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Human sperm. Coloured Scanning Electron Micrograph (SEM) of human sperm cells (also called spermatozoa). Sperm are the motile male sex cells produced in the testis. Each sperm is about 65 micrometers long and broadly divided into a round head (at right), neck and tail regions. The pear-shaped head contains the nucleus and genetic material of the male needed to fertilize the female egg (ovum). The head is joined to the tail by a short neck. The sperm's tail enables it to swim by whiplash movements, an action that propels it to reach the ovum. The 3 millilitres of semen ejaculated by a man contain about 200-300 million sperm. Magnification: x1250 at 6x6cm size.
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