Aborting embryo. Coloured scanning electron micrograph of an aborting 6-8 cell human embryo undergoing necrosis (tissue death). The blastomeres, the cells formed from divisions of the fertilized egg, are degenerating. Large blastomere cell fragments can be seen (green). The zona pellucida (orange), the membrane which surrounds the embryo, has become thick and compact. It has lost its typical striated appearance. Magnification: x2,000 at 6x6cm size.