DR YORGOS NIKAS / SCIENCE PHOTO LIBRARY DR YORGOS NIKAS / SCIENCE PHOTO LIBRARY
Two-cell embryo. Light micrograph of the blasto- meres of a 2-cell human embryo, two days after fertilisation. The blastomeres are the rounded cells formed by the first division of the fertilized egg. One cell is seen in front of the other here. An envelope, the zona pellucida, is seen surrounding the embryo, and the heads of some sperm are visible still attached to it. Magnification: x260 at 5x7cm size.
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