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 [...]
The cytoplasm of the egg, and particularly its cortex, starts the chain of reactions which eventually leads to the differentiation of parts of the embryo, it should not be assumed that the structure of the future embryo is rigidly determined by local differences in the cytoplasm of the egg. The local peculiarities of the egg cytoplasm are only some of [...]
In this article we will discuss about the manifestation of maternal genes during the early stages of development. Evidence has been presented that (1) the differences between the various parts of the embryo are not due to differences in their nuclei but to differences in the cytoplasm. From this it may be inferred that (2) the nuclei of the cleavage [...]