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Sperm. Light micrograph of a field of swimming human sperm (spermatozoa). These tiny male sex cells produced in the testes are responsible for fertilisation of 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. 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. Magnification: unknown.
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