The fate of germ cells in the testis of fetal Sex-reversed mice.

XX germ cells in the fetal testes of XX Sex-reverse male mice were observed mostly to develop in the same manner as do XY germ cells in a normal fetal testis; but some, in the vicinity of the mesonephric rete region, entered the prophase of meiosis at the same time as do XX germ cells in a normal fetal ovary. No germ cells in meiosis were found in the fetal testes of XY males, nor of XO Sex-reversed males. It is suggested that a second X chromosome renders a germ cell more susceptible to the meiosis-inducing influence of the mesonephric rete.