A ligature was placed between the testis and the epididymis, and changes observed for 2 mo. Retention of spermatogenic products in the testis causes the latter to become enlarged and hardened. This process reaches its height in about 48 hrs. and is followed by a gradual decrease in size and hardness. The change appears to be caused by a decrease or cessation of spermatogenesis and by absorption of the material retained by the ligature, which undergoes autolysis. Degeneration of germinal epithelium is accompanied by a decrease in size of the seminiferous tubules. No interstitial cell hypertrophy was found. Degeneration was progressing at the end of 2 mo. No regeneration was seen. The spermatic fluid appears to be largely the product of degenerating spermatids and spermatocytes. The quantity of material produced is considerable, as shown by the rapid increase in size of the testis following ligation of vasa efferentia.