth is provided
+with a pair of mandibles. From this point
+the metamorphoses of <i>Platygaster</i> do not appear to
+differ materially from those of other parasitic Hymenoptera.</p>
+
+<p>An allied genus, <i>Polynema</i>, has also very curious
+larv&aelig;. The perfect insect is aquatic in its habits,
+swimming by means of its wings; flying, if we may
+say so, under water.<a name="FNanchor_15" id="FNanchor_15"></a><a href="#Footnote_15" class="fnanchor">15</a> It lays its eggs inside those
+of Dragon-flies; and the embryo, as shown in
+Fig. <a href="#f28">28</a>, has the form of a bottle-shaped mass of undifferentiated
+embryonal cells, covered by a thin cuticle,
+but without any trace of further organization. Protected
+by the egg-shell of the Dragon-fly, and bathed
+in the nourishing fluid of the Dragon-fly&#8217;s egg, the
+young <i>Polynema</i> imbibes nourishment through its
+whole surface, and increases rapidly in size. The
+digestive canal gradually makes its appearance; the
+<span class='pagenum'><a name="Page_38" id="Page_38">38</a></span>cellular mass forms a new skin beneath the original
+cuticle, distinctly divided into segments, and provided
+with certain appendages. After a while the old
+cuticle is thrown off, and the larva gradually assumes
+the form shown in Fig. <a href="#f28">29</a>. The subsequent metamorphoses
+of <i>Polynema</i> offer no special peculiarities.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f28" id="f28"></a>
+<img src="images/fig_028-29.png" width="500" height="355"
+alt="Figs. 28-29" title="" />
+
+<p class="caption"><span class="smcap">Fig. 28</span>, Embryo of <i>Polynema</i> (after Ganin). 29, Larva of <i>Polynema</i>&mdash;<i>asch</i>,
+rudiments of the antenna; <i>flsch</i>, rudiments of the wings; <i>bsch</i>,
+rudiments of the legs; <i>vfg</i>. lateral projections; <i>gsch</i>, rudiments of
+the ovipositor; <i>fk</i>, fatty tissue.</p></div>
+
+<p>From these facts&mdash;and, if necessary, many more of
+the same nature might have been brought forward&mdash;it
+seems to me evident that while the form of any
+given larva depends to a certain extent on the group
+of insects to which it belongs, it is also greatly
+influenced by the external conditions to which it is
+subjected; that it is a function of the life which the
+larva leads and of the group to which it belongs.</p>
+
+<p>The larv&aelig; of insects are generally regarded as being
+nothing more than immature states&mdash;as stages in the<span class='pagenum'><a name="Page_39" id="Page_39">39</a></span>
+development of the egg into the imago; and this
+might more especially appear to be the case with
+those insects in which the larv&aelig; offer a general resemblance
+in form and structure (excepting of course
+so far as relates to the wings) to the perfect insect.
+Nevertheless we see that this would be a very incomplete
+view of the case. The larva and pupa undergo
+changes which have no relation to the form which
+the insect will ultimately assume. With a general
+tendency to this goal, as regards size and the development
+of the wings, there are coincident other
+changes having reference only to existing wants
+and condition. Nor is there in this, I think,
+anything which need surprise us. External circumstances
+act on the insect in its preparatory states,
+as well as in its perfect condition. Those who
+believe that animals are susceptible of great, though
+gradual, change through the influence of external
+conditions, whether acting, as Mr. Darwin has suggested,
+through natural selection, or in any other
+manner, will see no reason why these changes should
+be confined to the mature animal. And it is evident
+that creatures which, like the majority of insects,
+live during the successive periods of their existence
+in very different circumstances, may undergo considerable
+changes in their larval organization, in
+consequence of forces acting on them while in that
+condition; not, indeed, without affecting, but certainly
+without affecting to any corresponding extent, their
+ultimate form.</p>
+
+<p>I conclude, therefore, that the form of the larva
+in insects, whenever it departs from the hexapod<span class='pagenum'><a name="Page_40" id="Page_40">40</a></span>
+<i>Campodea</i> type, has been modified by the conditions
+under which it lives. The external forces acting
+upon it are different from those which affect the
+mature form; and thus changes are produced in
+the young which have reference to its immediate
+wants, rather than to its final form.</p>
+
+<p>And, lastly, as a consequence, that metamorphoses
+may be divided into two kinds, developmental and
+adaptional or adaptive.</p>
+
+<hr />
+
+<p><span class='pagenum'><a name="Page_41" id="Page_41">41</a></span></p>
+
+
+
+<h4>CHAPTER III.</h4>
+
+<h4><i>ON THE NATURE OF METAMORPHOSES.</i></h4>
+
+<p>In the preceding chapters we have considered the
+life history of insects after they have quitted the
+egg; but it is obvious that to treat the subject in
+a satisfactory manner we must take the development
+as a whole, from the commencement of the
+changes in the egg, up to the maturity of the animal,
+and not suffer ourselves to be confused by the fact
+that insects leave the egg in very different stages
+of embryonal development. For though all young
+insects when they quit the egg are termed &#8220;larv&aelig;,&#8221;
+whatever their form may be (the case of the so-called
+Pupipara not constituting a true exception), still it
+must be remembered that some of these larv&aelig; are
+much more advanced than others. It is evident that
+the larva of a fly, as regards its stage of development,
+corresponds in reality neither with that of a
+moth nor with that of a grasshopper. The maggots
+of flies, in which the appendages of the head are rudimentary,
+belong to a lower grade than the grubs of
+bees, &amp;c., which have antenn&aelig;, mandibles, maxill&aelig;,<span class='pagenum'><a name="Page_42" id="Page_42">42</a></span>
+labrum, labium, and, in fact, all the mouth parts of a
+perfect insect.</p>
+
+<p>The caterpillars of Lepidoptera are generally classed
+with the vermiform larva of Diptera and Hymenoptera,
+and contrasted with those of Orthoptera,
+Hemiptera, &amp;c.; but, in truth, the possession of thoracic
+legs places them, together with the similar larv&aelig;
+of the Tenthredinid&aelig;, on a decidedly higher level.
+Thus, then, the period of growth (that in which the
+animal eats and increases in size) occupies sometimes
+one stage in the development of an insect, sometimes
+another; sometimes, as for instance in the case of
+<i>Chlo&euml;on</i>, it continues through more than one; or, in
+other words, growth is accompanied by development.
+But, in fact, the question is even more complicated
+than this. It is not only that the larv&aelig; of insects at
+their birth offer the most various grades of development,
+from the grub of a fly to the young of a grasshopper
+or a cricket; but that, if we were to classify
+larv&aelig; according to their development, we should have
+to deal, not with a simple case of gradations only, but
+with a series of gradations, which would be different
+according to the organ which we took as our test.</p>
+
+<p>Apart, however, from the adaptive changes to which
+special reference was made in the previous chapter,
+the differences which larv&aelig; present are those of gradation,
+not of direction. The development of a grasshopper
+does not pursue a different course from that
+of a butterfly, but the embryo attains a higher state
+before quitting the egg in the former than in the
+latter: while in most Hymenoptera, as for instance
+in Bees, Wasps, Ants, &amp;c., the young are hatched<span class='pagenum'><a name="Page_43" id="Page_43">43</a></span>
+without thoracic appendages; in the Orthoptera, on
+the contrary, the legs are fully developed before the
+young animal quits the egg.</p>
+
+<p>Prof. Owen,<a name="FNanchor_16" id="FNanchor_16"></a><a href="#Footnote_16" class="fnanchor">16</a> indeed, goes so far as to say that the
+Orthoptera and other Homomorphous insects are, &#8220;at
+one stage of their development, apodal and acephalous
+larv&aelig;, like the maggot of the fly; but instead of quitting
+the egg in this stage, they are quickly transformed
+into another, in which the head and rudimental
+thoracic feet are developed to the degree which characterizes
+the hexapod larv&aelig; of the <i>Carabi</i> and
+<i>Petalocera</i>.&#8221;</p>
+
+<p>I quite believe that this may have been true of
+such larv&aelig; at an early geological period, but the
+fact now appears to be, so far at least as can be
+judged from the observations yet recorded, that the
+legs of those larv&aelig; which leave the egg with these
+appendages generally make their appearance before
+the body-walls have closed, or the internal organs
+<span class='pagenum'><a name="Page_44" id="Page_44">44</a></span>have approached to completion. Indeed, when the
+legs first appear, they are merely short projections,
+which it is not always easy to distinguish from the
+segments themselves. It must, however, be admitted,
+that the observations are neither so numerous, nor
+in most cases so full, as could be wished.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f30" id="f30"></a>
+<img src="images/fig_030-31.png" width="500" height="233"
+alt="Figs. 30-31" title="" />
+
+<p class="caption"><span class="smcap">Fig. 30</span>, Egg of <i>Phryganea</i> (Mystacides)&mdash;<i>A<sup>1</sup></i>, mandibular segment; <i>C<sup>1</sup></i>
+to <i>C<sup>5</sup></i>, maxillary, labial, and three thoracic segments; <i>D</i>, abdomen
+(after Zaddach). 31, Egg of <i>Phryganea</i> somewhat more advanced&mdash;<i>b</i>,
+mandibles; <i>c</i>, maxill&aelig;; <i>cfs</i>, rudiments of the three pairs of legs.</p></div>
+
+<p>Fig. <a href="#f30">30,</a> represents an egg of a May-fly (<i>Phryganea</i>),
+as represented by Zaddach in his excellent
+memoir,<a name="FNanchor_17" id="FNanchor_17"></a><a href="#Footnote_17" class="fnanchor">17</a> just before the appearance of the appendages.
+It will be seen that a great part of the
+yolk is still undifferentiated, that the side walls are
+incomplete, the back quite open, and the segments
+merely indicated by undulations. This stage is
+rapidly passed through, and Zaddach only once met
+with an egg in this condition; in every other specimen
+which had indications of segments, the rudiments
+of the legs had also made their appearance,
+as in Fig. <a href="#f30">31</a>, which, however, as will be seen, does
+not in other respects show much advance on Fig. <a href="#f30">30.</a></p>
+
+<p>Again in <i>Aphis</i>, the embryology of which has been
+so well worked out by Huxley,<a name="FNanchor_18" id="FNanchor_18"></a><a href="#Footnote_18" class="fnanchor">18</a> the case is very
+similar, although the legs are somewhat later in
+making their appearance. When the young was 1/140th
+of an inch in length, he found the cephalic portion
+of the embryo beginning, he says, &#8220;to extend upwards
+again over the anterior face of the germ, so
+as to constitute its anterior and a small part of its
+superior wall. This portion is divided by a median
+fissure into two lobes, which play an important part
+<span class='pagenum'><a name="Page_45" id="Page_45">45</a></span>in the development of the head, and will be termed
+the &#8216;procephalic lobes.&#8217; I have already made use
+of this term for the corresponding parts in the embryos
+of Crustacea. The rudimentary thorax presents
+traces of a division into three segments; and
+the dorso-lateral margins of the cephalic blastoderm,
+behind the procephalic lobes, have a sinuous margin.
+It is in embryos between this and 1/100th of an inch in
+length, that the rudiments of the appendages make
+their appearance; and by the growth of the cephalic,
+thoracic, and abdominal blastoderm, curious changes
+are effected in the relative position of those regions.&#8221;</p>
+
+<p>In <i>Chrysopa oculata</i>, one of the Hemerobiid&aelig;,
+Packard has described<a name="FNanchor_19" id="FNanchor_19"></a><a href="#Footnote_19" class="fnanchor">19</a> and figured a stage in which
+the body segments have made their appearance, but
+in which he says &#8220;there are no indications of limbs.
+The primitive band is fully formed, the protozorites
+being distinctly marked, the transverse impressed
+lines indicating the primitive segments being distinct,
+and the median furrow easily discerned.&#8221; Here
+also, again, the dorsal walls are incomplete, and the
+internal organs as yet unformed.</p>
+
+<p>In certain Dragon-flies (<i>Calepteryx</i>), and Hemiptera
+(<i>Hydrometra</i>), the legs, according to Brandt,<a name="FNanchor_20" id="FNanchor_20"></a><a href="#Footnote_20" class="fnanchor">20</a> appear
+at a still earlier stage.</p>
+
+<p>According to the observations of K&ouml;lliker,<a name="FNanchor_21" id="FNanchor_21"></a><a href="#Footnote_21" class="fnanchor">21</a> it
+would appear that in the Coleopterous genus <i>Donacia</i>
+the segments and appendages appear simultaneously.</p>
+
+<p><span class='pagenum'><a name="Page_46" id="Page_46">46</a></span></p><p>K&ouml;lliker himself, however, frankly admits that &#8220;me&aelig;
+de hoc insecto observationes satis sunt manca,&#8221; and
+it is possible that he may never have met with an
+embryo in the state immediately preceding the appearance
+of the legs; especially as it appears from
+the observations of Kowalevski that in <i>Hydrophilus</i>
+the appendages do not make their appearance until
+after the segments.<a name="FNanchor_22" id="FNanchor_22"></a><a href="#Footnote_22" class="fnanchor">22</a></p>
+
+<p>On the whole, as far as we can judge from the
+observations as yet recorded, it seems that in Homomorphous
+insects the ventral wall is developed and
+divided into segments, before the appearance of the
+legs; but that the latter are formed almost simultaneously
+with the cephalic appendages, and before
+either the dorsal walls of the body or the internal
+organs.</p>
+
+<div class="figcenter" style="width: 250px;"><a name="f32" id="f32"></a>
+<img src="images/fig_032.png" width="250" height="257"
+alt="Fig. 32" title="" /></div>
+
+<p class="center"><span class="smcap">Fig. 32.</span>&mdash;Egg of <i>Pholcus opilionides</i> (after Clapar&egrave;de).</p>
+
+<p>As it is interesting, from this point of view, to
+compare the development of other Articulata with
+that of insects, I give a figure (Fig. <a href="#f32">32</a>), representing
+an early stage in the development of a spider
+(<i>Pholcus</i>) after Clapar&egrave;de,<a name="FNanchor_23" id="FNanchor_23"></a><a href="#Footnote_23" class="fnanchor">23</a> who says, &#8220;C&#8217;est &agrave; ce
+<span class='pagenum'><a name="Page_47" id="Page_47">47</a></span>moment qu&#8217;a lieu la formation des <i>protozonites</i> ou
+segments primordiaux du corps de l&#8217;embryon. Le
+rudiment ventral s'&eacute;paissit suivant six z&ocirc;nes dispos&eacute;es
+transversalement entre le capuchon anal et le capuchon
+c&eacute;phalique.&#8221;</p>
+
+<div class="figcenter" style="width: 250px;"><a name="f33" id="f33"></a>
+<img src="images/fig_033.png" width="250" height="293"
+alt="Fig. 33" title="" /></div>
+
+<p class="center"><span class="smcap">Fig. 33.</span>&mdash;Embryo of <i>Julus</i> (after Newport).</p>
+
+<p>Among Centipedes the development of <i>Julus</i> has
+been described by Newport.<a name="FNanchor_24" id="FNanchor_24"></a><a href="#Footnote_24" class="fnanchor">24</a> The first period, from
+the deposition of the egg to the gradual bursting of
+the shell, and exposure of the embryo within it,
+which, however, remains for some time longer in
+connection with the shell, lasts for twenty-five days.
+The segments of the body, originally six in number,
+make their appearance on the twentieth day after
+the deposition of the egg, at which time there
+were no traces of legs. The larva, when it leaves
+the egg, is a soft, white, legless grub (Fig. <a href="#f33">33</a>), consisting
+of a head and seven segments, the head being
+somewhat firmer in texture than the rest of the body.
+It exhibits rudimentary antenn&aelig;, but the legs are
+still only represented by very slight papilliform processes<span class='pagenum'><a name="Page_48" id="Page_48">48</a></span>
+on the undersides of the segments to which
+they belong.</p>
+
+<p>As already mentioned, it is possible that at one time
+the vermiform state of the Homomorphous insects&mdash;which,
+as we have seen, is now so short, and passed
+through at so early a stage of development&mdash;was
+more important, more prolonged, and accompanied by
+a more complete condition of the internal organs.
+The compression, and even disappearance of those embryonal
+stages which are no longer adapted to the
+mode of life&mdash;which do not benefit the animal&mdash;is
+a phenomenon not without a parallel in other parts
+of the animal or even of the vegetable kingdom.
+Just as in language long compound words have
+a tendency to concision, and single letters sometimes
+linger on, indicating the history of a word, like
+the &#8220;l&#8221; in &#8220;alms,&#8221; or the &#8220;b&#8221; in &#8220;debt,&#8221; long
+after they have ceased to influence the sound; so in
+embryology useless stages, interesting as illustrations
+of past history, but without direct advantage
+under present conditions, are rapidly passed through,
+and even, as it would appear, in some cases altogether
+omitted.</p>
+
+<div class="figcenter" style="width: 350px;"><a name="f34" id="f34"></a>
+<img src="images/fig_034.png" width="350" height="452"
+alt="Fig. 34" title="" />
+
+<p class="center"><span class="smcap">Fig. 34.</span>&mdash;Colony of <i>Bougainvillea fruticosa</i>, natural size, to the underside
+of a piece of floating timber (after Allman).</p></div>
+
+<p>For instance, among the Hydroida, in the great
+majority of cases, the egg produces a body more
+or less resembling the common <i>Hydra</i> of our ponds,
+and known technically as the &#8220;trophosome,&#8221; which
+develops into the well-known Medus&aelig; or jelly-fishes.
+The group, however, for which Prof. Allman has proposed
+the term Monopsea,<a name="FNanchor_25" id="FNanchor_25"></a><a href="#Footnote_25" class="fnanchor">25</a> and of which the genus
+<span class='pagenum'><a name="Page_49" id="Page_49">49</a></span>
+<i>&AElig;gina</i> may be taken as the type, is, as he says,
+distinguished by the absence of a hydriform stage,
+&#8220;the ovum becoming developed through direct
+metamorphosis into a medusiform body, just as in
+the other orders it is developed into a hydriform
+body.&#8221; Fig. <a href="#f34">34</a> represents, after Allman, a colony of
+<i>Bougainvillea fruticosa</i> of the natural size. It is a
+British species, which is found growing on buoys,
+floating timber, &amp;c., and, says Allman,<a name="FNanchor_26" id="FNanchor_26"></a><a href="#Footnote_26" class="fnanchor">26</a> &#8220;when in
+health and vigour, offers a spectacle unsurpassed in
+interest by any other species&mdash;every branchlet
+crowned by its graceful hydranth and budding with
+<span class='pagenum'><a name="Page_50" id="Page_50">50</a></span>
+Medus&aelig; in all stages of development (Fig. <a href="#f35">35</a>), some
+still in the condition of minute buds, in which no
+trace of the definite Medusa-form can yet be detected;
+others, in which the outlines of the Medusa can be
+distinctly traced within the transparent <i>ectoth&egrave;que</i> (external
+layer); others, again, just casting off this thin
+outer pellicle, and others completely freed from it,<span class='pagenum'><a name="Page_51" id="Page_51">51</a></span>
+struggling with convulsive efforts to break loose
+from the colony, and finally launched forth in the
+full enjoyment of their freedom into the surrounding
+water. I know of no form in which so many
+of the characteristic features of a typical hydroid
+are more finely expressed than in this beautiful
+species.&#8221;</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f35" id="f35"></a>
+<img src="images/fig_035.png" width="500" height="566"
+alt="Fig. 35" title="" />
+
+<p class="center"><span class="smcap">Fig. 35.</span>&mdash;Portion of colony of <i>Bougainvillea fruticosa</i>, more magnified.</p></div>
+
+<div class="figcenter" style="width: 250px;"><a name="f36" id="f36"></a>
+<img src="images/fig_036.png" width="250" height="436"
+alt="Fig. 36" title="" /></div>
+
+<p class="center"><span class="smcap">Fig. 36.</span>&mdash;The Medusa form of the same species.</p>
+
+<p>Fig. <a href="#f36">36</a> represents the Medusa form of this species,
+and the development thus described may be regarded
+as typical of the Hydroida; yet, as already
+mentioned, the &AElig;ginid&aelig; do not present us with
+any stage corresponding to the fixed condition of
+Bougainvillea, but, on the contrary, are developed
+into Medus&aelig; direct from the egg.</p>
+
+<p>On the other hand, there are groups in which<span class='pagenum'><a name="Page_52" id="Page_52">52</a></span>
+the Medusiform stage becomes less and less important.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f37" id="f37"></a>
+<img src="images/fig_037-38.png" width="500" height="412"
+alt="Figs. 37-38" title="" />
+
+<p class="center"><span class="smcap">Fig. 37</span>, Larva of Prawn, Nauplius stage (after F. M&uuml;ller). 38, Larva of Prawn,
+more advanced, Zo&euml;a stage.</p></div>
+
+<p>The great majority of the higher Crustacea go
+through well-marked metamorphoses. Figs. <a href="#f37">37 and
+38</a> represent two stages in the development of the
+prawn. In the first (Fig. <a href="#f37">37</a>), representing the young
+animal as it quits the egg, the body is more or less
+oval and unsegmented; there is a median frontal
+eye, and three pairs of natatory feet, the first pair
+simple, while the two posterior are two-branched.
+Very similar larv&aelig; occur in various other groups of
+Crustacea. They were at first regarded as mature<span class='pagenum'><a name="Page_53" id="Page_53">53</a></span>
+forms, and O. F. M&uuml;ller gave them the name of Nauplius.
+So also, the second or Zo&euml;a form (Fig. <a href="#f37">38</a>) was
+at first supposed to be a mature animal, until its true
+nature was discovered by Vaughan Thompson.</p>
+
+<p>The Zo&euml;a form of larva differs from the perfect
+prawn or crab in the absence of the middle portion of
+the body and its appendages. The mandibles have
+no palpi, the maxillipeds or foot-jaws are used as
+feet, whereas in the mature form they serve as jaws.
+Branchi&aelig; are either wanting or rudimentary, respiration
+being principally effected through the walls of
+the carapace. The abdomen and tail are destitute of
+articulate appendages. The development of Zo&euml;a
+into the perfect animal has been well described by
+Mr. Spence Bate<a name="FNanchor_27" id="FNanchor_27"></a><a href="#Footnote_27" class="fnanchor">27</a> in the case of the common crab
+(<i>Carcinus m&aelig;nas</i>).</p>
+
+<p>All crabs, as far as we know, with the exception of
+a species of land crab (<i>Gegarcinus</i>), described by
+Westwood, pass through a stage more or less resembling
+that shown in Fig. <a href="#f37">38</a>. On the other hand,
+the great group of Edriopthalma, comprising Amphipoda
+(shore-hoppers, &amp;c.) and Isopoda (wood-lice, &amp;c.)
+pass through no such metamorphosis; the development
+is direct, as in the Orthoptera. It is true that
+one species, <i>Tanais Dulongii</i>, though a typical Isopod
+in form and general character, is said to retain in some
+points, and especially in the mode of respiration,
+some peculiarities of the Zo&euml;a type; but this is quite
+an exceptional case. In <i>Mysis</i>, says F. M&uuml;ller,<a name="FNanchor_28" id="FNanchor_28"></a><a href="#Footnote_28" class="fnanchor">28</a>
+&#8220;there is still a trace of the Nauplius stage; being
+<span class='pagenum'><a name="Page_54" id="Page_54">54</a></span>transferred back to a period when it had not to
+provide for itself, the Nauplius has become degraded
+into a mere skin; in <i>Ligia</i> this larva-skin has lost
+the traces of limbs, and in <i>Philoscia</i> it is scarcely
+demonstrable.&#8221;</p>
+
+<p>The Echinodermata in most cases &#8220;go through a
+very well-marked metamorphosis, which often has
+more than one larval stage.... The mass of more
+or less differentiated sarcode, of which the larva, or
+pseud-embryo, as opposed to the Echinoderm within
+it, is made up, always carries upon its exterior certain
+bilaterally-arranged ciliated bands, by the action of
+which the whole organism is moved from place to
+place; and it may be strengthened by the super-addition
+to it of a framework of calcareous rods.&#8221;<a name="FNanchor_29" id="FNanchor_29"></a><a href="#Footnote_29" class="fnanchor">29</a>
+M&uuml;ller considered that the mouth and pharynx of
+the larva were either absorbed or cast off with the
+calcareous rods, but were never converted into the
+corresponding organs of the perfect Echinoderm.
+According to A. Agassiz, however, this is not the
+case, but on the contrary &#8220;the whole larva and all
+its appendages are gradually drawn into the body,
+and appropriated.&#8221;<a name="FNanchor_30" id="FNanchor_30"></a><a href="#Footnote_30" class="fnanchor">30</a></p>
+
+<div class="figcenter" style="width: 350px;"><a name="f39" id="f39"></a>
+<img src="images/fig_039.png" width="350" height="437"
+alt="Fig. 39" title="" />
+
+<p class="center"><span class="smcap">Fig. 39.</span>&mdash;Larva of <i>Echino-cidaris</i>, seen from above &#10005; 6/10 (after M&uuml;ller).</p></div>
+
+<p>Fig. <a href="#f39">39</a> represents the larva of a sea-egg (<i>Echino-cidaris</i>)
+after M&uuml;ller.<a name="FNanchor_31" id="FNanchor_31"></a><a href="#Footnote_31" class="fnanchor">31</a> The body is transparent,
+shaped somewhat like a double easel, but with two
+long horns in front, which, as well as the posterior
+<span class='pagenum'><a name="Page_55" id="Page_55">55</a></span>processes, are supported by calcareous rods. This
+larva swims by means of minute vibratile hairs, or
+cili&aelig;. It has a mouth, stomach, and in fact a well-defined
+alimentary canal; but no nerves or other internal
+organs have yet been discovered in it. After
+swimming about in this condition for a while, it
+begins to show signs of change. An involution of the
+integument takes place on one side of the back, and
+continues to deepen till it reaches a mass or store of
+what is called blastema, or the raw material of the
+animal body. This blastema then begins to change,
+and gradually assumes the form of the perfect
+Echinoderm.<a name="FNanchor_32" id="FNanchor_32"></a><a href="#Footnote_32" class="fnanchor">32</a></p>
+
+<p><span class='pagenum'><a name="Page_56" id="Page_56">56</a></span></p>
+
+<div class="figcenter" style="width: 350px;"><a name="f40" id="f40"></a>
+<img src="images/fig_040.png" width="350" height="442"
+alt="Fig. 40" title="" />
+
+<p class="caption"><span class="smcap">Fig. 40</span>, Larva of <i>Echinus</i>, &#10005; 100. <i>A</i>, front arm; <i>F</i>, arms of the mouth
+process; <i>B</i>, posterior side arm; <i>E<sub>1</sub></i>, accessory arm of the mouth process;
+<i>a</i>, mouth; <i>a&acute;</i>, &oelig;sophagus; <i>b</i>, stomach; <i>b&acute;</i>, intestine; <i>o</i>, posterior
+orifice; <i>d</i>, ciliated bands; <i>f</i>, ciliated epaulets; <i>c</i>, disc of future <i>Echinus</i>
+(after M&uuml;ller).</p></div>
+
+<p>Fig. <a href="#f40">40</a> represents a larva, probably of another sea-egg
+(<i>Echinus lividus</i>), from the Mediterranean, and
+shows the commencement of the sea-egg within the
+body of the larva. The capital letters denote the
+different arms: <i>a</i> is the mouth, <i>a&acute;</i> the &oelig;sophagus, <i>b</i>
+the stomach, <i>b&acute;</i> the intestine, <i>f</i> the ciliated lobes or
+epaulets, <i>c</i> the young sea-egg.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f41" id="f41"></a>
+<img src="images/fig_041.png" width="500" height="485"
+alt="Fig. 41" title="" />
+
+<p class="center"><span class="smcap">Fig. 41.</span>&mdash;<i>Comatula rosacea</i> (after Forbes).</p></div>
+
+<p>The development of the beautiful <i>Comatula rosacea</i>
+(Fig. <a href="#f41">41</a>) has been described in the &#8220;Philosophical
+Transactions,&#8221; by Prof. Wyville Thomson and Dr.
+Carpenter.<a name="FNanchor_33" id="FNanchor_33"></a><a href="#Footnote_33" class="fnanchor">33</a> The larva quits the egg, as shown in
+Fig. <a href="#f42">42</a>, in the form of an oval body about 1/30 inch
+<span class='pagenum'><a name="Page_57" id="Page_57">57</a></span>in length, something like a barrel, surrounded by
+four bands orops of long vibratile hairs or cili&aelig;.
+There is also a tuft of still longer hairs at the
+narrower posterior end of the body. Gradually a
+number of minute calcareous spines and plates make
+their appearance (Fig. <a href="#f42">43</a>) in the body of this larva,
+and at length arrange themselves in a definite order,
+so as to form a bent calcareous club or rod with an
+enlarged head.</p>
+
+<p><span class='pagenum'><a name="Page_58" id="Page_58">58</a></span></p>
+
+<div class="figcenter" style="width: 500px;"><a name="f42" id="f42"></a>
+<img src="images/fig_042-44.png" width="500" height="789"
+alt="Figs. 42-44" title="" />
+
+<p class="caption"><span class="smcap">Fig. 42</span>, Larva of <i>Comatula rosacea</i> (after Thomson). 43, Larva of <i>Comatula
+rosacea</i>, more advanced. 44, Larva of <i>Comatula rosacea</i>, in the
+Pentacrinus state.</p></div>
+
+<p><span class='pagenum'><a name="Page_59" id="Page_59">59</a></span></p>
+
+<p>As this process continues, the little creature gradually
+loses its power of swimming, and, sinking to the
+bottom, looses the bands of cili&aelig;, and attaches itself
+by its base to some stone or other solid substance,
+the knob of the club being free. The calcareous
+framework increases in size, and the expanded head
+forms itself into a cup, round which from five to
+fifteen delicate tentacles, as shown in Fig. <a href="#f42">44</a>, make
+their appearance.</p>
+
+<p>In this stage the young animal resembles one of
+the stalked Crinoids, a family of Echinoderms very
+abundant in earlier geological periods, but which
+has almost disappeared, being, as we see, now represented
+by the young states of existing more advanced,
+free, species. This attached, plant-like condition
+of <i>Comatula</i> was indeed at first supposed
+to be a mature form, and was named Pentacrinus;
+but we now know that it is only a stage in the development
+of <i>Comatula</i>. The so-called Pentacrinus
+increases considerably in size, and after various gradual
+changes, which time does not now permit me
+to describe, quits the stalk, and becomes a free
+<i>Comatula</i>.</p>
+
+<p>The metamorphoses of the Starfishes are also very
+remarkable. Sars discovered, in the year 1835, a
+curious little creature about an inch in length, which
+he named <i>Bipinnaria asterigera</i> (Figs. <a href="#f45">45-47</a>), and
+which he then supposed to be allied to the ciliograde
+Medus&aelig;. Subsequent observations, however, made
+in 1844, suggested to him that it was the larva of a
+Starfish, and in 1847 MM. Koren and Danielssen
+satisfied themselves that this was the case.</p>
+
+<p>Figs. <a href="#f45">45 and 46</a> represent the front and side view<span class='pagenum'><a name="Page_60" id="Page_60">60</a></span>
+of a Bipinnaria found by M&uuml;ller<a name="FNanchor_34" id="FNanchor_34"></a><a href="#Footnote_34" class="fnanchor">34</a> near Marseilles.
+<i>a</i> is the mouth, <i>b</i> the &oelig;sophagus, <i>c</i> the stomach, <i>c</i>&acute;
+the intestine. Fig. <a href="#f45">47</a> represents a somewhat older
+specimen, in which the Starfish (<i>k</i>) is already beginning
+to make its appearance.</p>
+
+<div class="figcenter" style="width: 500px;"><a name="f45" id="f45"></a>
+<img src="images/fig_045-47.png" width="500" height="305"
+alt="Figs. 45-47" title="" />
+
+<p class="caption"><span class="smcap">Fig. 45</span>, Larva of Starfish (Bipinnaria), &#10005; 100 (after M&uuml;ller). 46, Larva of
+Starfish (Bipinnaria), &#10005; 100, seen from the side&mdash;<i>a</i>, mouth; <i>b</i>, &oelig;sophagus;
+<i>c</i>, stomach; <i>c&acute;</i>, intestine. 47, Larva of another Bipinnaria,
+showing the commencement of the Starfish&mdash;<i>g</i>, canal of the ciliated sac;
+<i>i</i>, rudiments of tentacles; <i>d</i>, ciliated band.</p></div>
+
+<p>But while certain Starfishes thus go through metamorphoses
+similar in character, and not less remarkable
+than those of sea-eggs, there are others&mdash;as, for
+instance, the genus <i>Asteracanthion</i>&mdash;in which development
+may be said to be direct&mdash;the organs and
+appendages special to the Pseudembryo being in
+abeyance; while in another genus, Pteraster, they
+are reduced to a mere investing membrane.<a name="FNanchor_35" id="FNanchor_35"></a><a href="#Footnote_35" class="fnanchor">35</a></p>
+
+<p><span class='pagenum'><a name="Page_61" id="Page_61">61</a></span></p><p>Among the Ophiurans also we find two well-marked
+types of development. Some passing through metamorphoses,
+while others, as for instance <i>Ophiopholis
+bellis</i>, &#8220;is developed very much after the method of
+<i>Asteracanthion M&uuml;lleri</i>, without passing through the
+Plutean stage.&#8221;<a name="FNanchor_36" id="FNanchor_36"></a><a href="#Footnote_36" class="fnanchor">36</a></p>
+
+<p>Even in the same species of Echinoderm the degree
+of development attained by the larva differs to a
+certain extent according to the temperature, the
+supply of food, &amp;c. Thus in <i>Comatula</i>, specimens
+which are liberally supplied with sea-water, and kept
+warm, hurry as it were through their early stages, and
+the free larva becomes distorted by the growing
+Pentacrinus (see Fig. <a href="#f42">43</a>), almost before it has attained
+its perfect form. On the other hand, under less
+favourable conditions, if the temperature is low and
+food less abundant, the early stages are prolonged,
+the larva is longer lived, and reaches a much higher
+degree of independent development. Similar differences
+occur in the development of other animals,
+as for instance, in the Hydroids,<a name="FNanchor_37" id="FNanchor_37"></a><a href="#Footnote_37" class="fnanchor">37</a> and among the insects
+themselves, in Flies;<a name="FNanchor_38" id="FNanchor_38"></a><a href="#Footnote_38" class="fnanchor">38</a> and it is obvious that these
+facts throw much light on the nature and origin of
+the metamorphoses of insects, which subject we
+shall now proceed to consider.</p>
+
+<hr />
+
+<p><span class='pagenum'><a name="Page_62" id="Page_62">62</a></span></p>
+
+<h4>CHAPTER IV.</h4>
+
+<h4><i>ON THE ORIGIN OF METAMORPHOSES.</i></h4>
+
+<p>The question still remains, Why do insects pass
+through metamorphoses? Messrs. Kirby and Spence
+tell us they &#8220;can only answer that such is the will of
+the Creator;&#8221;<a name="FNanchor_39" id="FNanchor_39"></a><a href="#Footnote_39" class="fnanchor">39</a> this, however, is a general confession
+of faith, not an explanation of metamorphoses.
+So indeed they themselves appear to have felt; for
+they immediately proceed to make a suggestion.
+&#8220;Yet one reason,&#8221; they say, &#8220;for this conformation
+may be hazarded. A very important part assigned
+to insects in the economy of nature, as we shall hereafter
+show, is that of speedily removing superabundant
+and decaying animal and vegetable matter. For such
+agents an insatiable voracity is an indispensable
+qualification, and not less so unusual powers of multiplication.
+But these faculties are in a great degree
+incompatible; an insect occupied in the work of
+reproduction could not continue its voracious feeding.
+Its life, therefore, after leaving the egg, is divided into
+three stages.&#8221;</p>
+
+<p>But there are some insects&mdash;as, for instance, the
+<span class='pagenum'><a name="Page_63" id="Page_63">63</a></span>Aphides&mdash;which certainly are not among the least
+voracious, and which grow and breed at the same
+time. There are also many scavengers among
+other groups of animals&mdash;such, for instance, as the
+dog, the pig, and the vulture&mdash;which undergo no
+metamorphosis.</p>
+
+<p>It is certainly true that, as a general rule, growth
+and reproduction do not occur together; and it follows,
+almost as a necessary consequence, that in such cases
+the first must precede the second. But this has no
+immediate connection with the occurrence of metamorphoses.
