Chamæleons, armature of, 167 Cicada, music of, 222 Cockles, blindness of, 274 Coloration, cause of iridescent, 189 — forms of, 186 Conger-eel, huge size of females in, 178 Cooke, Mr. John, and the behaviour of sheep, 69 Courtship, meaning of, 21 Crabs, courtship of, 258 — seizing mates, 260 — stridulating organs of, 255 Crane, dances of, 120 Crocodile, courtship of, 164 Cunningham, J. T., and secondary sexual characters, 14 Dancing in birds, 119 Darwin, his theory of Sexual Selection, 12 Darwin on coloration of beetles, 210, 211 — on coloration of mollusca, 275 — on “horns” of beetles, 212 — on mane of baboons, 44 — on sexual selection in butterflies, 194 Deer, antlers of, 53, 62 — courtship of, 53 — fatal encounters of, 55 “Diathetic” types, meaning of, 50 “Display,” function of, 183 — in birds, need of, 147, 149 Double-eyed fish, 176 Dragon-flies, antiquity of, 227 Dragonet, courtship of, 177 Eland, horns of, 65 — strange habits of, 68 Elephant, courtship of, 71 — remarkable scent glands of, 69 — use of tusks in, 70 Elephant-seal, courtship of, 87 Emotions and human evolution, 32 — and sexual selection, 17 Emu, air-sacs of, 112 Eunuchs, peculiar features of, 145 Extinction, causes of, 17 Fabre on courtship of scorpions, 252 Fashions among savages, 33 _et seq._ Fighting-fish, ferocity of, 182 Fish, disparity in size of sexes 178 Forbes, Dr. H. O., on deceptive coloration in a spider, 240 Frigate-bird, air-sacs in display of, III Frilled-lizard, courtship of, 165 Frogs, concerts of, 171 — courtship of, 169 — singing like a Greenfinch, 173 Fur-seals, courtship of, 81 — polygamy of, 81 — precocious sexual instincts in, 86 Germ-plasm, nature of, 11 Giraffe, kick of, 73 — strong smell of, 68 Grasshopper, air-bladder of, 219 — stridulating organs of, 218, 221 Grebe, Great-crested, courtship of, 151 Groos, Professor, on emotions, 18 Hippopotamus, bloody sweat of, 69 — teeth of, 72 Hooded-seal, air-sac of, 88 Hormones, nature of, 16 — part played by, 146, 147 Horns, evolution of, 51 Hottentots, remarkable peculiarities of, 31 Howard, H. E., on importance of “territory” 140 — on play in warblers, 121 — on sexual selection, 138 Huxley, Mr. Julian, on the behaviour of Mallard, 149 — on the Great-crested Grebe, 151 Hypertely, meaning of, 125, 127 Image, Professor Selwyn, on Vapourer Moth, 201 Impotency, possible consequences of, 155 Ingram, Sir William, on display of King Bird-of-Paradise, 102 Insects and sexual selection, 192 Katydid, song of, 222 Kinetogenesis, meaning of, 80 Leptodora, olfactory sense of, 262 Life, lowest forms of, 3 _et seq._ Lion, mane of, 77 — polygamy in, 81 Lizards, courtship of, 165 _et seq._ — fighting among, 167 Locusts, ear of, 220