Sperm production site. Coloured scanning electron micrograph (SEM) showing sperm cells in a seminiferous tubule of the testis. The tubule has been freeze fractured to show its cross section. Seminiferous tubules are the site of sperm production (spermatogenesis) by the process of meiotic cell division. Sperm begin their development towards the outside of the tubule (pink) and move inwards (beige) as they mature. Mature sperm cells are seen here with their heads embedded in the tubule, and their long tails pointing outwards. Magnification: x1500 when printed 10 centimetres wide.