DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Seminiferous tubules. Phase contrast micrograph of a section through the testis showing seminiferous tubules (round). This is the site of sperm production (spermatogenesis). Sperm cells are made up of a head, containing genetic material, and a tail. Mature sperm cells can be seen closest to the tubules' lumen (centre, blue). Moving away from the lumen are increasingly immature precursor cells; first spermatids, then spermatocytes and finally spermatogonia. The outermost cells are sertoli cells, which nourish the maturing sperm. Surrounding the tubules are leydig cells, which produce hormones needed for sperm production. Magnification: x37 when printed at 10 centimetres wide.
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