Differentiation of the rat testis between 20 and 120 days of age.

The differentiation of the seminiferous epithelium was studied in 20-120-day-old Sprague-Dawley rats. Body weights and the weights of the testes, seminal vesicles, and kidneys were determined. The best way of defining the development of the testis was to denote the most differentiated germ cell present. Spermatogenesis is complete at 56 days of age, but the testis continues to grow up to 108 days of age. The development of certain parameters has been calculated, and it is very important to define the age of the animals in experimental studies and to include sufficient numbers of controls.