The results show that irradiation affects both the size of the gonads and the number of germ cells they contain. At stage 64, gonads from irradiated animals were smaller than those from unirradiated ones. The reduced length and thickness of gonads of the test animals were probably due to cell killing. The variation in size of gonads of different test animals and the difference between the left and right ovary of a single individual are indicative of the degree of radiation sensitivity.