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Published online by Cambridge University Press: 11 June 2012
In 1930 ovulation in ferrets outside the breeding season was obtained by Hill and Parkes (1930) by means of gonadotrophic extracts. Later, similar results were obtained in sheep and thus it became possible to induce pregnancy outside the normal breeding season (Cole and Miller, 1933), and its practical importance was investigated by Parkes and Hammond (1940). Similar experiments on the golden hamster, Cricetus auratus, are described below, as this animal has proved to be a most interesting subject for the study of sex hormones (Klein, 1937 and 1938; Peczenik, 1942).