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Stage 3 begins when a cavity first appears in the morula and ends after the zona (capsula) pellucida is shed and the embryo makes contact with the endometrial lining of the uterus. Stage 3 embryos are called free blastocysts. They have an estimated postfertilization age in vivo of between four and five days and measure 0.1 to 0.2 mm in diameter.


Section 5

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