i. 11;

adult age of the, i. 13; ears of the, i. 21; vermiform appendage of, i. 27; platforms built by the, i. 36; alarmed at the sight of a turtle, i. 43; using a stick as a lever, i. 51; using missiles, i. 52; using the leaves of the _Pandanus_ as a night covering, i. 53; hands of the, i. 139; absence of mastoid processes in the, i. 143; direction of the hair on the arms of the, i. 192; its aberrant characters, i. 197; supposed evolution of the, i. 230; voice of the, ii. 276; monogamous habits of the, ii. 361; male, beard of the, ii. 284.

ORANGES, treatment of, by monkeys, i. 139.

ORANGE-TIP butterfly, i. 388, 393, 394.

_Orchestia Darwinii_, dimorphism of males of, i. 332.

_Orchestia Tucuratinga_, limbs of, i. 330, 331, 337.

ORDEAL, i. 68.

_Oreas canna_, colours of, ii. 288.

_Oreas derbyanus_, colours of, ii. 288, 299.

ORGANS, prehensile, i. 256; utilised for new purposes, ii. 335.

ORGANIC scale, von Baer's definition of progress in, i. 211.

ORIOLES, nidification of, ii. 167.

_Oriolus_, species of, breeding in immature plumage, ii. 214, 215.

_Oriolus melanocephalus_, coloration of the sexes in, ii. 178.

ORNAMENTS, prevalence of similar, i. 233; fondness of savages for, ii. 338; of male birds, ii. 50.

ORNAMENTAL characters, equal transmission of, to both sexes, in mammals, ii. 297; of monkeys, ii. 306.

_Ornithoptera croesus_, i. 310.

_Ornithorhynchus_, i. 200; spur of the male, ii. 242; reptilian tendency of, i. 204.

_Orocetes erythrogastra_, young of, ii. 219.

ORRONY, Grotto of, i. 28.

_Orsodacna atra_, difference of colour in the sexes of, i. 368.

ORTHOPTERA, i. 352; metamorphosis of, i. 292; stridulating, auditory apparatus of, i. 353; colours of, i. 360; rudimentary stridulating organs in female, i. 359; stridulation of the, and Homoptera, discussed, i. 360.

_Ortygornis gularis_, pugnacity of the male, ii. 44.

_Oryctes_, stridulation of, i. 381; sexual differences in the stridulant organs of, i. 383.

_Oryx leucoryx_, use of the horns of, ii. 251, 263.

_Osphranter rufus_, sexual difference in the colour of, ii. 286.

OSTRICH, African, sexes and incubation of the, ii. 205.

OSTRICHES, stripes of young, ii. 184.

_Otaria jubata_, mane of the male, ii. 267.

_Otaria nigrescens_, difference in the coloration of the sexes of, ii. 287.

_Otis bengalensis_, love-antics of the male, ii. 68.

_Otis tarda_, polygamous, i. 269; throat-pouch of the male, ii. 58.

OUZEL, ring-, colours and nidification of the, ii. 179.

OUZEL, water-, colours and nidification of the, ii. 170.

_Ovibos moschatus_, horns of, ii. 247.

OVIPOSITOR of insects, i. 254.

_Ovis cycloceros_, mode of fighting of, ii. 249.

OVULE of man, i. 14.

OWEN, Prof., on the Corpora Wolffiana, i. 16; on the great toe in man, i. 16; on the nictitating membrane and semilunar fold, i. 23; on the development of the posterior molars in different races of man, i. 26; on the length of the caecum in the Koala, i. 27; on the coccygeal vertebrae, i. 29; on rudimentary structures belonging to the reproductive system,