False-colour scanning electron micrograph of seminiferous tubules in the human testis (cross section), the site of production and maturation of sperm. Round undifferentiated cells lining the tubule wall (brown, pink) become sperm by halving their chromosome number, and transforming in a process which takes about two months. During this time the cells move toward the centre of the tubule and develop tails (orange). Mature sperm migrate up the cavity of the tubule & are stored in the epididymis. 200-300 million sperm are released in an average ejaculation. Magnification: x220 at 4x5 inch size x135 at 6x7cm size.