+The question is not, why an insect does
+not generally begin to breed until it has ceased to
+grow, but why, in attaining to its perfect form, it
+passes through such remarkable changes; why these
+changes are so sudden and apparently violent; and
+why they are so often closed by a state of immobility&mdash;that
+of the chrysalis or pupa; for undoubtedly
+the quiescent and death-like condition of the pupa is
+one of the most remarkable phenomena of insect-metamorphoses.</p>
+
+<p>In the first place, it must be observed that many
+animals which differ considerably in their mature state,
+resemble one another more nearly when young. Thus
+birds of the same genus, or of closely allied genera,
+which, when mature, differ much in colour, are often
+very similarly coloured when young. The young of
+the lion and the puma are often striped, and the f&oelig;tal
+Black whale has teeth, like its ally the Sperm whale.</p>
+
+<p>In fact, the great majority of animals do go through
+well-marked metamorphoses, though in many cases
+they are passed through within the egg, and thus do<span class='pagenum'><a name="Page_64" id="Page_64">64</a></span>
+not come within the popular ken. &#8220;La larve,&#8221; says,
+Quatrefages, &#8220;n&#8217;est qu&#8217;un embryon &agrave; vie ind&eacute;pendante.&#8221;<a name="FNanchor_40" id="FNanchor_40"></a><a href="#Footnote_40" class="fnanchor">40</a>
+Those naturalists who accept in any form
+the theory of evolution, consider that &#8220;the embryonal
+state of each species reproduces more or less completely
+the form and structure of its less modified progenitors.&#8221;<a name="FNanchor_41" id="FNanchor_41"></a><a href="#Footnote_41" class="fnanchor">41</a>
+&#8220;Each organism,&#8221; says Herbert Spencer,<a name="FNanchor_42" id="FNanchor_42"></a><a href="#Footnote_42" class="fnanchor">42</a>
+&#8220;exhibits within a short space of time a series of
+changes which, when supposed to occupy a period
+indefinitely great, and to go on in various ways
+instead of one way, give us a tolerably clear conception
+of organic evolution in general.&#8221;</p>
+
+<p>The naturalists of the older school do not, as
+Darwin and Fritz M&uuml;ller have already pointed out,
+dispute these facts, though they explain them in a different
+manner&mdash;generally by the existence of a supposed
+tendency to diverge from an original type.
+Thus Johannes M&uuml;ller says, &#8220;The idea of development
+is not that of mere increase of size, but that of
+progress from what is not yet distinguished, but which
+potentially contains the distinction in itself, to the
+actually distinct. It is clear that the less an organ is
+developed, so much the more does it approach the
+type, and that during its development it acquires
+more and more peculiarities. The types discovered
+by comparative anatomy and developmental history
+must therefore agree.&#8221; And again, &#8220;What is true in
+this idea is, that every embryo at first bears only the
+<span class='pagenum'><a name="Page_65" id="Page_65">65</a></span>type of its section, from which the type of the class,
+order, &amp;c., is only afterwards developed.&#8221; Agassiz
+also observes that &#8220;the embryos of different animals
+resemble each other the more the younger they are.&#8221;</p>
+
+<p>There are, no doubt, cases in which the earlier
+states are rapidly passed through, or but obscurely
+indicated; yet we may almost state it as a general
+proposition, that either before or after birth animals
+undergo metamorphoses. The state of development
+of the young animal at birth varies immensely.
+The kangaroo (<i>Macropus major</i>), which attains
+a height of seven feet ten inches, does not when
+born exceed one inch and two lines in length;
+the chick leaves the egg in a much more advanced
+condition than the thrush; and so, among insects,
+the young cricket is much more highly developed,
+when it leaves the egg, than the larva of the fly
+or of the bee; and, as I have already mentioned,
+differences occur even within the limit of one species,
+though not of course to anything like the same
+extent.</p>
+
+<p>In oviparous animals the condition of the young
+at birth depends much on the size of the egg: where
+the egg is large, the abundant supply of nourishment
+enables the embryo to attain a high stage of
+development; where the egg is small, and the yolk
+consequently scanty, the embryo requires an additional
+supply of food before it can do so. In the
+former case the embryo is more likely to survive; but
+when the eggs are large, they cannot be numerous,
+and a multiplicity of germs may be therefore in some
+circumstances a great advantage. Even in the same<span class='pagenum'><a name="Page_66" id="Page_66">66</a></span>
+species the development of the egg presents certain
+differences.<a name="FNanchor_43" id="FNanchor_43"></a><a href="#Footnote_43" class="fnanchor">43</a></p>
+
+<p>The metamorphoses of insects depend then primarily
+on the fact that the young quit the egg at
+a more or less early stage of development; and
+that consequently the external forces, acting upon
+them in this state, are very different from those by
+which they are affected when they arrive at maturity.</p>
+
+<p>Hence it follows that, while in many instances
+mature forms, differing greatly from one another,
+arise from very similar larv&aelig;, in other cases, as we
+have seen, among some the parasitic Hymenoptera,
+insects agreeing closely with one another, are produced
+from larv&aelig; which are very unlike. The same
+phenomenon occurs in other groups. Thus, while in
+many cases very dissimilar jelly-fishes arise from
+almost identical Hydroids, we have also the reverse
+of the proposition in the fact that in some species,
+Hydroids of an entirely distinct character produce
+very similar Medus&aelig;.<a name="FNanchor_44" id="FNanchor_44"></a><a href="#Footnote_44" class="fnanchor">44</a></p>
+
+<p>We may now pass to the second part of our subject:
+the apparent suddenness and abruptness of
+the changes which insects undergo during metamorphosis.
+But before doing so I must repeat that these
+changes are not always, even apparently, sudden and
+great. The development of an Orthopterous insect,
+say a grasshopper, from its leaving the egg to
+maturity, is so gradual that the ordinary nomen<span class='pagenum'><a name="Page_67" id="Page_67">67</a></span>clature
+of entomological works (larva state and pupa
+state) does not apply to it; and even in the case
+of Lepidoptera, the change from the caterpillar to
+the chrysalis and from this to the butterfly is in
+reality less rapid than might at first sight be supposed;
+the internal organs are metamorphosed very
+gradually, and even the sudden and striking change
+in external form is very deceptive, consisting merely
+of a throwing off of the outer skin&mdash;the drawing
+aside, as it were of a curtain and the revelation of
+a form which, far from being new, has been in preparation
+for days; sometimes even for months.</p>
+
+<p>Swammerdam, indeed, supposed (and his view was
+adopted by Kirby and Spence) that the larva contained
+within itself &#8220;the germ of the future butterfly,
+enclosed in what will be the case of the pupa, which
+is itself included in three or more skins, one over the
+other, that will successively cover the larva.&#8221; This
+was a mistake; but it is true that, if a larva be examined
+shortly before it is full grown, the future
+pupa may be traced within it. In the same manner,
+if we examine a pupa which is about to disclose
+the butterfly, we find the future insect, soft indeed
+and imperfect, but still easily recognizable, lying
+more or less loosely within the pupa-skin.</p>
+
+<p>One important difference between an insect and a
+vertebrate animal is, that whereas in the latter&mdash;as, for
+instance, in ourselves&mdash;the muscles are attached to an
+internal bony skeleton, in insects no such skeleton
+exists. They have no bones, and their muscles are
+attached to the skin; whence the necessity for the
+hard and horny dermal investment of insects, so<span class='pagenum'><a name="Page_68" id="Page_68">68</a></span>
+different from the softness and suppleness of our
+own skin. The chitine, or horny substance, of which
+the outside of an insect consists, is formed by a layer
+of cells lying beneath it, and, once secreted, cannot be
+altered. From this the result is, that without a change
+of skin, a change of form is impossible. In some
+cases, as for instance in <i>Chlo&euml;on</i>, each change of skin
+is accompanied by a change of form, and thus the
+perfect insect is gradually evolved. In others, as
+in caterpillars, several changes of skin take place
+without any material alteration of form, and the
+change, instead of being spread over many, is confined
+to the last two moults.</p>
+
+<p>One explanation of this difference between the
+larv&aelig; which change their form with every change of
+skin, and those which do not, is, I believe, to be found
+in the structure of the mouth. That of the caterpillar
+is provided with a pair of strong jaws, fitted
+to eat leaves; and the digestive organs are adapted
+for this kind of food. On the contrary, the mouth of
+the butterfly is suctorial; it has a long proboscis,
+beautifully adapted to suck the nectar from flowers,
+but which would be quite useless, and indeed only
+an embarrassment to the larva. The digestive organs
+also of the butterfly are adapted for the assimilation,
+not of leaves, but of honey. Now it is evident that
+if the mouth-parts of the larva were slowly metamorphosed
+into those of the perfect insect, through
+a number of small changes, the insect would in the
+meantime be unable to feed, and liable to perish of
+starvation in the midst of plenty. In the Orthoptera,
+and among those insects in which the changes are<span class='pagenum'><a name="Page_69" id="Page_69">69</a></span>
+gradual, the mouth of the so-called larva resembles
+that of the perfect insect, and the principal difference
+consists in the presence of wings.</p>
+
+<p>Similar considerations throw much light on the
+nature of the chrysalis or pupa state&mdash;that remarkable
+period of death-like quiescence which is one of
+the most striking characteristics of insect metamorphosis.
+The quiescence of the pupa is mainly owing
+to the rapidity of the changes going on in it. In
+that of a butterfly, not only (as has been already
+mentioned) are the mouth and the digestive organs
+undergoing change, but the muscles are in a similar
+state of transition. The powerful ones which move
+the wings are in process of formation; and even the
+nervous system, by which the movements are set
+on foot and regulated, is in a state of rapid change.<a name="FNanchor_45" id="FNanchor_45"></a><a href="#Footnote_45" class="fnanchor">45</a></p>
+
+<p>It must not be forgotten that all insects are inactive
+for a longer or shorter space of time after
+each moult. The slighter the change, as a general
+rule, the shorter is the period of inaction. Thus,
+after the ordinary moult of a caterpillar, the insect
+only requires a short rest until the new skin is
+hardened. When, however, the change is great, the
+period of inaction is correspondingly prolonged.
+Most pup&aelig; indeed have some slight powers of
+motion; those which assume the chrysalis state in
+wood or beneath the ground usually come to the surface
+when about to assume the perfect state, and the
+aquatic pup&aelig; of certain Diptera swim about with
+much activity. Among the Neuroptera, certain families
+have pup&aelig; as quiescent as those of the Lepidoptera:
+<span class='pagenum'><a name="Page_70" id="Page_70">70</a></span>others&mdash;as, for instance, <i>Raphidia</i>&mdash;are quiescent at
+first, but at length acquire sufficient strength to walk,
+though still enclosed within the pupa-skin: a power
+dependent partly on the fact that this skin is very
+thin. Others again&mdash;as, for instance, dragon-flies&mdash;are
+not quiescent on assuming the so-called pupa state
+for any longer time than at their other changes of
+skin. The inactivity of the pupa is therefore not
+a new condition peculiar to this stage, but a prolongation
+of the inaction which has accompanied
+every previous change of skin.</p>
+
+<p>Nevertheless the metamorphoses of insects have
+always seemed to me one of the greatest difficulties
+of the Darwinian theory. In most cases, the development
+of the individual reproduces to a certain extent
+that of the race; but the motionless, imbecile pupa
+cannot represent a mature form. No one, so far as
+I know, has yet attempted to explain, in accordance
+with Mr. Darwin&#8217;s views, a life-history in which the
+mouth is first mandibulate and then suctorial, as, for
+example, in a butterfly. A clue to the difficulty may,
+I think, be found in the distinction between developmental
+and adaptive changes; to which I have
+called attention in a previous chapter. The larva
+of an insect is by no means a mere stage in the development
+of the perfect animal. On the contrary,
+it is subject to the influence of natural selection,
+and undergoes changes which have reference entirely
+to its own requirements and condition. It is evident,
+then, that while the embryonic development
+of an animal in the egg may be an epitome of its
+specific history, this is by no means the case with<span class='pagenum'><a name="Page_71" id="Page_71">71</a></span>
+species in which the immature forms have a separate
+and independent existence. If an animal which,
+when young, pursues one mode of life, and lives on
+one kind of food, subsequently, either from its own
+growth in size and strength, or from any change
+of season, alters its habits or food, however slightly,
+it immediately becomes subject to the action of new
+forces: natural selection affects it in two different,
+and, it may be, very distinct manners, gradually
+tending to changes which may become so great as
+to involve an intermediate period of change and
+quiescence.</p>
+
+<p>There are, however, peculiar difficulties in those
+cases in which, as among the Lepidoptera, the same
+species is mandibulate as a larva, and suctorial as an
+imago. From this point of view <i>Campodea</i> and the
+Collembola (<i>Podura</i>, &amp;c.) are peculiarly interesting.
+There are in insects three principal types of mouth:&mdash;</p>
+
+<div class="blockquot"><p>First, the mandibulate;</p>
+
+<p>Secondly, the suctorial; and</p>
+
+<p>Thirdly, that of <i>Campodea</i> and the Collembola
+generally,</p></div>
+
+<p>in which the mandibles and maxill&aelig; are retracted,
+but have some freedom of motion, and can be used
+for biting and chewing soft substances. This type is,
+in some respects, intermediate between the other two.
+Assuming that certain representatives of such a type
+were placed under conditions which made a suctorial
+mouth advantageous, those individuals in which the
+mandibles and maxill&aelig; were best calculated to pierce
+or prick would be favoured by natural selection, and
+their power of lateral motion would tend to fall into<span class='pagenum'><a name="Page_72" id="Page_72">72</a></span>
+abeyance; while, on the other hand, if masticatory
+jaws were an advantage, the opposite process would
+take place.</p>
+
+<p>There is yet a third possibility&mdash;namely, that
+during the first portion of life, the power of mastication
+should be an advantage, and during the second
+that of suction, or <i>vice vers&acirc;</i>. A certain kind of food
+might abound at one season and fail at another;
+might be suitable for the animal at one age and
+not at another. Now in such cases we should have
+two forces acting successively on each individual, and
+tending to modify the organization of the mouth in
+different directions. It cannot be denied that the
+innumerable variations in the mouth-parts of insects
+have special reference to their mode of life, and are of
+some advantage to the species in which they occur.
+Hence, no believer in natural selection can doubt
+the possibility of the three cases above suggested,
+the last of which seems to throw some light on the
+possible origin of species which are mandibulate in
+one period of life and not in another. Granting then
+the transition from the one condition to the other, this
+would no doubt take place contemporaneously with a
+change of skin. At such times we know that, even
+when there is no change in form, the softness of the
+organs temporarily precludes the insect from feeding
+for a time, as, for instance, in the case of caterpillars.
+If, however, any considerable change were
+involved, this period of fasting must be prolonged,
+and would lead to the existence of a third condition,
+that of the pupa, intermediate between the other two.
+Since the acquisition of wings is a more conspicuous<span class='pagenum'><a name="Page_73" id="Page_73">73</a></span>
+change than any relating to the mouth, we are apt
+to associate with it the existence of a pupa-state:
+but the case of the Orthoptera (grasshoppers, &amp;c.) is
+sufficient proof that the development of wings is perfectly
+compatible with permanent activity; the necessity
+for prolonged rest is in reality much more intimately
+connected with the change in the constitution
+of the mouth, although in many cases, no doubt, this
+is accompanied by changes in the legs, and in the
+internal organization. An originally mandibulate
+mouth, however, like that of a beetle, could not, I
+think, have been directly modified into a suctorial
+organ like that of a butterfly or a gnat, because the
+intermediate stages would necessarily be injurious.
+Neither, on the other hand, for the same reasons,
+could the mouth of the Hemiptera be modified into
+a mandibulate type like that of the Coleoptera. But
+in <i>Campodea</i> and the <i>Collembola</i> we have a type of
+animal closely resembling certain larv&aelig; which occur
+both in the mandibulate and suctorial series of insects,
+possessing a mouth neither distinctly mandibulate
+nor distinctly suctorial, but constituted on a
+peculiar type, capable of modification in either direction
+by gradual change, without loss of utility.</p>
+
+<p>In discussing this subject, it is necessary also to
+take into consideration the nature and origin of wings.
+Whence are they derived? why are there normally
+two pairs? and why are they attached to the meso-and
+meta-thorax? These questions are as difficult
+as they are interesting. It has been suggested, and
+I think with justice, that the wings of insects originally
+served for aquatic and respiratory purposes.</p>
+
+<p><span class='pagenum'><a name="Page_74" id="Page_74">74</a></span>
+In the larva of <i>Chlo&euml;on</i> (Pl. <a href="#p4">IV.</a>, Fig. 1), for instance,
+which in other respects so singularly resembles
+<i>Campodea</i> (Pl. <a href="#p3">III.</a>, Fig. 5), several of the segments
+are provided with foliaceous expansions which serve
+as respiratory organs. These so-called branchi&aelig; are in
+constant agitation, and the muscles which move them
+in several points resemble those of true wings. It
+is true that in <i>Chlo&euml;on</i> the vibration of the branchi&aelig;
+is scarcely, if at all, utilized for the purpose of locomotion;
+the branchi&aelig; are, in fact, placed too far back
+to act efficiently. The situation of these branchi&aelig;
+differs in different groups; indeed, it seems probable
+that originally there were a pair on each segment.
+In such a case, those branchi&aelig; situated near the
+centre of the body, neither too much in front nor too
+far back, would serve the most efficiently as propellers:
+the same causes which determined the position of
+the legs would also affect the wings. Thus a division
+of labour would be effected; the branchi&aelig; on the
+thorax would be devoted to locomotion; those on
+the abdomen to respiration. This would tend to
+increase the development of the thoracic segments,
+already somewhat enlarged, in order to receive the
+muscles of the legs.</p>
+
+<p>That wings may be of use to insects under water
+is proved by the very interesting case of <i>Polynema
+natans</i>,<a name="FNanchor_46" id="FNanchor_46"></a><a href="#Footnote_46" class="fnanchor">46</a> which uses its wings for swimming. This,
+however, is a rare case, and it is possible that the
+principal use of the wings was, primordially, to
+enable the mature forms to pass from pond to pond,
+thus securing fresh habitats and avoiding in-and-in
+<span class='pagenum'><a name="Page_75" id="Page_75">75</a></span>breeding. If this were so, the development of wings
+would gradually have been relegated to a late period
+of life; and by the tendency to the inheritance of
+characters at corresponding ages, which Mr. Darwin
+has pointed out,<a name="FNanchor_47" id="FNanchor_47"></a><a href="#Footnote_47" class="fnanchor">47</a> the development of wings would
+have thus become associated with the maturity of
+the insect. Thus the late acquisition of wings in the
+Insecta generally seems to be itself an indication of
+their descent from a stock which was at one period,
+if not originally, aquatic, and which probably resembled
+the present larv&aelig; of <i>Chlo&euml;on</i> in form, but
+had thoracic as well as abdominal branchi&aelig;.</p>
+
+<p>Finally, from the subject of metamorphosis we
+pass naturally to that most remarkable phenomenon
+which is known as the &#8220;Alternation of Generations:&#8221;
+for the first systematic view of which we are indebted
+to my eminent friend Prof Steenstrup.<a name="FNanchor_48" id="FNanchor_48"></a><a href="#Footnote_48" class="fnanchor">48</a></p>
+
+<p>I have always felt it very difficult to understand
+why any species should have been created in this
+double character; nor, so far as I am aware, has any
+explanation of the fact yet been attempted. Nevertheless
+insects offer, in their metamorphoses, a phenomenon
+not altogether dissimilar, and give a clue to
+the manner in which alternation of generations may
+have originated.</p>
+
+<p>The caterpillar owes its difference from the butterfly
+to the undeveloped state in which it leaves the
+egg; but its actual form is mainly due to the influence
+of the conditions under which it lives. If the cater<span class='pagenum'><a name="Page_76" id="Page_76">76</a></span>pillar,
+instead of changing into one butterfly, produced
+several, we should have an instance of alternation of
+generations. Until lately, however, we knew of no
+such case among insects; each larva produced one
+imago, and that not by generation, but by development.
+It has long been known, indeed, that there
+are species in which certain individuals remain always
+apterous, while others acquire wings. Many entomologists,
+however, regard these abnormal individuals as
+perfect, though wingless insects; and therefore I shall
+found no argument upon these cases, although they
+appear to me deserving of more attention than they
+have yet received.</p>
+
+<p>Recently, however, Prof. Wagner<a name="FNanchor_49" id="FNanchor_49"></a><a href="#Footnote_49" class="fnanchor">49</a> has discovered
+that, among certain small gnats, the larv&aelig; do not
+directly produce in all cases perfect insects, but give
+birth to other larv&aelig;, which undergo metamorphoses
+of the usual character, and eventually become gnats.
+His observations have been confirmed, as regards
+this main fact, by other naturalists; and Grimm has
+met with a species of <i>Chironomus</i> in which the pup&aelig;
+lay eggs.<a name="FNanchor_50" id="FNanchor_50"></a><a href="#Footnote_50" class="fnanchor">50</a></p>
+
+<p>Here, then, we have a distinct case of alternation of
+generations, as characterized by Steenstrup. Probably
+other cases will be discovered in which insects undeniably
+in the larval state will be found fertile. Nay,
+it seems to me possible, if not probable, that some
+larv&aelig; which do not now breed may, in the course of
+ages, acquire the power of doing so. If this idea is
+correct, it shows how the remarkable phenomenon,
+<span class='pagenum'><a name="Page_77" id="Page_77">77</a></span>known as alternation of generations, may have originated.</p>
+
+<p>Summing up, then, the preceding argument, we find
+among insects various modes of development; from
+simple growth on the one hand, to well-marked
+instances of the so-called alternation of generation on
+the other. In the wingless species of Orthoptera
+there is little external difference, excepting in size,
+between the young larva and the perfect insect. The
+growth is gradual, and there is nothing which would,
+in ordinary language, be called a metamorphosis. In
+the majority of Orthoptera, though the presence of
+wings produces a marked difference between the
+larva and the imago, the habits are nearly the same
+throughout life, and consequently the action of external
+circumstances affects the larva in the same
+manner as it does the perfect insect.</p>
+
+<p>This is not the case with the Neuroptera. The
+larv&aelig; do not live under the same conditions as the
+perfect insects: external forces accordingly affect them
+in a different manner; and we have seen that they
+pass through some changes which bear no reference
+to the form of the perfect insect: these changes, however,
+are for the most part very gradual. The caterpillars
+of Lepidoptera have even more extensive
+modifications to undergo; the mouth of the larva,
+for instance, being remarkably unlike that of the
+perfect insect. A change in this organ, however,
+could hardly take place while the insect was growing
+fast, and consequently feeding voraciously; nor,
+even if the change could be thus effected, would the
+mouth, in its intermediate stages, be in any way fitted<span class='pagenum'><a name="Page_78" id="Page_78">78</a></span>
+for biting and chewing leaves. The same reasoning
+applies also to the digestive organs. Hence the
+caterpillar undergoes little, if any, change, except
+in size, and the metamorphosis is concentrated, so
+to say, into the last two moults. The changes then
+become so rapid and extensive, that the intermediate
+period is necessarily one of quiescence. In
+some exceptional cases, as in <i>Sitaris</i> (<i>ante</i>, p. 30) we
+even find that, the conditions of life not being
+uniform throughout the larval period, the larva itself
+undergoes metamorphoses.</p>
+
+<p>Owing to the fact that the organs connected with
+the reproduction of the species come to maturity at a
+late period, larv&aelig; are generally incapable of breeding.
+There are, however, some flies which have viviparous
+larv&aelig;, and thus offer a typical case of alternation of
+generations.</p>
+
+<p>Thus, then, we find among insects every gradation,
+from simple growth to alternation of generations; and
+see how, from the single fact of the very early period
+of development at which certain animals quit the
+egg, we can throw some light on their metamorphoses,
+and for the still more remarkable phenomenon that,
+among many of the lower animals, the species is
+represented by two very different forms. We may
+even conclude, from the same considerations, that this
+phenomenon may in the course of ages become still
+more common than it is at present. As long, however,
+as the external organs arrive at their mature form
+before the internal generative organs are fully developed,
+we have metamorphosis; but if the reverse is
+the case, then alternation of generations often results.<span class='pagenum'><a name="Page_79" id="Page_79">79</a></span></p>
+
+<p>The same considerations throw much light on the
+remarkable circumstance, that in alternation of generations
+the reproduction is, as a general rule, agamic
+in one form. This results from the fact that reproduction
+by distinct sexes requires the perfection both
+of the external and internal organs; and if the phenomenon
+arise, as has just been suggested, from the
+fact that the internal organs arrive at maturity before
+the external ones, reproduction will result in those
+species only which have the power of agamic multiplication.</p>
+
+<p>Moreover, it is evident that we have in the animal
+kingdom two kinds of dimorphism.</p>
+
+<p>This term has usually been applied to those cases
+in which animals or plants present themselves at
+maturity under two forms. Ants and Bees afford us
+familiar instances among animals; and among plants
+the interesting case of the genus <i>Primula</i> has recently
+been described by Mr. Darwin. Even more recently
+he has made known to us the still more remarkable
+phenomenon afforded by the genus <i>Lythrum</i>,
+in which there are three distinct forms, and which
+therefore offers an instance of polymorphism.<a name="FNanchor_51" id="FNanchor_51"></a><a href="#Footnote_51" class="fnanchor">51</a></p>
+
+<p>The other kind of dimorphism or polymorphism
+differs from the first in being the result of the differentiating
+action of external circumstances, not on the
+mature, but on the young individual. Such different
+forms, therefore, stand towards one another in the
+relation of succession. In the first kind the chain
+of being divides at the extremity; in the other it
+<span class='pagenum'><a name="Page_80" id="Page_80">80</a></span>is composed of dissimilar links. Many instances of
+this second form of dimorphism have been described
+under the name of alternation of generations.</p>
+
+<p>The term, however, has met with much opposition,
+and is clearly inapplicable to the differences exhibited
+by insects in various periods of their life. Strictly
+speaking, the phenomena are frequently not alternate,
+and in the opinion of some eminent naturalists they
+are not, strictly speaking, cases of generation at all.<a name="FNanchor_52" id="FNanchor_52"></a><a href="#Footnote_52" class="fnanchor">52</a></p>
+
+<p>In order, then, to have some name for these remarkable
+phenomena, and to distinguish them from those
+cases in which the <i>mature</i> animal or plant is represented
+by two or more different forms, I think it would
+be convenient to retain exclusively for these latter
+the terms dimorphism and polymorphism; and those
+cases in which animals or plants pass through a succession
+of different forms might be distinguished by
+the name of dieidism or polyeidism.</p>
+
+<p>The conclusions, then, which I think we may draw
+from the preceding considerations, are:&mdash;</p>
+
+<p>1. That the occurrence of metamorphoses arises
+from the immaturity of the condition in which some
+animals quit the egg.</p>
+
+<p>2. That the form of the insect larva depends in
+great measure on the conditions in which it lives.
+The external forces acting upon it are different
+from those which affect the mature form; and thus
+changes are produced in the young, having refer<span class='pagenum'><a name="Page_81" id="Page_81">81</a></span>ence
+to its immediate wants, rather than to its final
+form.</p>
+
+<p>3. That metamorphoses may therefore be divided
+into two kinds, developmental and adaptional or
+adaptive.</p>
+
+<p>4. That the apparent abruptness of the changes
+which insects undergo, arises in great measure from
+the hardness of their skin, which admits of no gradual
+alteration of form, and which is itself necessary in
+order to afford sufficient support to the muscles.</p>
+
+<p>5. The immobility of the pupa or chrysalis depends
+on the rapidity of the changes going on in it.</p>
+
+<p>6. Although the majority of insects go through
+three well-marked stages after leaving the egg, still a
+large number arrive at maturity through a greater or
+smaller number of slight changes.</p>
+
+<p>7. When the external organs arrive at this final
+form before the organs of reproduction are matured,
+these changes are known as metamorphoses; when,
+on the contrary, the organs of reproduction are
+functionally perfect before the external organs, or
+when the creature has the power of budding, then the
+phenomenon is known as alternation of generations.</p>
+
+<hr />
+
+<p><span class='pagenum'><a name="Page_82" id="Page_82">82</a></span></p>
+
+<h4>CHAPTER V.</h4>
+
+<h4><i>ON THE ORIGIN OF INSECTS.</i></h4>
+
+<p>"Personne," says Carl Vogt, &#8220;en Europe au moins,
+n&#8217;ose plus soutenir la Cr&eacute;ation ind&eacute;pendante et de
+toutes pi&egrave;ces des esp&egrave;ces,&#8221; and though this statement
+is perhaps not strictly correct, still it is no
+doubt true, that the Doctrine of Evolution, in some
+form or other, is accepted by most, if not by all, the
+greatest naturalists of Europe. Yet it is surprising
+how much, in spite of all that has been written,
+Mr. Darwin&#8217;s views are still misunderstood. Thus
+Browning, in one of his recent poems, says:&mdash;</p>
+
+<div class="poem">
+<div class="stanza">
+<span class="i05">"That mass man sprang from was a jelly lump</span>
+<span class="i0">Once on a time; he kept an after course</span>
+<span class="i0">Through fish and insect, reptile, bird, and beast,</span>
+<span class="i0">Till he attained to be an ape at last,</span>
+<span class="i0">Or last but one."<a name="FNanchor_53" id="FNanchor_53"></a><a href="#Footnote_53" class="fnanchor">53</a></span>
+</div></div>
+
+<p>This theory, though it would be regarded by many as
+a fair statement of his views, is one which Mr. Darwin
+would entirely repudiate. Whether fish and insect,
+reptile, bird and beast, are derived from one original
+stock or not, they are certainly not links in one
+<span class='pagenum'><a name="Page_83" id="Page_83">83</a></span>
+sequence. I do not, however, propose to discuss the
+question of Natural Selection, but may observe that
+it is one thing to acknowledge that in Natural Selection,
+or the survival of the fittest, Mr. Darwin has
+called attention to a <i>vera causa</i>, has pointed out
+the true explanation of certain phenomena; but
+it is quite another thing to maintain that all animals
+are descended from some primordial source.</p>
+
+<p>For my own part, I am satisfied that Natural
+Selection is a true cause, and, whatever may be the
+final result of our present inquiries&mdash;whether animated
+nature be derived from one ancestral source,
+or from many&mdash;the publication of the Origin of
+Species will none the less have constituted an epoch
+in the History of Biology. But, how far the present
+condition of living beings is due to that cause; how
+far, on the other hand, the action of Natural Selection
+has been modified and checked by other natural
+laws&mdash;by the unalterability of types, by atavism, &amp;c.;
+how many types of life originally came into being;
+and whether they arose simultaneously or successively,&mdash;these
+and many other similar questions
+remain unsolved, even admitting the theory of Natural
+Selection. All this has indeed been clearly pointed
+out by Mr. Darwin himself, and would not need repetition
+but for the careless criticism by which in
+too many cases the true question has been obscured.
+Without, however, discussing the argument for and
+against Mr. Darwin&#8217;s conclusions, so often do we
+meet with travesties of it like that which I have
+just quoted, that it is well worth while to consider
+the stages through which some group, say for in<span class='pagenum'><a name="Page_84" id="Page_84">84</a></span>stance
+that of insects, have probably come to be what
+they are, assuming them to have developed under
+natural laws from simpler organisms. The question
+is one of great difficulty. It is hardly necessary to
+say that insects cannot have passed through all the
+lower forms of animal life, and naturalists do not at
+present agree as to the actual line of their development.</p>
+
+<p>In the case of insects, the gradual course of evolution
+through which the present condition of the
+group has probably been reached, has been discussed
+by Mr. Darwin, by Fritz M&uuml;ller, Haeckel, Brauer,
+myself and others.</p>
+
+<p>In other instances Pal&aelig;ontology throws much light
+on this question. Leidy has shown that the milk-teeth
+of the genus <i>Equus</i> resemble the permanent
+teeth of the ancient <i>Anchitherium</i>, while the milk-teeth
+of <i>Anchitherium</i> again approximate to the dental system
+of the still earlier <i>Merychippus</i>. R&uuml;timeyer, while
+calling attention to this interesting observation, adds
+that the milk-teeth of <i>Equus caballus</i> in the same way,
+and still more those of <i>E. fossilis</i>, resemble the permanent
+teeth of <i>Hipparion</i>.</p>
+
+<p>"If we were not acquainted with the horse," says
+Flower,<a name="FNanchor_54" id="FNanchor_54"></a><a href="#Footnote_54" class="fnanchor">54</a> &#8220;we could scarcely conceive of an animal
+whose only support was the tip of a single toe on
+each extremity, to say nothing of the singular conformation
+of its teeth and other organs. So striking
+have these characters appeared to many zoologists,
+that the animals possessing them have been reckoned
+as an order apart, called Solidungula; but pal&aelig;on<span class='pagenum'><a name="Page_85" id="Page_85">85</a></span>tology
+has revealed that in the structure of its skull,
+its teeth, its limbs, the horse is nothing more than a
+modified <i>Pal&aelig;otherium</i>; and though still with gaps
+in certain places, many of the intermediate stages
+of these modifications are already known to us, being
+the <i>Pal&aelig;otherium</i>, <i>Anchitherium</i>, <i>Merychippus</i>, and
+<i>Hipparion</i>.&#8221;</p>
+
+<p>"All Echinoids," says A. Agassiz,<a name="FNanchor_55" id="FNanchor_55"></a><a href="#Footnote_55" class="fnanchor">55</a> &#8220;pass, in their
+early stages, through a condition which recalls to us
+the first Echinoids which made their appearance in
+geological ages.&#8221; On embryological grounds, he
+observes, we should &#8220;place true Echini lowest, then
+the Clypeastroids, next the Echinolamps, and finally
+the Spatangoids.&#8221; Now among the Echinoids of the
+Trias there are no Clypeastroids, Echinolamps, or
+Spatangoids. The Clypeastroids make their appearance
+in the Lias, the Echinolamps in the Jurassic, while
+the Spatangoids commence in the Cretaceous period.</p>
+
+<p>Again<a name="FNanchor_56" id="FNanchor_56"></a><a href="#Footnote_56" class="fnanchor">56</a> &#8220;in the Radiates, the Acalephs in their
+first stages of growth, that is, in their Hydroid condition,
+remind us of the adult forms among Polyps,
+showing the structural rank of the Acalephs to be
+the highest, since they pass beyond a stage which
+is permanent with the Polyps; while the Adult forms
+of the Acalephs have in their turn a certain resemblance
+to the embryonic phases of the class next
+above them, the Echinoderms; within the limits
+of the classes, the same correspondence exists as
+between the different orders; the embryonic forms of
+the highest Polyps recall the adult forms of the lower
+<span class='pagenum'><a name="Page_86" id="Page_86">86</a></span>ones, and the same is true of the Acalephs as far as
+these phenomena have been followed and compared
+among them.&#8221; Indeed, the accomplished authors
+from whom I have taken the above quotation, do
+not hesitate to say<a name="FNanchor_57" id="FNanchor_57"></a><a href="#Footnote_57" class="fnanchor">57</a> that &#8220;whenever such comparisons
+have been successfully carried out, the result is
+always the same; the present representatives of the
+fossil types recall in their embryonic condition the
+ancient forms, and often explain their true position
+in the animal kingdom.&#8221;</p>
+
+<p>Fossil insects are unfortunately rare, there being
+but few strata in which the remains of this group
+are well preserved. Moreover, well-characterized
+Orthoptera and Neuroptera occur as early as the
+Devonian strata; Coleoptera and Hemiptera in the
+Coal-measures; Hymenoptera and Diptera in the
+Jurassic; Lepidoptera, on the contrary, not until the
+Tertiary. But although it appears from these facts
+that, as far as our present information goes, the
+Orthoptera and Neuroptera are the most ancient
+orders, it is not, I think, conceivable that the latter
+should have been derived from any known species of
+the former; on the other hand, the earliest known
+Neuroptera and Orthoptera, though in some respects
+less specialized than existing forms, are as truly, and
+as well characterized, Insects, as any now existing;
+nor are we acquainted with any earlier forms, which
+in any way tend to bridge over the gap between them
+and lower groups, though, as we shall see, there are
+types yet existing which throw much light on the
+subject.</p>
+
+<p><span class='pagenum'><a name="Page_87" id="Page_87">87</a></span></p>
+
+<p>In the consideration then of this question, we must
+rely principally on Embryology and Development.
+I have already referred to the cases in which species,
+very unlike in their mature condition, are very similar
+one to another when young. Haeckel, in his &#8220;Naturliche
+Sch&ouml;pfungsgeschichte,&#8221; gives a diagram which
+illustrates this very well as regards Crustacea. Pls. 1-4
+show the same to be the case with Insects.</p>
+
+<p>The Stag-beetle, the Dragon-fly, the Moth, the
+Bee, the Ant, the Gnat, the Grasshopper,&mdash;these and
+other less familiar types seem at first to have little
+in common. They differ in size, in form, in colour,
+in habits, and modes of life. Yet the researches of
+entomologists, following the clue supplied by the
+illustrious Savigny, have proved, not only that while
+differing greatly in details, they are constructed on
+one common plan; but also that other groups, as
+for instance, Crustacea (Lobsters, Crabs, &amp;c.) and
+Arachnida (Spiders and Mites), can be shown to be
+fundamentally similar. In Pl. <a href="#p4">IV</a> I have figured the
+larv&aelig; of an <i>Ephemera</i> (Fig. 1), of a <i>Melo&euml;</i> (Fig. 2),
+of a Dragon-fly (Fig. 3), of a <i>Sitaris</i> (Fig. 4), of a
+<i>Campodea</i> (Fig. 5), of a <i>Dyticus</i> (Fig. 6), of a Termite
+(Fig. 7), of a <i>Stylops</i> (Fig. 8), and of a <i>Thrips</i> (Fig. 9).
