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,