Bufo bufo embryos were subjected to 800r X-ray panirradiation at the III₈ stage and killed for the histological examination stage by stage in the following days. In their genital bodies the number of germ-cells persists almost unchanged during the first 16 days. Then, at the larval stages in which, in normal developmental conditions, should have begun the mitotic multiplication of germ-cells, their number suddenly decreases to complete sterility.