Transmission electron micrograph (TEM) of the ultrastructure of the seminiferous epithelium. Spermatogonia are seen on the basal lamina, above which are several large primary spermatocytes with patches of chromatin in their nuclei. A pyramidal-shaped Sertoli cell nucleus extends its columnar cytoplasm upwards through the seminiferous epithelium to reach the lumen. Round spermatids occupy the remainder of the epithelium, and several spermatozoa are being released into the lumen. Thin lateral processes of Sertoli cell cytoplasm provide structural and metabolic support for all germ cells. Magnification: x1,000 when height printed at 10cm.