Light micrograph of seminiferous epithelium of the testis showing in basal region Sertoli cells and spermatogonia above which are large primary spermatocytes with nuclei showing patchy deposits of chromatin. Elongating spermatids occupy the adluminal region of the epithelium. Proliferation and maturation of germ cells in the testis is called spermatogenesis. In humans this requires about 70 days, in the rat (shown here) about 50 days. Epoxy resin section, Toluidine blue stain. Magnification x600 when printed 10cm wide.