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Meroblastic Segmentation


Due to the difference in calf distribution, there are two basic types of meroblastic segmentation: a discoidal and the superficial.

In targeting discoidal meroblastic, the divisions occur only in the region of the scar (region of the cell without calf), forming a disk of cells over the calf mass. This type of segmentation occurs in telolecith eggs.

The segmentation superficial meroblastic occurs in centrolecith eggs. Embryonic cells are arranged on the surface of the egg.

Segmentation Phases

Although there are different types of segmentation, they typically take place in two phases:

  • morula, in which a cell mass with few cells is formed;
  • blastula, in which the number of cells is increased and an internal fluid-filled cavity is formed.

The central cavity observed in the blastula is called blastocele (cell = cavity) and is filled with fluid synthesized by the cells that form its boundaries.

In isolated eggs and heteroliths, blastocele is well developed.

In the blastula originated from the segmentation of telolecith eggs, the true blastocele (cell = cavity) is not observed and is filled with fluid synthesized by the cells that form its boundaries.

In isolated eggs and heteroliths, blastocele is well developed.

In the blastula originated from the segmentation of telolecith eggs, the true blastocele is not observed, since the formed cavity is not entirely delimited by the blastomers. This cavity is partly delimited by the blastomers and partly by the calf. In this case, the formed cavity is called the subgerminal cavity, which is also filled with fluid synthesized by the cells. The blastula that forms from the segmentation of the telolecith eggs is called discoblastula.