INDEX. 753 



Ibisis, decomposed feathers in, 437; white, 560; and black, 562. 



Ichneumonidie, difference oi' the sexes in, 331. 



Ichtkyopterygia, 43. 



Ichthyosauriaus, 180. 



Idiots, inicrocephalous, their characters and habits, 40; hairiness 

 and animal nature of their actions, 41; niicrocephalous imitative 

 faculties of, 98. 



Iguana tuberculata, 402. 



Iguanas, 402. 



Illegitimate and legitimate children, proportion of the sexes in, 276. 



Imagination, existence of, in animals, 84. 



Imitation, 77; of man by monkeys, 82: tendency to. in monkeys, 

 inicrocephalous idiots and savages, 98; influence of", 146. 



Immature plumage of birds, 528, 531. 



Implacentata, 179. 



Implements, employed by monkeys. 91; fashioning of, peculiar to 

 man, 92. 



Impregnation, period of, influence of. upon sex. 277. 



Improvement, progressive, man alone suppposed to be capable 

 of, 89. 



Incisor teeth, knocked out or filed by some savages, 656. 



Increase, rate of, 50; necessity of checks in, 53. 



Indecency, hatred of, a modern virtue, 135. 



India, difficulty of distinguishing the native races of, 190; 

 Cyprinida? of, 389; color of the beard in races of men of. 637 



Indian, North American, honored for scalping a man of another 

 tribe, 132. 



Individuality, in animals, 93. 



Indolence of man, when free from a struggle for existence, 161. 



Indopicus carlotta, colors of the sexes of, 52L 



Infanticide, prevalence of, 52, 132, 289, 290; supposed cause of, 658; 

 prevalence and causes of, 675 et seq. 



Inferiority, supposed physical, of man, 72. 



Inflammation of the bowels, occurrence of, in Cebus Azarce, 7. 



Inheritance, 31; of long and short sight, 37: of effects of u. c e of 

 vocal and mental organs, 100; of moral tendencies, 139, 143; laws of 

 257; sexual, 262; sexually limited. 506. 



Inquisition, influence of the, 159. 



Insanity, hereditary, 31. 



Insect, 'fossil, from the Devonian, 327. 



Insectivora, 610; absence of secondary sexual characters in. 247 



Insects, relative nixe of the cerebral ganglU in. GO: male, appear 

 ance of, before the females, 240: pursuit of female. l)y*the males 250. 

 period of development of sexual characters in. 268: secondary 

 sexual characters of, 311; kept in cages, 319, 327; stridulaiion, 646. 



Insessorec, vocal organs of, 421. 



Instep, depth of, in soldiers and sailors, 36. 



Instinct and intelligence, 75; migratory, vanquishing the maternal, 

 122, 128. 



Instinctive actions, the result of inheritance. 119; impulses, dif- 

 ference of the force, 125 et seq ; and moral impulses, alliance of, 126. 



Instincts, 74; complex origin of, through natural selection. 76; 

 possible origin Q| some, 7b; acquired, of domestic animals, 118: 



