Sperm production site. Coloured scanning electron micrograph (SEM) showing a seminiferous tubule in 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 (orange) and move inwards (yellow) as they mature. Magnification: x430 when printed 10 centimetres wide.