CHAPTER X.
THE THEORY OF SEXUAL SELECTION, AND CONCLUDING REMARKS 379
* * * * *
APPENDIX TO CHAPTER V. 421
NOTE A TO PAGE 257 443
NOTE B TO PAGE 295 445
NOTE C TO PAGE 394 448
INDEX 451
LIST OF ILLUSTRATIONS
FIG. PAGE
1. Successive forms of Paludina, from the Tertiary deposits of Slavonia 19
2. Skeleton of Seal 52
3. Skeleton of Greenland Whale 53
4. Paddle of Whale compared with Hand of Man 54
5. Wing of Reptile, Mammal, and Bird 56
6. Skeleton of _Dinornis gravis_ 61
7. Hermit crabs compared with the cocoa-nut crab 64
8. Rudimentary or vestigial hind-limbs of Python 67
9. _Apteryx Australis_ 69
10. Illustrations of the nictitating membrane in various animals named 75
11. Rudimentary, or vestigial and useless, muscles of the human ear 76
12. Portrait of a young male gorilla 78
13. Portrait of a young male child 79
14. An infant, three weeks old, supporting its own weight 81
15. Sacrum of Gorilla compared with that of Man, showing the rudimentary tail-bones of each 82
16. Diagrammatic outline of the human embryo when about seven weeks old 83
17. Front and back view of adult human sacrum 84
18. _Appendix vermiformis_ in Orang and in Man 85
19. The same, showing variation in the Orang 85
20. Human ear 86
21. Foetus of an Orang 87
22. Vestigial characters of human ears 88
23. Hair-tracts on the arms and hands of Man, as compared with those on the arms and hands of Chimpanzee 90
24. Molar teeth of lower jaw in Gorilla, Orang, and Man 93
25. Perforation of the humerus (supra-condyloid foramen) in three species of Quadrumana where it normally occurs, and in Man, where it does not normally occur 95
26. Antlers of stag, showing successive addition of branches in successive years 100
27. Fission of a Protozoön 107
28. _Hydra viridis_, partly in section 111
29. Successive stages in the division of the ovum, or egg-cell, of a worm 113
30. Ovarian ovum of a Mammal 121
31. Amoeboid movements of young egg-cells 122
32. Human ovum, mature and greatly magnified 123
33. Stages in the formation of the polar bodies in the ovum of a star-fish 125
34. Fertilization of the ovum of an echinoderm 126
35. Fertilization of the ovum of a star-fish 127
36. Karyokinesis of a typical tissue-cell (epithelium of Salamander) 129
37. Study of successive changes taking place in the nucleus of an epithelium-cell, preparatory to division of the cell 131
38. Formation and conjugation of the pronuclei in _Ascaris megalocephala_ 132, 133
39. Segmentation of ovum 135
40. The contents of an ovum in an advanced stage of segmentation, drawn in perspective 135
41. Formation of the gastrula of _Amphioxus_ 137
42. Gastrulation 138
43. Gastrula of a Chalk Sponge 139
44. _Prophysema primordiale_, an extant gastræa-form 140
45. Ideal primitive vertebrate, seen from the left side 143
46. The same in transverse section through the ovaries 144
47. _Amphioxus lanceolatus_ 145
48. _Balanoglossus_ 148
49. A large Sea-lamprey (_Petromyzon marinus_) 148
50. Adult Shark (_Carcharias melanopterus_) 149
51. Diagram of heart and gill-arches of a fish 150
52. One gill-arch, with branchial fringe attached 150
53. Diagram of heart and gill-arches in a lizard 150
54. Ideal diagram of primitive gill-or aortic-arches 151
55. The same, modified for a bird 151
56. The same, modified for a mammal 151
57. A series of embryos at three comparable and progressive stages of development, representing each of the classes of vertebrated animals below the Mammalia 152
58. Another series of embryos, also at three comparable and progressive stages of development, representing four different divisions of the class Mammalia 153
59. Diagram of geological succession of the classes of the Animal Kingdom 165
60. Skull of _Oreodon Culbertsoni_ 167
61,62. Horns of _Cervus dicrocerus_ 168
63. Horns of _C. matheronis_ 168
64. Horns of _C. pardinensis_ 168
65. Horns of _C. issiodorensis_ 168
66. Horns of _C. Sedgwickii_ 168
67. Successive stages in the development of an existing Deer's Antlers 169
68. Homocercal tail 169
69. Heterocercal tail 170
70. Vertebrated but symmetrical fin (diphycercal) 170
71. Tail of _Archæopteryx_ 171
72. Tail of modern Bird 171
73. _Archæopteryx macura_, restored 172
74. Skeleton of Polar Bear 174
75. Skeleton of Lion 175
76. Anterior limb of Man, Dog, Hog, Sheep, and Horse 176
77. Posterior limb of Man, Monkey, Dog, Sheep, and Horse 177
78. Posterior limb of _Baptanodon discus_, and anterior limb of _Chelydra serpentina_ 179
79. Paddle of a Whale 180
80. Fossil skeleton of _Phenacodus primævus_ 184
81. Bones of the foot of four different forms of the perissodactyl type 186
82. Bones of the foot of four different forms of the artiodactyl type 187
83. Feet and teeth In fossil pedigree of the Horse 189
84. _Palæotherium_. (Lower Tertiary of Paris Basin) 190
85. _Hipparion_. (New World Pliocene) 192
86. Comparative series of Brains 194
87. Ideal section through all the above stages 195
88. Skulls of Canadian Stag, _Cervalces Americanus_, and Elk 198
89. Transmutations of _Planorbis_ 200
90. Transformation of _Strombus_ 202
91. Pigeons. Drawn from life 298
92. Pigeons (_continued_). Drawn from life 299
93. Fowls. Drawn from life 300
94. Fowls (_continued_). Drawn from life 301
95. Pair of Japanese Fowls, long-tailed breed 302
96. Canaries. Drawn from life 303
97. Sebastopol, or Frizzled Goose 304
98. The Dingo, or wild dog of Australia 304
99. Dogs. Drawn from life 305
100. Dogs (_continued_). Drawn from life 306
101. The Hairless Dog of Japan 307
102. The skull of a Bull-dog compared with that of a Deer-hound 307
103. Rabbits. Drawn from life 308
104. Horses. Drawn from life 309
105. Sheep. Drawn from life 310
106. Cattle. Drawn from life 311
107. Wild Boar contrasted with a modern Domesticated Pig 312
108. Seasonal changes of colour in Ptarmigan (_Lagopus mutus_) 317
109. _Oedicneus crepitans_, showing the instinctive attitude of concealment 320
110. Imitative forms and colours in insects 322
111. The larva of Puss Moth (_Cerura vinula_) 325
112. The larva of Puss Moth in disturbed attitude 326
113. Three cases of mimicry 328
114. Two further cases of mimicry; flies resembling a wasp in the one and a bee in the other 329
115. A case of mimicry where a non-venomous species of snake resembles a venomous one 330
116. A case of mimicry where a homopterous resembles a leaf-cutting ant 332
117. Feather-footed pigeon 359
118. _Raia radiata_ 368
119. Electric organ of the Skate 369
120. Electric cells of _Raia radiata_ 370
121. The Garden Bower-bird (_Amblyornis inornata_) 382
122. Courtship of Spiders 388
123. Courtship of Spiders (_continued_) 389
124. The Bell-bird (_Chasmorhynchus niveus_) 396
125. _C. tricarunculatus_ 397
SECTION I
_EVOLUTION_