A correct interpretation of gastrulation is impossible without a knowledge of the position which the presumptive germinal layers occupy in the blastula. This position may be ascertained in various ways. A chart, showing the fate of each part of an early embryo, in particular, a blastula, is called a fate map. In tracing the fate of various parts of the [...]
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 this article we will discuss about the role of meiotic divisions in reduction of chromosomes. The somatic (body) cells in multicellular animals have, as a rule, a diploid or double number of chromosomes; that is, apart from some exceptions due to the presence of sex chromosomes, every kind of chromosome in the set is represented by a pair of [...]