Spermatozoa (sperm)

A group of sperm, with detail of a single sperm

Spermatozoa (sperm) are the male sex cells that carry a man's genetic material. They are so tiny that they can't be seen without a microscope. In a healthy man, one ejaculation usually contains between 40 million and 600 million sperm.

Sperm have an oval head, a short middle, and a long tail. They move by whipping their tails. A sperm fertilizes a woman's egg (ovum) by breaking through the membrane that surrounds the egg.

Sperm develop in a man's testicles. They are added to semen before a man ejaculates.

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