+All these larv&aelig; possess many characters in common.
+The mature forms are represented in the corresponding
+figures of Plate 3, and it will at once be seen
+how considerably they differ from one another. The
+same fact is also illustrated in Figs. <a href="#f48">48-55</a>, where
+Figs. <a href="#f48">48-51</a> represent the larval states of the mature
+forms represented in Figs. <a href="#f52">52-55</a>. Fig. <a href="#f48">48</a> is the
+larva of a moth, <i>Agrotis suffusa</i> (Fig. <a href="#f52">52</a>); Fig. <a href="#f48">49</a> of<span class='pagenum'><a name="Page_88" id="Page_88">88</a></span>
+a beetle, <i>Haltica</i> (Fig. <a href="#f52">53</a>); Fig. <a href="#f48">50</a> of a Saw-fly,
+<i>Cimbex</i> (Fig. <a href="#f54">54</a>); and Fig. <a href="#f48">51</a> of a Centipede, <i>Julus</i>
+(Fig. <a href="#f55">55</a>).</p>
+
+<div class="figcenter" style="width: 450px;"><a name="f48" id="f48"></a>
+<img src="images/fig_048-51.png" width="450" height="305"
+alt="Figs. 48-51" title="" />
+
+<p class="caption"><span class="smcap">Fig. 48</span>, Larva of Moth (<i>Agrotis suffusa</i>), after Packard. 49, Larva of Beetle
+(<i>Haltica</i>), after Westwood. 50, Larva of Sawfly (<i>Cimbex</i>), Brischke and
+Zaddach. Beob. ub d. arten. der Blatt und Holzwespen, Fig. 8. 51, Larva of
+<i>Julus</i>. Newport, Philos. Transactions, 1841.</p></div>
+
+<p>Thus, then, although it can be demonstrated that
+perfect insects, however much they differ in appearance,
+are yet reducible to one type, the fact becomes much
+more evident if we compare the larv&aelig;. M. Brauer<a name="FNanchor_58" id="FNanchor_58"></a><a href="#Footnote_58" class="fnanchor">58</a>
+and I<a name="FNanchor_59" id="FNanchor_59"></a><a href="#Footnote_59" class="fnanchor">59</a> have pointed out that two types of larv&aelig;,
+which I have proposed to call <i>Campodea</i>-form and
+<i>Lindia</i>-form, and which Packard has named Leptiform
+and Eruciform, run through the principal groups of
+insects. This is obviously a fact of great importance:
+as all individual <i>Melo&euml;</i>s are derived from a form
+resembling Pl. <a href="#p2">II</a>, Fig. 2, it is surely no rash hypothesis
+to suggest that the genus itself may have been so.</p>
+
+<p><span class='pagenum'><a name="Page_89" id="Page_89">89</a></span></p>
+
+<div class="figcenter" style="width: 500px;"><a name="f52" id="f52"></a>
+<img src="images/fig_052-53.png" width="500" height="225"
+alt="Figs. 52-53" title="" />
+
+<p class="center"><span class="smcap">Fig. 52</span>, <i>Agrotis suffusa</i> (after Packard). 53, <i>Haltica</i> (after Westwood).</p></div>
+
+<div class="figcenter" style="width: 250px;"><a name="f54" id="f54"></a>
+<img src="images/fig_054.png" width="250" height="240"
+alt="Fig. 54" title="" />
+
+<p class="center"><span class="smcap">Fig. 54</span>, <i>Cimbex</i>, Brischae and Zaddach. l.c. T. 2, Fig. 9.</p></div>
+
+<div class="figcenter" style="width: 400px;"><a name="f55" id="f55"></a>
+<img src="images/fig_055.png" width="400" height="63"
+alt="Fig. 55" title="" />
+
+<p class="center"><span class="smcap">Fig. 55.</span> <i>Julus</i> (after Gervais).</p></div>
+
+<p>Firstly, however, let me say a word as to the
+general Insect type. It may be described shortly as
+consisting of animals possessing a head, with mouth
+parts, eyes and antenn&aelig;; a many segmented body,
+with three pairs of legs on the segments immediately
+following the head; with, when mature, either one or
+two pairs of wings, generally with caudal appendages
+I will not now enter into a description of
+their internal anatomy. It will be seen that, except<span class='pagenum'><a name="Page_90" id="Page_90">90</a></span>
+as regards the wings, Pl. <a href="#p4">IV</a>, Fig. 4, representing the
+larva of a small beetle named <i>Sitaris</i>, answers very
+well to this description. Many other Beetles are
+developed from larv&aelig; closely resembling those of
+<i>Melo&euml;</i> (Pl. <a href="#p4">IV</a>, Fig. 2), and <i>Sitaris</i> (Pl. <a href="#p4">IV</a>, Fig. 4); in
+fact&mdash;except those species the larv&aelig; of which, as, for
+instance of the <i>Weevils</i> (Pl. <a href="#p2">II</a>, Fig. 6), are internal
+feeders, and do not require legs&mdash;we may say that
+the Coleoptera generally are derived from larv&aelig; of
+this type.</p>
+
+<p>I will now pass to a second order, the Neuroptera.
+Pl. <a href="#p4">IV</a>, Fig. 1, represents the larva of <i>Chlo&euml;on</i>, a
+species the metamorphoses of which I described
+some years ago in the Linnean Transactions,<a name="FNanchor_60" id="FNanchor_60"></a><a href="#Footnote_60" class="fnanchor">60</a> and
+it is obvious that in essential points it closely resembles
+the form to which I have just alluded.</p>
+
+<p>The Orthoptera, again, the order to which Grasshoppers,
+Crickets, Locusts, &amp;c. belong, commence
+life in a similar condition; and the same may also
+be said of the Trichoptera.</p>
+
+<p>The larv&aelig; of Bees when they quit the egg are
+entirely legless, but in an earlier stage they possess
+well-marked rudiments of thoracic legs, showing, as
+it seems to me, that their apodal condition is an
+adaptation to their circumstances. Other Hymenopterous
+larv&aelig;, those for example of <i>Sirex</i> (Fig. <a href="#f9">9</a>),
+and of the Saw-flies (Fig. <a href="#f48">50</a>) have well-developed
+thoracic legs.</p>
+
+<p>From the difference in external form, and especially
+from the large comparative size of the abdomen,
+these larv&aelig;, as well as those of Lepidoptera (Fig. <a href="#f48">48</a>),
+<span class='pagenum'><a name="Page_91" id="Page_91">91</a></span>have generally been classed with the maggots of Flies,
+<i>Weevils</i>, &amp;c., rather than with the more active form
+of larva just adverted to. This seems to me, as I
+have already pointed out,<a name="FNanchor_61" id="FNanchor_61"></a><a href="#Footnote_61" class="fnanchor">61</a> to be a mistake. The
+caterpillar type differs, no doubt, in its general appearance,
+owing to its greater clumsiness, but still
+essentially agrees with that already described.</p>
+
+<p>No Dipterous larva, so far as I know, belongs truly
+to this type; in fact, the early stages of the pupa
+in the Diptera seem in some respects to correspond
+to the larv&aelig; of other Insect orders. The Development
+of the Diptera is, however, as Weissman<a name="FNanchor_62" id="FNanchor_62"></a><a href="#Footnote_62" class="fnanchor">62</a> has
+shown, very abnormal in other respects.</p>
+
+<p>Thus, then, we find in many of the principal
+groups of insects that, greatly as they differ from
+one another in their mature condition, when they
+leave the egg they more nearly resemble the typical
+insect type; consisting of a head; a three-segmented
+thorax, with three pairs of legs; and a many-jointed
+abdomen, often with anal appendages. Now,
+is there any mature animal which answers to this
+description? We need not have been surprised if
+this type, through which it would appear that
+insects must have passed so many ages since (for
+winged Neuroptera have been found in the carboniferous
+strata) had long ago become extinct. Yet it
+is not so. The interesting genus <i>Campodea</i> (Pl. <a href="#p3">III</a>,
+Fig. 5) still lives; it inhabits damp earth, and
+closely resembles the larva of <i>Chlo&euml;on</i> (Pl. <a href="#p2">II</a>, Fig. 1),
+constituting, indeed, a type which, as shown in Pl. 4,
+<span class='pagenum'><a name="Page_92" id="Page_92">92</a></span>occurs in many orders of insects. It is true that the
+mouth-parts of <i>Campodea</i> do not resemble either
+the strongly mandibulate form which prevails among
+the larv&aelig; of Coleoptera, Orthoptera, Neuroptera,
+Hymenoptera, Lepidoptera; or the suctorial type of
+the Homoptera and Heteroptera. It is, however, not
+the less interesting or significant on that account,
+since, as I have elsewhere<a name="FNanchor_63" id="FNanchor_63"></a><a href="#Footnote_63" class="fnanchor">63</a> pointed out, its mouth-parts
+are intermediate between the mandibulate
+and haustellate types; a fact which seems to me
+most suggestive.</p>
+
+<p>It appears, then, that there are good grounds for
+considering that the various types of insects are
+descended from ancestors more or less resembling
+the genus <i>Campodea</i>, with a body divided into head,
+thorax, and abdomen: the head provided with
+mouth-parts, eyes, and one pair of antenn&aelig;; the
+thorax with three pairs of legs; and the abdomen, in
+all probability, with caudal appendages.</p>
+
+<p>If these views are correct, the genus <i>Campodea</i>
+must be regarded as a form of remarkable interest
+since it is the living representative of a prim&aelig;val
+type, from which not only the Collembola and Thysanura,
+but the other great orders of insects have
+derived their origin.</p>
+
+<p>From what lower group the <i>Campodea</i> type was
+itself derived is a question of great difficulty. Fritz
+M&uuml;ller indeed says,<a name="FNanchor_64" id="FNanchor_64"></a><a href="#Footnote_64" class="fnanchor">64</a> &#8220;if all the classes of Arthropoda
+(Crustacea, Insecta, Myriopoda, and Arachnida) are
+indeed all branches of a common stem (and of this
+there can scarcely be a doubt), it is evident that
+<span class='pagenum'><a name="Page_93" id="Page_93">93</a></span>the water-inhabiting and water-breathing Crustacea
+must be regarded as the original stem from which
+the other terrestrial classes, with their tracheal respiration,
+have branched off.&#8221; Haeckel, moreover, is of
+the opinion that the Tracheata are developed from
+the Crustacea, and probably from the Zo&euml;poda.
+For my own part, though I feel very great diffidence
+in expressing an opinion at variance with that of
+such high authorities, I am rather disposed to suggest
+that the <i>Campodea</i> type may possibly have been
+derived from a less highly developed one, resembling
+the modern Tardigrade,<a name="FNanchor_65" id="FNanchor_65"></a><a href="#Footnote_65" class="fnanchor">65</a> a (Fig. <a href="#f56">56</a>) smaller and much
+less highly organized being than <i>Campodea</i>. It possesses
+two eyes, three anterior pairs of legs, and one
+at the posterior end of the body, giving it a curious
+resemblance to some Lepidopterous larv&aelig;.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="f56" id="f56"></a>
+<img src="images/fig_056.png" width="400" height="140"
+alt="Fig. 56" title="" />
+
+<p class="center"><span class="smcap">Fig. 56</span>, Tardigrade (after Dujardin).</p></div>
+
+<p>These legs, however, as will be seen, are reduced
+to mere projections. But for them, the Tardigrada
+<span class='pagenum'><a name="Page_94" id="Page_94">94</a></span>would closely resemble the vermiform larva so common
+among insects. Among Trichoptera the larva early
+acquires three pairs of legs, but as Zaddach has
+shown,<a name="FNanchor_66" id="FNanchor_66"></a><a href="#Footnote_66" class="fnanchor">66</a> there is a stage, though it is quickly passed
+through, in which the divisions of the body are indicated,
+but no trace of legs is yet present. Indeed,
+there appear to be reasons for considering that while
+among Crustacea the appendages appear before the
+segments, in Insects the segments precede the appendages,
+although this stage of development is very
+transitory, and apparently, in some cases, altogether
+suppressed. I say &#8220;apparently,&#8221; because, as I have
+already mentioned, I am not yet satisfied that it will
+not eventually be found to be so in all cases.
+Zaddach, in his careful observations of the embryology
+of <i>Phryganea</i>, only once found a specimen
+in this stage, which also, according to the researches
+of Huxley,<a name="FNanchor_67" id="FNanchor_67"></a><a href="#Footnote_67" class="fnanchor">67</a> seems to be little more than indicated
+in <i>Aphis</i>. It is therefore possible that in other cases,
+when no such stage has been observed, it not really
+may be absent, but, from its transitoriness, may have
+hitherto escaped attention.</p>
+
+<p>Fritz M&uuml;ller has expressed the opinion<a name="FNanchor_68" id="FNanchor_68"></a><a href="#Footnote_68" class="fnanchor">68</a> that this
+vermiform type is of comparatively recent origin. He
+says: &#8220;The ancient insects approached more nearly to
+the existing Orthoptera, and perhaps to the wingless
+Blattid&aelig;, than to any other order, and the complete
+metamorphosis of the Beetles, Lepidoptera, &amp;c., is of
+later origin.&#8221; &#8220;There were,&#8221; he adds, &#8220;perfect insects
+<span class='pagenum'><a name="Page_95" id="Page_95">95</a></span>before larv&aelig; and pup&aelig;.&#8221; This opinion has been
+adopted by Mr. Packard<a name="FNanchor_69" id="FNanchor_69"></a><a href="#Footnote_69" class="fnanchor">69</a> in his &#8220;Embryological
+Studies on Hexapodous Insects.&#8221;</p>
+
+<p>M. Brauer<a name="FNanchor_70" id="FNanchor_70"></a><a href="#Footnote_70" class="fnanchor">70</a> also considers that the vermiform larva
+is a more recent type than the Hexapod form, and is
+to be regarded not as a developmental form, but as
+an adaptational modification of the earlier active
+hexapod type. In proof of this he quotes the case of
+<i>Sitaris</i>.</p>
+
+<div class="figcenter" style="width: 350px;"><a name="f57" id="f57"></a>
+<img src="images/fig_057-58.png" width="350" height="532"
+alt="Figs. 57-58" title="" />
+
+<p class="center"><span class="smcap">Fig. 57</span>, Larva of <i>Cecidomyia</i> (After Packard). 58, <i>Lindia
+torulosa</i> (after Dujardin).</p></div>
+
+<p>Considering, however, the peculiar habits of this
+genus, to which I have already referred, and also that
+the vermiform type is altogether lower in organization
+and less differentiated than the <i>Campodea</i> form, I
+cannot but regard this case as exceptional; one in
+which the development has been, as it were, to use an
+expression of Fritz M&uuml;ller&#8217;s, &#8220;falsified&#8221; by the struggle
+for existence, and which therefore does not truly indicate
+the successive stages of evolution. On the
+whole, the facts seem to me to point to the conclusion
+that, though the grublike larv&aelig; of Coleoptera
+and some other insects, owe their present form mainly
+to the influence of external circumstances, and partially
+also to atavism, still the <i>Campodea</i> type is
+itself derived from earlier vermiform ancestors.
+Nicolas Wagner has shown in the case of a small
+gnat, allied to <i>Cecidomyia</i>, that even now, in some
+instances, the vermiform larv&aelig; possess the power of
+reproduction. Such a larva (as, for instance, Fig. <a href="#f57">57</a>)
+very closely resembles some of the Rotatoria, such
+for instance as <i>Albertia</i> or <i>Notommata</i>, which however
+<span class='pagenum'><a name="Page_96" id="Page_96">96</a></span>
+possess vibratile cilia. There is, indeed,
+one genus&mdash;<i>Lindia</i> (Fig. <a href="#f57">58</a>)&mdash;in which these cili&aelig;
+are altogether absent, and which, though resembling
+<i>Macrobiotus</i> in many respects, differs from that genus
+in being entirely destitute of legs. I have never
+met with it myself, but it is described by Dujardin,
+who found it in a ditch near Paris, as being oblong,
+vermiform, divided into rings, and terminating posteriorly
+in two short conical appendages. The jaws
+are not unlike those of the larv&aelig; of Flies, and indeed
+many naturalists meeting with such a creature would,
+I am sure, regard it as a small Dipterous larva; yet<span class='pagenum'><a name="Page_97" id="Page_97">97</a></span>
+Dujardin figures a specimen containing an egg, and
+seems to have no doubt that it is a mature form.<a name="FNanchor_71" id="FNanchor_71"></a><a href="#Footnote_71" class="fnanchor">71</a></p>
+
+<p>For the next descending stage we must, I think,
+look among the Infusoria, through such genera as
+<i>Ch&aelig;tonotus</i> or <i>Ichthydium</i>. Other forms of the
+Rotatoria, such for instance as <i>Rattulus</i>, and still
+more the very remarkable species discovered in 1871
+by Mr. Hudson,<a name="FNanchor_72" id="FNanchor_72"></a><a href="#Footnote_72" class="fnanchor">72</a> and described under the name of
+<i>Pedalion mira</i>, seem to lead to the Crustacea through
+the Nauplius form. Dr. Cobbold tells me that he
+regards the <i>Gordii</i> as the lowest of the Scolecida;
+Mr. E. Ray Lankester considers some of the Turbellaria,
+such genera as <i>Mesostomum</i>, <i>Vortex</i>, &amp;c., to be
+the lowest of existing worms; excluding the parasitic
+groups. Haeckel<a name="FNanchor_73" id="FNanchor_73"></a><a href="#Footnote_73" class="fnanchor">73</a> also regards the Turbellaria as
+forming the nearest approach to the Infusoria. The
+true worms seem, however, to constitute a separate
+branch of the animal kingdom.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="f59" id="f59"></a>
+<img src="images/fig_059.png" width="400" height="101"
+alt="Fig. 59" title="" />
+
+<p class="center"><span class="smcap">Fig. 59</span>, <i>Prorhynchus stagnaus</i>.<a name="FNanchor_75" id="FNanchor_75"></a><a href="#Footnote_75" class="fnanchor">75</a></p></div>
+
+<p>We may take, as an illustration of the lower worms,
+the genus <i>Prorhynchus</i> (Fig. <a href="#f59">59</a>), which consists of
+a hollow cylindrical body, containing a straight
+simple tube, the digestive organ.</p>
+
+<p>But however simple such a creature as this may be,
+there are others which are far less complex, far less
+differentiated; which therefore, on Mr. Darwin&#8217;s principles,
+may be considered still more closely to repre<span class='pagenum'><a name="Page_98" id="Page_98">98</a></span>sent
+the prim&aelig;val ancestor from which these more
+highly-developed types have been derived, and which,
+in spite of their great antiquity&mdash;in spite of, or perhaps
+in consequence of, their simplicity, still maintain
+themselves almost unaltered.</p>
+
+<p>Thus the form which Haeckel has described<a name="FNanchor_74" id="FNanchor_74"></a><a href="#Footnote_74" class="fnanchor">74</a> under
+the name <i>Protam&oelig;ba primitiva</i>, Pl. <a href="#p5">V</a>, Fig. 1-5, consists
+of a homogeneous and structureless substance,
+which continually alters its form; putting out and
+drawing in again more or less elongated processes,
+and creeping about like a true <i>Am&oelig;ba</i>, from which,
+however, <i>Protam&oelig;ba</i> differs, in the absence of a
+nucleus. It seems difficult to imagine anything
+simpler; indeed, as described, it appears to be an
+illustration of properties without structure. It takes
+into itself any suitable particle with which it comes in
+contact, absorbs that which is nutritious, and rejects
+the rest. From time to time a constriction appears at
+the centre (Pl. <a href="#p5">V</a>, Fig. 2), its form approximates more
+and more to that of an hour-glass (Pl. <a href="#p5">V</a>, Fig. 3), and
+at length the two halves separate, and each commences
+an independent existence (Pl. <a href="#p5">V</a>, Fig. 5).</p>
+
+<p><span class='pagenum'><a name="Page_99" id="Page_99">99</a></span></p>
+
+<div class="figcenter" style="width: 500px;"><a name="p5" id="p5"></a>
+<img src="images/plate_005.png" width="500" height="779"
+alt="PLATE V." title="" />
+
+<p class="center"><span class="smcap">PLATE V.</span></p>
+
+<p class="caption"><span class="smcap">Figs. 1-5</span>, <i>Protam&oelig;ba</i> 6-9, <i>Protamyxa aurantiaca</i>, Haeckel, Beit. zur Monog.
+der Moneren, pl. 1; 10-18, <i>Magosph&oelig;ra planula</i>, Haeckel, loc. cit. pl. 5.]<span class='pagenum'><a name="Page_100" id="Page_100">100</a></span></p></div>
+
+<p>In the true <i>Am&oelig;bas</i>, on the contrary, we find a
+differentiation between the exterior and the interior:
+the body being more or less distinctly divisible into an
+outer layer and an inner parenchyme. In the <i>Am&oelig;bas</i>,
+as in <i>Protam&oelig;ba</i>, multiplication takes place by self-division,
+and nothing corresponding to sexual reproduction
+has yet been discovered.</p>
+
+<p>Somewhat more advanced, but still of great simplicity,
+is the <i>Protomyxa aurantiaca</i> (Pl. <a href="#p5">V</a>, Fig. 8), discovered
+by Haeckel<a name="FNanchor_76" id="FNanchor_76"></a><a href="#Footnote_76" class="fnanchor">76</a> on dead shells of <i>Spirula</i>, where
+it appears as a minute orange speck, which shows well
+against the clear white of the <i>Spirula</i>. Examined
+with a microscope, the speck is seen to be a spherical
+mass of orange-coloured, homogeneous, albuminous
+matter, surrounded by a delicate, structureless membrane.
+It is obvious from this description that
+these bodies closely resemble eggs, for which indeed
+Haeckel at first mistook them. Gradually, however,
+the yellow sphere broke itself up into smaller
+spherules (Pl. <a href="#p5">V</a>, Fig. 9), after which the containing
+membrane burst, and the separate spherules, losing
+their globular form, crept out as small Am&oelig;b&aelig; (Pl. <a href="#p5">V</a>,
+Fig. 6), or am&oelig;boid bodies. These little bodies moved
+about, assimilated the minute particles of organic
+matter, with which they came in contact, and gradually
+increased in size (Pl. <a href="#p5">V</a>, Fig. 7) with more or less
+rapidity according to the amount of nourishment they
+were able to obtain. They threw out arms in various
+directions, and if divided each section maintained its
+individual existence. After a while their movements
+ceased, they contracted into a ball, and again secreted
+round themselves a clear structureless envelope.</p>
+<p><span class='pagenum'><a name="Page_101" id="Page_101">101</a></span></p>
+<p>This completes their life history as observed by
+Haeckel, who found it easy to retain them in his
+glasses in perfect health, and who watched them
+closely.</p>
+
+<p>As another illustration I may take the <i>Magosph&aelig;ra
+planula</i>, discovered by Haeckel on the coast of
+Norway.</p>
+
+<p>In one stage of its existence (Pl. <a href="#p5">V</a>, Fig. 10) it is a
+minute mass of gelatinous matter, which continually
+alters its form, moves about, feeds, and in fact behaves
+altogether like the <i>Am&oelig;ba</i> just described. It does
+not, however, remain always in this condition. After
+a while it contracts into a spherical form (Pl. <a href="#p5">V</a>, Fig.
+ii), and secretes round itself a structureless envelope,
+which, with the nucleus, gives it a very close resemblance
+to a minute egg.</p>
+
+<p>Gradually the nucleus divides, and the protoplasm
+also separates into two spherules (Pl. <a href="#p5">V</a>, Fig. 12); these
+two subdivide into four (Pl. <a href="#p5">V</a>, Fig. 13), and so on
+(Pl. 5, Fig 14), until at length thirty-two are present,
+compressed into a more or less polygonal form (Pl. <a href="#p5">V</a>,
+Fig. 15). Here this process ends. The separate
+spherules now begin to lose their smooth outline, to
+throw out processes, and to show am&oelig;boid movements
+like those of the creatures just described. The
+processes or pseudopods grow gradually longer, thinner,
+and more pointed. Their movements become more
+active, until at length they take the form of cili&aelig;.
+The spherical <i>Magosph&aelig;ra</i>, the upper surface of
+which has thus become covered with cili&aelig;, now begins
+to rotate within the cyst or envelope, which at length
+gives way and sets free the contained sphere, which<span class='pagenum'><a name="Page_102" id="Page_102">102</a></span>
+then swims about freely in the water (Pl. <a href="#p5">V</a>, Fig. 16),
+thus closely resembling <i>Synura</i>, or one of the Volvocine&aelig;.
+After swimming about in this condition for a
+certain time, the sphere breaks up into the separate
+cells of which it is composed (Pl. <a href="#p5">V</a>, Fig. 17). As long
+as the individual cells remained together, they had
+undergone no changes of form, but after separating
+they show considerable contractility, and gradually
+alter their form, until they become undistinguishable
+from true Am&oelig;b&aelig; (Pl. <a href="#p5">V</a>, Fig. 18). Finally, according
+to Haeckel, these am&oelig;boid bodies, after living for a
+certain time in this condition, return to a state of rest,
+again contract into a spherical form, and secrete round
+themselves a structureless envelope. The life history
+of some other low organisms, as for instance <i>Gregarina</i>,
+is of a similar character.</p>
+
+<p>It may be said, and said truly, that the difference
+between such beings as these and the <i>Campodea</i>, or
+Tardigrade, is immense. But if it be considered
+incredible that even during the long lapse of geological
+time such great changes should have taken
+place as are implied in the belief that there is genetic
+connection between them and these lower groups, let
+us consider what happens under our eyes in the
+development of each one of these little creatures in
+the proverbially short space of their individual life.</p>
+
+<p>I will take for instance the first stages, and for the
+sake of brevity only the first stages, of the life-history
+of a Tardigrade.<a name="FNanchor_77" id="FNanchor_77"></a><a href="#Footnote_77" class="fnanchor">77</a> As shown in Fig. <a href="#f60">60</a>, the egg is at
+first a round body or cell, with a clear central nucleus&mdash;the germinal
+<span class='pagenum'><a name="Page_103" id="Page_103">103</a></span>vesicle; it increases in size, and after
+a while the yolk and the germinal vesicle divide into
+two (Fig. <a href="#f60">61</a>), then into four (Fig. <a href="#f60">62</a>), and so on, just
+as we have seen to be the case in <i>Magosph&aelig;ra</i>. From
+the minute cells (Fig. <a href="#f60">63</a>) arising through this process
+of yolk-segmentation, the body of the Tardigrade is
+then built up.<a name="FNanchor_78" id="FNanchor_78"></a><a href="#Footnote_78" class="fnanchor">78</a></p>
+
+<div class="figcenter" style="width: 500px;"><a name="f60" id="f60"></a>
+<img src="images/fig_060-63.png" width="500" height="149"
+alt="Figs. 60-63" title="" />
+
+<p class="caption"><span class="smcap">Fig. 60</span>, Egg of Tardigrade, Kaufmann, Zeit f. Wiss. Zool. 1851, Pl. 1. 61, Egg
+of Tardigrade after the yolk has subdivided. 62, Egg of Tardigrade in the
+next stage. 63, Egg of Tardigrade more advanced.</p></div>
+
+<p>Though I will not now attempt to point out the full
+bearing of these facts on the study of embryology
+generally, yet I cannot resist calling attention to the
+similarity of the development of <i>Magosph&oelig;ra</i> with
+the first stages of development of other animals,
+because it appears to me to possess a significance, the
+importance of which it would be difficult to overestimate.</p>
+
+<p>Among the Zoophytes Prof. Allman thus describes<a name="FNanchor_79" id="FNanchor_79"></a><a href="#Footnote_79" class="fnanchor">79</a>
+the process in <i>Laomedea</i>, as representing the Hydroids
+(Pl. <a href="#p6">VI</a>, Fig. 1, represents the young egg):&mdash;"The first
+step observable in the segmentation-process is the
+<span class='pagenum'><a name="Page_104" id="Page_104">104</a></span>cleavage of the yolk into two segments (Pl. <a href="#p6">VI</a>, Fig. 2),
+immediately followed by the cleavage of these into
+other two, so that the vitellus is now composed of
+four cleavage spheres (Pl. <a href="#p6">VI</a>, Fig. 3)." These spheres
+again divide (Pl. <a href="#p6">VI</a>, Fig. 4) and subdivide, thus at
+length forming minute cells, of which the body of the
+embryo is built up.</p>
+
+<p>In Pl. <a href="#p6">VI</a>, Figs. 5-9 represent the corresponding
+stages in the development of a small parasitic worm&mdash;the
+<i>Filaria mustelarum</i>&mdash;as given by Van Beneden.<a name="FNanchor_80" id="FNanchor_80"></a><a href="#Footnote_80" class="fnanchor">80</a>
+The first process is that within the egg, which represents,
+so to say, the encysted condition of <i>Magosph&oelig;ra</i>,
+the yolk divides itself into two balls (Pl. <a href="#p6">VI</a>,
+Fig. 6), then into four, eight, and so on, the cells
+thus constituted finally forming the young worm.
+I have myself observed the same stages in the eggs
+of the very remarkable and abnormal <i>Sph&aelig;rularia
+bombi</i>.<a name="FNanchor_81" id="FNanchor_81"></a><a href="#Footnote_81" class="fnanchor">81</a></p>
+
+<p>Among the Echinoderms M. Derb&egrave;s thus describes
+the first stages (Pl. <a href="#p6">VI</a>, Figs. 10-13) in the development
+of the egg of an <i>Echinus</i> (<i>Echinus esculentus</i>):&mdash;"Le
+jaune commence &agrave; se segmenter, d&#8217;abord en
+deux, puis en quatre et ainsi de suite, chacune des
+nouvelles cellules se partageant &agrave; son tour en deux."<a name="FNanchor_82" id="FNanchor_82"></a><a href="#Footnote_82" class="fnanchor">82</a>
+Sars has observed the same thing in the star-fish.<a name="FNanchor_83" id="FNanchor_83"></a><a href="#Footnote_83" class="fnanchor">83</a></p>
+
+<div class="figcenter" style="width: 500px;"><a name="p6" id="p6"></a>
+<img src="images/plate_006.png" width="500" height="840"
+alt="PLATE VI." title="" />
+
+<p class="center">PLATE. 6.</p></div>
+
+<p>In the Rotatoria, as shown by Huxley in <i>Lacinularia</i>,<a name="FNanchor_84" id="FNanchor_84"></a><a href="#Footnote_84" class="fnanchor">84</a>
+and by Williamson in <i>Melicerta</i>,<a name="FNanchor_85" id="FNanchor_85"></a><a href="#Footnote_85" class="fnanchor">85</a> the yolk is at
+<span class='pagenum'><a name="Page_106" id="Page_106">106</a></span><span class='pagenum'><a name="Page_105" id="Page_105">105</a></span>first a single globular mass, the first changes which take
+place in it being as follows:&mdash;"The central nucleus
+becomes drawn out and subdivides into two, this
+division being followed by a corresponding segmentation
+of the yolk. The same process is repeated again
+and again, until at length the entire yolk is converted
+into a mass of minute cells." Among the Crustacea
+the total segmentation of the yolk occurs among the
+Copepoda, Rhizocephala, and Cirripedia. Sars has
+described the same process in one of the nudibranchiate
+mollusca<a name="FNanchor_86" id="FNanchor_86"></a><a href="#Footnote_86" class="fnanchor">86</a> (<i>Tritonia</i>), M&uuml;ller in Entochocha,<a name="FNanchor_87" id="FNanchor_87"></a><a href="#Footnote_87" class="fnanchor">87</a>
+Haeckel in Ascidia,<a name="FNanchor_88" id="FNanchor_88"></a><a href="#Footnote_88" class="fnanchor">88</a> Lacaze Duthiers in <i>Dentalium</i>.<a name="FNanchor_89" id="FNanchor_89"></a><a href="#Footnote_89" class="fnanchor">89</a>
+Figures 18 to 21, Pl. <a href="#p6">VI</a>, are taken from Koren and
+Danielssen&#8217;s<a name="FNanchor_90" id="FNanchor_90"></a><a href="#Footnote_90" class="fnanchor">90</a> memoir on the development of <i>Purpura
+lapillus</i>.</p>
+
+<p>Figs. <a href="#p6">22-24</a> show the same stages in a fish
+(<i>Amphioxus</i>) as given by Haeckel, and it is unnecessary
+to point out the great similarity.</p>
+
+<p>Lastly, figures 25 to 29, Pl. 6, are given by Dr.
+Allen Thomson,<a name="FNanchor_91" id="FNanchor_91"></a><a href="#Footnote_91" class="fnanchor">91</a> as illustrating the first stages in the
+development of the vertebrata.</p>
+
+<p>I might have given many other examples, but the
+above are probably sufficient, and will show that the
+processes which constitute the life-history of the
+lowest organized beings very closely resemble the
+first stages in the development of more advanced
+<span class='pagenum'><a name="Page_107" id="Page_107">107</a></span>groups; that as Allen Thomson has truly observed,<a name="FNanchor_92" id="FNanchor_92"></a><a href="#Footnote_92" class="fnanchor">92</a>
+&#8220;the occurrence of segmentation and the regularity of
+its phenomena are so constant that we may regard it
+as one of the best established series of facts in organic
+nature.&#8221;</p>
+
+<p>It is true that normal yolk-segmentation is not
+universal in the animal kingdom; that there are
+great groups in which the yolk does not divide in
+this manner,&mdash;perhaps owing to some difference in
+its relation to the germinal vesicle, or perhaps because
+one of the suppressed stages in embryological
+development, many examples might be given, not
+only in zoology, but, as I may state on the authority
+of Dr. Hooker, in botany also. But, however, this
+may be, it is surely not uninteresting, nor without
+significance, to find that changes which constitute
+the life-history of the lowest creatures for the initial
+stages even of the highest.</p>
+
+<p>Returning, in conclusion, to the immediate subject
+of this work, I have pointed out that many beetles and
+other insects are derived from larv&aelig; closely resembling
+<i>Campodea</i>.</p>
+
+<p>Since, then, individual insects are certainly in many
+cases developed from larv&aelig; closely resembling the
+genus <i>Campodea</i>, why should it be regarded as incredible
+that insects as a group have gone through
+similar stages? That the ancestors of beetles under
+the influence of varying external conditions, and in
+the lapse of geological ages, should have undergone
+changes which the individual beetle passes
+through under our own eyes and in the space of a few
+<span class='pagenum'><a name="Page_108" id="Page_108">108</a></span>
+days, is surely no wild or extravagant hypothesis.
+Again, other insects come from vermiform larv&aelig;
+much resembling the genus <i>Lindia</i>, and it has
+been also repeatedly shown that in many particulars
+the embryo of the more specialized forms
+resembles the full-grown representatives of lower
+types. I conclude, therefore, that the Insecta generally
+are descended from ancestors resembling the
+existing genus <i>Campodea</i>, and that these again have
+arisen from others belonging to a type represented
+more or less closely by the existing genus <i>Lindia</i>.</p>
+
+<p>Of course it may be argued that these facts have
+not really the significance which they seem to me to
+possess. It may be said that when Divine power
+created insects, they were created with these remarkable
+developmental processes. By such arguments the
+conclusions of geologists were long disputed. When
+God made the rocks, it was tersely said, He made the
+fossils in them. No one, I suppose, would now be
+found to maintain such a theory; and I believe the
+time will come when it will be generally admitted
+that the structure of the embryo, and its developmental
+changes, indicate as truly the course of
+organic development in ancient times as the contents
+of rocks and their sequence teach us the past history
+of the earth itself.</p>
+
+<h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_1" id="Footnote_1"></a><a href="#FNanchor_1"><span class="label">1</span></a> Darwin&#8217;s &#8220;Researches into the Geology and Natural History of the
+Countries visited by H.M.S. <i>Beagle</i>,&#8221; p. 326.</p></div>
+
+<div class="footnote"><p><a name="Footnote_2" id="Footnote_2"></a><a href="#FNanchor_2"><span class="label">2</span></a> Introduction to Entomology, vi. p. 50.</p></div>
+
+<div class="footnote"><p><a name="Footnote_3" id="Footnote_3"></a><a href="#FNanchor_3"><span class="label">3</span></a> Manual of Entomology, p. 30.</p></div>
+
+<div class="footnote"><p><a name="Footnote_4" id="Footnote_4"></a><a href="#FNanchor_4"><span class="label">4</span></a> Linnean Journal, vol. xi.</p></div>
+
+<div class="footnote"><p><a name="Footnote_5" id="Footnote_5"></a><a href="#FNanchor_5"><span class="label">5</span></a> Introduction to the Modern Classification of Insects, p. 17.</p></div>
+
+<div class="footnote"><p><a name="Footnote_6" id="Footnote_6"></a><a href="#FNanchor_6"><span class="label">6</span></a> Linnean Transactions, 1863&mdash;"On the Development of <i>Chlo&euml;on</i>."</p></div>
+
+<div class="footnote"><p><a name="Footnote_7" id="Footnote_7"></a><a href="#FNanchor_7"><span class="label">7</span></a> The figures on the first four plates are principally borrowed from
+Mr. Westwood&#8217;s excellent &#8220;Introduction to the Modern Classification
+of Insects.&#8221;</p></div>
+
+<div class="footnote"><p><a name="Footnote_8" id="Footnote_8"></a><a href="#FNanchor_8"><span class="label">8</span></a> &#8220;Sur la Domestication des <i>Clavigers</i> par les Fourmis.&#8221; Bull. de
+la Soc. d&#8217;Anthropologie de Paris, 1868, p. 315.</p></div>
+
+<div class="footnote"><p><a name="Footnote_9" id="Footnote_9"></a><a href="#FNanchor_9"><span class="label">9</span></a> Westwood&#8217;s Introduction, vol. i. p. 36.</p></div>
+
+<div class="footnote"><p><a name="Footnote_10" id="Footnote_10"></a><a href="#FNanchor_10"><span class="label">10</span></a> Westwood&#8217;s Introduction, vol. ii. p. 52.</p></div>
+
+<div class="footnote"><p><a name="Footnote_11" id="Footnote_11"></a><a href="#FNanchor_11"><span class="label">11</span></a> Die Fortpflanzung und Entwickelung der Pupiparen. Von Dr.
