<P> Spermatogenesis takes place within several structures of the male reproductive system . The initial stages occur within the testes and progress to the epididymis where the developing gametes mature and are stored until ejaculation . The seminiferous tubules of the testes are the starting point for the process, where spermatogonial stem cells adjacent to the inner tubule wall divide in a centripetal direction--beginning at the walls and proceeding into the innermost part, or lumen--to produce immature sperm . Maturation occurs in the epididymis . The location (Testes / Scrotum) is specifically important as the process of spermatogenesis requires a lower temperature to produce viable sperm, specifically 1 ° - 8 ° C lower than normal body temperature of 37 ° C (98.6 ° F). Clinically, small fluctuations in temperature such as from an athletic support strap, causes no impairment in sperm viability or count . </P> <P> For humans, the entire process of spermatogenesis is variously estimated as taking 74 days (according to tritium - labelled biopsies) and approximately 120 days (according to DNA clock measurements). Including the transport on ductal system, it takes 3 months . Testes produce 200 to 300 million spermatozoa daily . However, only about half or 100 million of these become viable sperm . </P> <P> The entire process of spermatogenesis can be broken up into several distinct stages, each corresponding to a particular type of cell in humans . In the following table, ploidy, copy number and chromosome / chromatid counts are for one cell, generally prior to DNA synthesis and division (in G1 if applicable). The primary spermatocyte is arrested after DNA synthesis and prior to division . </P> <Table> <Tr> <Td> Cell type </Td> <Td> ploidy / chromosomes in human </Td> <Td> DNA copy number / chromatids in human </Td> <Td> Process entered by cell </Td> </Tr> <Tr> <Td> spermatogonium (types Ad, Ap and B) </Td> <Td> diploid (2N) / 46 </Td> <Td> 2C / 46 </Td> <Td> spermatocytogenesis (mitosis) </Td> </Tr> <Tr> <Td> primary spermatocyte </Td> <Td> diploid (2N) / 46 </Td> <Td> 4C / 2x46 </Td> <Td> spermatidogenesis (meiosis I) </Td> </Tr> <Tr> <Td> two secondary spermatocytes </Td> <Td> haploid (N) / 23 </Td> <Td> 2C / 2x23 </Td> <Td> spermatidogenesis (meiosis II) </Td> </Tr> <Tr> <Td> four spermatids </Td> <Td> haploid (N) / 23 </Td> <Td> C / 23 </Td> <Td> spermiogenesis </Td> </Tr> <Tr> <Td> four functional spermatozoids </Td> <Td> haploid (N) / 23 </Td> <Td> C / 23 </Td> <Td> spermiation </Td> </Tr> </Table>

When do the processes of human spermatogenesis and oogenesis begin