Among white rats, which are very sexual animals, Steinach found that, when deprived of females, the males practise homosexuality, though only with males with whom they have long associated; the weaker rats play the passive part. But when a female is introduced they immediately turn to her; although they are occasionally altogether indifferent to sex, they never actually prefer their own sex.[6] With regard to the playing of the female part by the weaker rats it is interesting to observe that Féré found among insects that the passive part in homosexual relations is favored by fatigue; among cockchafers it was the male just separated from the female who would take the passive part (on the rare occasions when homosexual relations occurred) with a fresh male.[7] Homosexuality appears to be specially common among birds. It was among birds that it attracted the attention of the ancients, and numerous interesting observations have been made in more recent times. Thus Selous, a careful bird-watcher, finds that the ruff, the male of the _Machetes pugnax_, suffers from sexual repression owing to the coyness of the female (the reeve), and consequently the males often resort to homosexual intercourse. It is still more remarkable that the reeves also, even in the presence of the males, will court each other and have intercourse.[8] We may associate this with the high erotic development of birds, the difficulty with which tumescence seems to occur in them, and their long courtships. Among the higher animals, again, female monkeys, even when grown up (as Moll was informed), behave in a sexual way to each other, though it is difficult to say how far this is merely in play. Dr. Seitz, Director of the Frankfurt Zoölogical Garden, gave Moll a record of his own careful observations of homosexual phenomena among the males and females of various animals confined in the Garden (_Antelope cervicapra, Bos Indicus, Capra hircus, Ovis steatopyga_).[9] In all such cases we are not concerned with sexual inversion, but merely with the accidental turning of the sexual instinct into an abnormal channel, the instinct being called out by an approximate substitute, or even by diffused emotional excitement, in the absence of the normal object.