Human seminiferous epithelium, light micrograph. In contact with the basal lamina are the spermatogonia, some of which are stem cells that differentiate and divide to produce the germ cells for spermatogenesis. Above these are larger primary spermatocytes with chromatin patches in their nuclei. Spermatocytes divide by meiosis to form spermatids seen here as slightly elliptical smaller nuclei stained blue. In man the production of mature sperm from the spermatogonia requires about 70 days. The non-dividing Sertoli cells with irregular nuclei are located between the spermatogonia and spermatocytes. Sertoli cell lipid inclusions are stained green. Epoxy resin section, Toluidine blue stain. Magnification: x 500 when width printed at 10cm.