All eggs, like any other cells, are of course covered by the cell membrane or plasmalemma. Under the electron microscope the plasmalemma sometimes can be seen to be double, with two layers of electron-dense material about 50 Å thick separated by a less dense interval of about 60 Å. In addition to the plasmalemma, eggs of all animals, with the [...]
In the female sex the first stage of the development of gametes is similar to that found in spermatogenesis – the oogonia—the cells eventually giving rise to the eggs— undergo proliferation by mitotic divisions. They then become oocytes and enter a period of growth. Owing to the fact that the egg contributes the greater part of the substances used in [...]
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 [...]