The immature egg is released into the Fallopian tube after undergoing the first meiotic division and formation of the first polar body. The egg consists of a nucleus and cytoplasm enclosed in the vitelline membrane and surrounded by the zona pellucida, which is itself covered by a layer of loose cells, the corona radiata. The sperm passes through all these layers to reach the nucleus of the egg, and on penetration of the egg it stimulates the second meiotic division of the ovum and the formation of a second polar body.
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