DR YORGOS NIKAS / SCIENCE PHOTO LIBRARY DR YORGOS NIKAS / SCIENCE PHOTO LIBRARY
Fertilisation. Coloured scanning electron micro- graph (SEM) of sperm on the surface of a human egg (ovum) during fertilisation. The egg has a furry surface (brown). The sperm (coloured yellow) attached to it are hair-like structures; each sperm has a head, neck, and a long tail. Here they are attempting to penetrate the thick surface of the egg that attracts the sperm and enables them to attach. The human female usually produces a single large egg, and only one of the millions of male sperm released may penetrate the egg to fuse with the egg nucleus. Once fertilised, the egg begins its process of growth into a human embryo. Magnification: x1,600 at 5x7cm size. Magnification: x5,500 at 8x10 inch size.
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