Orsodacna atra, difference of colour in the sexes of.
Orsodacna ruficollis.
Orthoptera, metamorphosis of; stridulating apparatus of; colours of; rudimentary stridulating organs in female; stridulation of the, and Homoptera, discussed.
Ortygornis gularis, pugnacity of the male.
Oryctes, stridulation of; sexual differences in the stridulant organs of.
Oryx leucoryx, use of the horns of.
Osphranter rufus, sexual difference in the colour of.
Ostrich, African, sexes and incubation of the.
Ostriches, stripes of young.
Otaria jubata, mane of the male.