PROFESSORS P.M. MOTTA & S. MAKABE / SCIENCE PHOTO LIBRARY PROFESSORS P.M. MOTTA & S. MAKABE / SCIENCE PHOTO LIBRARY
Coloured scanning electron micrograph of layers of a 6-8 cell embryo. The blastomeres (yellow) are the cells formed from divisions of the fertilized egg. Much of the membranous envelope, the zona pellucida (blue), which in life would surround the embryo has been destroyed in preparation. Only fragments of this layer remain. At left a group of the metabolically active cumulus cells has been preserved (red). This cell layer must be penetrated by the sperm in order to fertilize the egg (oocyte). Sperm tails can just be seen at centre left (thin, green). Magnification: x1,500 at 6x7cm size.
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