Embryology
The cleavage occurs more readily in the active cytoplasm than the yolk-laden cytoplasm or deutoplasm of the egg. The yolk which occurs in all animal eggs in little (e.g., microlecithal eggs) or larger (e.g., mesolecithal and macrolecithal eggs) amounts and remains distributed evenly (e.g., isolecithal eggs) or unevenly (e.g., telolecithal eggs) in the ooplasm of [...]
The cleavage is a phase of intensified chemical activity and a great amount of turn over of molecules occurs during its metabolism. The metabolism of cleavage can be studied under following two headings: A. Catabolic activities of cleavage- The cleavage requires large amount of chemical energy in the form of ATP molecules for its completion. [...]
By studying the cleavage in the eggs of different animal groups, it has been concluded that in all animal eggs, the cleavage seems to be governed by certain basic principles, rules of laws. Certain fundamental rules or laws of cleavage are following: 1. Sach’s law- In 1877, Sach proposed following two laws: a) Cells tend [...]
During cleavages, differnt cleavage furrows may divide the egg from different planes. Few important cleavage planes are following: 1. Meridional plane- When cleavage furrow passes through the centre of animal-vegetal axis and bisects the both poles of the egg, then such plane of cleavage is called meridional plane, e.g., Rana pipiens, Lepidosteus osseus and first [...]
The rate of cleavage varies from species to species. For example, in the gold fish, divisions follow each other continuously at regular intervals of 20 minutes. The inter-cleavage interval of frog is one hour and of mouse is 10 to 12 hours. In most of these cases, the cleavage rate remains rapid (synchronous) during completion [...]
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