EDELMANN / SCIENCE PHOTO LIBRARY EDELMANN / SCIENCE PHOTO LIBRARY
Eight-cell human embryo. Image 4 of 4. Light micrograph of a human embryo at the eight-cell stage. This ball of cells is known as a morula. Each of the large cells is called a blastomere. The embryo reaches this stage around three days after fertilisation. At this stage in its development, the embryo is travelling down the woman's fallopian tube to the uterus. It will divide several more times, forming a hollow ball of cells (a blastocyst), before it implants in the uterine wall. For a sequence showing this embryo developing, see images P680/512-515. Magnification unknown.
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