438 
IMMATURE. 
INDEX. 
JACQUINOT. 
i. 44 ; tendency to, in monkeys, 
microcephalous idiots and savages, 
i. 56 ; influence of, i. 161. 
Immature plumage of birds, ii. 183, 
187. 
Implacentata, i. 202. 
Implements, employed by monkeys, 
i. 51 ; fashioning of, peculiar to 
man, i. 52. 
Impregnation, period of, influence of, 
upon sex, i. 303. 
Improvement, progressive, man alone 
supposed to be capable of i. 49. 
Incisor teeth, knocked out or filed 
by some savages, ii. 340. 
Increase, rate of, i. 131 ; necessity of 
checks in, i. 135. 
Indecency, hatred of, a modern 
virtue, i. 96. 
India, difficulty of distinguishing the 
native races of, i. 215 ; Cyprinida 3 
of, ii. 17 ; colour of the beard in 
races of men of, ii. 319. 
Indian, North American, honoured 
for scalping a man of another tribe, 
i. 93. 
Individuality, i. 62. 
Individuation, i. 318. 
Indopicus carlotta, colours of the sexes 
of, ii. 175. 
Infanticide, prevalence of, i. 94, 
134; supposed cause of, ii. 344; 
prevalence and causes of, ii. 363 
et seq. 
Inferiority, supposed physical, of 
man, i. 156. 
Inflammation of the bowels, occur- 
rence of, in Cebus Azar^, i. 12. 
Inheritance, i. 110 ; of effects of use 
of vocal and mental organs, i. 58 ; 
of moral tendencies, i. 102, 104 ; of 
long and short sight, i. 118 ; laws 
of, i. 279; sexual, i. 285; sexually 
limited, ii. 154. 
Inquisition, influence of the, i. 179. 
Insanity, hereditary, i. 111. 
Insect, fossil, from the Devonian, i. 
360. 
Insectivora, ii. 286 ; absence of 
secondary sexual characters in, i. 
268. 
Insects, relative size of the cerebral 
ganglia in, i. 145 ; male, appearance 
of, before the females, i. 260 ; pur- 
suit of female, by the males, i. 
272 ; period of development of 
sexual characters in, i. 291 ; secon- 
dary sexual characters of, i. 341 ; 
stridulation of ii. 331. 
Insessores, vocal organs of, ii. 55. 
Instep, depth of, in soldiers and 
sailors, i. 117. 
Instinct and intelligence, i. 37. 
Instinct, migratory, vanquishing the 
maternal, i. 83, 90. 
Instinctive actions, the result of in- 
heritance, i. 80. 
Instinctive impulses, difference of 
the force of, i. 87, 89 ; and moral 
impulses, alliance of, i. 88. 
Instincts, i. 36 ; complex origin of, 
through natural selection, i. 38 ; 
possible origin of some, i. 38 ; ac- 
quired, of domestic animals, i. 79 ; 
variability of the force of, i. 83 ; 
difference of force between the 
social and other, i. 89, 104; utilised 
for new purposes, ii. 335. 
Instrumental music of birds, ii. 61, 
66 . 
Intellect, influence of, in natural 
selection in civilised society, i. 171. 
Intellectual faculties, their influ- 
ence on natural selection in man, i. 
158; probably perfected through 
natural selection, i. 160. 
Intelligence, Mr. H. Spencer on the 
dawn of, i. 37. 
Intemperance, no reproach among 
savages, i. 96 ; its destructiveness, 
i. 172. 
Intoxication in monkeys, i. 12. 
Iphias glaucippe, i. 394. 
Iris, sexual difference in the colour of 
the, in birds, ii. 72, 128. 
IscHio-PUBic muscle, i. 127. 
Ithaginis cruentus^ number of spurs 
in, ii. 46. 
lulus, tarsal suckers of the males of, 
i. 340. 
J. 
Jackals learning to bark from dogs, 
i. 44. 
Jack-snipe, coloration of the, ii. 226. 
Jacquinot, on the number of species 
of man, i. 226. 
