I.

IBEX, male, falling on his horns, ii. 249; beard of the, ii. 283.

IBIS, scarlet, young of the, ii. 208; white, change of colour of naked skin in, during the breeding season, ii. 80.

_Ibis tantalus_, age of mature plumage in, ii. 213; breeding in immature plumage, ii. 214, 215.

IBISES, decomposed feathers in, ii. 74; white, ii. 228, and black, ii. 230.

ICHNEUMONIDÆ, difference of the sexes in, i. 365.

ICHTHYOPTERYGIA, i. 125.

ICHTHYOSAURIANS, i. 204.

IDEAS, general, i. 62.

IDIOTS, microcephalous, imitative faculties of, i. 57; microcephalous, their characters and habits, i. 121.

_Iguana tuberculata_, ii. 32.

IGUANAS, ii. 32.

ILLEGITIMATE and legitimate children, proportion of the sexes in, i. 302.

IMAGINATION, existence of, in animals, i. 45.

IMITATION, i. 39; of man by monkeys, 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; Cyprinidæ 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, occurrence of, in _Cebus Azaræ_, 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; pursuit of female, by the males, i. 272; period of development of sexual characters in, i. 291; secondary 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 inheritance, 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; acquired, 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 influence 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.

_Iulus_, 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.

JAEGER, Dr., on the difficulty of approaching herds of wild animals, i. 74; on the increase of length in bones, i. 116; on the deposition of a male Silver pheasant on account of spoiled plumage, ii. 120.

JAGUARS, black, ii. 294.

JANSON, E. W., on the proportions of the sexes in _Tomicus villosus_, i. 314; on stridulant beetles, i. 379.

JAPAN, encouragement of licentiousness in, i. 134.

JAPANESE, general beardlessness of the, ii. 321; aversion of the, to whiskers, ii. 349.

JARDINE, Sir W., on the Argus pheasant, ii. 72, 97.

JARROLD, Dr., on modifications of the skull induced by unnatural position, i. 147.

JAVANESE, relative height of the sexes of, ii. 320; notions of female beauty, ii. 347.

JAW, influence of the muscles of the, upon the physiognomy of the apes, i. 144.

JAWS, smaller in the same ratio with the extremities, i. 117; influence of food upon the size of, i. 118; diminution of, in man, i. 144; in man, reduced by correlation, ii. 325.

JAY, young of the, ii. 209; Canada, young of the, ii. 209.

JAYS, new mates found by, ii. 104; distinguishing persons, ii. 110.

JEFFREYS, J. Gwyn, on the form of the shell in the sexes of the Gasteropoda, i. 324; on the influence of light upon the colours of shells, i. 326.

JELLY-FISH, bright colours of some, i. 322.

JENNER, Dr., on the voice of the rook, ii. 61; on the finding of new mates by magpies, ii. 103; on retardation of the generative organs in birds, ii. 107.

JENYNS, L., on the desertion of their young by swallows, i. 84; on male birds singing after the proper season, ii. 107.

JERDON, Dr., on birds dreaming, 46; on the pugnacity of the male bulbul, ii. 41; on the pugnacity of the male _Ortygornis gularis_, ii. 44; on the spurs of _Galloperdix_, ii. 46; on the habits of _Lobivanellus_, ii. 48; on the spoonbill, ii. 60; on the drumming of the Kalij pheasant, ii. 63; on Indian bustards, ii. 65; on _Otis bengalensis_, ii. 69; on the ear-tufts of _Sypheotides auritus_, ii. 73; on the double moults of certain birds, ii. 82; on the moulting of the honey-suckers, ii. 83; on the moulting of bustards, plovers, and drongos, ii. 84; on display in male birds, ii. 86; on the spring change of colour in some finches, ii. 86; on the display of the under tail-coverts by the male bulbul, ii. 96; on the Indian honey-buzzard, ii. 126; on sexual differences in the colour of the eyes of hornbills, ii. 129; on the markings of the Tragopan pheasant, ii. 134; on the nidification of the Orioles, ii. 168; on the nidification of the hornbills, ii. 169; on the Sultan yellow-tit, ii. 174; on _Palæornis javanicus_, ii. 180; on the immature plumage of birds, ii. 186 _et seq._; on representative species of birds, ii. 190; on the habits of _Turnix_, ii. 202; on the continued increase of beauty of the peacock, ii. 216; on coloration in the genus _Palæornis_, ii. 231.

