Testicular activity in mice selected for increased body weight

Parameters of testicular function were studied in mice selected for increased body weight and in contemporaneous unselected controls. Spermatogenesis occurred at the same time in the two lines. Body weight, testis weight, mean seminiferous tubular diameter and serum testosterone were increased significantly in the high growth mice. It is suggested that some genetically determined differences in body size are brought about by the differential secretion of testosterone.