Page:Descent of Man 1875.djvu/681

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femora of the male, and on the head and thorax of the female, 297.
 * Onthophagus, 295.
 * rangifer, sexual differences of, 296; variation in the horns of the male, 297.
 * Ophidia, sexual differences of, 351.
 * Ophidium, 347.
 * Opossum, wide range of, in America, 169.
 * Optic nerve, atrophy of the, caused by destruction of the eye, 32.
 * Orang-Outan, 561; Bischoff on the agreement of the brain of the, with that of man, 6; adult age of the, 8; ears of the, 14; vermiform appendage of, 21; hands of the, 50; absence of mastoid processes in the, 53; platforms built by the, 66; alarmed at the sight of a turtle, 72; using a stick as a lever, 81; using missiles, 81; using the leaves of the Pandanus as a night covering, 82; direction of the hair on the arms of the, 151; its aberrant characters, 154; supposed evolution of the, 177; voice of the, 527; monogamous habits of the, 590; male, beard of the, 531.
 * Oranges, treatment of, by monkeys, 50.
 * Orange-tip butterfly, 308, 312, 313.
 * Orchestia Darwinii, dimorphism of males of, 268.
 * Tucuratinga, limbs of, 267, 271.
 * Ordeal, trial by, 96.
 * Oreas canna, colours of, 535.
 * Derbianus, colours of, 535, 543.
 * Organs, prehensile, 209; utilised for new purposes, 571.
 * Organic scale, von Baer's definition of progress in, 164.
 * Orioles, nidification of, 453.
 * Oriolus, species of, breeding in immature plumage, 484.
 * melanocephalus, coloration of the sexes in, 460.
 * Ornaments, prevalence of similar, 179; of male birds, 367; fondness of savages for, 574.
 * Ornamental characters, equal transmission of, to both sexes, in mammals, 541; of monkeys, 549.
 * Ornithoptera crœsus, 250.
 * Ornithorhynchus, 156; reptilian tendency of, 159; spur of the male, 502.
 * Orocetes erythrogastra, young of, 487.
 * Orrony, Grotto of, 22.
 * Orsodacna atra, difference of colour in the sexes of, 294.
 * Orthoptera, 282; metamorphosis of, 237; stridulating apparatus of, 283, 288; colours of, 289; rudimentary stridulating organs in female, 288; stridulation of the, and Homoptera, discussed, 288.
 * Ortygornis gularis, pugnacity of the male, 363.
 * Oryctes, stridulation of, 303; sexual differences in the stridulant organs of, 305.
 * Oryx leucoryx, use of the horns of, 509, 518.
 * Osphranter rufus, sexual difference in the colour of, 533.
 * Ostrich, African, sexes and incubation of the, 478.
 * Ostriches, stripes of young, 464.
 * Otaria jubata, mane of the male, 521.
 * nigrescens, difference in the coloration of the sexes of, 534.
 * Otis bengalensis, love-antics of the male, 380.
 * tarda, throat-pouch of the male, 373; polygamous, 219.
 * Ouzel, ring-, colours and nidification of the, 455.
 * , water-, colours and nidification of the, 455.
 * Ovibos moschatus, horns of, 505.
 * Ovipositor of insects, 208.
 * Ovis cycloceros, mode of fighting of, 508, 513.
 * Ovule of man, 9.
 * Owen, Prof., on the Corpora Wolffiana, 11; on the great toe in man, 11; on the nictitating membrane and semilunar fold, 17; on the development of the posterior molars in different races of man, 20; on the length of the cœcum in the Koala, 20; on the coccygeal vertebræ, 23; on rudimentary structures belonging to the reproductive system, 24; on abnormal conditions of the human uterus, 38,