Sperm. Computer artwork of a field of swimming human sperm (spermatozoa). These tiny male sex cells are produced in the testes, and are responsible for fertilisation of the ovum (egg) of the female. Each sperm has a rounded head which contains the male hereditary material (DNA) and a long, whip-like tail which propels it along. Sperm production commences at puberty and is dependent on the male sex hormone testosterone. Some 300 million sperm are released by the male, while the human female usually produces a single large egg. The sperm travel through the uterus (womb) and up the fallopian tubes to reach the egg. Only one sperm can fertilise the egg.