+R. Leuckart. Halle. 1848.</p></div>
+
+<div class="footnote"><p><a name="Footnote_12" id="Footnote_12"></a><a href="#FNanchor_12"><span class="label">12</span></a> Ann. des Sci. Nat., s&eacute;r. 4, tome vii. See also <i>Natural History
+Review</i>, April 1862.</p></div>
+
+<div class="footnote"><p><a name="Footnote_13" id="Footnote_13"></a><a href="#FNanchor_13"><span class="label">13</span></a> Ann. and Mag. of Nat. Hist. 1852.</p></div>
+
+<div class="footnote"><p><a name="Footnote_14" id="Footnote_14"></a><a href="#FNanchor_14"><span class="label">14</span></a> Zeits. f&uuml;r Wiss. Zool. 1869.</p></div>
+
+<div class="footnote"><p><a name="Footnote_15" id="Footnote_15"></a><a href="#FNanchor_15"><span class="label">15</span></a> Transactions of the Linnean Society, 1863.</p></div>
+
+<div class="footnote"><p><a name="Footnote_16" id="Footnote_16"></a><a href="#FNanchor_16"><span class="label">16</span></a> Lectures on the Anatomy, &amp;c. of the Invertebrate Animals.</p></div>
+
+<div class="footnote"><p><a name="Footnote_17" id="Footnote_17"></a><a href="#FNanchor_17"><span class="label">17</span></a> Untersuchungen &uuml;ber die Entwickelung und den Bau der Gliederthiere,
+1854.</p></div>
+
+<div class="footnote"><p><a name="Footnote_18" id="Footnote_18"></a><a href="#FNanchor_18"><span class="label">18</span></a> Linnean Transactions, vol. xxii. 1858.</p></div>
+
+<div class="footnote"><p><a name="Footnote_19" id="Footnote_19"></a><a href="#FNanchor_19"><span class="label">19</span></a> &#8220;Embryological Studies on Hexapodous Insects.&#8221; Peabody Academy
+of Science. Third Memoir.</p></div>
+
+<div class="footnote"><p><a name="Footnote_20" id="Footnote_20"></a><a href="#FNanchor_20"><span class="label">20</span></a> M&eacute;m. de l&#8217;Acad. Imp. des Sci. de St. P&eacute;tersbourg. 1869.</p></div>
+
+<div class="footnote"><p><a name="Footnote_21" id="Footnote_21"></a><a href="#FNanchor_21"><span class="label">21</span></a> Observationes de Prima Insectorum Genesi, p. 14.</p></div>
+
+<div class="footnote"><p><a name="Footnote_22" id="Footnote_22"></a><a href="#FNanchor_22"><span class="label">22</span></a> M&eacute;m. de l&#8217;Acad. Imp. des Sci. de St. P&eacute;tersbourg. tome xvi. 1871,
+p. 35.</p></div>
+
+<div class="footnote"><p><a name="Footnote_23" id="Footnote_23"></a><a href="#FNanchor_23"><span class="label">23</span></a> Recherches sur l&#8217;Evolution des Araign&eacute;es.</p></div>
+
+<div class="footnote"><p><a name="Footnote_24" id="Footnote_24"></a><a href="#FNanchor_24"><span class="label">24</span></a> Philosophical Transactions, 1841.</p></div>
+
+<div class="footnote"><p><a name="Footnote_25" id="Footnote_25"></a><a href="#FNanchor_25"><span class="label">25</span></a> Monog. of the Gymnoblastic or Tubularian Hydroids. See also
+Hincks, British Hydroid Zoophytes. Pl. x.</p></div>
+
+<div class="footnote"><p><a name="Footnote_26" id="Footnote_26"></a><a href="#FNanchor_26"><span class="label">26</span></a> Loc. cit. p. 315.</p></div>
+
+<div class="footnote"><p><a name="Footnote_27" id="Footnote_27"></a><a href="#FNanchor_27"><span class="label">27</span></a> Philosophical Transactions, 1859, p. 589.</p></div>
+
+<div class="footnote"><p><a name="Footnote_28" id="Footnote_28"></a><a href="#FNanchor_28"><span class="label">28</span></a> &#8220;Facts for Darwin,&#8221; Eng. Trans. p. 127.</p></div>
+
+<div class="footnote"><p><a name="Footnote_29" id="Footnote_29"></a><a href="#FNanchor_29"><span class="label">29</span></a> Rolleston, &#8220;Forms of Animal Life,&#8221; p. 146.</p></div>
+
+<div class="footnote"><p><a name="Footnote_30" id="Footnote_30"></a><a href="#FNanchor_30"><span class="label">30</span></a> A. Agassiz, &#8220;Embryology of the Starfish,&#8221; p. 25; &#8220;Embryology
+of Echinoderms.&#8221; Mem. of Am. Ac. of Arts and Sciences N.S.
+vol. ix. p. 9.</p></div>
+
+<div class="footnote"><p><a name="Footnote_31" id="Footnote_31"></a><a href="#FNanchor_31"><span class="label">31</span></a> Ueber die Gattungen der Seeigellarven. Siebente Abhandlung. K&ouml;n.
+Akad. d. Wiss. zu Berlin. Von Joh. M&uuml;ller, 1855, Pl. iii. fig. 3.</p></div>
+
+<div class="footnote"><p><a name="Footnote_32" id="Footnote_32"></a><a href="#FNanchor_32"><span class="label">32</span></a> Huxley, Introduction to the Classification of Animals, p. 45.</p></div>
+
+<div class="footnote"><p><a name="Footnote_33" id="Footnote_33"></a><a href="#FNanchor_33"><span class="label">33</span></a> Philosophical Transactions, 1865 and 1866.</p></div>
+
+<div class="footnote"><p><a name="Footnote_34" id="Footnote_34"></a><a href="#FNanchor_34"><span class="label">34</span></a> Loc. cit. Zweit. Abh. Pl. i., figs. 8 and 9.</p></div>
+
+<div class="footnote"><p><a name="Footnote_35" id="Footnote_35"></a><a href="#FNanchor_35"><span class="label">35</span></a> Thomson, on the Embryology of the Echinodermata, <i>Natural
+History Review</i>, 1863, p. 415. See also Agassiz, &#8220;Embryology of the
+Starfish,&#8221; p. 62.</p></div>
+
+<div class="footnote"><p><a name="Footnote_36" id="Footnote_36"></a><a href="#FNanchor_36"><span class="label">36</span></a> A. Agassiz, Embryology of Echinoderms, p. 18.</p></div>
+
+<div class="footnote"><p><a name="Footnote_37" id="Footnote_37"></a><a href="#FNanchor_37"><span class="label">37</span></a> Hincks. British Hydroid Zoophytes, pp. 120-147.</p></div>
+
+<div class="footnote"><p><a name="Footnote_38" id="Footnote_38"></a><a href="#FNanchor_38"><span class="label">38</span></a> Zeits. f&uuml;r Wiss. Zool. 1864, p. 228.</p></div>
+
+<div class="footnote"><p><a name="Footnote_39" id="Footnote_39"></a><a href="#FNanchor_39"><span class="label">39</span></a> Introduction to Entomology, 6th ed. vol. i. p. 61.</p></div>
+
+<div class="footnote"><p><a name="Footnote_40" id="Footnote_40"></a><a href="#FNanchor_40"><span class="label">40</span></a> M&eacute;tamorphoses de l&#8217;Homme et des Animaux, p. 133. See also
+Carpenter, Principles of Physiology. 1851, p. 389.</p></div>
+
+<div class="footnote"><p><a name="Footnote_41" id="Footnote_41"></a><a href="#FNanchor_41"><span class="label">41</span></a> Darwin, Origin of Species, 4th ed. p. 532.</p></div>
+
+<div class="footnote"><p><a name="Footnote_42" id="Footnote_42"></a><a href="#FNanchor_42"><span class="label">42</span></a> Principles of Biology, vi. p. 349.</p></div>
+
+<div class="footnote"><p><a name="Footnote_43" id="Footnote_43"></a><a href="#FNanchor_43"><span class="label">43</span></a> For differences in larva consequent on variation in the external condition,
+see <i>ante</i>, p. 61.</p></div>
+
+<div class="footnote"><p><a name="Footnote_44" id="Footnote_44"></a><a href="#FNanchor_44"><span class="label">44</span></a> See Hincks. British Hydroid Zoophytes, P. lxii. Agassiz, Sea-side
+Studies, p. 43.</p></div>
+
+<div class="footnote"><p><a name="Footnote_45" id="Footnote_45"></a><a href="#FNanchor_45"><span class="label">45</span></a> See Newport, Phil. Trans., 1832.</p></div>
+
+<div class="footnote"><p><a name="Footnote_46" id="Footnote_46"></a><a href="#FNanchor_46"><span class="label">46</span></a> Linnean Transactions, 1862.</p></div>
+
+<div class="footnote"><p><a name="Footnote_47" id="Footnote_47"></a><a href="#FNanchor_47"><span class="label">47</span></a> Origin of Species, 4th ed., pp. 14 and 97.</p></div>
+
+<div class="footnote"><p><a name="Footnote_48" id="Footnote_48"></a><a href="#FNanchor_48"><span class="label">48</span></a> On the Alternation of Generations. By J. J. Steenstrup. Trans.
+by C. Busk, Esq. Ray Society. 1842.</p></div>
+
+<div class="footnote"><p><a name="Footnote_49" id="Footnote_49"></a><a href="#FNanchor_49"><span class="label">49</span></a> Zeit. f&uuml;r Wiss. Zool. 1863.</p></div>
+
+<div class="footnote"><p><a name="Footnote_50" id="Footnote_50"></a><a href="#FNanchor_50"><span class="label">50</span></a> M&eacute;m. de l&#8217;Acad. Imp. de St. P&eacute;tersbourg. vol. xv. 1870.</p></div>
+
+<div class="footnote"><p><a name="Footnote_51" id="Footnote_51"></a><a href="#FNanchor_51"><span class="label">51</span></a> Of course all animals in which the sexes are distinct are in one
+sense dimorphic.</p></div>
+
+<div class="footnote"><p><a name="Footnote_52" id="Footnote_52"></a><a href="#FNanchor_52"><span class="label">52</span></a> &#8220;There is no such thing as a true case of &#8216;alternation of generations
+in the animal kingdom;&#8217; there is only an alternation of true
+generation with the totally distinct process of gemmation or fission.&#8221;&mdash;<span class="smcap">Huxley</span>
+<i>on Animal Individuality</i>, Ann. and Mag. of Nat. Hist.
+June 1852.</p></div>
+
+<div class="footnote"><p><a name="Footnote_53" id="Footnote_53"></a><a href="#FNanchor_53"><span class="label">53</span></a> Prince Hohenstiel Schwangau, p. 68.</p></div>
+
+<div class="footnote"><p><a name="Footnote_54" id="Footnote_54"></a><a href="#FNanchor_54"><span class="label">54</span></a> Journal of the Royal Institution. April 1873.</p></div>
+
+<div class="footnote"><p><a name="Footnote_55" id="Footnote_55"></a><a href="#FNanchor_55"><span class="label">55</span></a> &#8220;Embryology of Echinoderms,&#8221; l. c. p. 15.</p></div>
+
+<div class="footnote"><p><a name="Footnote_56" id="Footnote_56"></a><a href="#FNanchor_56"><span class="label">56</span></a> Mr. and Mrs. Agassiz: &#8220;Seaside Studies,&#8221; p. 139.</p></div>
+
+<div class="footnote"><p><a name="Footnote_57" id="Footnote_57"></a><a href="#FNanchor_57"><span class="label">57</span></a> l. c. p. 138.</p></div>
+
+<div class="footnote"><p><a name="Footnote_58" id="Footnote_58"></a><a href="#FNanchor_58"><span class="label">58</span></a> Wien. Zool. Bot. Gesells, 1869.</p></div>
+
+<div class="footnote"><p><a name="Footnote_59" id="Footnote_59"></a><a href="#FNanchor_59"><span class="label">59</span></a> Linnean Transactions, 1863.</p></div>
+
+<div class="footnote"><p><a name="Footnote_60" id="Footnote_60"></a><a href="#FNanchor_60"><span class="label">60</span></a> Linnean Transactions, 1866, vol. xxv.</p></div>
+
+<div class="footnote"><p><a name="Footnote_61" id="Footnote_61"></a><a href="#FNanchor_61"><span class="label">61</span></a> Linnean Transactions, vol. xxiv. p. 65.</p></div>
+
+<div class="footnote"><p><a name="Footnote_62" id="Footnote_62"></a><a href="#FNanchor_62"><span class="label">62</span></a> Siebold und Kolliker&#8217;s Zeitschr. f. Wiss. Zool., 1864.</p></div>
+
+<div class="footnote"><p><a name="Footnote_63" id="Footnote_63"></a><a href="#FNanchor_63"><span class="label">63</span></a> Linnean Journal, vol. xi.</p></div>
+
+<div class="footnote"><p><a name="Footnote_64" id="Footnote_64"></a><a href="#FNanchor_64"><span class="label">64</span></a> Facts for Darwin, p. 120.</p></div>
+
+<div class="footnote"><p><a name="Footnote_65" id="Footnote_65"></a><a href="#FNanchor_65"><span class="label">65</span></a> A still nearer approach is afforded by the genus <i>Peripatus</i>, which
+since the above was written has been carefully described, especially by
+Moseley and Hutton. There are several species, scattered over the
+southern hemisphere. In general appearance they look like a link
+between a caterpillar and a centipede. They have a pair of antenn&aelig;,
+two pairs of jaws, and (according to the species) from fourteen to
+thirty-three pairs of legs. They breathe by means of trache&aelig;, which
+open diffusely all over the body.</p></div>
+
+<div class="footnote"><p><a name="Footnote_66" id="Footnote_66"></a><a href="#FNanchor_66"><span class="label">66</span></a> Unters. &uuml;b. die Entwick, und den Bau der Gliederthiere, p. 73.</p></div>
+
+<div class="footnote"><p><a name="Footnote_67" id="Footnote_67"></a><a href="#FNanchor_67"><span class="label">67</span></a> Linnean Transactions, v. xxii.</p></div>
+
+<div class="footnote"><p><a name="Footnote_68" id="Footnote_68"></a><a href="#FNanchor_68"><span class="label">68</span></a> Facts for Darwin, trans. by Dallas, p. 118. See also Darwin,
+&#8220;Origin of Species,&#8221; p. 530. 4th ed.</p></div>
+
+<div class="footnote"><p><a name="Footnote_69" id="Footnote_69"></a><a href="#FNanchor_69"><span class="label">69</span></a> Mem. Peabody Academy of Science, v. I. No, 3.</p></div>
+
+<div class="footnote"><p><a name="Footnote_70" id="Footnote_70"></a><a href="#FNanchor_70"><span class="label">70</span></a> Wien. Zool. Bott. Gesells. 1869, p. 310.</p></div>
+
+<div class="footnote"><p><a name="Footnote_71" id="Footnote_71"></a><a href="#FNanchor_71"><span class="label">71</span></a> See also the descriptions given by Dujardin (Ann. des Sci. Nat.
+1851, v. xv.) and Clapar&egrave;de (Anat. und Entwickl. der Wirbel osen
+Thiere) of the interesting genus <i>Echinoderes</i>, which these two eminent
+naturalists unite in regarding as intermediate between the Annelides and
+the Crustacea.</p></div>
+
+<div class="footnote"><p><a name="Footnote_72" id="Footnote_72"></a><a href="#FNanchor_72"><span class="label">72</span></a> &#8220;On a New Rotifer.&#8221; <i>Monthly Microscopical Journal</i>, Sept. 1871.</p></div>
+
+<div class="footnote"><p><a name="Footnote_73" id="Footnote_73"></a><a href="#FNanchor_73"><span class="label">73</span></a> Generelle Morphologie, vol. ii. p. 79.</p></div>
+
+<div class="footnote"><p><a name="Footnote_74" id="Footnote_74"></a><a href="#FNanchor_74"><span class="label">74</span></a> Monographie der Moneren, p. 43.</p></div>
+
+<div class="footnote"><p><a name="Footnote_75" id="Footnote_75"></a><a href="#FNanchor_75"><span class="label">75</span></a> Gegenbaur. Grund. d. Vergleich. Anat. p. 210. See also
+Dr. M. S. Schultze, Beitr&auml;ge zur Naturg. der. Turbellarien. 1851.
+Pl. vi. fig. 1.</p></div>
+
+<div class="footnote"><p><a name="Footnote_76" id="Footnote_76"></a><a href="#FNanchor_76"><span class="label">76</span></a> Monographieder Moneren, p. 10.</p></div>
+
+<div class="footnote"><p><a name="Footnote_77" id="Footnote_77"></a><a href="#FNanchor_77"><span class="label">77</span></a> See Kauffmann, Ueber die Entwickelung and systematische Stellung
+der Tardigraden. Zeits. f. Wiss. Zool. 1851, p. 220.</p></div>
+
+<div class="footnote"><p><a name="Footnote_78" id="Footnote_78"></a><a href="#FNanchor_78"><span class="label">78</span></a> It is true that among the Insecta generally the first stages of development
+differ in appearance considerably from those above described;
+those of <i>Platygaster</i>, as figured by Ganin (ante Figs. <a href="#f17">17-22</a>), being
+very exceptional.</p></div>
+
+<div class="footnote"><p><a name="Footnote_79" id="Footnote_79"></a><a href="#FNanchor_79"><span class="label">79</span></a> Monograph of the Gymnoblastic or Tubularian Hydroids, by G. J.
+Allman, Ray Soc. 1871, p. 86.</p></div>
+
+<div class="footnote"><p><a name="Footnote_80" id="Footnote_80"></a><a href="#FNanchor_80"><span class="label">80</span></a> M&eacute;m. sur les Vers Intestinaux, 1858.</p></div>
+
+<div class="footnote"><p><a name="Footnote_81" id="Footnote_81"></a><a href="#FNanchor_81"><span class="label">81</span></a> Natural History Review, 1861, p. 44.</p></div>
+
+<div class="footnote"><p><a name="Footnote_82" id="Footnote_82"></a><a href="#FNanchor_82"><span class="label">82</span></a> Ann. des Sci. Nat. 1847, p. 90.</p></div>
+
+<div class="footnote"><p><a name="Footnote_83" id="Footnote_83"></a><a href="#FNanchor_83"><span class="label">83</span></a> Fauna littoralis Norvegi&aelig;, pl. viii.</p></div>
+
+<div class="footnote"><p><a name="Footnote_84" id="Footnote_84"></a><a href="#FNanchor_84"><span class="label">84</span></a> Trans. of the Microsc. Soc. of London, 1851.</p></div>
+
+<div class="footnote"><p><a name="Footnote_85" id="Footnote_85"></a><a href="#FNanchor_85"><span class="label">85</span></a> Quarterly Journal of Microsc. Science, 1853.</p></div>
+
+<div class="footnote"><p><a name="Footnote_86" id="Footnote_86"></a><a href="#FNanchor_86"><span class="label">86</span></a> Wiegmann&#8217;s Archiv., 1840, p. 196.</p></div>
+
+<div class="footnote"><p><a name="Footnote_87" id="Footnote_87"></a><a href="#FNanchor_87"><span class="label">87</span></a> Ueber die Erzeugung von Schnecken in Holothurier. Berlin, Bericht,
+1851. Ann. Nat. Hist. 1852, v. ix. M&uuml;ller&#8217;s Archiv., 1852.</p></div>
+
+<div class="footnote"><p><a name="Footnote_88" id="Footnote_88"></a><a href="#FNanchor_88"><span class="label">88</span></a> Nat&uuml;rliche Sch&ouml;pfungsgeschichte, pl. x.</p></div>
+
+<div class="footnote"><p><a name="Footnote_89" id="Footnote_89"></a><a href="#FNanchor_89"><span class="label">89</span></a> Ann. des Sci. Nat. 1853, p. 89.</p></div>
+
+<div class="footnote"><p><a name="Footnote_90" id="Footnote_90"></a><a href="#FNanchor_90"><span class="label">90</span></a> Ann. des Sci. Nat. 1857, pl. vi.</p></div>
+
+<div class="footnote"><p><a name="Footnote_91" id="Footnote_91"></a><a href="#FNanchor_91"><span class="label">91</span></a> Cyclop&aelig;dia of Anatomy and Physiology. Art. Ovum, p. 4.</p></div>
+
+<div class="footnote"><p><a name="Footnote_92" id="Footnote_92"></a><a href="#FNanchor_92"><span class="label">92</span></a> Thomson, loc. cit. Article, Ovum, p. 139.</p></div>
+
+<h4>THE END.</h4>
+<hr />
+<h6>RICHARD CLAY AND SONS, LIMITED, LONDON AND BUNGAY.</h6>
+<hr />
+<h3><span class='pagenum'><a name="Page_109" id="Page_109">109</a></span>BY THE SAME AUTHOR.</h3>
+
+<div class="blockquot"><p>PRE-HISTORIC TIMES. As Illustrated by Ancient
+Remains and the Manners and Customs of Modern Savages.
+Fifth Edition. 8vo. 18<i>s.</i> (Williams &amp; Norgate.)</p>
+
+<p>THE ORIGIN OF CIVILIZATION AND THE PRIMITIVE
+CONDITION OF MAN. Fifth Edition. 8vo. 18<i>s.</i>
+(Longmans, Green &amp; Co.)</p>
+
+<p>MONOGRAPH OF THE COLLEMBOLA AND THYSANURA.
+1871. (Ray Society.)</p>
+
+<p>ON BRITISH WILD FLOWERS CONSIDERED IN
+RELATION TO INSECTS. Illustrated. Fifth Edition. Cr. 8vo.
+4<i>s.</i> 6<i>d.</i> (Macmillan &amp; Co.)</p>
+
+<p>ADDRESSES, POLITICAL AND EDUCATIONAL. 8vo.
+8<i>s.</i> 6<i>d.</i> (Macmillan &amp; Co.)</p>
+
+<p>SCIENTIFIC LECTURES. Second Edition. 8vo. 8<i>s.</i> 6<i>d.</i>
+(Macmillan &amp; Co.)</p>
+
+<p>FIFTY YEARS OF SCIENCE. Being the Address
+delivered at York to the British Association, August, 1881. Third
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+
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+12mo. 1<i>s.</i> 6<i>d.</i> (National Society.)</p>
+
+<p>ANTS, BEES, AND WASPS. With Illustrations. Ninth
+Edition. Crown 8vo. 5<i>s.</i> (Kegan Paul, Trench &amp; Co.)</p>
+
+<p>ON REPRESENTATION. Fifth Edition. Crown 8vo. 1<i>s.</i>
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+
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+Second Edition. Crown 8vo. 4<i>s.</i> 6<i>d.</i> (Macmillan &amp; Co.)</p>
+
+<p>ON THE SENSES, INSTINCTS, AND INTELLIGENCE
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+The Project Gutenberg eBook, On the Origin and Metamorphoses of Insects,
+by Sir John Lubbock
+
+
+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
+
+
+
+
+
+Title: On the Origin and Metamorphoses of Insects
+
+
+Author: Sir John Lubbock
+
+
+
+Release Date: December 3, 2011  [eBook #38207]
+
+Language: English
+
+Character set encoding: ISO-646-US (US-ASCII)
+
+
+***START OF THE PROJECT GUTENBERG EBOOK ON THE ORIGIN AND METAMORPHOSES OF
+INSECTS***
+
+
+E-text prepared by Bryan Ness, Turgut Dincer, and the Online Distributed
+Proofreading Team (http://www.pgdp.net) from page images generously made
+available by Internet Archive/American Libraries
+(http://www.archive.org/details/americana)
+
+
+
+Note: Project Gutenberg also has an HTML version of this
+      file which includes the original illustrations.
+      See 38207-h.htm or 38207-h.zip:
+      (http://www.gutenberg.org/files/38207/38207-h/38207-h.htm)
+      or
+      (http://www.gutenberg.org/files/38207/38207-h.zip)
+
+
+      Images of the original pages are available through
+      Internet Archive/American Libraries. See
+      http://www.archive.org/details/onoriginmetamorp00lubb
+
+
+      +--------------------------------------------------------------+
+      | Transcriber's note:                                          |
+      |                                                              |
+      | All non-italic genus names in the text have been italicized. |
+      +--------------------------------------------------------------+
+
+
+
+
+
+[Illustration: NATURE SERIES]
+
+
+
+
+ORIGIN AND METAMORPHOSES OF INSECTS.
+
+[Illustration]
+
+Nature Series
+
+ON THE ORIGIN AND METAMORPHOSES OF INSECTS
+
+BY
+
+Sir John Lubbock, Bart., M.P., F.R.S., D.C.L., LL.D.
+
+Principal of the London Working Men's College; President of the London
+Chamber of Commerce; and Vice-Chairman of the London County Council
+
+With Numerous Illustrations
+
+
+
+
+
+
+
+London Macmillan and Co. and New York 1890
+
+The Right of Translation and Reproduction is Reserved
+
+Richard Clay and Sons, Limited, London and Bungay.
+
+First Edition 1873. Reprinted 1874. New Edition 1890.
+
+
+
+
+PREFACE.
+
+
+For some years, much of my leisure time has been devoted to the study of
+the anatomy, development, and habits of the Annulosa, and especially of
+Insects, on which subjects I have published various memoirs, chiefly in
+the Transactions of the Royal, Linnaean, and Entomological Societies: of
+these papers I subjoin a list. Although the details, of which these
+memoirs necessarily for the most part consist, offer little interest,
+excepting to those persons who are specially devoted to Entomology,
+still there are portions which, having reference to the nature of
+metamorphoses and to the origin of insects, are of a more general
+character. I have also briefly referred to these questions in a
+Monograph of the Collembola and Thysanura, recently published by the Ray
+Society, and in the Opening Address to the Biological Section of the
+British Association at Brighton in 1872. Under these circumstances, it
+has been suggested to me that a small volume, containing, at somewhat
+greater length, in a more accessible form, and with the advantage of
+illustrations, the conclusions to which I have been led on this
+interesting subject, might not be altogether without interest to the
+general reader. The result, which has already appeared in the pages of
+_Nature_, is now submitted to the public, with some additions. I am well
+aware that it has no pretence to be in any sense a complete treatise;
+that the subject itself is one as to which our knowledge is still very
+incomplete, and on which the highest authorities are much divided in
+opinion. Whatever differences of opinion, however, there may be as to
+the views here put forward, the facts on which they are based will, I
+believe, be found correct. On this point I speak with the more
+confidence, on account of the valuable assistance I have received from
+many friends: to Mr. and Mrs. Busk and Dr. Hooker I am especially
+indebted.
+
+The papers above referred to are as follows:--
+
+   1. _On Labidocera._--Annals and Magazine of Natural History,
+        vol. xi., 1853.
+
+   2. On Two New Sub-genera of Calanidae.--Annals and Magazine of
+        Natural History, vol. xii., 1853.
+
+   3. On Two New Species of Calanidae.--Annals and Magazine of
+        Natural History, vol. xii., No. lxvii., 1853.
+
+   4. On Two New Species of Calanidae.--Annals and Magazine of
+        Natural History, vol. xii., No. lxix., 1853.
+
+   5. On some Arctic Calanidae.--Annals and Magazine of Natural
+        History, 1854.
+
+   6. On the Freshwater Entomostraca of South
+        America.--Transactions of the Entomological Society, vol.
+        iii., 1855.
+
+   7. On some New Entomostraca.--Transactions of the
+        Entomological Society, vol. iv., 1856.
+
+   8. On some Marine Entomostraca found at Weymouth.--Annals and
+        Magazine of Natural History, vol. xx., 1857.
+
+   9. On the Respiration of Insects.--Entomological Annual, 1857.
+
+  10. An Account of the Two Methods of Reproduction in
+         _Daphnia_.--Transactions of the Royal Society, 1857.
+
+  11. On the Ova and Pseudova of Insects.--Transactions of the
+        Royal Society, 1858.
+
+  12. On the Arrangement of the Cutaneous Muscles of _Pygaera
+        Bucephala_.--Linnean Society's Transactions, vol. xxii., 1858.
+
+  13. On the Freshwater Entomostraca of South
+        America.--Entomological Society's Transactions, 1858.
+
+  14. On _Coccus Hesperidum_.--Royal Society Proceedings, vol.
+        ix., 1858.
+
+  15. On the Distribution of Tracheae in Insects.--Linnean
+        Society's Transactions, vol. xxiii., 1860.
+
+  16. On the Generative Organs and on the Formation of the Egg
+        in Annulosa. Transactions of the Royal Society, 1861.
+
+  17. On _Sphaerularia Bombi._--Natural History Review, 1861.
+
+  18. On some Oceanic Entomostraca.--Linnean Society's
+        Transactions, vol. xxiii., 1860.
+
+  19. On the Thysanura. Part 1.--Linnean Society's Transactions,
+        1862.
+
+  20. On the Development of Lonchoptera.--Entomological
+        Society's Transactions, 1862.
+
+  21. On the Thysanura. Part 2.--Linnean Society's Transactions,
+        1862.
+
+  22. On the Development of Chloeon. Part 1.--Linnean Society's
+        Transactions, 1863.
+
+  23. On Two Aquatic Hymenoptera.--Linnean Society's
+        Transactions, 1863.
+
+  24. On some little-known Species of Freshwater
+        Entomostraca.--Linnean Society's Transactions, vol. xxiv.,
+        1863.
+
+  25. On _Sphaerularia Bombi_.--Natural History Review, 1864.
+
+  26. On the Development of Chloeon. Part 2.--Linnean Society's
+        Transactions, 1865.
+
+  27. Metamorphoses of Insects.--Journal of the Royal
+        Institution, 1866.
+
+  28. On _Pauropus_.--Linnean Society's Transactions, 1866.
+
+  29. On the Thysanura. Part 3.--Linnean Society's Transactions,
+        1867.
+
+  30. Address to the Entomological Society.--Entomological
+        Society's Transactions, 1867.
+
+  31. On the Larva of Micropeplus Staphilinoides.--Entomological
+        Society's Transactions, 1868.
+
+  32. On the Thysanura. Part 4.--Linnean Society's Transactions,
+        1869.
+
+  33. Addresses to the Entomological Society.--Entomological
+        Society's Transactions, 1867-1868.
+
+  34. On the Origin of Insects.--Journal of the Linnean Society,
+        vol. xi.
+
+  35. Opening Address to the Biological Section of the British
+        Association.--British Association Report, 1872.
+
+  36. Observations on Ants, Bees, and Wasps. Part 1.--Journal of
+        the Linnean Society, 1873.
+
+  37. On British Wild Flowers considered in relation to Insects,
+        1874.
+
+  38. Observations on Ants, Bees, and Wasps. Part 2.--Journal of
+        the Linnean Society, 1874.
+
+  39. Observations on Ants, Bees, and Wasps. Part 3.--Journal of
+        the Linnean Society, 1875.
+
+  40. Observations on Ants, Bees, and Wasps. Part 4.--Journal of
+        the Linnean Society, 1877.
+
+  41. On some Points in the Anatomy of Ants.--Quekett Lecture,
+        1877.--Microscopical Journal.
+
+  42. On the Colors of Caterpillars.--Entomological Society's
+        Transactions, 1878.
+
+  43. Observations on Ants, Bees, and Wasps. Part 5.--Journal of
+        the Linnean Society, 1878.
+
+  44. Observations on Ants, Bees, and Wasps. Part 6.--Journal of
+        the Linnean Society, 1879.
+
+  45. On the Anatomy of Ants.--Linnean Society's Transactions,
+        1880.
+
+  46. Observations on Ants, Bees, and Wasps. Part 7.--Journal of
+        the Linnean Society, 1880.
+
+  47. Observations on Ants, Bees, and Wasps. Part 8.--Journal of
+        the Linnean Society, 1881.
+
+  48. On Fruits and Seeds.--Journal of the Royal Institution,
+        1881.
+
+  49. Observations on Ants, Bees, and Wasps. Part 9.--Journal of
+        the Linnean Society, 1881.
+
+  50. On the Limits of Vision among some of the lower
+        Animals.--Journal of the Linnean Society, 1881.
+
+  51. Observations on Ants, Bees, and Wasps. Part 10.--Journal
+        of the Linnean Society, 1882.
+
+
+
+
+CONTENTS.
+
+
+  CHAPTER I.
+
+  THE CLASSIFICATION OF INSECTS.
+
+  Introduction.--Stages in the Life of an Insect.--Classification
+    of Insects.--Characters derived from the Wings; from the parts
+    of the Mouth; from the Metamorphoses.--The Classes of Insects:
+    Hymenoptera, Strepsiptera, Coleoptera, Euplexoptera,
+    Orthoptera, Thysanoptera, Neuroptera, Trichoptera, Diptera,
+    Aphaniptera, Heteroptera, Homoptera, Lepidoptera          _page_ 1-26
+
+
+  CHAPTER II.
+
+  THE INFLUENCE OF EXTERNAL CONDITIONS ON THE FORM AND STRUCTURE
+  OF LARVAE.
+
+  Larvae depend partly on the group to which they
+    belong.--Wood-eating Larvae.--Larvae of Lamellicorns.--Larvae
+    depend also in part on mode of life.--Larvae of Hymenoptera, of
+    _Sirex_; of _Tenthredo_; of Ichneumons; of Bees.--Rudimentary
+    legs of Bee Embryo.--Beetles, _Weevils_, _Scolytus_,
+    _Crioceris_, _Sitaris_, Metamorphoses of Pteromalidae.
+    _Platygaster_, _Polynema_.--Influence of external
+    conditions.--Developmental and adaptive Metamorphoses    _page_ 27-41
+
+
+  CHAPTER III.
+
+  THE NATURE OF METAMORPHOSES.
+
+  The life history of an Insect must be considered as a
+    whole.--Vagueness of the term Larva.--Some larvae much more
+    advanced than others.--Organs develope in different order, in
+    different groups.--Suppressed stages.--Apod condition of
+    _Phryganea_; of _Aphis_; of
+    _Chrysopa_.--Libellulidae.--_Donacia_.--Spiders.--Myriapods.--Apod
+    stage of Homomorphous Insects once probably longer than
+    now.--Suppression of embryonic stages.--Metamorphoses of
+    Hydroida, Crustacea, Isopods, and
+    Amphipods.--Echinoderms.--Variations in development induced by
+    the influence of external conditions.                    _page_ 41-62
+
+
+  CHAPTER IV.
+
+  THE ORIGIN OF METAMORPHOSES.
+
+  Origin of Metamorphoses.--Views of Messrs. Kirby and
+    Spence.--Nature of the question.--Young animals often more
+    similar than mature.--Views of Darwin, Herbert Spencer,
+    Johannes Mueller, Fritz Mueller, and Agassiz.--Effect of size of
+    egg.--Insects leave the egg in a more or less developed
+    condition.--Consideration of pupal condition.--Quiescence of
+    pupa.--Period of quiescence at each moult.--Changes not so
+    abrupt as generally supposed.--Change in
+    mouth-parts.--Difficulty in reference to Darwinian
+    theory.--Mouth-parts of _Campodea_ and Collembola, as
+    intermediate between the mandibulate and haustellate
+    types.--Change in mouth-parts as connected with pupal
+    conditions.--Origin of wings.--Use of wings under
+    water.--Connection of metamorphoses with alternation of
+    generations.--Parthenogenetic larvae of _Cecidomyia_.--In
+    alternation of generations one form always agamic.--Dimorphism
+    and Dieidism.--Summary and Conclusions                   _page_ 62-81
+
+
+  CHAPTER V.
