DAVID GIFFORD / SCIENCE PHOTO LIBRARY DAVID GIFFORD / SCIENCE PHOTO LIBRARY
Fertilisation and implantation. Artwork of the first week of human life, from egg fertilisation to embryo implantation in the uterus (womb). At lower left the ovary (white) releases a round egg into the fallopian tube (pink). Sperm reaches the egg & fertilises it 12-24 hours after egg release. The egg divides (upper left) into a two-celled embryo after 30 hours; at 3 days the embryo (called a morula) is 16 cells (top centre); at 4 days the advanced morula (centre right) nears the womb. At 4.5 days it is a blastocyst (hollow ball of cells) that enters the womb; at day 6 it implants on the womb, the thickened region forming the embryo and the placenta which will nourish it.
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