Abstract
SUMMARY: The relation between fertility and number of oocytes in the ovary has been investigated in rats whose ovaries had been X-irradiated. The number of oocytes was reduced by means of graded doses of X-rays and the animals were then mated with fertile males. The number of females which gave birth became fewer and litter-size decreased significantly with increasing doses of irradiation. It was also observed that animals which had lost all their oocytes at the end of the experiment displayed continuous vaginal cornification. The probability that the impaired fertility is directly due to the depletion in the number of available germ cells is discussed.