EDELMANN / SCIENCE PHOTO LIBRARY EDELMANN / SCIENCE PHOTO LIBRARY
Four-cell human embryo. Image 3 of 4. Light micrograph of a human embryo at the four-cell stage. Each of the large cells is known as a blastomere. The embryo reaches this stage around 40 hours 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 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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