Light micrograph of a section through a testis showing the seminiferous tubules (light orange). The seminiferous tubules are the site of sperm production (spermatogenesis). Mature sperm cells can be seen closest to each tubule's lumen (white), with their tails protruding into the lumen. Moving away from the lumen are increasingly immature precursor cells; first spermatids, then spermatocytes and finally spermatogonia. The outermost cells are Sertoli cells that nourish the maturing sperm. Magnification: x100 when printed at 15cm wide.