D. PHILLIPS / SCIENCE PHOTO LIBRARY D. PHILLIPS / SCIENCE PHOTO LIBRARY
Fertilisation. Coloured Scanning Electron Micro- graph (SEM) of a sperm on the surface of a human egg (ovum) during fertilisation. The egg has a furry surface (blue). The sperm attached to it is a hair-like structure (red); it has a head (upper centre) and a long tail. Here, it is penetrating this thick surface of the egg that attracts the sperm and enables it 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: x4,600 at 6x9cm size.
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