Sperm. Light micrograph of a field of human sperm (spermatozoa) swimming through a physiological medium. These tiny male sex cells produced in the testes are responsible for fertilising the female's ovum (egg). Each sperm has a rounded head which contains the male hereditary material (DNA), and a long whip-like tail that propels it along. 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. Magnification: unknown.