PROFESSOR P.M. MOTTA ET AL / SCIENCE PHOTO LIBRARY PROFESSOR P.M. MOTTA ET AL / SCIENCE PHOTO LIBRARY
Fertilised egg. Coloured Scanning Electron Micro- graph (SEM) of a fertilised human egg cell after 24 hours, with sperm still attached. Sperm appear as small yellow objects with tails on the surface of the egg. The egg cell or oocyte (purple) has a thick zona pellucida layer which gives its surface a spongy appearance. Corona cumulus cells (white) are seen also attached to the egg surface; these remnant cells originally enclosed the egg while it was developing in the ovary. If a sperm penetrates the egg, as it has done here, the egg begins its process of growth through cell division. Magnification: x560 at 6x7cm size.
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