[Limitation on the number of germ cells in the fetal ovary of the rat by older ovaries, in vitro].

Ovaries from 9-day-old rats co-cultured for 4 days in vitro with ovaries from 13.5-day-old fetal rats prevent the proliferation of the oogonia in the fetal ovaries (germinostatic effect) and produce the anti-Müllerian substance. The hypothesis that the germinostatic and anti-Müllerian activities are not due to the same factor is discussed.