Abstract
Sixty-nine ground squirrels received injs. of testosterone or testosterone propionate shortly before the peak of the annual sexual cycle or, in a few instances, while the animals were immature. The daily dose ranged from 0.05 to 20.0 mgs. and injs. were made for 18-20 days. Controls were given blank injs. In all animals, one testis was removed surgically before injs. The other testis was secured at autopsy. After weighing the testes and the seminal vesicles, histological observations of the testes were made. Judging from testicular weights, the testes were inhibited in a majority of the cases. The interstitial cells of the testis were severely injured; therefore it appears that the interstitial cell stimulating hormone of the hypophysis was radically depressed. The germinal epithelium did not show signs of damage. The number of spermatozoa was not reduced. In immature animals, the formation of spermatozoa was not prevented. The hypophyseal gametogenic hormone was not inhibited.