![]() More recently, the method of local vital staining has been applied to the study of Amphioxus development. The crescent of basophilic cytoplasm is the material which gives rise to the muscles and the lining of the body cavity and thus represents a mesodermal area. The granular cytoplasm, which takes up the region around the vegetal pole of the blastula, develops into the lining of the alimentary canal. The fate of the three regions is the following- The clear cytoplasm that later becomes the animal hemisphere of the blastula develops mainly into skin epidermis. They are the smallest cells in the blastula, even smaller than the animal cells, and they are rather loosely packed, the external surfaces bulging out, as is usually found in the earlier cleavage stages. The cells containing the basophilic cytoplasm are clearly discernible even as to shape. The cells are columnar and form a very closely packed columnar epithelium. The animal hemisphere is made up of cells containing the clear cytoplasm. The vegetal material is now contained in a number of rather large cells taking up the position on and around the vegetal pole of the blastula. The distinctions which could be traced in the cytoplasm of the egg now become accentuated by further distinctions in the size and shape of the blastomeres. The mass of cytoplasm of this kind has a crescentic shape, the attenuated ends of the crescent being drawn out along the equator of the egg about halfway around.ĭuring the period of cleavage the three regions become subdivided into blastomeres without the cytoplasmic substances having been displaced to any great extent. On one side of the egg, in a position roughly corresponding to the marginal zone of the amphibian egg, there is a special type of cytoplasm it does not contain much yolk, but it can be distinguished from the animal cytoplasm by its ability to be deeply stained by basic dyes. The animal hemisphere of the egg consists of cytoplasm that has less yolk and is consequently more transparent. ![]() Near the vegetal pole a mass of cytoplasm is found which contains the greatest amount of yolk (although yolk in this case is not abundant and the yolk granules are relatively very small). In Amphioxus, there are differences in the various regions of the egg cytoplasm which permitted Conklin (1932) to trace these regions into the later stages of development and thus to reconstruct a fate map, at least in rough outlines.Īt the beginning of cleavage three regions can be distinguished in the Amphioxus egg. In this article we will discuss about the process of gastrulation in amphioxus and amphibians. ![]()
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