+
+  THE ORIGIN OF INSECTS.
+
+  The Origin of Insects.--Mistaken views of Darwinian
+    theory.--Natural selection a _vera causa_.--Application of
+    Darwin's views to Insects.--Similarity of young Crustacea as
+    compared with mature forms; ditto in Insects.--Type of
+    Insecta.--Two principal types of larvae: Hexapod and
+    Apod.--Conclusions to be drawn from them.--_Campodea_ the modern
+    representative of the Insect-stock.--_Campodea_, perhaps
+    derived from Tardigrade.--Vermiform or Apod type of
+    larva.--Views of Fritz Mueller, Brauer, and Packard.--Represents
+    a still earlier ancestor.--Modern representatives.--_Notommata_,
+    _Albertia_, _Lindia_.--Earlier forms difficult to trace.--Lowest
+    forms of animal life.--Yolk-segmentation.--Embryology and
+    Evolution.--Light thrown by the evolution of the individual on
+    that of the species                                     _page_ 82-108
+
+  DESCRIPTION OF THE PLATES.
+
+
+  PLATE I. p. 7.
+
+  FIG.
+
+  1. Cricket. Westwood, Intro. to the Modern Classification of
+       Insects, vol. i. p. 440.
+
+  2. Earwig. Westwood, loc. cit. vol. i. p. 399.
+
+  3. _Aphis_. Packard, Guide to the Study of Insects, pp. 521, 522.
+
+  4. _Scolytus_. Westwood, loc. cit. vol. i. p. 350.
+
+  5. _Anthrax_. Westwood, loc. cit. vol. ii. p. 538.
+
+  6. _Balaninus_.
+
+  7. _Cynips_. Westwood, loc. cit. vol. ii. p. 121.
+
+  8. Ant (_Formica_). Westwood, loc. cit. vol. ii. p. 218.
+
+  9. Wasp. Ormerod, Nat. Hist. of Wasps, pl. i. fig. 1.
+
+
+  PLATE II. p. 8.
+
+  FIG.
+
+  1. Larva of Cricket. Westwood, loc. cit. vol. i. p. 440.
+
+  2. Larva of _Aphis_. Packard, loc. cit. pp. 521, 522.
+
+  3. Larva of Earwig. Westwood, loc. cit. vol. i. p. 399.
+
+  4. Larva of _Scolytus_. Westwood, loc. cit. vol. i. p. 350.
+
+  5. Larva of _Anthrax_. Westwood, loc. cit. vol. ii. p. 546.
+
+  6. Larva of _Balaninus_.
+
+  7. Larva of _Cynips_. Westwood, loc. cit. vol. ii. p. 121.
+
+  8. Larva of Ant (_Formica_). Westwood, loc. cit. vol. ii. p. 226.
+
+  9. Larva of Wasp. Newport, Art. Insecta, Todd's Cycl. Anat. and
+       Phys., p. 871.
+
+
+  PLATE III. p. 14.
+
+  FIG.
+
+  1. _Chloeon_. Linn. Trans. 1866.
+
+  2. _Meloe_. Spry and Shuckard, Coleoptera Delineated, pl. 56.
+
+  3. _Calepteryx_.
+
+  4. _Sitaris_. Spry and Shuckard, loc. cit. pl. 56.
+
+  5. _Campodea_. Suites a Buffon. Apteres.
+
+  6. _Acilius_. Westwood, loc. cit. vol. i. p. 100.
+
+  7. _Termes_. Westwood, loc. cit. vol. ii. p. 12.
+
+  8. _Stylops_. Duncan, Met. of Insects, p. 387; Packard, p. 482.
+
+  9. _Thrips_. Westwood, loc. cit. vol. ii. p. 1.
+
+
+  PLATE IV. p. 15.
+
+  FIG.
+
+  1. Larva of _Chloeon_. Linn. Trans. 1863.
+
+  2. Larva of _Meloe_. Chapuis and Candeze, Mem. Soc. Roy. Liege,
+       1853, pp. 1, 7.
+
+  3. Larva of _Calepteryx_. Dufour, Ann. Sci. Nat. 1852.
+
+  4. Larva of _Sitaris_. Duncan, Met. of Insects, p. 309.
+
+  5. Larva of _Campodea_. Gervais' Suites a Buffon. Apteres.
+
+  6. Larva of _Acilius_. Westwood, loc. cit. vol. i. p. 100.
+
+  7. Larva of _Termes_. Duncan, loc. cit. p. 348.
+
+  8. Larva of _Stylops_. Westwood, Trans. Ent. Soc. 1839, vol. ii.
+       pl. xv. fig. 13a.
+
+  9. Larva of _Thrips_. Westwood, loc. cit. vol. ii. p. i.
+
+
+  PLATE V. p. 99.
+
+  FIG.
+
+  1-5. _Protamoeba_.
+
+  6-9. _Protamyxa aurantiaca_. Haeckel Beit. zur. Monog. der
+         Moneren, pl. 1.
+
+  10-18. _Magosphoera planula_. Haeckel, loc. cit. pl. v.
+
+
+  PLATE VI. p. 105.
+
+  FIG.
+
+  1-4. Yolk-segmentation in _Laomedea_. After Allman. Mon. of
+         Tubularian Hydroids. Ray Society.
+
+  5-9. Yolk-segmentation in _Filaria_. After Van Beneden. Mem. sur
+         les Vers Intestinaux.
+
+  10-13. Yolk-segmentation in _Echinus_. After Derbes. Ann. des.
+           Sci. Nat. 1847.
+
+  14-17. Yolk-segmentation in _Lacinularia_. After Huxley. J. of
+           Mic. Sci. 1853.
+
+  18-21. Yolk-segmentation in _Purpura_. After Koren and
+           Danielssen. Ann. des. Sci. Nat. 1853.
+
+  22-24. Yolk-segmentation in _Amphioxus_. After Haeckel.
+           Naturliche Schoepfungsgeschichte, pl. x.
+
+  25-29. Yolk-segmentation in Vertebrate. After Allen Thompson.
+           Art. Ovum. Cyclop. of Anatomy and Physiology.
+
+
+  DESCRIPTION OF THE FIGURES.
+
+
+  FIG. 1. Larva of the Cockchafer (_Melolontha_)
+
+   2. Larva of _Cetonia_.
+
+   3. Larva of _Trox_.
+
+   4. Larva of _Oryctes_.
+
+   5. Larva of _Aphodius_.
+
+   6. Larva of _Lucanus_.
+
+   7. Larva of _Brachytarsus_.
+
+   8. Larva of _Crioceris_.
+
+   9. Larva of _Sitaris humeralis_.
+
+  10. Larva of _Sitaris humeralis_, in the second stage.
+
+  11. Larva of _Sitaris humeralis_, in the third stage.
+
+  12. Larva of _Sitaris humeralis_, in the fourth stage.
+
+  13. Pupa of _Sitaris_.
+
+  14. Larva of _Sirex_.
+
+  15. Egg of _Rhynchites_, showing the parasitic larva.
+
+  16. The parasitic larva, more magnified.
+
+  17. Egg of _Platygaster_.
+
+  18. Egg of _Platygaster_, showing the central cell.
+
+  19. Egg of _Platygaster_, after the division of the central cell.
+
+  20. Egg of _Platygaster_, more advanced.
+
+  21. Egg of _Platygaster_, more advanced.
+
+  22. Egg of _Platygaster_, showing the rudiment of the embryo.
+
+  23. Larva of _Platygaster_.--_mo_, mouth; _a_, antenna; _kf_,
+        hooked feet; _r_, toothed process; _lfg_, lateral
+        process; _f_, branches of the tail.
+
+  24. Larva of another species of _Platygaster_. (The letters
+        indicate the same parts as in the preceding figure.)
+
+  25. Larva of a third species of _Platygaster_. (The letters
+        indicate the same parts as in the preceding figure.)
+
+  26. Larva of _Platygaster_ in the second stage.--_mo_, mouth;
+        _slkf_, oesophagus; _gsae_, supra-oesophagal ganglion;
+        _lm_, muscles; _bsm_, nervous system; _gagh_, rudiments
+        of the reproductive glands.
+
+  27. Larva of _Platygaster_ in the third stage.--_mo_, mouth;
+        _ma_, mandibles; _gsae_, supra-oesophagal ganglion; _slk_,
+        oesophagus; _ag_, ducts of the salivary glands; _bnm_,
+        ventral nervous system; _sp_, salivary glands; _msl_,
+        stomach; _im_, imaginal discs; _tr_, tracheae; _fk_, fatty
+        tissue; _ed_, intestine; _ga_, rudiments of reproductive
+        organs; _ew_, wider portion of intestine; _ao_, posterior
+        opening.
+
+  28. Embryo of _Polynema_.
+
+  29. Larva of _Polynema_.--_asch_, rudiments of the antennae;
+        _flsch_, of the wings; _bsch_, of the legs; _vfg_,
+        lateral projections; _gsch_, rudiments of the ovipositor;
+        _fk_, fatty tissue.
+
+  30. Egg of _Phryganea_ (Mystacides).--_A_^1, mandibular segment;
+        _C_^1-_C_^5, maxillary, labial, and three thoracic
+        segments; _D_, abdomen.
+
+  31. Egg of _Phryganea_ somewhat more advanced.--_b_, mandibles;
+        _c_, maxillae; _cfs_, rudiments of the three pairs of
+        legs.
+
+  32. Egg of _Pholcus opilionides_, showing the Protozonites.
+
+  33. Embryo of _Julus_.
+
+  34. Colony of _Bougainvillea fruticosa_, natural size, attached
+        to the underside of a piece of floating timber.
+
+  35. Portion of the same, more magnified.
+
+  36. The Medusa from the same species.
+
+  37. Larva of Prawn, Nauplius stage.
+
+  38. Larva of Prawn, more advanced, Zoea stage.
+
+  39. Larva of Echino-cidaris oequituberculata seen from above x6/10.
+
+  40. Larva of _Echinus_ x 100.--_A_, front arm; _F_, arms of the
+        mouth-process; _B_, posterior side arm; _E_^1, accessory
+        arm of the mouth-process; _a_, mouth; _a_^1, oesophagus;
+        _b_, stomach; _b_^1, intestine; _o_, posterior orifice;
+        _d_, ciliated bands; _f_, ciliated epaulets; _c_, disc of
+        future _Echinus_.
+
+  41. _Comatula rosacea_.
+
+  42. Larva of _Comatula rosacea_.
+
+  43. Larva of _Comatula rosacea_, more advanced.
+
+  44. Larva of _Comatula rosacea_, in the Pentacrinus state.
+
+  45. Larva of Starfish (Bipinnaria), x 100.
+
+  46. Larva of Starfish (Bipinnaria), x 100, seen from the
+  side.--_a_, mouth; _b_, oesophagus; _c_, stomach; _c_^1,
+  intestine.
+
+  47. Larva of another Bipinnaria, showing the commencement of
+  the Starfish.--_g_, canal of the ciliated sac; _i_, rudiments
+  of tentacles; _d_, ciliated band.
+
+  48. Larva of Moth (_Agrotis_).
+
+  49. Larva of Beetle (_Haltica_).
+
+  50. Larva of Saw-fly (_Cimbex_).
+
+  51. Larva of _Julus_.
+
+  52. _Agrotis suffusa_.
+
+  53. _Haltica_.
+
+  54. _Cimbex_.
+
+  55. _Julus_.
+
+  56. Tardigrade.
+
+  57. Larva of _Cecidomyia_.
+
+  58. _Lindia torulosa_.
+
+  59. _Prorhynchus stagnalis_.
+
+  60. Egg of Tardigrade.
+
+  61. Egg of Tardigrade, after the yolk has subdivided.
+
+  62. Egg of Tardigrade, in the next stage.
+
+  63. Egg of Tardigrade, more advanced.
+
+
+
+
+
+ON THE ORIGIN AND METAMORPHOSES OF INSECTS.
+
+
+
+
+CHAPTER I.
+
+  _THE CLASSIFICATION OF INSECTS._
+
+
+About forty years ago the civil and ecclesiastical authorities of St.
+Fernando in Chili arrested a certain M. Renous on a charge of
+witchcraft, because he kept some caterpillars which turned into
+butterflies.[1] This was no doubt an extreme case of ignorance; it is
+now almost universally known that the great majority of insects quit the
+egg in a state very different from that which they ultimately assume;
+and the general statement in works on entomology has been that the life
+of an insect may be divided into four periods.
+
+Thus, according to Kirby and Spence,[2] "The states through which
+insects pass are four: the _egg_, the _larva_, the _pupa_, and the
+_imago_." Burmeister,[3] also, says that, excluding certain very rare
+anomalies, "we may observe four distinct periods of existence in every
+insect,--namely, those of the egg, the larva, the pupa, and the imago,
+or perfect insect." In fact, however, the various groups of insects
+differ widely from one another in the metamorphoses they pass through:
+in some, as in the grasshoppers and crickets, the changes consist
+principally in a gradual increase of size, and in the acquisition of
+wings; while others, as for instance the common fly, acquire their full
+bulk in a form very different from that which they ultimately assume,
+and pass through a period of inaction in which not only is the whole
+form of the body altered, not only are legs and wings acquired, but even
+the internal organs themselves are almost entirely disintegrated and
+re-formed. It will be my object, after having briefly described these
+changes, to throw some light on the causes to which they are due, and on
+the indications they afford of the stages through which insects have
+been evolved.
+
+The following list gives the orders or principal groups into which the
+Class Insecta may be divided. I will not, indeed, here enter upon my own
+views, but will adopt the system given by Mr. Westwood in his excellent
+"Introduction to the Modern Classification of Insects," from which also,
+as a standard authority, most of the figures on Plates I. to IV., when
+not otherwise acknowledged, have been taken. He divides insects into
+thirteen groups, and with reference to eight of them it may be said that
+there is little difference of opinion among entomologists. These orders
+are by far the most numerous, and I have placed them in capital
+letters. As regards the other five there is still much difference of
+opinion. It must also be observed that Prof. Westwood omits the
+parasitic Anoplura, as well as the Thysanura and Collembola.
+
+
+ORDERS OF INSECTS ACCORDING TO WESTWOOD.
+
+   1. HYMENOPTERA   Bees, Wasps, Ants, &c.
+   2. STREPSIPTERA  _Stylops_, _Zenos_, &c.
+   3. COLEOPTERA    Beetles.
+   4. EUPLEXOPTERA  Earwigs.
+   5. ORTHOPTERA    Grasshoppers, Crickets, Cockroaches, &c.
+   6. THYSANOPTERA  _Thrips_.
+   7. NEUROPTERA    _Ephemeras_, &c.
+   8. TRICHOPTERA   _Phryganea_.
+   9. DIPTERA       Flies and Gnats.
+  10. APHANIPTERA   Fleas.
+  11. HETEROPTERA   Bugs.
+  12. HOMOPTERA     _Aphis_, _Coccus_, &c.
+  13. LEPIDOPTERA   Butterflies and Moths.
+
+Of these thirteen orders, the eight which I have placed in capital
+letters--namely the first, third, fifth, seventh, ninth, eleventh,
+twelfth, and thirteenth, are much the most important in the number and
+variety of their species; the other five form comparatively small
+groups. The Strepsiptera are minute insects, parasitic on Hymenoptera:
+Rossi, by whom they were discovered, regarded them as Hymenopterous;
+Lamarck placed them among the Diptera; by others they have been
+considered to be most closely allied to the Coleoptera, but they are now
+generally treated as an independent order.
+
+The Euplexoptera or Earwigs are only too familiar to most of us. Linnaeus
+classed them among the Coleoptera, from which, however, they differ in
+their transformations. Fabricius, Olivier, and Latreille regarded them
+as Orthoptera; but Dr. Leach, on account of the structure of their
+wings, considered them as forming the type of a distinct order, in which
+view he has been followed by Westwood, Kirby, and many other
+entomologists.
+
+The Thysanoptera, consisting of the Linnaean genus _Thrips_, are minute
+insects well known to gardeners, differing from the Coleoptera in the
+nature of their metamorphoses, in which they resemble the Orthoptera and
+Hemiptera. The structure of the wings and mouth-parts, however, are
+considered to exclude them from these two orders.
+
+The Trichoptera, or Caddis worms, offer many points of resemblance to
+the Neuroptera, while in others they approach more nearly to the
+Lepidoptera. According to Westwood, the genus _Phryganea_ "forms the
+connecting link between the Neuroptera and Lepidoptera."
+
+The last of these small aberrant orders is that of the Aphaniptera,
+constituted for the family Pulicidae. In their transformations, as in
+many other respects, they closely resemble the Diptera. Strauss
+Durckheim indeed said that "_la puce est un diptere sans ailes_."
+Westwood, however, regards it as constituting a separate order.
+
+As indicated by the names of these orders, the structure of the wings
+affords extremely natural and convenient characters by which the various
+groups may be distinguished from one another. The mouth-parts also are
+very important; and, regarded from this point of view, the Insecta have
+been divided into two series--the Mandibulata and Haustellata, or
+mandibulate and suctorial groups, between which, as I have elsewhere
+shown,[4] the Collembola (_Podura_, _Smynthurus_, &c.) occupy an
+intermediate position. These two series are:--
+
+MANDIBULATA.
+
+  Hymenoptera.
+  Strepsiptera.
+  Coleoptera.
+  Euplexoptera.
+  Orthoptera.
+  Trichoptera?
+  Thysanoptera?
+
+HAUSTELLATA.
+
+  Lepidoptera.
+  Diptera.
+  Aphaniptera.
+  Hemiptera.
+  Homoptera.
+
+Again--and this is the most important from my present point of
+view--insects have sometimes been divided into two other series,
+according to the nature of their metamorphoses: "Heteromorpha," to use
+the terminology of Prof. Westwood,[5] "or those in which there is no
+resemblance between the parent and the offspring; and Homomorpha, or
+those in which the larva resembles the imago, except in the absence of
+wings. In the former the larva is generally worm-like, of a soft and
+fleshy consistence, and furnished with a mouth, and often with six short
+legs attached in pairs to the three segments succeeding the head. In the
+Homomorpha, including the Orthoptera, Hemiptera, Homoptera, and certain
+Neuroptera, the body, legs, and antennae are nearly similar in their form
+to those of the perfect insect, but the wings are wanting."
+
+HETEROMORPHA.
+
+  Hymenoptera.
+  Strepsiptera.
+  Coleoptera.
+  Trichoptera.
+  Diptera.
+  Aphaniptera.
+  Lepidoptera.
+
+HOMOMORPHA.
+
+  Euplexoptera.
+  Orthoptera.
+  Hemiptera.
+  Homoptera.
+  Thysanoptera.
+  Neuroptera.
+
+But though the Homomorphic insects do not pass through such striking
+changes of form as the Heteromorphic, and are active throughout life,
+still it was until within the last few years generally (though
+erroneously) considered, that in them, as in the Heteromorpha, the life
+fell into four distinct periods; those of (1) the egg, (2) the larva,
+characterized by the absence of wings, (3) the pupa with imperfect
+wings, and (4) the imago, or perfect insect.
+
+I have, however, elsewhere[6] shown that there are not, as a matter of
+fact, four well-marked stages, and four only, but that in many cases the
+process is much more gradual.
+
+The species belonging to the order Hymenoptera are among the most
+interesting of insects. To this order belong the gallflies, the
+sawflies, the ichneumons, and, above all, the ants and bees. We are
+accustomed to class the Anthropoid apes next to man in the scale of
+creation, but if we were to judge animals by their works, the chimpanzee
+and the gorilla must certainly give place to the bee and the ant. The
+larvae of the sawflies, which live on leaves, and of the Siricidae or
+long-tailed wasps, which feed on wood, are very much like caterpillars,
+having three pairs of legs, and in the former case abdominal pro-legs
+as well: but in the great majority of Hymenoptera the larvae are legless,
+fleshy grubs (Plate II., Figs. 7-9); and the various modes by which the
+females provide for, or secure to, them a sufficient supply of
+appropriate nourishment constitutes one of the most interesting pages of
+Natural History.
+
+The species of Hymenoptera are very numerous; in this country alone
+there are about 3,000 kinds, most of which are very small. In the pupa
+state they are inactive, and show distinctly all the limbs of the
+perfect insect, encased in distinct sheaths, and folded on the breast.
+In the perfect state they are highly organized and very active. The
+working ants and some few species are wingless, but the great majority
+have four strong membranous wings, a character distinguishing them at
+once from the true flies, which have only one pair of wings.
+
+The saw-flies are so called because they possess at the end of the body a
+curious organ, corresponding to the sting of a wasp, but which is in the
+form of a fine-toothed saw. With this instrument the female sawfly cuts
+a slit in the stem or leaf of a plant, into which she introduces her
+egg. The larva much resembles a caterpillar, both in form and habits. To
+this group belongs the nigger, or black caterpillar of the turnip, which
+is often in sufficient numbers to do much mischief. Some species make
+galls, but the greater number of galls are formed by insects of another
+family, the Cynipidae.
+
+[Illustration: PLATE I.[7]--MATURE INSECTS.
+
+Fig. 1, Cricket; 2, Earwig; 3, _Aphis_; 4, _Scolytus_; 5, Anthrax;
+6, _Balaninus_; 7, _Cynips_; 8, Ant; 9, Wasp.]
+
+[Illustration: PLATE II.--LARVAE OF THE INSECTS REPRESENTED ON PLATE I.
+
+Fig. 1, Larva of Cricket; 2, Larva of Aphis; 3, Larva of Earwig; 4,
+Larva of _Scolytus_ (Beetle); 5, Larva of _Anthrax_ (Fly); 6, Larva of
+_Balaninus_ (Nut Weevil); 7, Larva of _Cynips_; 8, Larva of Ant;
+9, Larva of Wasp.]
+
+In the Cynipidae (Plate I., Fig. 7) the female is provided with an organ
+corresponding to the saw of the sawfly, but resembling a needle. With
+this she stings or punctures the surface of leaves, buds, stalks, or
+even roots of various plants. In the wound thus produced she lays one or
+more eggs. The effects of this proceeding, and particularly of the
+irritating fluid which she injects into the wound, is to produce a
+tumour or gall, within which the egg hatches, and on which the larva, a
+thick fleshy grub (Plate II., Fig. 7), feeds. In some species each gall
+contains a single larva; in others, several live together.
+
+The oak supports several kinds of gallflies: one produces the well-known
+oak-apple, one a small swelling on the leaf resembling a currant,
+another a gall somewhat like an acorn, another attacks the root; the
+species making the bullet-like galls, which are now so common, has only
+existed for a few years in this country; the beautiful little spangles
+so common in autumn on the under side of oak leaves are the work of
+another species, the _Cynus longipennis_. One curious point about this
+group is, that in some of the commonest species the females alone are
+known, no one yet having ever succeeded in finding a male.
+
+Another great family of the Hymenoptera is that of the ichneumons; the
+females lay their eggs either in or on other insects, within the bodies
+of which the larvae live. These larvae are thick, fleshy, legless grubs,
+and feed on the fatty tissues of their hosts, but do not attack the
+vital organs. When full-grown, the grubs eat their way through the skin
+of the insect, and turn into chrysalides. Almost every kind of insect
+is subject to the attacks of these little creatures, which are no doubt
+useful in preventing the too great multiplication of insects, and
+especially of caterpillars. Some species are so minute that they
+actually lay their eggs within those of other insects (Figs. 15, 16).
+These parasites assume very curious forms in their larval state.
+
+But of all the Hymenoptera, the group containing the ant, the bee, and
+the wasp is the most interesting. This is especially the case with the
+social species, though the solitary ones also are extremely remarkable.
+The solitary bee or wasp, for instance, forms a cell generally in the
+ground, places in it a sufficient amount of food, lays an egg, and
+closes the cell. In the case of bees, the food consists of honey; in
+that of wasps, the larva requires animal food, and the mother therefore
+places a certain number of insects in the cell, each species having its
+own special prey, some selecting small caterpillars, some beetles, some
+spiders. _Cerceris bupresticida_, as its name denotes, attacks beetles
+belonging to the genus _Buprestis_. Now if the Cerceris were to kill the
+beetle before placing it in the cell, it would decay, and the young
+larva, when hatched, would find only a mass of corruption. On the other
+hand, if the beetle were buried uninjured, in its struggles to escape it
+would be almost certain to destroy the egg. The wasp has, however, the
+instinct of stinging its prey in the centre of the nervous system, thus
+depriving it of motion, and let us hope of suffering, but not of life;
+consequently, when the young larva leaves the egg, it finds ready a
+sufficient store of wholesome food.
+
+Other wasps are social, and, like the bees and ants, dwell together in
+communities. They live for one season, dying in autumn, except some of
+the females, which hibernate, awake in the spring, and form new
+colonies. These, however, do not, under ordinary circumstances, live
+through a second winter. One specimen which I kept tame through last
+spring and summer, lived until the end of February, but then died. The
+larvae of wasps (Plate II., Fig. 9) are fat, fleshy, legless grubs. When
+full-grown they spin for themselves a silken covering, within which they
+turn into chrysalides. The oval bodies which are so numerous in ants'
+nests, and which are generally called ants' eggs, are really not eggs
+but cocoons. Ants are very fond of the honey-dew which is formed by the
+Aphides, and have been seen to tap the Aphides with their antennae, as if
+to induce them to emit some of the sweet secretion. There is a species
+of _Aphis_ which lives on the roots of grass, and some ants collect these
+into their nests, keeping them, in fact, just as we do cows. Moreover
+they collect the eggs in the autumn and tend them through the winter
+(when they are of no use) with the same care as their own, so as to have
+a supply of young Aphides in the spring. This is one of the most
+remarkable facts I know in the whole history of animal life. One species
+of red ant does no work for itself, but makes slaves of a black kind,
+which then do everything for their masters. The slave makers will not
+even put food into their own mouths, but would starve in the midst of
+plenty, if they had not a slave to feed them. I found, however, that I
+could keep them in life and health for months if I gave them a slave for
+an hour or two in a week to clean and feed them.
+
+Ants also keep a variety of beetles and other insects in their nests.
+That they have some reason for this seems clear, because they readily
+attack any unwelcome intruder; but what that reason is, we do not yet
+know. If these insects are to be regarded as the domestic animals of the
+ants, then we must admit that the ants possess more domestic animals
+than we do.
+
+Some indeed of these beetles produce a secretion which is licked by the
+ants like the honey-dew; there are others, however, which have not yet
+been shown to be of any use to the ants, and yet are rarely, if ever,
+found, excepting in ants' nests.
+
+M. Lespes, who regards these insects as true domestic animals, has
+recorded[8] some interesting observations on the relations between one
+of them (_Claviger Duvalii_) and the ants (_Lasius niger_) with which it
+lives. This species of _Claviger_ is never met with except in ants'
+nests, though on the other hand there are many communities of _Lasius_
+which possess none of these beetles; and M. Lespes found that when he
+placed _Clavigers_ in a nest of ants which had none of their own, the
+beetles were immediately killed and eaten, the ants themselves being on
+the other hand kindly received by other communities of the same species.
+He concludes from these observations that some communities of ants are
+more advanced in civilization than others; the suggestion is no doubt
+ingenious, and the fact curiously resembles the experience of navigators
+who have endeavoured to introduce domestic animals among barbarous
+tribes; but M. Lespes has not yet, so far as I am aware, published the
+details of his observations, without which it is impossible to form a
+decided opinion. I have sometimes wondered whether the ants have any
+feeling of reverence for these beetles; but the whole subject is as yet
+very obscure, and would well repay careful study.
+
+[Illustration: PLATE III.--MATURE INSECTS.
+
+Fig. 1, _Chloeon_; 2, _Meloe_ (after Shuckard); 3, _Calepteryx_;
+4, _Sitaris_ (after Shuckard); 5, _Campodea_ (after Gervais);
+6, _Acilius_; 7, _Termes_; 8, _Stylops_ (female); 9, _Thrips_.]
+
+[Illustration: PLATE IV. YOUNG FORMS OF THE INSECTS REPRESENTED ON PLATE
+III.--Fig. 1, Larva of _Chloeon_; 2, Larva of _Meloe_ (after Chapuis and
+Candeze); 3, Larva of _Calepteryx_ (after Leon Dufour); 4, Larva of
+_Sitaris_; 5, Larva of _Campodea_; 6, Larva of _Acilius_;
+7, Larva of Termes (after Blanchard); 8, Larva of _Stylops_; 9, Larva
+of _Thrips_.]
+
+The order Strepsiptera are a small, but very remarkable group of
+insects, parasitic on bees and wasps. The larva (Pl. IV., Fig. 8) is
+minute, six-legged, and very active; it passes through its
+transformations within the body of the bee or wasp. The male and female
+are very dissimilar. The males are minute, very active, short-lived, and
+excitable, with one pair of large membranous wings. The females (Pl.
+III., Fig. 8), on the contrary, are almost motionless, and shaped very
+much like a bottle; they never quit the body of the bee, but only thrust
+out the top of the bottle between the abdominal rings of the bee.
+
+In the order Coleoptera, the larvae differ very much in form. The
+majority are elongated, active, hexapod, and more or less depressed; but
+those of the Weevils (Pl. II., Fig. 6), of _Scolytus_ (Pl. II., Fig. 4),
+&c., which are vegetable feeders, and live surrounded by their
+food,--as, for instance, in grain, nuts, &c.,--are apod, white, fleshy
+grubs, not unlike those of bees and ants. The larvae of the Longicorns,
+which live inside trees, are long, soft, and fleshy, with six short
+legs. The Geodephaga, corresponding with the Linnaean genera _Cicindela_
+and _Carabus_, have six-legged, slender, carnivorous larvae; those of
+_Cicindela_, which waylay their prey, being less active than the hunting
+larvae of the Carabidae. The Hydradephaga, or water-beetles (Dyticidae and
+Gyrinidae), have long and narrow larvae (Pl. IV., Fig. 6), with strong
+sickle-shaped jaws, short antennae, four palpi, and six small eyes on
+each side of the head; they are very voracious. The larvae of the
+Staphylinidae are by no means unlike the perfect insect, and are found in
+similar situations; their jaws are powerful, and their legs moderately
+strong. The larvae of the Lamellicorn beetles (Figs. 1-6)--cockchafers,
+stag-beetles, &c.--feed on vegetable substances or on dead animal
+matter. They are long, soft, fleshy grubs, with the abdomen somewhat
+curved, and generally lie on their side. The larvae of the Elateridae,
+known as wireworms, are long and slender, with short legs. That of the
+glowworm (Lampyridae) is not unlike the apterous female. The male
+glowworm, on the contrary, is very different. It has long, thin, brown
+wing-cases, and often flies into rooms at night, attracted by the light,
+which it probably mistakes for that of its mate.
+
+The metamorphoses of the Cantharidae are very remarkable, and will be
+described subsequently. The larvae are active and hexapod. The Phytophaga
+(_Crioceris_, _Galeruca_, _Haltica_, _Chrysomela_, &c.) are vegetable
+feeders, both as larvae and in the perfect state. The larvae are furnished
+with legs, and are not unlike the caterpillars of certain Lepidoptera.
+
+The larva of _Coccinella_ (the Ladybird) is somewhat depressed, of an
+elongated ovate form, with a small head, and moderately strong legs. It
+feeds on Aphides.
+
+Thus, then, we see that there are among the Coleoptera many different
+forms of larvae. Macleay considered that there were five principal types.
+
+1. Carnivorous hexapod larvae, with an elongated, more or less flattened
+body, six eyes on each side of the head, and sharp falciform mandibles
+(_Carabus_, _Dyticus_, &c.).
+
+2. Herbivorous hexapod larvae, with fleshy, cylindrical bodies, somewhat
+curved, so that they lie on their side.
+
+3. Apod grub-like larvae, with scarcely the rudiments of antennae
+(_Curculio_).
+
+4. Hexapod antenniferous larvae, with a subovate body, the second segment
+being somewhat larger than the others (_Chrysomela_, _Coccinella_).
+
+5. Hexapod antenniferous larvae, of oblong form, somewhat resembling the
+former, but with caudal appendages (_Meloe_, _Sitaris_).
+
+The pupa of the Coleoptera is quiescent, and "the parts of the future
+beetle are plainly perceivable, being encased in distinct sheaths; the
+head is applied against the breast; the antennae lie along the sides of
+the thorax; the elytra and wings are short and folded at the sides of
+the body, meeting on the under side of the abdomen; the two anterior
+pairs of legs are entirely exposed, but the hind pair are covered by
+wing-cases, the extremity of the thigh only appearing beyond the sides
+of the body."[9]
+
+In the next three orders--namely, the Orthoptera (grasshoppers, locusts,
+crickets, walking-stick insects, cockroaches, &c.), Euplexoptera
+(earwigs), and Thysanoptera, a small group of insects well known to
+gardeners under the name of _Thrips_ (Pl. I. and II., Figs. 1 and 2)--the
+larvae when they quit the egg already much resemble the mature form,
+differing, in fact, principally in the absence of wings, which are more
+or less gradually acquired, as the insect increases in size. They are
+active throughout life. Those specimens which have rudimentary wings
+are, however, usually called pupae.
+
+The Neuroptera present, perhaps, more differences in the character of
+their metamorphoses than any other order of insects. Their larvae are
+generally active, hexapod little creatures, and do not vary from one
+another in appearance so much, for instance, as those of the Coleoptera,
+but their pupae differ essentially; some groups, namely, the Psocidae,
+Termitidae, Libellulidae, Ephemeridae, and Perlidae, remaining active
+throughout life, like the Orthoptera; while a second division, including
+the Myrmeleonidae, Hemerobiidae, Sialidae, Panorpidae, Raphidiidae, and
+Mantispidae, have quiescent pupae, which, however, in some cases, acquire
+more or less power of locomotion shortly before they assume the mature
+state; thus that of _Raphidia_, though motionless at first, at length
+acquires strength enough to walk, even while still enclosed in the pupa
+skin, which is very thin.[10]
+
+One of the most remarkable families belonging to this order is that of
+the Termites, or white ants. They abound in the tropics, where they are
+a perfect pest, and a serious impediment to human development. Their
+colonies are extremely numerous, and they attack woodwork and furniture
+of all kinds, generally working from within, so that their presence is
+often unsuspected, until it is suddenly found that they have completely
+eaten away the interior of some post or table, leaving nothing but a
+thin outer shell. Their nests, which are made of earth, are sometimes
+ten or twelve feet high, and strong enough to bear a man. One species,
+_Termes lucifugus_, is found in the South of France, where it has been
+carefully studied by Latreille. He found in these communities five kinds
+of individuals--(1) males; (2) females, which grow to a very large size,
+their bodies being distended with eggs, of which they sometimes lay as
+many as 80,000 in a day; (3) a form described by some observers as Pupae,
+but by others as neuters. These differ very much from the others, having
+a long, soft body without wings, but with an immense head, and very
+large, strong jaws. These individuals act as soldiers, doing apparently
+no work, but keeping watch over the nest and attacking intruders with
+great boldness. (4) Apterous, eyeless individuals, somewhat resembling
+the winged ones, but with a larger and more rounded head; these
+constitute the greater part of the community, and, like the workers of
+ants and bees, perform all the labour, building the nest and collecting
+food. (5) Latreille mentions another kind of individual which he regards
+as the pupa, and which resembles the workers, but has four white
+tubercles on the back, where the wings afterwards make their appearance.
+There is still, however, much difference of opinion among entomologists,
+with reference to the true nature of these different classes of
+individuals. M. Lespes, who has recently studied the same species,
+describes a second kind of male and a second kind of female, and the
+subject, indeed, is one which offers a most promising field for future
+study.
+
+Another interesting family of Neuroptera is that of the Ephemerae, or
+Mayflies (Pl. III., Fig. 1), so well known to fishermen. The larvae (Pl.
+IV., Fig. 1) are semi-transparent, active, six-legged little creatures,
+which live in water; having at first no gills, they respire through the
+general surface of the body. They grow rapidly and change their skin
+every few days. After one or two moults they acquire seven pairs of
+branchiae, or gills, which are generally in the form of leaves, one pair
+to the segment. When the larvae are about half grown, the posterior
+angles of the two posterior thoracic segments begin to elongate. These
+elongations become more and more marked with every change of skin. One
+morning, in the month of June, some years ago, I observed a full-grown
+larva, which had a glistening appearance, owing to the presence of a
+film of air under the skin. I put it under the microscope, and, having
+added a drop of water with a pipette, looked through the glass. To my
+astonishment, the insect was gone, and an empty skin only remained. I
+then caught a second specimen, in a similar condition, and put it under
+the microscope, hoping to see it come out. Nor was I disappointed. Very
+few moments had elapsed, when I had the satisfaction of seeing the
+thorax open along the middle of the back; the two sides turned over; the
+insect literally walked out of itself, unfolded its wings, and in an
+instant flew up to the window. Several times since, I have had the
+pleasure of witnessing this marvellous change, and it is really
+wonderful how rapidly it takes place: from the moment when the skin
+first cracks, not ten seconds are over before the insect has flown away.
