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IN a previous communication [Shapiro, 1936] it was shown that methyl testosterone, in common with certain other steroids, can induce ovulation in Xenopus laevis, the South African clawed frog. Zwarenstein [1936] showed previously that progesterone could also induce ovulation in Xenopus. His results have been reported more fully [1937].

Xenopus does not ovulate spontaneously under laboratory conditions of captivity. Even at the height of the breeding season, sexual activity disappears as soon as the animals are brought into the laboratory. The animal appears therefore specially suited for the investigation of gonadotrophic substances.

Shapiro and Shapiro [1934] described a seasonal cycle in the gonad ratio, i.e. the mass of the ovaries relative to the body-weight of the animal. This ratio reached a peak during the breeding season, which in South Africa extends approximately from July to September.

The following investigation was therefore undertaken with the object of constructing dose-response curves at