INDEX. 769 



Onthophagus, 336; ontJiopliagus rangifer, sexual differences of, 335; 

 variation in the horns of the male, 386. 

 Opliidia, sexual differences of, 898. 



Ophidium, 394. 



Opossum, wide range of, in America, 193. 



Optic nerve, atrophy of the, caused by destruction of the eye, 36. 



Orang-outang, 640; 'Biscliott' on the agreement of the brain of the, 

 with that of man, 6; adult age of the, 9; ears of the, 15; vermiform 

 appendage of, 23; hands of the, 56; absence of mastoid processes in 

 the, 59; platforms built by the, 75; alarmed at the sight of a turtle, 

 81; using a stick as a lever, 91; using missiles, 92; using the leaves 

 of the Pandanus as a night covering, 93; direction of the hair on 

 the arms of the, 172; its aberrant characters, 175; supposed evolu- 

 tion of the, 202; voice of the, C02; monogamous habits of the, 674; 

 male, beard of the, 607. 



Oranges, treatment of, by monkeys, 56. 



Orange tip butterfly, 350, 354. 



Orchentia Darwinii, dimorphism of males of, 303 ; orchestic, 

 tucumtinga, limbs of. 302, 307. 



Ordeal, trial by, 108. 



Oreas canna, colors of 612; areas derUanus, colors of. 612. 621. 



Organs, prehensile, 237: utilized for new purposes, 651. 



Organic scale, von Baer's definition of progress in, 186. 



Orioles, nidification of, 516. 



Oriolus, species of, breeding in immature plumage, 552; oriolua 

 melanocephalus, coloration of the sexes in, 524. 



Ornaments, prevalence of similar, 203; of male birds, 416; fond' 

 ness of savages for, 654. 



Ornamental characters, equal transmission of, to both sexes, in 

 mammals, 619; of monkeys, 626. 



Ornithoptera crcesxs. 283. 



Ornithorymhus, 178 ; reptilian tendency of, 180 ; spur of the 

 male, 573. 



Orocetes erythrogastra, young of, 554. 



Orrony, Grotto of, 24. 



Orsodacna atra, difference of color in the sexes of, 333; orsodacna 

 rujic.ollis, 333. 



Orthoptera, 320; metamorphosis of, 268; stridulating apparatus of, 

 321, 326; colors of, 827; rudimentary stridulating organs in female, 

 326; stridtilation of the, and Homoptera, discussed, b27. 



Ortyyornis gularis, pugnacity of the male, 412. 



Oryetett stridulation of, 344; sexual differences in the stridulant 

 organs of, 345. 



Oryx leucoryx, use of the horns of, 580, 585. 590. 



OupJtranter rufus, sexual difference in the color of, 609. 



Ostrich, African, sexes and incubation of the, 544. 



Ostriches, stripes of young, 529. 



Otanajubata, mane of the male, 594; otaria niffrescens, difference 

 in the coloration of the sexes of, 610. 



Otis bengalensis, love -antics of the male, 432; otis tarda, throat- 

 pouch of the male, 423; polygamous, 248. 



Ouzel, ring, colors and nidification of the, 518; water, singing in 

 the autumn, 420; colors and nidification of the, 518. 