+
+Another family of Neuroptera, the Dragon-flies, or Horse-stingers, as
+they are sometimes called, from a mistaken idea that they sting severely
+enough to hurt a horse, though in fact they are quite harmless, also
+spend their early days in the water. The larvae are brown, sluggish, ugly
+creatures, with six legs. They feed on small water-animals, for which
+they wait very patiently, either at the bottom of the water, or on some
+aquatic plant. The lower jaws are attached to a long folding rod; and
+when any unwary little creature approaches too near the larva, this
+apparatus is shot out with such velocity that the prey which comes
+within its reach seldom escapes. In their perfect condition, also,
+Dragon-flies feed on other insects, and may often be seen hawking round
+ponds. The so-called Ant-lions in many respects resemble the
+Dragon-flies, but the habits of the larvae are very dissimilar. They do
+not live in the water, but prefer dry places, where they bury themselves
+in the loose sand, and seize with their long jaws any small insect which
+may pass. The true Ant-lion makes itself a round, shallow pit in loose
+ground or sand, and buries itself at the bottom. Any inattentive little
+insect which steps over the edge of this pit immediately falls to the
+bottom, and is instantaneously seized by the Ant-lion. Should the insect
+escape, and attempt to climb up the side of the pit, the Ant-lion is
+said to throw sand at it, knocking it down again.
+
+One other family of Neuroptera which I must mention, is the
+Hemerobiidae. The perfect insect is a beautiful, lace-winged, very
+delicate, green creature, something like a tender Dragon-fly, and with
+bright, green, touching eyes. The female deposits her eggs on leaves,
+not directly on the plant itself, but attached to it by a long white
+slender footstalk. The larva has six legs and powerful jaws, and makes
+itself very useful in destroying the Hop-fly.
+
+The insects forming the order Trichoptera are well known in their larval
+condition, under the name of caddis worms. These larvae are not
+altogether unlike caterpillars in form, but they live in water--which is
+the case with very few lepidopterous larvae--and form for themselves
+cylindrical cases or tubes, built up of sand, little stones, bits of
+stick, leaves, or even shells. They generally feed on vegetable
+substances, but will also attack minute freshwater animals. When full
+grown, the larva fastens its case to a stone, the stem of a plant, or
+some other fixed substance, and closes the two ends with an open grating
+of silken threads, so as to admit the free access of water, while
+excluding enemies. It then turns into a pupa which bears some
+resemblance to the perfect insect, "except that the antennae, palpi,
+wings, and legs are shorter, enclosed in separate sheaths, and arranged
+upon the breast." The pupa remains quiet in the tube until nearly ready
+to emerge, when it comes to the surface, and in some cases creeps out of
+the water. It is not therefore so completely motionless as the pupae of
+Lepidoptera.
+
+The Diptera, or Flies, comprise insects with two wings only, the hinder
+pair being represented by minute club-shaped organs called "halteres."
+Flies quit the egg generally in the form of fat, fleshy, legless grubs.
+They feed principally on decaying animal or vegetable matter, and are no
+doubt useful as scavengers. Other species, as the gadflies, deposit
+their eggs on the bodies of animals, within which the grubs feed, when
+hatched. The mouth is generally furnished with two hooks which serve
+instead of jaws. The pupae of Diptera are of two kinds. In the true
+flies, the outer skin of the full-grown larva is not shed, but contracts
+and hardens, thus assuming the appearance of an oval brownish shell or
+case, within which the insect changes into a chrysalis. The pupae of the
+gnats, on the contrary, have the limbs distinct and enclosed in sheaths.
+They are generally inactive, but some of the aquatic species continue to
+swim about.
+
+One group of Flies, which is parasitic on horses, sheep, bats, and other
+animals, has been called the Pupipara, because it was supposed that they
+were not born until they had arrived at the condition of pupae. They come
+into the world in the form of smooth, ovate bodies, much resembling
+ordinary dipterous pupae, but as Leuckart has shown,[11] they are true,
+though abnormal, larvae.
+
+The next order, that of the Aphaniptera, is very small in number,
+containing only the different species of Flea. The larva is long,
+cylindrical, and legless; the chrysalis is motionless, and the perfect
+insect is too well known, at least, as regards its habits, to need any
+description.
+
+The Heteroptera, unlike the preceding orders of insects, quit the egg in
+a form differing from that of the perfect insect principally in the
+absence of wings, which are gradually acquired. In their metamorphoses
+they resemble the Orthoptera, and are active through life. The majority
+are dull in colour, though some few are very beautiful. The species
+constituting this group, though very numerous, are generally small, and
+not so familiarly known to us as those of the other large orders, with
+indeed one exception, the well-known Bug. This is not, apparently, an
+indigenous insect, but seems to have been introduced. The word is indeed
+used by old writers, but either as meaning a bugbear, or in a general
+sense, and not with reference to this particular insect. In this country
+it never acquires wings, but is stated to do so sometimes in warmer
+climates. The Heteroptera cannot exactly be said either to sting or
+bite. The jaws, of which, as usual among insects, there are two pairs,
+are like needles, which are driven into the flesh, and the blood is then
+sucked up the lower lip, which has the form of a tube. This peculiar
+structure of the mouth prevails throughout the whole order; consequently
+their nutriment consists almost entirely of the juices of animals or
+plants. The Homoptera agree with the Heteroptera in the structure of the
+mouth, and in the metamorphoses. They differ principally in the front
+wings, which in Homoptera are membranous throughout, while in the
+Heteroptera, the front part is thickened and leathery. As in the
+Heteroptera, however, so also in the Homoptera, some species do not
+acquire wings. The Cicada, celebrated for its chirp, and the lanthorn
+fly, belong to this group. So also does the so-called Cuckoo-spit, so
+common in our gardens, which has the curious faculty of secreting round
+itself a quantity of frothy fluid which serves to protect it from its
+enemies. But the best known insects of this group are the Aphides or
+Plant-lice; while the most useful belong to the Coccidae, or scale
+insects, from one species of which we obtain the substance called lac,
+so extensively used in the manufacture of sealing-wax and varnish.
+Several species also have been used in dyeing, especially the Cochineal
+insect of Mexico, a species which lives on the cactus. The male _Coccus_
+is a minute, active insect, with four large wings; while the female, on
+the contrary, never acquires wings, but is very sluggish, broad, more or
+less flattened, and in fact, when full grown, looks like a small brown,
+red, or white scale.
+
+The larva of the order Lepidoptera are familiar to us all, under the
+name of caterpillars. The insects of this order in their larval
+condition are almost all phytophagous, and are very uniform both in
+structure and in habits. The body is long and cylindrical, consisting of
+thirteen segments; the head is armed with powerful jaws; the three
+following segments, the future prothorax, mesothorax, and meta-thorax,
+each bears a pair of simple articulated legs. Of the posterior segments,
+five also bear false or pro-legs, which are short, unjointed, and
+provided with a number of hooklets. A caterpillar leads a dull and
+uneventful life; it eats ravenously, and grows rapidly, casting its skin
+several times during the process, which generally lasts only a few
+weeks; though in some cases, as for instance that of the goat-moth, it
+extends over a period of two or three years, after which the larva
+changes into a quiescent pupa or chrysalis.
+
+
+
+
+CHAPTER II.
+
+_THE INFLUENCE OF EXTERNAL CONDITIONS ON THE FORM AND STRUCTURE OF
+LARVAE._
+
+
+The facts recapitulated briefly in the preceding chapter show, that the
+forms of insect larvae depend greatly on the group to which they belong.
+Thus the same tree may harbour larvae of Diptera, Hymenoptera,
+Coleoptera, and Lepidoptera; each presenting the form typical of the
+family to which it belongs.
+
+If, again, we take a group, such, for instance, as the Lamellicorn
+beetles, we shall find larvae extremely similar in form, yet very
+different in habits. Those, for instance, of the common cockchafer (Fig.
+1) feed on the roots of grass; those of _Cetonia aurata_ (Fig. 2)
+inhabit ants' nests; the larvae of the genus _Trox_ (Fig. 3) are found on
+dry animal substances; of _Oryctes_ (Fig. 4) in tan-pits; of _Aphodius_
+(Fig. 5) in dung; of _Lucanus_ (the stag-beetle, Fig. 6) in wood.
+
+[Illustration: FIG. 1, Larva of the Cockchafer (_Melolontha_).
+(Westwood, Int. to the Modern Classification of Insects, vol. i. p.
+194.). 2, Larva of _Cetonia_. 3, Larva of _Trox_. 4, Larva of _Oryctes_.
+5, Larva of _Aphodius_ (Chapuis and Candeze, Mem. Soc. Roy. Liege,
+1853). 6, Larva of _Lucanus_. (Packard, Guide to the Study of Insects,
+Fig. 403).]
+
+On the other hand, in the present chapter it will be my object to show
+that the form of the larva depends very much on the conditions of its
+life. Thus, those larvae which are internal parasites, whether in
+animals or plants, are vermiform, as are those which live in cells, and
+depend on their parents for food. On the other hand, larvae which burrow
+in wood have strong jaws and generally somewhat weak thoracic legs;
+whilst those which feed on leaves have the thoracic legs more developed,
+but less so than the carnivorous species. Now, the Hymenoptera, as a
+general rule, belong to the first category: the larvae of the Ichneumons,
+&c., which live in animals,--those of the Cynipidae, inhabiting
+galls,--and those of ants, bees, wasps, &c., which are fed by their
+parents, are fleshy, apodal grubs; though the remarkable fact that the
+embryos of bees in one stage of their development possess rudiments of
+thoracic legs which subsequently disappear, seems to show, not indeed
+that the larvae of bees were ever hexapod, but that bees are descended
+from ancestors which had hexapod larvae, and that the present apod
+condition of these larvae is not original, but results from their mode of
+life.
+
+On the other hand, the larvae of _Sirex_ (Fig. 14) being wood-burrowers,
+possess well-developed thoracic legs. Again, the larvae of the
+Tenthredinidae, which feed upon leaves, closely resemble the caterpillars
+of Lepidoptera, even to the presence of abdominal pro-legs.
+
+[Illustration: FIG. 7, Larva of _Brachytarsus_ (Ratzeburg, Forst.
+Insecten). 8, Larva of _Crioceris_ (Westwood, loc. cit.).]
+
+The larvae of most Coleoptera (Beetles) are active, hexapod, and more or
+less flattened: but those which live inside vegetable tissues, such as
+the weevils, are apod fleshy grubs, like those of Hymenoptera. Pl. II.,
+Fig. 6, represents the larva of the nut-weevil, _Balaninus_ (Pl. I., Fig.
+6), and it will be seen that it closely resembles Pl. II., Fig. 5, which
+represents that of a fly (_Anthrax_), Pl. I., Fig. 5, and Pl. II., Figs.
+7, 8, and 9, which represent respectively those of a _Cynips_ or gall-fly
+(Pl. I., Fig. 7), an ant (Pl. I., Fig. 8), and wasp (Pl. I., Fig. 9).
+Nor is _Balaninus_ the only genus of Coleoptera which affords us examples
+of this fact. Thus in the genus _Scolytus_ (Pl. I., Fig. 4), the larvae
+(Pl. II., Fig. 4), which, as already mentioned, feed on the bark of the
+elm, closely resemble those just described, as also do those of
+_Brachytarsus_ (Fig. 7). On the other hand, the larvae of certain beetles
+feed on leaves, like the caterpillars of Lepidoptera; thus that of
+_Crioceris Asparagi_ (Fig. 8)--which, as its name denotes, feeds on the
+asparagus--closely resembles the larvae of certain Lepidoptera, as for
+instance of _Thecla spini_. From this point of view the transformations
+of the genus _Sitaris_ (Pl. III., Fig. 4), which have been very carefully
+investigated by M. Fabre, are peculiarly interesting.[12]
+
+[Illustration: FIG. 9, Larva of _Sitaris numeralis_ (Fabre, Ann. des Sci.
+Nat., ser. 4, tome vii.). 10, Larva of _Sitaris humeralis_, in the second
+stage. 11, Larva of _Sitaris humeralis_, in the third stage. 12, Larva of
+_Sitaris humeralis_, in the fourth stage. 13, Pupa of _Sitaris_.]
+
+The genus _Sitaris_ (a small beetle allied to Cantharis, the blister-fly,
+and to _Meloe_, the oil-beetle) is parasitic on a kind of Bee
+(Anthophora), which excavates subterranean galleries, each leading to a
+cell. The eggs of the _Sitaris_, which are deposited at the entrance of
+these galleries, are hatched at the end of September or beginning of
+October; and M. Fabre not unnaturally expected that the young larvae,
+which are active little creatures with six serviceable legs (Fig. 9),
+would at once eat their way into the cells of the Anthophora. No such
+thing: till the month of April following they remain without leaving
+their birthplace, and consequently without food; nor do they in this
+long time change either in form or size. M. Fabre ascertained this, not
+only by examining the burrows of the _Anthophoras_, but also by direct
+observation of some young larvae kept in captivity. In April, however,
+his captives at last awoke from their long lethargy, and hurried
+anxiously about their prisons. Naturally inferring that they were in
+search of food, M. Fabre supposed that this would consist either of the
+larvae or pupae of the Anthophora, or of the honey with which it stores
+its cell. All three were tried without success. The first two were
+neglected, and the larvae, when placed on the latter, either hurried
+away, or perished in the attempt, being evidently unable to deal with
+the sticky substance. M. Fabre was in despair: "Jamais experience," he
+says, "n'a eprouve pareille deconfiture. Larves, nymphes, cellules,
+miel, je vous ai tous offert; que voulez-vous donc, bestioles maudites?"
+The first ray of light came to him from our countryman, Newport, who
+ascertained that a small parasite found by Leon Dufour on one of the
+wild bees, and named by him Triungulinus, was, in fact, the larva of
+_Meloe_. The larvae of _Sitaris_ much resembled Dufour's Triungulinus;
+and acting on this hint, M. Fabre examined many specimens of Anthophora,
+and found on them at last the larvae of his _Sitaris_. The males of
+Anthophora emerge from the pupae sooner than the females, and M. Fabre
+ascertained that, as they come out of their galleries, the little
+_Sitaris_ larvae fasten upon them. Not, however, for long: instinct
+teaches them that they are not yet in the straight path of development;
+and, watching their opportunity, they pass from the male to the female
+bee. Guided by these indications, M. Fabre examined several cells of the
+Anthophora: in some, the egg of the Anthophora floated by itself on the
+surface of the honey; in others, on the egg, as on a raft, sat the still
+more minute larva of the _Sitaris_. The mystery was solved. At the
+moment when the egg is laid the _Sitaris_ larva springs upon it. Even
+while the poor mother is carefully fastening up her cell, her mortal
+enemy is beginning to devour her offspring: for the egg of the
+Anthophora serves not only as a raft, but as a repast. The honey which
+is enough for either, would be too little for both; and the _Sitaris_,
+therefore, at its first meal, relieves itself from its only rival. After
+eight days the egg is consumed, and on the empty shell the _Sitaris_
+undergoes its first transformation, and makes its appearance in a very
+different form, as shown in Fig. 10.
+
+The honey which was fatal before is now necessary; the activity which
+before was necessary is now useless; consequently, with the change of
+skin, the active, slim larva changes into a white, fleshy grub, so
+organized as to float on the surface of the honey, with the mouth
+beneath, and the spiracles above the surface: "grace a l'embonpoint du
+ventre," says M. Fabre, "la larve est a l'abri de l'asphyxie." In this
+state it remains until the honey is consumed; then the animal
+contracts, and detaches itself from its skin, within which the further
+transformations take place. In the next stage, which M. Fabre calls the
+pseudo-chrysalis (Fig. 11), the larva has a solid corneous envelope and
+an oval shape; and in its colour, consistency, and immobility reminds
+one of a Dipterous pupa. The time passed in this condition varies much.
+When it has elapsed, the animal moults again, again changes its form,
+and assumes that shown in Fig. 12; after this it becomes a pupa (Fig.
+13) without any remarkable peculiarities. Finally, after these wonderful
+changes and adventures, in the month of August the perfect _Sitaris_ (Pl.
+III., Fig. 4) makes its appearance.
+
+On the other hand, there are cases in which larvae diverge remarkably
+from the ordinary type of the group to which they belong, without, as it
+seems in our present imperfect state of information, any sufficient
+reason.
+
+Thus the ordinary type of Hymenopterous larva, as we have already seen,
+is a fleshy apod grub; although those of the leaf-eating and wood-boring
+groups, Tenthredinidae and Siricidae (Fig. 14), are caterpillars, more or
+less closely resembling those of Lepidoptera. There is, however, a group
+of minute Hymenoptera, the larvae of which reside within the eggs or
+larvae of other insects. It is difficult to understand why these larvae
+should differ from those of Ichneumons, which are also parasitic
+Hymenoptera, and should be, as will be seen by the accompanying figures,
+of such remarkable and grotesque forms. The first known of these curious
+larvae was observed by De Filippi,[13] who, having collected some of the
+transparent eggs of a small Beetle (_Rhynchites betuleti_), to his great
+surprise found more than half of them attacked by a parasite, which
+proved to be the larva of a minute Hymenopterous insect belonging to the
+Pteromalidae. Fig. 15 shows the egg of the Beetle, with the parasitic
+larva, which is represented on a larger scale in Fig. 16.
+
+[Illustration: FIG. 14, Larva of _Sirex_ (Westwood, loc. cit.). 15, Egg of
+_Rhynchites_, showing the parasitic Larva in the interior. 16, the
+parasitic Larva more magnified.]
+
+More recently this group has been studied by M. Ganin,[14] who thus
+describes the development of _Platygaster_. The egg, as in allied
+Hymenopterous families, for instance in _Cynips_, is elongated and
+club-shaped (Fig. 17). After a while a large nucleated cell appears in
+the centre (Fig. 18). This nucleated cell divides (Fig. 19) and
+subdivides. The outermost cells continue the same process, thus forming
+an outer investing layer. The central, on the contrary, enlarges
+considerably, and develops within itself a number of daughter cells
+(Figs. 20 and 21), which gradually form a mulberry-like mass, thus
+giving rise to the embryo (Fig. 22).
+
+[Illustration: FIG. 17, Egg of _Platygaster_ (after Ganin). 18, Egg of
+_Platygaster_ showing the central cell. 19, Egg of _Platygaster_ after the
+division of the central wall. 20, Egg of Platygaster more advanced. 21,
+Egg of _Platygaster_ more advanced. 22, Egg of Platygaster showing the
+rudiment of the embryo.]
+
+Ganin met with the larvae of _Platygaster_ in those of a small gnat,
+_Cecidomyia_. Sometimes as many as fifteen parasites occurred in one gnat,
+but as a rule only one of these attained maturity. The three species of
+_Platygaster _differ considerably in form, as shown in Figs. 23-25. They
+creep about within the larva of _Cecidomyia_ by means of the strong hooked
+feet, _kf_, somewhat aided by movements of the tail. They possess a
+mouth, stomach, and muscles, but the nervous, vascular, and respiratory
+systems do not make their appearance until later. After some time the
+larva (Fig. 23) changes its skin, assuming the form represented in Fig.
+26. In this moult the last abdominal segment of the first larva is
+entirely thrown off: not merely the outer skin, as in the case of the
+other segments, but also the hypodermis and the muscles. This larva, as
+will be seen by the figure, resembles a barrel or egg in form, and is
+.870 mm. in length, the external appendages having disappeared, and the
+segments being indicated only by the arrangement of the muscles. _slkf_
+is the oesophagus leading into a wide stomach which occupies nearly
+the whole body, _gsae_ is the rudiment of the supra-oesophageal
+ganglia, _bsm_ the ventral nervous cords. The ventral nervous mass has
+the form of a broad band, with straight sides; it consists of embryonal
+cells, and remains in this undeveloped condition during the whole larval
+state.
+
+[Illustration: FIG. 23, Larva of _Platygaster_ (after Ganin)--_mo_, mouth;
+_a_, antenna; _kf_, hooked feet; _z_, toothed process; _lfg_, lateral
+process; _f_, branches of the tail. 24, Larva of another species of
+_Platygaster_. The letters indicate the same parts as in the preceding
+figure. 25, Larva of a third species of _Platygaster_. The letters
+indicate the same parts as in the preceding figures. 26, Larva of
+_Platygaster_ in the second stage--_mo_, mouth; _slkf_, oesophagus;
+_gsae_, supra-oesophageal ganglion; _lm_, muscles; _bsm_, nervous
+system; _ga_, _gh_, rudiments of the reproductive glands. 27, Larva of
+_Platygaster_ in the third stage--_mo_, mouth; _md_, mandibles; _gsae_,
+supra-oesophageal ganglion; _slk_, oesophagus; _ag_, ducts of the
+salivary glands; _bnm_, ventral nervous system; _sp_, salivary glands;
+_msl_, stomach; _im_, imaginal discs; _tr_, tracheae; _fk_, fatty tissue;
+_ed_, intestine; _ga_, rudiments of reproductive organs; _ew_, wider
+portion of intestine; _ao_, posterior opening.]
+
+At the next moult the larva enters its third state, which, as far as the
+external form (Fig. 27) is concerned, differs from the second only in
+being somewhat more elongated. The internal organs, however, are much
+more complex and complete. The tracheae have made their appearance, and
+the mouth is provided with a pair of mandibles. From this point the
+metamorphoses of _Platygaster_ do not appear to differ materially from
+those of other parasitic Hymenoptera.
+
+An allied genus, _Polynema_, has also very curious larvae. The perfect
+insect is aquatic in its habits, swimming by means of its wings; flying,
+if we may say so, under water.[15] It lays its eggs inside those of
+Dragon-flies; and the embryo, as shown in Fig. 28, has the form of a
+bottle-shaped mass of undifferentiated embryonal cells, covered by a
+thin cuticle, but without any trace of further organization. Protected
+by the egg-shell of the Dragon-fly, and bathed in the nourishing fluid
+of the Dragon-fly's egg, the young _Polynema_ imbibes nourishment through
+its whole surface, and increases rapidly in size. The digestive canal
+gradually makes its appearance; the cellular mass forms a new skin
+beneath the original cuticle, distinctly divided into segments, and
+provided with certain appendages. After a while the old cuticle is
+thrown off, and the larva gradually assumes the form shown in Fig. 29.
+The subsequent metamorphoses of _Polynema_ offer no special peculiarities.
+
+[Illustration: FIG. 28, Embryo of _Polynema_ (after Ganin). 29, Larva of
+_Polynema_--_asch_, rudiments of the antenna; _flsch_, rudiments of the
+wings; _bsch_, rudiments of the legs; _vfg_. lateral projections;
+_gsch_, rudiments of the ovipositor; _fk_, fatty tissue.]
+
+From these facts--and, if necessary, many more of the same nature might
+have been brought forward--it seems to me evident that while the form of
+any given larva depends to a certain extent on the group of insects to
+which it belongs, it is also greatly influenced by the external
+conditions to which it is subjected; that it is a function of the life
+which the larva leads and of the group to which it belongs.
+
+The larvae of insects are generally regarded as being nothing more than
+immature states--as stages in the development of the egg into the
+imago; and this might more especially appear to be the case with those
+insects in which the larvae offer a general resemblance in form and
+structure (excepting of course so far as relates to the wings) to the
+perfect insect. Nevertheless we see that this would be a very incomplete
+view of the case. The larva and pupa undergo changes which have no
+relation to the form which the insect will ultimately assume. With a
+general tendency to this goal, as regards size and the development of
+the wings, there are coincident other changes having reference only to
+existing wants and condition. Nor is there in this, I think, anything
+which need surprise us. External circumstances act on the insect in its
+preparatory states, as well as in its perfect condition. Those who
+believe that animals are susceptible of great, though gradual, change
+through the influence of external conditions, whether acting, as Mr.
+Darwin has suggested, through natural selection, or in any other manner,
+will see no reason why these changes should be confined to the mature
+animal. And it is evident that creatures which, like the majority of
+insects, live during the successive periods of their existence in very
+different circumstances, may undergo considerable changes in their
+larval organization, in consequence of forces acting on them while in
+that condition; not, indeed, without affecting, but certainly without
+affecting to any corresponding extent, their ultimate form.
+
+I conclude, therefore, that the form of the larva in insects, whenever
+it departs from the hexapod _Campodea_ type, has been modified by the
+conditions under which it lives. The external forces acting upon it are
+different from those which affect the mature form; and thus changes are
+produced in the young which have reference to its immediate wants,
+rather than to its final form.
+
+And, lastly, as a consequence, that metamorphoses may be divided into
+two kinds, developmental and adaptional or adaptive.
+
+
+
+
+CHAPTER III.
+
+_ON THE NATURE OF METAMORPHOSES._
+
+
+In the preceding chapters we have considered the life history of insects
+after they have quitted the egg; but it is obvious that to treat the
+subject in a satisfactory manner we must take the development as a
+whole, from the commencement of the changes in the egg, up to the
+maturity of the animal, and not suffer ourselves to be confused by the
+fact that insects leave the egg in very different stages of embryonal
+development. For though all young insects when they quit the egg are
+termed "larvae," whatever their form may be (the case of the so-called
+Pupipara not constituting a true exception), still it must be remembered
+that some of these larvae are much more advanced than others. It is
+evident that the larva of a fly, as regards its stage of development,
+corresponds in reality neither with that of a moth nor with that of a
+grasshopper. The maggots of flies, in which the appendages of the head
+are rudimentary, belong to a lower grade than the grubs of bees, &c.,
+which have antennae, mandibles, maxillae, labrum, labium, and, in fact,
+all the mouth parts of a perfect insect.
+
+The caterpillars of Lepidoptera are generally classed with the vermiform
+larva of Diptera and Hymenoptera, and contrasted with those of
+Orthoptera, Hemiptera, &c.; but, in truth, the possession of thoracic
+legs places them, together with the similar larvae of the Tenthredinidae,
+on a decidedly higher level. Thus, then, the period of growth (that in
+which the animal eats and increases in size) occupies sometimes one
+stage in the development of an insect, sometimes another; sometimes, as
+for instance in the case of _Chloeon_, it continues through more than
+one; or, in other words, growth is accompanied by development. But, in
+fact, the question is even more complicated than this. It is not only
+that the larvae of insects at their birth offer the most various grades
+of development, from the grub of a fly to the young of a grasshopper or
+a cricket; but that, if we were to classify larvae according to their
+development, we should have to deal, not with a simple case of
+gradations only, but with a series of gradations, which would be
+different according to the organ which we took as our test.
+
+Apart, however, from the adaptive changes to which special reference was
+made in the previous chapter, the differences which larvae present are
+those of gradation, not of direction. The development of a grasshopper
+does not pursue a different course from that of a butterfly, but the
+embryo attains a higher state before quitting the egg in the former than
+in the latter: while in most Hymenoptera, as for instance in Bees,
+Wasps, Ants, &c., the young are hatched without thoracic appendages; in
+the Orthoptera, on the contrary, the legs are fully developed before the
+young animal quits the egg.
+
+Prof. Owen,[16] indeed, goes so far as to say that the Orthoptera and
+other Homomorphous insects are, "at one stage of their development,
+apodal and acephalous larvae, like the maggot of the fly; but instead of
+quitting the egg in this stage, they are quickly transformed into
+another, in which the head and rudimental thoracic feet are developed to
+the degree which characterizes the hexapod larvae of the _Carabi_ and
+_Petalocera_."
+
+[Illustration: FIG. 30, Egg of _Phryganea_ (Mystacides)--_A_^1,
+mandibular segment; _C_^1 to _C_^5, maxillary, labial, and three
+thoracic segments; _D_, abdomen (after Zaddach). 31, Egg of _Phryganea_
+somewhat more advanced--_b_, mandibles; _c_, maxillae; _cfs_, rudiments
+of the three pairs of legs.]
+
+I quite believe that this may have been true of such larvae at an early
+geological period, but the fact now appears to be, so far at least as
+can be judged from the observations yet recorded, that the legs of those
+larvae which leave the egg with these appendages generally make their
+appearance before the body-walls have closed, or the internal organs
+have approached to completion. Indeed, when the legs first appear, they
+are merely short projections, which it is not always easy to distinguish
+from the segments themselves. It must, however, be admitted, that the
+observations are neither so numerous, nor in most cases so full, as
+could be wished.
+
+Fig. 30 represents an egg of a May-fly (_Phryganea_), as represented by
+Zaddach in his excellent memoir,[17] just before the appearance of the
+appendages. It will be seen that a great part of the yolk is still
+undifferentiated, that the side walls are incomplete, the back quite
+open, and the segments merely indicated by undulations. This stage is
+rapidly passed through, and Zaddach only once met with an egg in this
+condition; in every other specimen which had indications of segments,
+the rudiments of the legs had also made their appearance, as in Fig. 31,
+which, however, as will be seen, does not in other respects show much
+advance on Fig. 30.
+
+Again in _Aphis_, the embryology of which has been so well worked out by
+Huxley,[18] the case is very similar, although the legs are somewhat
+later in making their appearance. When the young was 1/140th of an inch
+in length, he found the cephalic portion of the embryo beginning, he
+says, "to extend upwards again over the anterior face of the germ, so as
+to constitute its anterior and a small part of its superior wall. This
+portion is divided by a median fissure into two lobes, which play an
+important part in the development of the head, and will be termed the
+'procephalic lobes.' I have already made use of this term for the
+corresponding parts in the embryos of Crustacea. The rudimentary thorax
+presents traces of a division into three segments; and the dorso-lateral
+margins of the cephalic blastoderm, behind the procephalic lobes, have a
+sinuous margin. It is in embryos between this and 1/100th of an inch in
+length, that the rudiments of the appendages make their appearance; and
+by the growth of the cephalic, thoracic, and abdominal blastoderm,
+curious changes are effected in the relative position of those regions."
+
+In _Chrysopa oculata_, one of the Hemerobiidae, Packard has described[19]
+and figured a stage in which the body segments have made their
+appearance, but in which he says "there are no indications of limbs. The
+primitive band is fully formed, the protozorites being distinctly
+marked, the transverse impressed lines indicating the primitive segments
+being distinct, and the median furrow easily discerned." Here also,
+again, the dorsal walls are incomplete, and the internal organs as yet
+unformed.
+
+In certain Dragon-flies (_Calepteryx_), and _Hemiptera_ (_Hydrometra_), the
+legs, according to Brandt,[20] appear at a still earlier stage.
+
+According to the observations of Koelliker,[21] it would appear that in
+the Coleopterous genus _Donacia_ the segments and appendages appear
+simultaneously.
+
+Koelliker himself, however, frankly admits that "meae de hoc insecto
+observationes satis sunt manca," and it is possible that he may never
+have met with an embryo in the state immediately preceding the
+appearance of the legs; especially as it appears from the observations
+of Kowalevski that in _Hydrophilus_ the appendages do not make their
+appearance until after the segments.[22]
+
+On the whole, as far as we can judge from the observations as yet
+recorded, it seems that in Homomorphous insects the ventral wall is
+developed and divided into segments, before the appearance of the legs;
+but that the latter are formed almost simultaneously with the cephalic
+appendages, and before either the dorsal walls of the body or the
+internal organs.
+
+[Illustration: FIG. 32.--Egg of _Pholcus opilionides_ (after Claparede).]
+
+As it is interesting, from this point of view, to compare the
+development of other Articulata with that of insects, I give a figure
+(Fig. 32), representing an early stage in the development of a spider
+(_Pholcus_) after Claparede,[23] who says, "C'est a ce moment qu'a lieu
+la formation des _protozonites_ ou segments primordiaux du corps de
+l'embryon. Le rudiment ventral s'epaissit suivant six zones disposees
+transversalement entre le capuchon anal et le capuchon cephalique."
+
+[Illustration: FIG. 33.--Embryo of _Julus_ (after Newport).]
+
+Among Centipedes the development of _Julus_ has been described by
+Newport.[24] The first period, from the deposition of the egg to the
+gradual bursting of the shell, and exposure of the embryo within it,
+which, however, remains for some time longer in connection with the
+shell, lasts for twenty-five days. The segments of the body, originally
+six in number, make their appearance on the twentieth day after the
+deposition of the egg, at which time there were no traces of legs. The
+larva, when it leaves the egg, is a soft, white, legless grub (Fig. 33),
+consisting of a head and seven segments, the head being somewhat firmer
+in texture than the rest of the body. It exhibits rudimentary antennae,
+but the legs are still only represented by very slight papilliform
+processes on the undersides of the segments to which they belong.
+
+As already mentioned, it is possible that at one time the vermiform
+state of the Homomorphous insects--which, as we have seen, is now so
+short, and passed through at so early a stage of development--was more
+important, more prolonged, and accompanied by a more complete condition
+of the internal organs. The compression, and even disappearance of those
+embryonal stages which are no longer adapted to the mode of life--which
+do not benefit the animal--is a phenomenon not without a parallel in
+other parts of the animal or even of the vegetable kingdom. Just as in
+language long compound words have a tendency to concision, and single
+letters sometimes linger on, indicating the history of a word, like the
+"l" in "alms," or the "b" in "debt," long after they have ceased to
+influence the sound; so in embryology useless stages, interesting as
+illustrations of past history, but without direct advantage under
+present conditions, are rapidly passed through, and even, as it would
+appear, in some cases altogether omitted.
+
+[Illustration: FIG. 34.--Colony of _Bougainvillea fruticosa_, natural
+size, to the underside of a piece of floating timber (after Allman).]
+
+For instance, among the Hydroida, in the great majority of cases, the
+egg produces a body more or less resembling the common _Hydra_ of our
+ponds, and known technically as the "trophosome," which develops into
+the well-known Medusae or jelly-fishes. The group, however, for which
+Prof. Allman has proposed the term Monopsea,[25] and of which the genus
+_Aegina_ may be taken as the type, is, as he says, distinguished by the
+absence of a hydriform stage, "the ovum becoming developed through
+direct metamorphosis into a medusiform body, just as in the other orders
+it is developed into a hydriform body." Fig. 34 represents, after
+Allman, a colony of _Bougainvillea fruticosa_ of the natural size. It is
+a British species, which is found growing on buoys, floating timber,
+&c., and, says Allman,[26] "when in health and vigour, offers a
+spectacle unsurpassed in interest by any other species--every branchlet
+crowned by its graceful hydranth and budding with Medusae in all stages
+of development (Fig. 35), some still in the condition of minute buds, in
+which no trace of the definite Medusa-form can yet be detected; others,
+in which the outlines of the Medusa can be distinctly traced within the
+transparent _ectotheque_ (external layer); others, again, just casting
+off this thin outer pellicle, and others completely freed from it,
+struggling with convulsive efforts to break loose from the colony, and
+finally launched forth in the full enjoyment of their freedom into the
+surrounding water. I know of no form in which so many of the
+characteristic features of a typical hydroid are more finely expressed
+than in this beautiful species."
+
+[Illustration: FIG. 35.--Portion of colony of _Bougainvillea fruticosa_,
+more magnified.]
+
+[Illustration: FIG. 36.--The Medusa form of the same species.]
+
+Fig. 36 represents the Medusa form of this species, and the development
+thus described may be regarded as typical of the Hydroida; yet, as
+already mentioned, the Aeginidae do not present us with any stage
+corresponding to the fixed condition of _Bougainvillea_, but, on the
+contrary, are developed into Medusae direct from the egg.
+
+On the other hand, there are groups in which the Medusiform stage
+becomes less and less important.
+
+[Illustration: FIG. 37, Larva of Prawn, Nauplius stage (after F.
+Mueller). 38, Larva of Prawn, more advanced, Zoea stage.]
+
+The great majority of the higher Crustacea go through well-marked
+metamorphoses. Figs. 37 and 38 represent two stages in the development
+of the prawn. In the first (Fig. 37), representing the young animal as
+it quits the egg, the body is more or less oval and unsegmented; there
+is a median frontal eye, and three pairs of natatory feet, the first
+pair simple, while the two posterior are two-branched. Very similar
+larvae occur in various other groups of Crustacea. They were at first
+regarded as mature forms, and O. F. Mueller gave them the name of
+Nauplius. So also, the second or Zoea form (Fig. 38) was at first
+supposed to be a mature animal, until its true nature was discovered by
+Vaughan Thompson.
+
+The Zoea form of larva differs from the perfect prawn or crab in the
+absence of the middle portion of the body and its appendages. The
+mandibles have no palpi, the maxillipeds or foot-jaws are used as feet,
+whereas in the mature form they serve as jaws. Branchiae are either
+wanting or rudimentary, respiration being principally effected through
+the walls of the carapace. The abdomen and tail are destitute of
+articulate appendages. The development of Zoea into the perfect animal
+has been well described by Mr. Spence Bate[27] in the case of the common
+crab (_Carcinus maenas_).
