There is considerable evidence that androgens facilitate the display of aggression in male vertebrates, while ovarian steroids do not (e.g. Guhl, 1961; Suchowsky, Pegrassi & Bonsignori, 1969). The golden hamster is unusual in that both sexes are aggressive, the female being dominant over the male (Dieterlen, 1959; Payne & Swanson, 1970). This study was undertaken to discover whether implanting ovarian tissue into castrated male hamsters influences their aggressive behaviour.
Twenty-eight adult male hamsters were castrated under ether anaesthesia. Simultaneously, in half of these a portion of ovarian tissue, freshly removed from an adult female, was implanted under the right kidney capsule. Six to 7 months later, both groups of castrated animals were tested by placing each animal in a neutral cage with a strange, intact male of the same body weight (± 3 g) for a 10-min observation period on 3 successive days. During each test the behaviour of both