PASCAL GOETGHELUCK / SCIENCE PHOTO LIBRARY PASCAL GOETGHELUCK / SCIENCE PHOTO LIBRARY
Morula embryo. Light micrograph of a human embryo at the morula stage of development. This ball of cells is formed about three days after fertilisation. The embryo is surrounded by the protective zona pellucida layer (clear). The embryo cells are called blastomeres. At this stage of development the embryo has yet to implant in the uterus. Magnification unknown.
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