Organic scale, von Baer’s definition of progress in.
Orioles, nidification of.
Oriolus, species of, breeding in immature plumage.
Oriolus melanocephalus, coloration of the sexes in.
Ornaments, prevalence of similar; of male birds; fondness of savages for.
Ornamental characters, equal transmission of, to both sexes, in mammals; of monkeys.
Ornithoptera croesus.
Ornithorhynchus, reptilian tendency of; spur of the male.
Orocetes erythrogastra, young of.
Orrony, Grotto of.