K.H. KJELDSEN / SCIENCE PHOTO LIBRARY K.H. KJELDSEN / SCIENCE PHOTO LIBRARY
Fertilisation. Coloured Scanning Electron Micro- graph (SEM) of sperm clustered around a human egg (ovum) during fertilisation. The round egg (green) is seen on human tissue (brown). Sperm attached to its surface are hair-like structures (yellow); each sperm has a rounded head and a long tail. They are penetrating the thick spongy 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 may penetrate the egg's wall to fuse with the egg nucleus. Once fertilised, the egg begins its process of growth by cell division. Magnification: x730 at 6x7cm size.
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