Sperm cells. Coloured light micrograph (LM) of sperm cells (spermatozoa). These male sex cells are produced in the testes and are responsible for fertilising the female egg (ovum). Each sperm has a rounded head which contains the male hereditary material (DNA) and a long whip-like tail that propels it along. Sperm production commences at puberty and is dependent on the male sex hormone testosterone. While a female produces one egg each month, 300 million sperm are released by the male during ejaculation. They enter the vagina and from there travel to the uterus (womb) and fallopian tubes, where only one sperm may fertilise the egg.