<unk>  is the process by which male spermatogonia develop into mature spermatozoa. Spermatozoa are the mature male gametes in many sexually reproducing organisms. Thus,<unk>  is the male version of gametogenesis. In mammals it occurs in the male testes and epididymis in a stepwise fashion, and for humans takes approximately 64 days.<unk>  is highly dependent upon optimal conditions for the process to occur correctly, and is essential for sexual reproduction. It starts at puberty and usually continues uninterrupted until death, although a slight decrease can be discerned in the quantity of produced sperm with increase in age. The entire process can be broken up into several distinct stages, each corresponding to a particular type of cell:
Spermatogenesis
Oogenesis
Reproduction
Eye development
Hematopoiesis
Limb development
Fermentation 
Ovulation