HENNING DALHOFF / SCIENCE PHOTO LIBRARY HENNING DALHOFF / SCIENCE PHOTO LIBRARY
Blastocyst implanted in uterus. Illustration of the blastocyst stage of human reproduction after implantation in the wall of the uterus. This cellular stage of reproduction is common to all mammals. It occurs around five days after fertilisation, and is the stage between the morula and the gastrula. During this stage, implantation takes place on the wall of the uterus (endometrium). The outer trophoblast layer implants to form the placenta (red fragments, far left). The inner fluid-filled cavity of the blastocyst is called the blastocoele. The inner cell mass (embryoblast) will form the embryo.
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