JEVONS, W. S., on the migrations of man, i. 135.

JEWS, ancient, use of flint tools by the, i. 183; uniformity of, in various parts of the world, i. 242; numerical proportion of male and female births among the, i. 301; ancient, tattooing practised by, ii. 339.

JOHNSTONE, Lieut., on the Indian elephant, i. 268.

JOLLOFS, fine appearance of the, ii. 357.

JONES, Albert, proportion of sexes of Lepidoptera, reared by, i. 313.

JUAN FERNANDEZ, humming-birds of, ii. 221.

_Junonia_, sexual differences of colouring in species of, i. 389.

JUPITER, Greek statues of, ii. 350.

K.

KAFIR skull, occurrence of the diastema in a, i. 126.

KAFIRS, their cruelty to animals, i. 94; lice of the, i. 220; colour of the, ii. 347; engrossment of the handsomest women by the chiefs of the, ii. 369; marriage-customs of the, ii. 373.

KALIJ-PHEASANT, drumming of the male, ii. 62; young of, ii. 190.

_Kallima_, resemblance of, to a withered leaf, i. 392.

KALMUCKS, aversion of, to hairs on the face, ii. 349; marriage-customs of the, ii. 373.

KANGAROO, great red, sexual difference in the colour of, ii. 286.

KANT, Imm., on duty, i. 70; on self-restraint, i. 86; on the number of species of man, i. 226.

KATY-DID, stridulation of the, i. 352.

KELLER, Dr., on the difficulty of fashioning stone implements, i. 138.

KESTRELS, new mates found by, ii. 104.

KIDNEY, i. 116.

KING, W. R., on the vocal organs of _Tetrao cupido_, ii. 56; on the drumming of grouse, ii. 63; on the reindeer, ii. 244; on the attraction of male deer by the voice of the female, ii. 276.

KING and Fitzroy, on the marriage-customs of the Fuegians, ii. 374.

KING-CROWS, nidification of, ii. 167.

KINGFISHER, ii. 56; racket-shaped feathers in the tail of a, ii. 73.

KINGFISHERS, colours and nidification of the, ii. 171, 173, 176; immature plumage of the, ii. 188, 190; young of the, ii. 209.

KING LORY, ii. 174; immature plumage of the, ii. 188.

KINGSLEY, C., on the sounds produced by _Umbrina_, ii. 23.

KIRBY and Spence, on the courtship of insects, i. 272; on sexual differences in the length of the snout in curculionidæ, i. 255; on the elytra of _Dytiscus_, i. 343; on peculiarities in the legs of male insects, i. 344; on the relative size of the sexes in insects, i. 345; on the luminosity of insects, i. 345; on the Fulgoridæ, i. 351; on the habits of _Termites_, i. 364; on difference of colour in the sexes of beetles, i. 367; on the horns of the male lamellicorn beetles, i. 371; on hornlike processes in male curculionidæ, i. 374; on the pugnacity of the male stag-beetle, i. 375.

KITE, killed by a game-cock, ii. 44.

KNOT, retention of winter plumage by the, ii. 82.

KNOX, R., on the semilunar fold, i. 23; on the occurrence of the supra-condyloid foramen in the humerus of man, i. 28; on the features of the young Memnon, i. 217.

KOALA, length of the cæcum in, i. 27.

KÖLREUTER, on the sterility of hybrid plants, i. 223.

_Kobus ellipsiprymnus_, proportion of the sexes in, i. 305.

KOODOO, development of the horns of the, i. 289; markings of the, ii. 300.

KÖPPEN, F. T., on the migratory locust, i. 352.

KORDOFAN, protuberances artificially produced in, ii. 339.

KOWALEVSKY, A., on the affinity of the Ascidia to the Vertebrata, i. 205.

KOWALEVSKY, W., on the pugnacity of the male Capercailzie, ii. 45; on the pairing of the Capercailzie, ii. 49.

KRAUSE, on a convoluted body at the extremity of the tail in a _Macacus_ and a cat, i. 30.

KUPPFER, Prof., on the affinity of the Ascidia to the Vertebrata, i. 205.