It is well known that Bidder's organ, which is found in all adult male and in some adult female Bufonids (Dubois, 1947), represents a rudimentary ovary. This follows from (1) the microscopical structure of the organ, and (2) the fact that in male toads Bidder's organ may develop after castration into a functional ovary (Harms, 1923; Ponse, 1924). Moreover, the adult male common toad (Bufo bufo) possesses distinct Müllerian ducts, which develop into functional oviducts after ablation of the testes. In view of the presence of these two female organs, some investigators believe that Bidder's organ secretes a hormone which is responsible for the presence and maintenance of the Müllerian ducts in adult male toads. According to Ponse (1924), however, no endocrine function can be ascribed to it.
The first assumption is supported by the fact that in the adult male toad a distinct correlation exists between the number of