Definitionn. double-walled stage of the embryo resulting from invagination of the blastula
Last update: July 13, 2015
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We may distinguish the following series of stages: (I) ovum; (2) cleavage, leading to formation of a blastula; (3) formation of an inner mass or parenchyma, the future endoderm, by immigration or delamination, leading to the so-called parenchymula-stage; (4) formation of an archenteric cavity, the future coelenteron, by a splitting of the internal parenchyma, and of a blastopore, the future mouth, by perforation at one pole, leading to the gastrula-stage; (5) the outgrowth of tentacles round the mouth (blastopore), leading to the actinula-stage; and (6) the actinula becomes the polyp or medusa in the manner described elsewhere (see articles Hydrozoa, POLYP and Medusa). [Please select]
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_ Slides or diagrams, showing various stages in the development of some animal through the gastrula stage. [Please select]
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It is the first stage in postembryonic development, and follows the gastrula stage. [Please select]
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Gastrula: that embryonic stage resembling a sac, with an outer layer of epiblastic cells and an inner layer of hypoblastic cells. [Please select]
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