+
+All crabs, as far as we know, with the exception of a species of land
+crab (_Gegarcinus_), described by Westwood, pass through a stage more or
+less resembling that shown in Fig. 38. On the other hand, the great
+group of Edriopthalma, comprising Amphipoda (shore-hoppers, &c.) and
+Isopoda (wood-lice, &c.) pass through no such metamorphosis; the
+development is direct, as in the Orthoptera. It is true that one
+species, _Tanais Dulongii_, though a typical Isopod in form and general
+character, is said to retain in some points, and especially in the mode
+of respiration, some peculiarities of the Zoea type; but this is quite
+an exceptional case. In _Mysis_, says F. Mueller,[28] "there is still a
+trace of the Nauplius stage; being transferred back to a period when it
+had not to provide for itself, the Nauplius has become degraded into a
+mere skin; in _Ligia_ this larva-skin has lost the traces of limbs, and
+in _Philoscia_ it is scarcely demonstrable."
+
+The Echinodermata in most cases "go through a very well-marked
+metamorphosis, which often has more than one larval stage.... The mass
+of more or less differentiated sarcode, of which the larva, or
+pseud-embryo, as opposed to the Echinoderm within it, is made up, always
+carries upon its exterior certain bilaterally-arranged ciliated bands,
+by the action of which the whole organism is moved from place to place;
+and it may be strengthened by the super-addition to it of a framework
+of calcareous rods."[29] Mueller considered that the mouth and pharynx of
+the larva were either absorbed or cast off with the calcareous rods, but
+were never converted into the corresponding organs of the perfect
+Echinoderm. According to A. Agassiz, however, this is not the case, but
+on the contrary "the whole larva and all its appendages are gradually
+drawn into the body, and appropriated."[30]
+
+Fig. 39 represents the larva of a sea-egg (_Echino cidaris_) after
+Mueller.[31] The body is transparent, shaped somewhat like a double
+easel, but with two long horns in front, which, as well as the posterior
+processes, are supported by calcareous rods. This larva swims by means
+of minute vibratile hairs, or ciliae. It has a mouth, stomach, and in
+fact a well-defined alimentary canal; but no nerves or other internal
+organs have yet been discovered in it. After swimming about in this
+condition for a while, it begins to show signs of change. An involution
+of the integument takes place on one side of the back, and continues to
+deepen till it reaches a mass or store of what is called blastema, or
+the raw material of the animal body. This blastema then begins to
+change, and gradually assumes the form of the perfect Echinoderm.[32]
+
+[Illustration: FIG. 39.--Larva of _Echino cidaris_, seen from above x 6/10
+(after Mueller).]
+
+[Illustration: FIG. 40, Larva of _Echinus_, x 100. _A_, front arm; _F_,
+arms of the mouth process; _B_, posterior side arm; _E_(1), accessory
+arm of the mouth process; _a_, mouth; _a'_, oesophagus; _b_, stomach;
+_b'_, intestine; _o_, posterior orifice; _d_, ciliated bands; _f_,
+ciliated epaulets; _c_, disc of future _Echinus_ (after Mueller).]
+
+Fig. 40 represents a larva, probably of another sea-egg (_Echinus
+lividus_), from the Mediterranean, and shows the commencement of the
+sea-egg within the body of the larva. The capital letters denote the
+different arms: _a_ is the mouth, _a'_ the oesophagus, _b_ the
+stomach, _b'_ the intestine, _f_ the ciliated lobes or epaulets, _c_ the
+young sea-egg.
+
+The development of the beautiful _Comatula rosacea_ (Fig. 41) has been
+described in the "Philosophical Transactions," by Prof. Wyville Thomson
+and Dr. Carpenter.[33] The larva quits the egg, as shown in Fig. 42, in
+the form of an oval body about 1/30 inch in length, something like a
+barrel, surrounded by four bands or hoops of long vibratile hairs or
+ciliae. There is also a tuft of still longer hairs at the narrower
+posterior end of the body. Gradually a number of minute calcareous
+spines and plates make their appearance (Fig. 43) in the body of this
+larva, and at length arrange themselves in a definite order, so as to
+form a bent calcareous club or rod with an enlarged head.
+
+[Illustration: FIG. 41.--_Comatula rosacea_ (after Forbes).]
+
+[Illustration: FIG. 42, Larva of Comatula rosacea (after Thomson). 43,
+Larva of _Comatula rosacea_, more advanced. 44, Larva of Comatula rosacea,
+in the Pentacrinus state.]
+
+As this process continues, the little creature gradually loses its power
+of swimming, and, sinking to the bottom, looses the bands of ciliae, and
+attaches itself by its base to some stone or other solid substance, the
+knob of the club being free. The calcareous framework increases in size,
+and the expanded head forms itself into a cup, round which from five to
+fifteen delicate tentacles, as shown in Fig. 44, make their appearance.
+
+In this stage the young animal resembles one of the stalked Crinoids, a
+family of Echinoderms very abundant in earlier geological periods, but
+which has almost disappeared, being, as we see, now represented by the
+young states of existing more advanced, free, species. This attached,
+plant-like condition of _Comatula_ was indeed at first supposed to be a
+mature form, and was named Pentacrinus; but we now know that it is only
+a stage in the development of _Comatula_. The so-called Pentacrinus
+increases considerably in size, and after various gradual changes, which
+time does not now permit me to describe, quits the stalk, and becomes a
+free _Comatula_.
+
+The metamorphoses of the Starfishes are also very remarkable. Sars
+discovered, in the year 1835, a curious little creature about an inch in
+length, which he named _Bipinnaria asterigera_ (Figs. 45-47), and which
+he then supposed to be allied to the ciliograde Medusae. Subsequent
+observations, however, made in 1844, suggested to him that it was the
+larva of a Starfish, and in 1847 MM. Koren and Danielssen satisfied
+themselves that this was the case.
+
+Figs. 45 and 46 represent the front and side view of a Bipinnaria found
+by Mueller[34] near Marseilles. _a_ is the mouth, _b_ the oesophagus,
+_c_ the stomach, _c_' the intestine. Fig. 47 represents a somewhat older
+specimen, in which the Starfish (_k_) is already beginning to make its
+appearance.
+
+[Illustration: FIG. 45, Larva of Starfish (Bipinnaria), x 100 (after
+Mueller). 46, Larva of Starfish (Bipinnaria), x 100, seen from the
+side--_a_, mouth; _b_, oesophagus; _c_, stomach; _c'_, intestine. 47,
+Larva of another Bipinnaria, showing the commencement of the
+Starfish--_g_, canal of the ciliated sac; _i_, rudiments of tentacles;
+_d_, ciliated band.]
+
+But while certain Starfishes thus go through metamorphoses similar in
+character, and not less remarkable than those of sea-eggs, there are
+others--as, for instance, the genus _Asteracanthion_--in which development
+may be said to be direct--the organs and appendages special to the
+Pseud-embryo being in abeyance; while in another genus, _Pteraster_, they
+are reduced to a mere investing membrane.[35]
+
+Among the Ophiurans also we find two well-marked types of development.
+Some passing through metamorphoses, while others, as for instance
+_Ophiopholis bellis_, "is developed very much after the method of
+_Asteracanthion Muelleri_, without passing through the Plutean
+stage."[36]
+
+Even in the same species of Echinoderm the degree of development
+attained by the larva differs to a certain extent according to the
+temperature, the supply of food, &c. Thus in _Comatula_, specimens which
+are liberally supplied with sea-water, and kept warm, hurry as it were
+through their early stages, and the free larva becomes distorted by the
+growing Pentacrinus (see Fig. 43), almost before it has attained its
+perfect form. On the other hand, under less favourable conditions, if
+the temperature is low and food less abundant, the early stages are
+prolonged, the larva is longer lived, and reaches a much higher degree
+of independent development. Similar differences occur in the development
+of other animals, as for instance, in the Hydroids,[37] and among the
+insects themselves, in Flies;[38] and it is obvious that these facts
+throw much light on the nature and origin of the metamorphoses of
+insects, which subject we shall now proceed to consider.
+
+
+
+
+CHAPTER IV.
+
+_ON THE ORIGIN OF METAMORPHOSES._
+
+
+The question still remains, Why do insects pass through metamorphoses?
+Messrs. Kirby and Spence tell us they "can only answer that such is the
+will of the Creator;"[39] this, however, is a general confession of
+faith, not an explanation of metamorphoses. So indeed they themselves
+appear to have felt; for they immediately proceed to make a suggestion.
+"Yet one reason," they say, "for this conformation may be hazarded. A
+very important part assigned to insects in the economy of nature, as we
+shall hereafter show, is that of speedily removing superabundant and
+decaying animal and vegetable matter. For such agents an insatiable
+voracity is an indispensable qualification, and not less so unusual
+powers of multiplication. But these faculties are in a great degree
+incompatible; an insect occupied in the work of reproduction could not
+continue its voracious feeding. Its life, therefore, after leaving the
+egg, is divided into three stages."
+
+But there are some insects--as, for instance, the Aphides--which
+certainly are not among the least voracious, and which grow and breed at
+the same time. There are also many scavengers among other groups of
+animals--such, for instance, as the dog, the pig, and the vulture--which
+undergo no metamorphosis.
+
+It is certainly true that, as a general rule, growth and reproduction do
+not occur together; and it follows, almost as a necessary consequence,
+that in such cases the first must precede the second. But this has no
+immediate connection with the occurrence of metamorphoses. The question
+is not, why an insect does not generally begin to breed until it has
+ceased to grow, but why, in attaining to its perfect form, it passes
+through such remarkable changes; why these changes are so sudden and
+apparently violent; and why they are so often closed by a state of
+immobility--that of the chrysalis or pupa; for undoubtedly the quiescent
+and death-like condition of the pupa is one of the most remarkable
+phenomena of insect-metamorphoses.
+
+In the first place, it must be observed that many animals which differ
+considerably in their mature state, resemble one another more nearly
+when young. Thus birds of the same genus, or of closely allied genera,
+which, when mature, differ much in colour, are often very similarly
+coloured when young. The young of the lion and the puma are often
+striped, and the foetal Black whale has teeth, like its ally the Sperm
+whale.
+
+In fact, the great majority of animals do go through well-marked
+metamorphoses, though in many cases they are passed through within the
+egg, and thus do not come within the popular ken. "La larve," says,
+Quatrefages, "n'est qu'un embryon a vie independante."[40] Those
+naturalists who accept in any form the theory of evolution, consider
+that "the embryonal state of each species reproduces more or less
+completely the form and structure of its less modified progenitors."[41]
+"Each organism," says Herbert Spencer,[42] "exhibits within a short
+space of time a series of changes which, when supposed to occupy a
+period indefinitely great, and to go on in various ways instead of one
+way, give us a tolerably clear conception of organic evolution in
+general."
+
+The naturalists of the older school do not, as Darwin and Fritz Mueller
+have already pointed out, dispute these facts, though they explain them
+in a different manner--generally by the existence of a supposed tendency
+to diverge from an original type. Thus Johannes Mueller says, "The idea
+of development is not that of mere increase of size, but that of
+progress from what is not yet distinguished, but which potentially
+contains the distinction in itself, to the actually distinct. It is
+clear that the less an organ is developed, so much the more does it
+approach the type, and that during its development it acquires more and
+more peculiarities. The types discovered by comparative anatomy and
+developmental history must therefore agree." And again, "What is true in
+this idea is, that every embryo at first bears only the type of its
+section, from which the type of the class, order, &c., is only
+afterwards developed." Agassiz also observes that "the embryos of
+different animals resemble each other the more the younger they are."
+
+There are, no doubt, cases in which the earlier states are rapidly
+passed through, or but obscurely indicated; yet we may almost state it
+as a general proposition, that either before or after birth animals
+undergo metamorphoses. The state of development of the young animal at
+birth varies immensely. The kangaroo (_Macropus major_), which attains a
+height of seven feet ten inches, does not when born exceed one inch and
+two lines in length; the chick leaves the egg in a much more advanced
+condition than the thrush; and so, among insects, the young cricket is
+much more highly developed, when it leaves the egg, than the larva of
+the fly or of the bee; and, as I have already mentioned, differences
+occur even within the limit of one species, though not of course to
+anything like the same extent.
+
+In oviparous animals the condition of the young at birth depends much on
+the size of the egg: where the egg is large, the abundant supply of
+nourishment enables the embryo to attain a high stage of development;
+where the egg is small, and the yolk consequently scanty, the embryo
+requires an additional supply of food before it can do so. In the former
+case the embryo is more likely to survive; but when the eggs are large,
+they cannot be numerous, and a multiplicity of germs may be therefore in
+some circumstances a great advantage. Even in the same species the
+development of the egg presents certain differences.[43]
+
+The metamorphoses of insects depend then primarily on the fact that the
+young quit the egg at a more or less early stage of development; and
+that consequently the external forces, acting upon them in this state,
+are very different from those by which they are affected when they
+arrive at maturity.
+
+Hence it follows that, while in many instances mature forms, differing
+greatly from one another, arise from very similar larvae, in other cases,
+as we have seen, among some the parasitic Hymenoptera, insects agreeing
+closely with one another, are produced from larvae which are very unlike.
+The same phenomenon occurs in other groups. Thus, while in many cases
+very dissimilar jelly-fishes arise from almost identical Hydroids, we
+have also the reverse of the proposition in the fact that in some
+species, Hydroids of an entirely distinct character produce very similar
+Medusae.[44]
+
+We may now pass to the second part of our subject: the apparent
+suddenness and abruptness of the changes which insects undergo during
+metamorphosis. But before doing so I must repeat that these changes are
+not always, even apparently, sudden and great. The development of an
+Orthopterous insect, say a grasshopper, from its leaving the egg to
+maturity, is so gradual that the ordinary nomenclature of entomological
+works (larva state and pupa state) does not apply to it; and even in the
+case of Lepidoptera, the change from the caterpillar to the chrysalis
+and from this to the butterfly is in reality less rapid than might at
+first sight be supposed; the internal organs are metamorphosed very
+gradually, and even the sudden and striking change in external form is
+very deceptive, consisting merely of a throwing off of the outer
+skin--the drawing aside, as it were of a curtain and the revelation of a
+form which, far from being new, has been in preparation for days;
+sometimes even for months.
+
+Swammerdam, indeed, supposed (and his view was adopted by Kirby and
+Spence) that the larva contained within itself "the germ of the future
+butterfly, enclosed in what will be the case of the pupa, which is
+itself included in three or more skins, one over the other, that will
+successively cover the larva." This was a mistake; but it is true that,
+if a larva be examined shortly before it is full grown, the future pupa
+may be traced within it. In the same manner, if we examine a pupa which
+is about to disclose the butterfly, we find the future insect, soft
+indeed and imperfect, but still easily recognizable, lying more or less
+loosely within the pupa-skin.
+
+One important difference between an insect and a vertebrate animal is,
+that whereas in the latter--as, for instance, in ourselves--the muscles
+are attached to an internal bony skeleton, in insects no such skeleton
+exists. They have no bones, and their muscles are attached to the skin;
+whence the necessity for the hard and horny dermal investment of
+insects, so different from the softness and suppleness of our own skin.
+The chitine, or horny substance, of which the outside of an insect
+consists, is formed by a layer of cells lying beneath it, and, once
+secreted, cannot be altered. From this the result is, that without a
+change of skin, a change of form is impossible. In some cases, as for
+instance in _Chloeon_, each change of skin is accompanied by a change of
+form, and thus the perfect insect is gradually evolved. In others, as in
+caterpillars, several changes of skin take place without any material
+alteration of form, and the change, instead of being spread over many,
+is confined to the last two moults.
+
+One explanation of this difference between the larvae which change their
+form with every change of skin, and those which do not, is, I believe,
+to be found in the structure of the mouth. That of the caterpillar is
+provided with a pair of strong jaws, fitted to eat leaves; and the
+digestive organs are adapted for this kind of food. On the contrary, the
+mouth of the butterfly is suctorial; it has a long proboscis,
+beautifully adapted to suck the nectar from flowers, but which would be
+quite useless, and indeed only an embarrassment to the larva. The
+digestive organs also of the butterfly are adapted for the assimilation,
+not of leaves, but of honey. Now it is evident that if the mouth-parts
+of the larva were slowly metamorphosed into those of the perfect insect,
+through a number of small changes, the insect would in the meantime be
+unable to feed, and liable to perish of starvation in the midst of
+plenty. In the Orthoptera, and among those insects in which the changes
+are gradual, the mouth of the so-called larva resembles that of the
+perfect insect, and the principal difference consists in the presence of
+wings.
+
+Similar considerations throw much light on the nature of the chrysalis
+or pupa state--that remarkable period of death-like quiescence which is
+one of the most striking characteristics of insect metamorphosis. The
+quiescence of the pupa is mainly owing to the rapidity of the changes
+going on in it. In that of a butterfly, not only (as has been already
+mentioned) are the mouth and the digestive organs undergoing change, but
+the muscles are in a similar state of transition. The powerful ones
+which move the wings are in process of formation; and even the nervous
+system, by which the movements are set on foot and regulated, is in a
+state of rapid change.[45]
+
+It must not be forgotten that all insects are inactive for a longer or
+shorter space of time after each moult. The slighter the change, as a
+general rule, the shorter is the period of inaction. Thus, after the
+ordinary moult of a caterpillar, the insect only requires a short rest
+until the new skin is hardened. When, however, the change is great, the
+period of inaction is correspondingly prolonged. Most pupae indeed have
+some slight powers of motion; those which assume the chrysalis state in
+wood or beneath the ground usually come to the surface when about to
+assume the perfect state, and the aquatic pupae of certain Diptera swim
+about with much activity. Among the Neuroptera, certain families have
+pupae as quiescent as those of the Lepidoptera: others--as, for
+instance, _Raphidia_--are quiescent at first, but at length acquire
+sufficient strength to walk, though still enclosed within the pupa-skin:
+a power dependent partly on the fact that this skin is very thin. Others
+again--as, for instance, dragon-flies--are not quiescent on assuming the
+so-called pupa state for any longer time than at their other changes of
+skin. The inactivity of the pupa is therefore not a new condition
+peculiar to this stage, but a prolongation of the inaction which has
+accompanied every previous change of skin.
+
+Nevertheless the metamorphoses of insects have always seemed to me one
+of the greatest difficulties of the Darwinian theory. In most cases, the
+development of the individual reproduces to a certain extent that of the
+race; but the motionless, imbecile pupa cannot represent a mature form.
+No one, so far as I know, has yet attempted to explain, in accordance
+with Mr. Darwin's views, a life-history in which the mouth is first
+mandibulate and then suctorial, as, for example, in a butterfly. A clue
+to the difficulty may, I think, be found in the distinction between
+developmental and adaptive changes; to which I have called attention in
+a previous chapter. The larva of an insect is by no means a mere stage
+in the development of the perfect animal. On the contrary, it is subject
+to the influence of natural selection, and undergoes changes which have
+reference entirely to its own requirements and condition. It is evident,
+then, that while the embryonic development of an animal in the egg may
+be an epitome of its specific history, this is by no means the case
+with species in which the immature forms have a separate and
+independent existence. If an animal which, when young, pursues one mode
+of life, and lives on one kind of food, subsequently, either from its
+own growth in size and strength, or from any change of season, alters
+its habits or food, however slightly, it immediately becomes subject to
+the action of new forces: natural selection affects it in two different,
+and, it may be, very distinct manners, gradually tending to changes
+which may become so great as to involve an intermediate period of change
+and quiescence.
+
+There are, however, peculiar difficulties in those cases in which, as
+among the Lepidoptera, the same species is mandibulate as a larva, and
+suctorial as an imago. From this point of view _Campodea_ and the
+Collembola (_Podura_, &c.) are peculiarly interesting. There are in
+insects three principal types of mouth:--
+
+First, the mandibulate;
+
+Secondly, the suctorial; and
+
+Thirdly, that of _Campodea_ and the Collembola generally,
+
+in which the mandibles and maxillae are retracted, but have some freedom
+of motion, and can be used for biting and chewing soft substances. This
+type is, in some respects, intermediate between the other two. Assuming
+that certain representatives of such a type were placed under conditions
+which made a suctorial mouth advantageous, those individuals in which
+the mandibles and maxillae were best calculated to pierce or prick would
+be favoured by natural selection, and their power of lateral motion
+would tend to fall into abeyance; while, on the other hand, if
+masticatory jaws were an advantage, the opposite process would take
+place.
+
+There is yet a third possibility--namely, that during the first portion
+of life, the power of mastication should be an advantage, and during the
+second that of suction, or _vice versa_. A certain kind of food might
+abound at one season and fail at another; might be suitable for the
+animal at one age and not at another. Now in such cases we should have
+two forces acting successively on each individual, and tending to modify
+the organization of the mouth in different directions. It cannot be
+denied that the innumerable variations in the mouth-parts of insects
+have special reference to their mode of life, and are of some advantage
+to the species in which they occur. Hence, no believer in natural
+selection can doubt the possibility of the three cases above suggested,
+the last of which seems to throw some light on the possible origin of
+species which are mandibulate in one period of life and not in another.
+Granting then the transition from the one condition to the other, this
+would no doubt take place contemporaneously with a change of skin. At
+such times we know that, even when there is no change in form, the
+softness of the organs temporarily precludes the insect from feeding for
+a time, as, for instance, in the case of caterpillars. If, however, any
+considerable change were involved, this period of fasting must be
+prolonged, and would lead to the existence of a third condition, that of
+the pupa, intermediate between the other two. Since the acquisition of
+wings is a more conspicuous change than any relating to the mouth, we
+are apt to associate with it the existence of a pupa-state: but the case
+of the Orthoptera (grasshoppers, &c.) is sufficient proof that the
+development of wings is perfectly compatible with permanent activity;
+the necessity for prolonged rest is in reality much more intimately
+connected with the change in the constitution of the mouth, although in
+many cases, no doubt, this is accompanied by changes in the legs, and in
+the internal organization. An originally mandibulate mouth, however,
+like that of a beetle, could not, I think, have been directly modified
+into a suctorial organ like that of a butterfly or a gnat, because the
+intermediate stages would necessarily be injurious. Neither, on the
+other hand, for the same reasons, could the mouth of the Hemiptera be
+modified into a mandibulate type like that of the Coleoptera. But in
+_Campodea_ and the _Collembola_ we have a type of animal closely
+resembling certain larvae which occur both in the mandibulate and
+suctorial series of insects, possessing a mouth neither distinctly
+mandibulate nor distinctly suctorial, but constituted on a peculiar
+type, capable of modification in either direction by gradual change,
+without loss of utility.
+
+In discussing this subject, it is necessary also to take into
+consideration the nature and origin of wings. Whence are they derived?
+why are there normally two pairs? and why are they attached to the
+meso-and meta-thorax? These questions are as difficult as they are
+interesting. It has been suggested, and I think with justice, that the
+wings of insects originally served for aquatic and respiratory
+purposes.
+
+In the larva of _Chloeon_ (Pl. IV., Fig. 1), for instance, which in
+other respects so singularly resembles _Campodea_ (Pl. III., Fig. 5),
+several of the segments are provided with foliaceous expansions which
+serve as respiratory organs. These so-called branchiae are in constant
+agitation, and the muscles which move them in several points resemble
+those of true wings. It is true that in _Chloeon_ the vibration of the
+branchiae is scarcely, if at all, utilized for the purpose of locomotion;
+the branchiae are, in fact, placed too far back to act efficiently. The
+situation of these branchiae differs in different groups; indeed, it
+seems probable that originally there were a pair on each segment. In
+such a case, those branchiae situated near the centre of the body,
+neither too much in front nor too far back, would serve the most
+efficiently as propellers: the same causes which determined the position
+of the legs would also affect the wings. Thus a division of labour would
+be effected; the branchiae on the thorax would be devoted to locomotion;
+those on the abdomen to respiration. This would tend to increase the
+development of the thoracic segments, already somewhat enlarged, in
+order to receive the muscles of the legs.
+
+That wings may be of use to insects under water is proved by the very
+interesting case of _Polynema natans_,[46] which uses its wings for
+swimming. This, however, is a rare case, and it is possible that the
+principal use of the wings was, primordially, to enable the mature forms
+to pass from pond to pond, thus securing fresh habitats and avoiding
+in-and-in breeding. If this were so, the development of wings would
+gradually have been relegated to a late period of life; and by the
+tendency to the inheritance of characters at corresponding ages, which
+Mr. Darwin has pointed out,[47] the development of wings would have thus
+become associated with the maturity of the insect. Thus the late
+acquisition of wings in the Insecta generally seems to be itself an
+indication of their descent from a stock which was at one period, if not
+originally, aquatic, and which probably resembled the present larvae of
+_Chloeon_ in form, but had thoracic as well as abdominal branchiae.
+
+Finally, from the subject of metamorphosis we pass naturally to that
+most remarkable phenomenon which is known as the "Alternation of
+Generations:" for the first systematic view of which we are indebted to
+my eminent friend Prof Steenstrup.[48]
+
+I have always felt it very difficult to understand why any species
+should have been created in this double character; nor, so far as I am
+aware, has any explanation of the fact yet been attempted. Nevertheless
+insects offer, in their metamorphoses, a phenomenon not altogether
+dissimilar, and give a clue to the manner in which alternation of
+generations may have originated.
+
+The caterpillar owes its difference from the butterfly to the
+undeveloped state in which it leaves the egg; but its actual form is
+mainly due to the influence of the conditions under which it lives. If
+the caterpillar, instead of changing into one butterfly, produced
+several, we should have an instance of alternation of generations. Until
+lately, however, we knew of no such case among insects; each larva
+produced one imago, and that not by generation, but by development. It
+has long been known, indeed, that there are species in which certain
+individuals remain always apterous, while others acquire wings. Many
+entomologists, however, regard these abnormal individuals as perfect,
+though wingless insects; and therefore I shall found no argument upon
+these cases, although they appear to me deserving of more attention than
+they have yet received.
+
+Recently, however, Prof. Wagner[49] has discovered that, among certain
+small gnats, the larvae do not directly produce in all cases perfect
+insects, but give birth to other larvae, which undergo metamorphoses of
+the usual character, and eventually become gnats. His observations have
+been confirmed, as regards this main fact, by other naturalists; and
+Grimm has met with a species of _Chironomus_ in which the pupae lay
+eggs.[50]
+
+Here, then, we have a distinct case of alternation of generations, as
+characterized by Steenstrup. Probably other cases will be discovered in
+which insects undeniably in the larval state will be found fertile. Nay,
+it seems to me possible, if not probable, that some larvae which do not
+now breed may, in the course of ages, acquire the power of doing so. If
+this idea is correct, it shows how the remarkable phenomenon, known as
+alternation of generations, may have originated.
+
+Summing up, then, the preceding argument, we find among insects various
+modes of development; from simple growth on the one hand, to well-marked
+instances of the so-called alternation of generation on the other. In
+the wingless species of Orthoptera there is little external difference,
+excepting in size, between the young larva and the perfect insect. The
+growth is gradual, and there is nothing which would, in ordinary
+language, be called a metamorphosis. In the majority of Orthoptera,
+though the presence of wings produces a marked difference between the
+larva and the imago, the habits are nearly the same throughout life, and
+consequently the action of external circumstances affects the larva in
+the same manner as it does the perfect insect.
+
+This is not the case with the Neuroptera. The larvae do not live under
+the same conditions as the perfect insects: external forces accordingly
+affect them in a different manner; and we have seen that they pass
+through some changes which bear no reference to the form of the perfect
+insect: these changes, however, are for the most part very gradual. The
+caterpillars of Lepidoptera have even more extensive modifications to
+undergo; the mouth of the larva, for instance, being remarkably unlike
+that of the perfect insect. A change in this organ, however, could
+hardly take place while the insect was growing fast, and consequently
+feeding voraciously; nor, even if the change could be thus effected,
+would the mouth, in its intermediate stages, be in any way fitted for
+biting and chewing leaves. The same reasoning applies also to the
+digestive organs. Hence the caterpillar undergoes little, if any,
+change, except in size, and the metamorphosis is concentrated, so to
+say, into the last two moults. The changes then become so rapid and
+extensive, that the intermediate period is necessarily one of
+quiescence. In some exceptional cases, as in _Sitaris_ (_ante_, p. 30) we
+even find that, the conditions of life not being uniform throughout the
+larval period, the larva itself undergoes metamorphoses.
+
+Owing to the fact that the organs connected with the reproduction of the
+species come to maturity at a late period, larvae are generally incapable
+of breeding. There are, however, some flies which have viviparous larvae,
+and thus offer a typical case of alternation of generations.
+
+Thus, then, we find among insects every gradation, from simple growth to
+alternation of generations; and see how, from the single fact of the
+very early period of development at which certain animals quit the egg,
+we can throw some light on their metamorphoses, and for the still more
+remarkable phenomenon that, among many of the lower animals, the species
+is represented by two very different forms. We may even conclude, from
+the same considerations, that this phenomenon may in the course of ages
+become still more common than it is at present. As long, however, as the
+external organs arrive at their mature form before the internal
+generative organs are fully developed, we have metamorphosis; but if the
+reverse is the case, then alternation of generations often results.
+
+The same considerations throw much light on the remarkable circumstance,
+that in alternation of generations the reproduction is, as a general
+rule, agamic in one form. This results from the fact that reproduction
+by distinct sexes requires the perfection both of the external and
+internal organs; and if the phenomenon arise, as has just been
+suggested, from the fact that the internal organs arrive at maturity
+before the external ones, reproduction will result in those species only
+which have the power of agamic multiplication.
+
+Moreover, it is evident that we have in the animal kingdom two kinds of
+dimorphism.
+
+This term has usually been applied to those cases in which animals or
+plants present themselves at maturity under two forms. Ants and Bees
+afford us familiar instances among animals; and among plants the
+interesting case of the genus _Primula_ has recently been described by
+Mr. Darwin. Even more recently he has made known to us the still more
+remarkable phenomenon afforded by the genus _Lythrum_, in which there
+are three distinct forms, and which therefore offers an instance of
+polymorphism.[51]
+
+The other kind of dimorphism or polymorphism differs from the first in
+being the result of the differentiating action of external
+circumstances, not on the mature, but on the young individual. Such
+different forms, therefore, stand towards one another in the relation of
+succession. In the first kind the chain of being divides at the
+extremity; in the other it is composed of dissimilar links. Many
+instances of this second form of dimorphism have been described under
+the name of alternation of generations.
+
+The term, however, has met with much opposition, and is clearly
+inapplicable to the differences exhibited by insects in various periods
+of their life. Strictly speaking, the phenomena are frequently not
+alternate, and in the opinion of some eminent naturalists they are not,
+strictly speaking, cases of generation at all.[52]
+
+In order, then, to have some name for these remarkable phenomena, and to
+distinguish them from those cases in which the _mature_ animal or plant
+is represented by two or more different forms, I think it would be
+convenient to retain exclusively for these latter the terms dimorphism
+and polymorphism; and those cases in which animals or plants pass
+through a succession of different forms might be distinguished by the
+name of dieidism or polyeidism.
+
+The conclusions, then, which I think we may draw from the preceding
+considerations, are:--
+
+1. That the occurrence of metamorphoses arises from the immaturity of
+the condition in which some animals quit the egg.
+
+2. That the form of the insect larva depends in great measure on the
+conditions in which it lives. The external forces acting upon it are
+different from those which affect the mature form; and thus changes are
+produced in the young, having reference to its immediate wants, rather
+than to its final form.
+
+3. That metamorphoses may therefore be divided into two kinds,
+developmental and adaptional or adaptive.
+
+4. That the apparent abruptness of the changes which insects undergo,
+arises in great measure from the hardness of their skin, which admits of
+no gradual alteration of form, and which is itself necessary in order to
+afford sufficient support to the muscles.
+
+5. The immobility of the pupa or chrysalis depends on the rapidity of
+the changes going on in it.
+
+6. Although the majority of insects go through three well-marked stages
+after leaving the egg, still a large number arrive at maturity through a
+greater or smaller number of slight changes.
+
+7. When the external organs arrive at this final form before the organs
+of reproduction are matured, these changes are known as metamorphoses;
+when, on the contrary, the organs of reproduction are functionally
+perfect before the external organs, or when the creature has the power
+of budding, then the phenomenon is known as alternation of generations.
+
+
+
+
+CHAPTER V.
+
+_ON THE ORIGIN OF INSECTS._
+
+
+"Personne," says Carl Vogt, "en Europe au moins, n'ose plus soutenir la
+Creation independante et de toutes pieces des especes," and though this
+statement is perhaps not strictly correct, still it is no doubt true,
+that the Doctrine of Evolution, in some form or other, is accepted by
+most, if not by all, the greatest naturalists of Europe. Yet it is
+surprising how much, in spite of all that has been written, Mr. Darwin's
+views are still misunderstood. Thus Browning, in one of his recent
+poems, says:--
+
+  "That mass man sprang from was a jelly lump
+   Once on a time; he kept an after course
+   Through fish and insect, reptile, bird, and beast,
+   Till he attained to be an ape at last,
+   Or last but one."[53]
+
+This theory, though it would be regarded by many as a fair statement of
+his views, is one which Mr. Darwin would entirely repudiate. Whether
+fish and insect, reptile, bird and beast, are derived from one original
+stock or not, they are certainly not links in one sequence. I do not,
+however, propose to discuss the question of Natural Selection, but may
+observe that it is one thing to acknowledge that in Natural Selection,
+or the survival of the fittest, Mr. Darwin has called attention to a
+_vera causa_, has pointed out the true explanation of certain phenomena;
+but it is quite another thing to maintain that all animals are descended
+from some primordial source.
+
+For my own part, I am satisfied that Natural Selection is a true cause,
+and, whatever may be the final result of our present inquiries--whether
+animated nature be derived from one ancestral source, or from many--the
+publication of the Origin of Species will none the less have constituted
+an epoch in the History of Biology. But, how far the present condition
+of living beings is due to that cause; how far, on the other hand, the
+action of Natural Selection has been modified and checked by other
+natural laws--by the unalterability of types, by atavism, &c.; how many
+types of life originally came into being; and whether they arose
+simultaneously or successively,--these and many other similar questions
+remain unsolved, even admitting the theory of Natural Selection. All
+this has indeed been clearly pointed out by Mr. Darwin himself, and
+would not need repetition but for the careless criticism by which in too
+many cases the true question has been obscured. Without, however,
+discussing the argument for and against Mr. Darwin's conclusions, so
+often do we meet with travesties of it like that which I have just
+quoted, that it is well worth while to consider the stages through which
+some group, say for instance that of insects, have probably come to be
+what they are, assuming them to have developed under natural laws from
+simpler organisms. The question is one of great difficulty. It is hardly
+necessary to say that insects cannot have passed through all the lower
+forms of animal life, and naturalists do not at present agree as to the
+actual line of their development.
+
+In the case of insects, the gradual course of evolution through which
+the present condition of the group has probably been reached, has been
+discussed by Mr. Darwin, by Fritz Mueller, Haeckel, Brauer, myself and
+others.
+
+In other instances Palaeontology throws much light on this question.
+Leidy has shown that the milk-teeth of the genus _Equus_ resemble the
+permanent teeth of the ancient _Anchitherium_, while the milk-teeth of
+_Anchitherium_ again approximate to the dental system of the still
+earlier _Merychippus_. Ruetimeyer, while calling attention to this
+interesting observation, adds that the milk-teeth of _Equus caballus_ in
+the same way, and still more those of _E. fossilis_, resemble the
+permanent teeth of _Hipparion_.
+
+"If we were not acquainted with the horse," says Flower,[54] "we could
+scarcely conceive of an animal whose only support was the tip of a
+single toe on each extremity, to say nothing of the singular
+conformation of its teeth and other organs. So striking have these
+characters appeared to many zoologists, that the animals possessing them
+have been reckoned as an order apart, called Solidungula; but
+palaeontology has revealed that in the structure of its skull, its teeth,
+its limbs, the horse is nothing more than a modified _Palaeotherium_; and
+though still with gaps in certain places, many of the intermediate
+stages of these modifications are already known to us, being the
+_Palaeotherium_, _Anchitherium_, _Merychippus_, and _Hipparion_."
+
+"All Echinoids," says A. Agassiz,[55] "pass, in their early stages,
+through a condition which recalls to us the first Echinoids which made
+their appearance in geological ages." On embryological grounds, he
+observes, we should "place true Echini lowest, then the Clypeastroids,
+next the Echinolamps, and finally the Spatangoids." Now among the
+Echinoids of the Trias there are no Clypeastroids, Echinolamps, or
+Spatangoids. The Clypeastroids make their appearance in the Lias, the
+Echinolamps in the Jurassic, while the Spatangoids commence in the
+Cretaceous period.
