D. PHILLIPS / SCIENCE PHOTO LIBRARY D. PHILLIPS / SCIENCE PHOTO LIBRARY
Fertilisation. Coloured Scanning Electron Micro- graph (SEM) of sperm on the surface of a human egg (ovum) during fertilisation. The round egg (brown) has a furry surface. Sperm attached to it are hair-like structures (yellow); each sperm has a head and a long tail. Here, they are penetrating this thick surface of the egg that attracts 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: x500 at 35mm size. Magnification: x1,100 at 6x7cm size.
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