The function of the spermatozoon, for which its whole organization is adapted, is to reach the egg and, by fusing with the egg, to cause the egg to start developing and to transmit to the developing embryo the paternal genes. In most cases this means that the spermatozoon must have a high degree of mobility, and in fact, the organization [...]
The development of the spermatozoa takes place in the male gonads, the testes. In vertebrates and insects, the testes are composite organs consisting of numerous seminiferous tubules, or seminiferous lobules, converging toward common ducts which lead the mature sperm to the exterior. Spermatogenesis is a continuous process, and various stages of development of the sperm may be observed in the [...]
As the oocyte grows and as various inclusions are produced in its cytoplasm, a pattern of organization gradually emerges, which will be of importance when the eggs start developing. The arrangement of various substances and cellular constituents in the advanced oocyte and, later, in the egg shows a polarity, that is, an unequal distribution with respect to what may be [...]