Human morula. Coloured Scanning Electron Micro- graph (SEM) of a human embryo of 8-12 cells. It is about three days old. Known as a morula, this is a cluster of 8-12 identical, rounded cells called blastomeres, each of which contains a central nucleus. This embryo is at the early stage of transformation into a human composed of millions of cells. The cells are still covered in a spongy zona pellucida layer of the initial single-celled egg, and are dividing by mitosis to form a hollow ball of cells (the blastocyst). At this stage the morula has not yet implanted into the uterus. Magnification: x560 at 6x7cm size. x740 at 4x5"~LANDSCAPE"