Transmission electron micrograph (TEM) of the ultrastructure of the basal aspect of the seminiferous epithelium showing a Sertoli cell nucleus (right) and a leptotene primary spermatocyte (left). Sertoli cells are non-dividing and provide physical and metabolic support for germ cell development. Dense patches in the spermatocyte nucleus represent condensations of chromosomes during the process of meiotic maturation. The basal lamina consists of several layers of peritubular myoid cells. Magnification: x6,000 when printed at a width of 10cm.