Chapter I: 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