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The principle reason for oogenesis, a complex ovarian activity, is the production of fertile gametes. The process is similar to sperm formation in the testis, but the timing of the events and the numbers of mitotic daughter cells are vastly different. The mitotic processes begin during fetal life, in utero. Several million oogonia are formed by this mitotic process which ceases at approximately 7 months of gestation in the human and will never be resumed. Oogonia formed in utero begin meiotic divisions but become arrested in the prophase of the first meiotic division and will remain so at least until puberty. For each ovulatory cycle, 20 - 50 primary oocytes will be consumed, but only one will carry on to form a secondary oocyte. In contrast, males are constantly producing sperm by the bucketful.