Light microscopy of the human testis. Seminiferous tubules are shown in section. Tubules are bordered by a well-defined peritubular tissue and they contain male germ cells and non-germinal Sertoli cells making up the seminiferous epithelium. Through the process of spermatogenesis, germ cells multiply and mature over a period of 70 days to produce spermatozoa. Between the tubules clusters of Leydig cells are noted. These cells secrete testosterone which stimulates spermatogenesis. Magnification x200 when printed at 10 cm.