Proliferation of primordial germ cells of frogs stimulated by a fraction of granules derived from Rana nigromaculata embryos at the tail-bud stage.

A fraction of heavy granules, obtained from embryos of the frog (Rana nigromaculata) at the tail-bud stage by centrifugation at 1700 x g, were shown to stimulate the formation of proliferation of the primordial germ cells not only of the same species but also of a closely related species.