+
+Again[56] "in the Radiates, the Acalephs in their first stages of
+growth, that is, in their Hydroid condition, remind us of the adult
+forms among Polyps, showing the structural rank of the Acalephs to be
+the highest, since they pass beyond a stage which is permanent with the
+Polyps; while the Adult forms of the Acalephs have in their turn a
+certain resemblance to the embryonic phases of the class next above
+them, the Echinoderms; within the limits of the classes, the same
+correspondence exists as between the different orders; the embryonic
+forms of the highest Polyps recall the adult forms of the lower ones,
+and the same is true of the Acalephs as far as these phenomena have been
+followed and compared among them." Indeed, the accomplished authors from
+whom I have taken the above quotation, do not hesitate to say[57] that
+"whenever such comparisons have been successfully carried out, the
+result is always the same; the present representatives of the fossil
+types recall in their embryonic condition the ancient forms, and often
+explain their true position in the animal kingdom."
+
+Fossil insects are unfortunately rare, there being but few strata in
+which the remains of this group are well preserved. Moreover,
+well-characterized Orthoptera and Neuroptera occur as early as the
+Devonian strata; Coleoptera and Hemiptera in the Coal-measures;
+Hymenoptera and Diptera in the Jurassic; Lepidoptera, on the contrary,
+not until the Tertiary. But although it appears from these facts that,
+as far as our present information goes, the Orthoptera and Neuroptera
+are the most ancient orders, it is not, I think, conceivable that the
+latter should have been derived from any known species of the former; on
+the other hand, the earliest known Neuroptera and Orthoptera, though in
+some respects less specialized than existing forms, are as truly, and as
+well characterized, Insects, as any now existing; nor are we acquainted
+with any earlier forms, which in any way tend to bridge over the gap
+between them and lower groups, though, as we shall see, there are types
+yet existing which throw much light on the subject.
+
+In the consideration then of this question, we must rely principally on
+Embryology and Development. I have already referred to the cases in
+which species, very unlike in their mature condition, are very
+similar one to another when young. Haeckel, in his "Naturliche
+Schoepfungsgeschichte," gives a diagram which illustrates this very well
+as regards Crustacea. Pls. 1-4 show the same to be the case with
+Insects.
+
+The Stag-beetle, the Dragon-fly, the Moth, the Bee, the Ant, the Gnat,
+the Grasshopper,--these and other less familiar types seem at first to
+have little in common. They differ in size, in form, in colour, in
+habits, and modes of life. Yet the researches of entomologists,
+following the clue supplied by the illustrious Savigny, have proved, not
+only that while differing greatly in details, they are constructed on
+one common plan; but also that other groups, as for instance, Crustacea
+(Lobsters, Crabs, &c.) and Arachnida (Spiders and Mites), can be shown
+to be fundamentally similar. In Pl. 4 I have figured the larvae of an
+_Ephemera_ (Fig. 1), of a _Meloe_ (Fig. 2), of a Dragon-fly (Fig. 3), of a
+Sitaris (Fig. 4), of a _Campodea_ (Fig. 5), of a _Dyticus_ (Fig. 6), of a
+Termite (Fig. 7), of a _Stylops_ (Fig. 8), and of a _Thrips_ (Fig. 9). All
+these larvae possess many characters in common. The mature forms are
+represented in the corresponding figures of Plate 3, and it will at once
+be seen how considerably they differ from one another. The same fact is
+also illustrated in Figs. 48-55, where Figs. 48-51 represent the larval
+states of the mature forms represented in Figs. 52-55. Fig. 48 is the
+larva of a moth, _Agrotis suffusa_ (Fig. 52); Fig. 49 of a beetle,
+_Haltica_ (Fig. 53); Fig. 50 of a Saw-fly, _Cimbex_ (Fig. 54); and Fig.
+51 of a Centipede, _Julus_ (Fig. 55).
+
+[Illustration: FIG. 48, Larva of Moth (_Agrotis suffusa_), after
+Packard. 49, Larva of Beetle (_Haltica_), after Westwood. 50, Larva of
+Saw-fly (_Cimbex_), Brischke and Zaddach. Beob. ub d. arten. der Blatt
+und Holzwespen, Fig. 8. 51, Larva of _Julus_. Newport, Philos.
+Transactions, 1841.]
+
+Thus, then, although it can be demonstrated that perfect insects,
+however much they differ in appearance, are yet reducible to one type,
+the fact becomes much more evident if we compare the larvae. M.
+Brauer[58] and I[59] have pointed out that two types of larvae, which I
+have proposed to call _Campodea_-form and _Lindia_-form, and which Packard
+has named Leptiform and Eruciform, run through the principal groups of
+insects. This is obviously a fact of great importance: as all individual
+_Meloes_ are derived from a form resembling Pl. 2, Fig. 2, it is surely no
+rash hypothesis to suggest that the genus itself may have been so.
+
+[Illustration: FIG. 52, _Agrotis suffusa_ (after Packard). 53, _Haltica_
+(after Westwood).]
+
+[Illustration: FIG. 54, _Cimbex_, Brischae and Zaddach. l.c. T. 2, Fig.
+9.]
+
+[Illustration: FIG. 55. _Julus_ (after Gervais).]
+
+Firstly, however, let me say a word as to the general Insect type. It
+may be described shortly as consisting of animals possessing a head,
+with mouth parts, eyes and antennae; a many segmented body, with three
+pairs of legs on the segments immediately following the head; with, when
+mature, either one or two pairs of wings, generally with caudal
+appendages I will not now enter into a description of their internal
+anatomy. It will be seen that, except as regards the wings, Pl. 4, Fig.
+4, representing the larva of a small beetle named _Sitaris_, answers very
+well to this description. Many other Beetles are developed from larvae
+closely resembling those of _Meloe_ (Pl. 4, Fig. 2), and Sitaris (Pl. 4,
+Fig. 4); in fact--except those species the larvae of which, as, for
+instance of the Weevils (Pl. 2, Fig. 6), are internal feeders, and do
+not require legs--we may say that the Coleoptera generally are derived
+from larvae of this type.
+
+I will now pass to a second order, the Neuroptera. Pl. 4, Fig. 1,
+represents the larva of _Chloeon_, a species the metamorphoses of which I
+described some years ago in the Linnean Transactions,[60] and it is
+obvious that in essential points it closely resembles the form to which
+I have just alluded.
+
+The Orthoptera, again, the order to which Grasshoppers, Crickets,
+Locusts, &c. belong, commence life in a similar condition; and the same
+may also be said of the Trichoptera.
+
+The larvae of Bees when they quit the egg are entirely legless, but in an
+earlier stage they possess well-marked rudiments of thoracic legs,
+showing, as it seems to me, that their apodal condition is an adaptation
+to their circumstances. Other Hymenopterous larvae, those for example of
+_Sirex_ (Fig. 9), and of the Saw-flies (Fig. 50) have well-developed
+thoracic legs.
+
+From the difference in external form, and especially from the large
+comparative size of the abdomen, these larvae, as well as those of
+Lepidoptera (Fig. 48), have generally been classed with the maggots of
+Flies, Weevils, &c., rather than with the more active form of larva just
+adverted to. This seems to me, as I have already pointed out,[61] to be
+a mistake. The caterpillar type differs, no doubt, in its general
+appearance, owing to its greater clumsiness, but still essentially
+agrees with that already described.
+
+No Dipterous larva, so far as I know, belongs truly to this type; in
+fact, the early stages of the pupa in the Diptera seem in some respects
+to correspond to the larvae of other Insect orders. The Development of
+the Diptera is, however, as Weissman[62] has shown, very abnormal in
+other respects.
+
+Thus, then, we find in many of the principal groups of insects that,
+greatly as they differ from one another in their mature condition, when
+they leave the egg they more nearly resemble the typical insect type;
+consisting of a head; a three-segmented thorax, with three pairs of
+legs; and a many-jointed abdomen, often with anal appendages. Now, is
+there any mature animal which answers to this description? We need not
+have been surprised if this type, through which it would appear that
+insects must have passed so many ages since (for winged Neuroptera have
+been found in the carboniferous strata) had long ago become extinct. Yet
+it is not so. The interesting genus _Campodea_ (Pl. 3, Fig. 5) still
+lives; it inhabits damp earth, and closely resembles the larva of
+_Chloeon_ (Pl. 2, Fig. 1), constituting, indeed, a type which, as shown in
+Pl. 4, occurs in many orders of insects. It is true that the
+mouth-parts of _Campodea_ do not resemble either the strongly mandibulate
+form which prevails among the larvae of Coleoptera, Orthoptera,
+Neuroptera, Hymenoptera, Lepidoptera; or the suctorial type of the
+Homoptera and Heteroptera. It is, however, not the less interesting or
+significant on that account, since, as I have elsewhere[63] pointed out,
+its mouth-parts are intermediate between the mandibulate and haustellate
+types; a fact which seems to me most suggestive.
+
+It appears, then, that there are good grounds for considering that the
+various types of insects are descended from ancestors more or less
+resembling the genus _Campodea_, with a body divided into head, thorax,
+and abdomen: the head provided with mouth-parts, eyes, and one pair of
+antennae; the thorax with three pairs of legs; and the abdomen, in all
+probability, with caudal appendages.
+
+If these views are correct, the genus _Campodea_ must be regarded as a
+form of remarkable interest since it is the living representative of a
+primaeval type, from which not only the Collembola and Thysanura, but the
+other great orders of insects have derived their origin.
+
+From what lower group the _Campodea_ type was itself derived is a question
+of great difficulty. Fritz Mueller indeed says,[64] "if all the classes
+of Arthropoda (Crustacea, Insecta, Myriopoda, and Arachnida) are indeed
+all branches of a common stem (and of this there can scarcely be a
+doubt), it is evident that the water-inhabiting and water-breathing
+Crustacea must be regarded as the original stem from which the other
+terrestrial classes, with their tracheal respiration, have branched
+off." Haeckel, moreover, is of the opinion that the Tracheata are
+developed from the Crustacea, and probably from the Zoepoda. For my own
+part, though I feel very great diffidence in expressing an opinion at
+variance with that of such high authorities, I am rather disposed to
+suggest that the _Campodea_ type may possibly have been derived from a
+less highly developed one, resembling the modern Tardigrade,[65] a (Fig.
+56) smaller and much less highly organized being than _Campodea_. It
+possesses two eyes, three anterior pairs of legs, and one at the
+posterior end of the body, giving it a curious resemblance to some
+Lepidopterous larvae.
+
+[Illustration: FIG. 56, Tardigrade (after Dujardin).]
+
+These legs, however, as will be seen, are reduced to mere projections.
+But for them, the Tardigrada would closely resemble the vermiform larva
+so common among insects. Among Trichoptera the larva early acquires
+three pairs of legs, but as Zaddach has shown,[66] there is a stage,
+though it is quickly passed through, in which the divisions of the body
+are indicated, but no trace of legs is yet present. Indeed, there appear
+to be reasons for considering that while among Crustacea the appendages
+appear before the segments, in Insects the segments precede the
+appendages, although this stage of development is very transitory, and
+apparently, in some cases, altogether suppressed. I say "apparently,"
+because, as I have already mentioned, I am not yet satisfied that it
+will not eventually be found to be so in all cases. Zaddach, in his
+careful observations of the embryology of _Phryganea_, only once found a
+specimen in this stage, which also, according to the researches of
+Huxley,[67] seems to be little more than indicated in _Aphis_. It is
+therefore possible that in other cases, when no such stage has been
+observed, it not really may be absent, but, from its transitoriness, may
+have hitherto escaped attention.
+
+Fritz Mueller has expressed the opinion[68] that this vermiform type is
+of comparatively recent origin. He says: "The ancient insects approached
+more nearly to the existing Orthoptera, and perhaps to the wingless
+Blattidae, than to any other order, and the complete metamorphosis of the
+Beetles, Lepidoptera, &c., is of later origin." "There were," he adds,
+"perfect insects before larvae and pupae." This opinion has been adopted
+by Mr. Packard[69] in his "Embryological Studies on Hexapodous Insects."
+
+M. Brauer[70] also considers that the vermiform larva is a more recent
+type than the Hexapod form, and is to be regarded not as a developmental
+form, but as an adaptational modification of the earlier active hexapod
+type. In proof of this he quotes the case of _Sitaris_.
+
+Considering, however, the peculiar habits of this genus, to which I have
+already referred, and also that the vermiform type is altogether lower
+in organization and less differentiated than the _Campodea_ form, I cannot
+but regard this case as exceptional; one in which the development has
+been, as it were, to use an expression of Fritz Mueller's, "falsified" by
+the struggle for existence, and which therefore does not truly indicate
+the successive stages of evolution. On the whole, the facts seem to me
+to point to the conclusion that, though the grub-like larvae of Coleoptera
+and some other insects, owe their present form mainly to the influence
+of external circumstances, and partially also to atavism, still the
+_Campodea_ type is itself derived from earlier vermiform ancestors.
+Nicolas Wagner has shown in the case of a small gnat, allied to
+_Cecidomyia_, that even now, in some instances, the vermiform larvae
+possess the power of reproduction. Such a larva (as, for instance, Fig.
+57) very closely resembles some of the Rotatoria, such for instance as
+_Albertia_ or _Notommata_, which however possess vibratile cilia. There is,
+indeed, one genus--_Lindia_ (Fig. 58)--in which these ciliae are altogether
+absent, and which, though resembling _Macrobiotus_ in many respects,
+differs from that genus in being entirely destitute of legs. I have
+never met with it myself, but it is described by Dujardin, who found it
+in a ditch near Paris, as being oblong, vermiform, divided into rings,
+and terminating posteriorly in two short conical appendages. The jaws
+are not unlike those of the larvae of Flies, and indeed many naturalists
+meeting with such a creature would, I am sure, regard it as a small
+Dipterous larva; yet Dujardin figures a specimen containing an egg, and
+seems to have no doubt that it is a mature form.[71]
+
+For the next descending stage we must, I think, look among the
+Infusoria, through such genera as _Chaetonotus_ or _Ichthydium_. Other
+forms of the Rotatoria, such for instance as _Rattulus_, and still more
+the very remarkable species discovered in 1871 by Mr. Hudson,[72] and
+described under the name of _Pedalion mira_, seem to lead to the
+Crustacea through the Nauplius form. Dr. Cobbold tells me that he
+regards the _Gordii_ as the lowest of the Scolecida; Mr. E. Ray
+Lankester considers some of the Turbellaria, such genera as
+_Mesostomum_, _Vortex_, &c., to be the lowest of existing worms;
+excluding the parasitic groups. Haeckel[73] also regards the Turbellaria
+as forming the nearest approach to the Infusoria. The true worms seem,
+however, to constitute a separate branch of the animal kingdom.
+
+We may take, as an illustration of the lower worms, the genus
+Prorhynchus (Fig. 59), which consists of a hollow cylindrical body,
+containing a straight simple tube, the digestive organ.
+
+But however simple such a creature as this may be, there are others
+which are far less complex, far less differentiated; which therefore, on
+Mr. Darwin's principles, may be considered still more closely to
+represent the primaeval ancestor from which these more highly-developed
+types have been derived, and which, in spite of their great
+antiquity--in spite of, or perhaps in consequence of, their simplicity,
+still maintain themselves almost unaltered.
+
+Thus the form which Haeckel has described[74] under the name
+_Protamoeba primitiva_, Pl. 5, Fig. 1-5, consists of a homogeneous and
+structureless substance, which continually alters its form; putting out
+and drawing in again more or less elongated processes, and creeping
+about like a true _Amoeba_, from which, however, _Protamoeba_ differs,
+in the absence of a nucleus. It seems difficult to imagine anything
+simpler; indeed, as described, it appears to be an illustration of
+properties without structure. It takes into itself any suitable particle
+with which it comes in contact, absorbs that which is nutritious, and
+rejects the rest. From time to time a constriction appears at the centre
+(Pl. 5, Fig. 2), its form approximates more and more to that of an
+hour-glass (Pl. 5, Fig. 3), and at length the two halves separate, and
+each commences an independent existence (Pl. 5, Fig. 5).
+
+[Illustration: FIG. 59, _Prorhynchus stagnaus_.[75]]
+
+[Illustration: PLATE V.
+
+FIGS. 1-5, _Protamoeba_; 6-9, _Protamyxa Aurantiaca_,
+Haeckel, Beit. zur Monog. der Moneren, pl. 1; 10-18, _Magosphaera planula_,
+Haeckel, loc. cit. pl. 5.]
+
+In the true _Amoebas_, on the contrary, we find a differentiation
+between the exterior and the interior: the body being more or less
+distinctly divisible into an outer layer and an inner parenchyme. In the
+_Amoebas_, as in _Protamoeba_, multiplication takes place by
+self-division, and nothing corresponding to sexual reproduction has yet
+been discovered.
+
+Somewhat more advanced, but still of great simplicity, is the _Protomyxa
+aurantiaca_ (Pl. 5, Fig. 8), discovered by Haeckel[76] on dead shells of
+_Spirula_, where it appears as a minute orange speck, which shows well
+against the clear white of the _Spirula_. Examined with a microscope, the
+speck is seen to be a spherical mass of orange-coloured, homogeneous,
+albuminous matter, surrounded by a delicate, structureless membrane. It
+is obvious from this description that these bodies closely resemble
+eggs, for which indeed Haeckel at first mistook them. Gradually,
+however, the yellow sphere broke itself up into smaller spherules (Pl.
+5, Fig. 9), after which the containing membrane burst, and the separate
+spherules, losing their globular form, crept out as small _Amoebae_ (Pl.
+5, Fig. 6), or amoeboid bodies. These little bodies moved about,
+assimilated the minute particles of organic matter, with which they came
+in contact, and gradually increased in size (Pl. 5, Fig. 7) with more or
+less rapidity according to the amount of nourishment they were able to
+obtain. They threw out arms in various directions, and if divided each
+section maintained its individual existence. After a while their
+movements ceased, they contracted into a ball, and again secreted round
+themselves a clear structureless envelope.
+
+This completes their life history as observed by Haeckel, who found it
+easy to retain them in his glasses in perfect health, and who watched
+them closely.
+
+As another illustration I may take the _Magosphaera planula_, discovered
+by Haeckel on the coast of Norway.
+
+In one stage of its existence (Pl. 5, Fig. 10) it is a minute mass of
+gelatinous matter, which continually alters its form, moves about,
+feeds, and in fact behaves altogether like the _Amoeba_ just described.
+It does not, however, remain always in this condition. After a while it
+contracts into a spherical form (Pl. 5, Fig. ii), and secretes round
+itself a structureless envelope, which, with the nucleus, gives it a
+very close resemblance to a minute egg.
+
+Gradually the nucleus divides, and the protoplasm also separates into
+two spherules (Pl. 5, Fig. 12); these two subdivide into four (Pl. 5,
+Fig. 13), and so on (Pl. 5, Fig 14), until at length thirty-two are
+present, compressed into a more or less polygonal form (Pl. 5, Fig. 15).
+Here this process ends. The separate spherules now begin to lose their
+smooth outline, to throw out processes, and to show amoeboid movements
+like those of the creatures just described. The processes or pseudopods
+grow gradually longer, thinner, and more pointed. Their movements become
+more active, until at length they take the form of ciliae. The spherical
+_Magosphaera_, the upper surface of which has thus become covered with
+ciliae, now begins to rotate within the cyst or envelope, which at length
+gives way and sets free the contained sphere, which then swims about
+freely in the water (Pl. 5, Fig. 16), thus closely resembling _Synura_, or
+one of the Volvocineae. After swimming about in this condition for a
+certain time, the sphere breaks up into the separate cells of which it
+is composed (Pl. 5, Fig. 17). As long as the individual cells remained
+together, they had undergone no changes of form, but after separating
+they show considerable contractility, and gradually alter their form,
+until they become undistinguishable from true _Amoebae_ (Pl. 5, Fig. 18).
+Finally, according to Haeckel, these amoeboid bodies, after living for
+a certain time in this condition, return to a state of rest, again
+contract into a spherical form, and secrete round themselves a
+structureless envelope. The life history of some other low organisms, as
+for instance _Gregarina_, is of a similar character.
+
+It may be said, and said truly, that the difference between such beings
+as these and the _Campodea_, or Tardigrade, is immense. But if it be
+considered incredible that even during the long lapse of geological time
+such great changes should have taken place as are implied in the belief
+that there is genetic connection between them and these lower groups,
+let us consider what happens under our eyes in the development of each
+one of these little creatures in the proverbially short space of their
+individual life.
+
+I will take for instance the first stages, and for the sake of brevity
+only the first stages, of the life-history of a Tardigrade.[77] As shown
+in Fig. 60, the egg is at first a round body or cell, with a clear
+central nucleus--the germinal vesicle; it increases in size, and after
+a while the yolk and the germinal vesicle divide into two (Fig. 61),
+then into four (Fig. 62), and so on, just as we have seen to be the case
+in _Magosphaera_. From the minute cells (Fig. 63) arising through this
+process of yolk-segmentation, the body of the Tardigrade is then built
+up.[78]
+
+[Illustration: FIG. 60, Egg of Tardigrade, Kaufmann, Zeit f. Wiss.
+Zool. 1851, Pl. 1. 61, Egg of Tardigrade after the yolk has subdivided.
+62, Egg of Tardigrade in the next stage. 63, Egg of Tardigrade more
+advanced.]
+
+Though I will not now attempt to point out the full bearing of these
+facts on the study of embryology generally, yet I cannot resist calling
+attention to the similarity of the development of _Magosphaera_ with the
+first stages of development of other animals, because it appears to me
+to possess a significance, the importance of which it would be difficult
+to overestimate.
+
+Among the Zoophytes Prof. Allman thus describes[79] the process in
+_Laomedea_, as representing the Hydroids (Pl. 6, Fig. 1, represents the
+young egg):--"The first step observable in the segmentation-process is
+the cleavage of the yolk into two segments (Pl. 6, Fig. 2), immediately
+followed by the cleavage of these into other two, so that the vitellus
+is now composed of four cleavage spheres (Pl. 6, Fig. 3)." These spheres
+again divide (Pl. 6, Fig. 4) and subdivide, thus at length forming
+minute cells, of which the body of the embryo is built up.
+
+In Pl. 6, Figs. 5-9 represent the corresponding stages in the
+development of a small parasitic worm--the _Filaria mustelarum_--as
+given by Van Beneden.[80] The first process is that within the egg,
+which represents, so to say, the encysted condition of _Magosphaera_, the
+yolk divides itself into two balls (Pl. 6, Fig. 6), then into four,
+eight, and so on, the cells thus constituted finally forming the young
+worm. I have myself observed the same stages in the eggs of the very
+remarkable and abnormal _Sphaerularia bombi_.[81]
+
+Among the Echinoderms M. Derbes thus describes the first stages (Pl. 6,
+Figs. 10-13) in the development of the egg of an _Echinus_ (_Echinus
+esculentus_):--"Le jaune commence a se segmenter, d'abord en deux, puis
+en quatre et ainsi de suite, chacune des nouvelles cellules se
+partageant a son tour en deux."[82] Sars has observed the same thing in
+the starfish.[83]
+
+[Illustration: PLATE. 6.]
+
+In the Rotatoria, as shown by Huxley in _Lacinularia_,[84] and by
+Williamson in _Melicerta_,[85] the yolk is at first a single globular
+mass, the first changes which take place in it being as follows:--"The
+central nucleus becomes drawn out and subdivides into two, this division
+being followed by a corresponding segmentation of the yolk. The same
+process is repeated again and again, until at length the entire yolk is
+converted into a mass of minute cells." Among the Crustacea the total
+segmentation of the yolk occurs among the Copepoda, Rhizocephala, and
+Cirripedia. Sars has described the same process in one of the
+nudibranchiate mollusca[86] (_Tritonia_), Mueller in Entochocha,[87]
+Haeckel in Ascidia,[88] Lacaze Duthiers in _Dentalium_.[89] Figures 18 to
+21, Pl. 6, are taken from Koren and Danielssen's[90] memoir on the
+development of _Purpura lapillus_.
+
+Figs. 22-24 show the same stages in a fish (_Amphioxus_) as given by
+Haeckel, and it is unnecessary to point out the great similarity.
+
+Lastly, figures 25 to 29, Pl. 6, are given by Dr. Allen Thomson,[91] as
+illustrating the first stages in the development of the vertebrata.
+
+I might have given many other examples, but the above are probably
+sufficient, and will show that the processes which constitute the
+life-history of the lowest organized beings very closely resemble the
+first stages in the development of more advanced groups; that as Allen
+Thomson has truly observed,[92] "the occurrence of segmentation and the
+regularity of its phenomena are so constant that we may regard it as one
+of the best established series of facts in organic nature."
+
+It is true that normal yolk-segmentation is not universal in the animal
+kingdom; that there are great groups in which the yolk does not divide
+in this manner,--perhaps owing to some difference in its relation to the
+germinal vesicle, or perhaps because one of the suppressed stages in
+embryological development, many examples might be given, not only in
+zoology, but, as I may state on the authority of Dr. Hooker, in botany
+also. But, however, this may be, it is surely not uninteresting, nor
+without significance, to find that changes which constitute the
+life-history of the lowest creatures for the initial stages even of the
+highest.
+
+Returning, in conclusion, to the immediate subject of this work, I have
+pointed out that many beetles and other insects are derived from larvae
+closely resembling _Campodea_.
+
+Since, then, individual insects are certainly in many cases developed
+from larvae closely resembling the genus _Campodea_, why should it be
+regarded as incredible that insects as a group have gone through similar
+stages? That the ancestors of beetles under the influence of varying
+external conditions, and in the lapse of geological ages, should have
+undergone changes which the individual beetle passes through under our
+own eyes and in the space of a few days, is surely no wild or
+extravagant hypothesis. Again, other insects come from vermiform larvae
+much resembling the genus _Lindia_, and it has been also repeatedly shown
+that in many particulars the embryo of the more specialized forms
+resembles the full-grown representatives of lower types. I conclude,
+therefore, that the Insecta generally are descended from ancestors
+resembling the existing genus _Campodea_, and that these again have arisen
+from others belonging to a type represented more or less closely by the
+existing genus _Lindia_.
+
+Of course it may be argued that these facts have not really the
+significance which they seem to me to possess. It may be said that when
+Divine power created insects, they were created with these remarkable
+developmental processes. By such arguments the conclusions of geologists
+were long disputed. When God made the rocks, it was tersely said, He
+made the fossils in them. No one, I suppose, would now be found to
+maintain such a theory; and I believe the time will come when it will be
+generally admitted that the structure of the embryo, and its
+developmental changes, indicate as truly the course of organic
+development in ancient times as the contents of rocks and their sequence
+teach us the past history of the earth itself.
+
+
+FOOTNOTES:
+
+[1] Darwin's "Researches into the Geology and Natural History of the
+Countries visited by H.M.S. _Beagle_," p. 326.
+
+[2] Introduction to Entomology, vi. p. 50.
+
+[3] Manual of Entomology, p. 30.
+
+[4] Linnean Journal, vol. xi.
+
+[5] Introduction to the Modern Classification of Insects, p. 17.
+
+[6] Linnean Transactions, 1863--"On the Development of _Chloeon_."
+
+[7] The figures on the first four plates are principally borrowed from
+Mr. Westwood's excellent "Introduction to the Modern Classification of
+Insects."
+
+[8] "Sur la Domestication des _Clavigers_ par les Fourmis." Bull. de la
+Soc. d'Anthropologie de Paris, 1868, p. 315.
+
+[9] Westwood's Introduction, vol. i. p. 36.
+
+[10] Westwood's Introduction, vol. ii. p. 52.
+
+[11] Die Fortpflanzung und Entwickelung der Pupiparen. Von Dr. R.
+Leuckart. Halle. 1848.
+
+[12] Ann. des Sci. Nat., ser. 4, tome vii. See also _Natural History
+Review_, April 1862.
+
+[13] Ann. and Mag. of Nat. Hist. 1852.
+
+[14] Zeits. fuer Wiss. Zool. 1869.
+
+[15] Transactions of the Linnean Society, 1863.
+
+[16] Lectures on the Anatomy, &c. of the Invertebrate Animals.
+
+[17] Untersuchungen ueber die Entwickelung und den Bau der Gliederthiere,
+1854.
+
+[18] Linnean Transactions, vol. xxii. 1858.
+
+[19] "Embryological Studies on Hexapodous Insects." Peabody Academy of
+Science. Third Memoir.
+
+[20] Mem. de l'Acad. Imp. des Sci. de St. Petersbourg. 1869.
+
+[21] Observationes de Prima Insectorum Genesi, p. 14.
+
+[22] Mem. de l'Acad. Imp. des Sci. de St. Petersbourg. tome xvi. 1871,
+p. 35.
+
+[23] Recherches sur l'Evolution des Araignees.
+
+[24] Philosophical Transactions, 1841.
+
+[25] Monog. of the Gymnoblastic or Tubularian Hydroids. See also Hincks,
+British Hydroid Zoophytes. Pl. x.
+
+[26] Loc. cit. p. 315.
+
+[27] Philosophical Transactions, 1859, p. 589.
+
+[28] "Facts for Darwin," Eng. Trans. p. 127.
+
+[29] Rolleston, "Forms of Animal Life," p. 146.
+
+[30] A. Agassiz, "Embryology of the Starfish," p. 25; "Embryology of
+Echinoderms." Mem. of Am. Ac. of Arts and Sciences N.S. vol. ix. p. 9.
+
+[31] Ueber die Gattungen der Seeigellarven. Siebente Abhandlung. Koen.
+Akad. d. Wiss. zu Berlin. Von Joh. Mueller, 1855, Pl. iii. fig. 3.
+
+[32] Huxley, Introduction to the Classification of Animals, p. 45.
+
+[33] Philosophical Transactions, 1865 and 1866.
+
+[34] Loc. cit. Zweit. Abh. Pl. i., figs. 8 and 9.
+
+[35] Thomson, on the Embryology of the Echinodermata, _Natural History
+Review_, 1863, p. 415. See also Agassiz, "Embryology of the Starfish,"
+p. 62.
+
+[36] A. Agassiz, Embryology of Echinoderms, p. 18.
+
+[37] Hincks. British Hydroid Zoophytes, pp. 120-147.
+
+[38] Zeits. fuer Wiss. Zool. 1864, p. 228.
+
+[39] Introduction to Entomology, 6th ed. vol. i. p. 61.
+
+[40] Metamorphoses de l'Homme et des Animaux, p. 133. See also
+Carpenter, Principles of Physiology. 1851, p. 389.
+
+[41] Darwin, Origin of Species, 4th ed. p. 532.
+
+[42] Principles of Biology, vi. p. 349.
+
+[43] For differences in larva consequent on variation in the external
+condition, see _ante_, p. 61.
+
+[44] See Hincks. British Hydroid Zoophytes, P. lxii. Agassiz, Sea-side
+Studies, p. 43.
+
+[45] See Newport, Phil. Trans., 1832.
+
+[46] Linnean Transactions, 1862.
+
+[47] Origin of Species, 4th ed., pp. 14 and 97.
+
+[48] On the Alternation of Generations. By J. J. Steenstrup. Trans. by
+C. Busk, Esq. Ray Society. 1842.
+
+[49] Zeit. fuer Wiss. Zool. 1863.
+
+[50] Mem. de l'Acad. Imp. de St. Petersbourg. vol. xv. 1870.
+
+[51] Of course all animals in which the sexes are distinct are in one
+sense dimorphic.
+
+[52] "There is no such thing as a true case of 'alternation of
+generations in the animal kingdom;' there is only an alternation of true
+generation with the totally distinct process of gemmation or
+fission."--HUXLEY _on Animal Individuality_, Ann. and Mag. of Nat. Hist.
+June 1852.
+
+[53] Prince Hohenstiel Schwangau, p. 68.
+
+[54] Journal of the Royal Institution. April 1873.
+
+[55] "Embryology of Echinoderms," l. c. p. 15.
+
+[56] Mr. and Mrs. Agassiz: "Sea-side Studies," p. 139.
+
+[57] l. c. p. 138.
+
+[58] Wien. Zool. Bot. Gesells, 1869.
+
+[59] Linnean Transactions, 1863.
+
+[60] Linnean Transactions, 1866, vol. xxv.
+
+[61] Linnean Transactions, vol. xxiv. p. 65.
+
+[62] Siebold und Kolliker's Zeitschr. f. Wiss. Zool., 1864.
+
+[63] Linnean Journal, vol. xi.
+
+[64] Facts for Darwin, p. 120.
+
+[65] A still nearer approach is afforded by the genus _Peripatus_, which
+since the above was written has been carefully described, especially by
+Moseley and Hutton. There are several species, scattered over the
+southern hemisphere. In general appearance they look like a link between
+a caterpillar and a centipede. They have a pair of antennae, two pairs of
+jaws, and (according to the species) from fourteen to thirty-three pairs
+of legs. They breathe by means of tracheae, which open diffusely all over
+the body.
+
+[66] Unters. ueb. die Entwick, und den Bau der Gliederthiere, p. 73.
+
+[67] Linnean Transactions, v. xxii.
+
+[68] Facts for Darwin, trans. by Dallas, p. 118. See also Darwin,
+"Origin of Species," p. 530. 4th ed.
+
+[69] Mem. Peabody Academy of Science, v. I. No, 3.
+
+[70] Wien. Zool. Bott. Gesells. 1869, p. 310.
+
+[71] See also the descriptions given by Dujardin (Ann. des Sci. Nat.
+1851, v. xv.) and Claparede (Anat. und Entwickl. der Wirbel osen Thiere)
+of the interesting genus _Echinoderes_, which these two eminent
+naturalists unite in regarding as intermediate between the Annelides and
+the Crustacea.
+
+[72] "On a New Rotifer." _Monthly Microscopical Journal_, Sept. 1871.
+
+[73] Generelle Morphologie, vol. ii. p. 79.
+
+[74] Monographie der Moneren, p. 43.
+
+[75] Gegenbaur. Grund. d. Vergleich. Anat. p. 210. See also Dr. M. S.
+Schultze, Beitraege zur Naturg. der. Turbellarien. 1851. Pl. vi. fig. 1.
+
+[76] Monographieder Moneren, p. 10.
+
+[77] See Kauffmann, Ueber die Entwickelung and systematische Stellung
+der Tardigraden. Zeits. f. Wiss. Zool. 1851, p. 220.
+
+[78] It is true that among the Insecta generally the first stages of
+development differ in appearance considerably from those above
+described; those of _Platygaster_, as figured by Ganin (ante Figs. 17-22),
+being very exceptional.
+
+[79] Monograph of the Gymnoblastic or Tubularian Hydroids, by G. J.
+Allman, Ray Soc. 1871, p. 86.
+
+[80] Mem. sur les Vers Intestinaux, 1858.
+
+[81] Natural History Review, 1861, p. 44.
+
+[82] Ann. des Sci. Nat. 1847, p. 90.
+
+[83] Fauna littoralis Norvegiae, pl. viii.
+
+[84] Trans. of the Microsc. Soc. of London, 1851.
+
+[85] Quarterly Journal of Microsc. Science, 1853.
+
+[86] Wiegmann's Archiv., 1840, p. 196.
+
+[87] Ueber die Erzeugung von Schnecken in Holothurier. Berlin, Bericht,
+1851. Ann. Nat. Hist. 1852, v. ix. Mueller's Archiv., 1852.
+
+[88] Natuerliche Schoepfungsgeschichte, pl. x.
+
+[89] Ann. des Sci. Nat. 1853, p. 89.
+
+[90] Ann. des Sci. Nat. 1857, pl. vi.
+
+[91] Cyclopaedia of Anatomy and Physiology. Art. Ovum, p. 4.
+
+[92] Thomson, loc. cit. Article, Ovum, p. 139.
+
+
+   THE END.
+
+
+RICHARD CLAY AND SONS, LIMITED, LONDON AND BUNGAY.
+
+BY THE SAME AUTHOR.
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+   ON REPRESENTATION. Fifth Edition. Crown 8vo. 1_s._ (Swan
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+     Illustrations. 3 vols. Crown 8vo. Vol. I. CONSTITUTION OF
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+   ON THE ORIGIN AND METAMORPHOSES OF INSECTS. By Sir JOHN
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+     Illustrations. Fifth Edition. Crown 8vo. 3_s._ 6_d._
+
+   ON BRITISH WILD FLOWERS CONSIDERED IN RELATION TO INSECTS. By
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+     Illustrations. Fifth Edition. Crown 8vo. 4_s._ 6_d._
+
+   FLOWERS, FRUITS, AND LEAVES. By Sir JOHN LUBBOCK, F.R.S., &c.
+     Second Edition. Crown 8vo. 4_s._ 6_d._
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+   CHARLES DARWIN. Memorial Notices reprinted from _Nature_. By
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+   TIMBER AND SOME OF ITS DISEASES. By H. MARSHALL WARD, F.R.S,
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+   FIRST LESSONS IN PRACTICAL BOTANY. By G. T. BETTANY, M.A.,
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+   A COURSE OF PRACTICAL INSTRUCTION IN BOTANY. By F. O. BOWER.
+     D.Sc., F.L.S., Regius Professor of Botany in the University of
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+     Translated and Edited by D'Arcy W. THOMPSON, B.A., Professor
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