Aborting embryo cells. Coloured scanning electron micrograph (SEM) of blastomere fragments of an aborting 6-8 cell human embryo. The embryo is undergoing necrosis (tissue death). Blastomeres, the cells formed from divisions of the fertilized egg, have degenerated into fragments (green). Remains of sperm tails (orange) can also be seen. The zona pellucida (bottom, yellow), the membrane which surrounds the embryo, has been artificially fractured (opened up). It has become thick and compact and has lost its usual striated appearance. Magnification: x3,800 at 5x7cm size.