Abstract
Normal, sexually inactive, adult [male] Fundulus injd. intraperit. or implanted in-tramusc. with testosterone propionate showed a marked hyperplasia of the testicular ducts and a development of the yellow body coloration characteristic of the breeding [male]. Stimulation of spermatogenesis was very slight. [male][male] hypo-physectomized during the breeding season and injected with testosterone propionate maintained the yellow body coloration better than did normal and hypophysectomized controls. The duct system was maintained better than in hypophysectomized controls, but less well than in normal controls. The hormone did not markedly check the germ-cell involution resulting from hypophysectomy. Testosterone injected into normal sexually active fish had no effect on the testis, and only partially maintained the yellow body coloration. Within the methods used, andro-genic material seems capable of stimulating the testicular duct system and the yellow body coloration. The stimulating effects on the germ cells are very slight.