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The stage of development in animals in which the endoderm is formed and invagination of the blastula has occurred.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



one of the stages of embryonic development in multicellular animals. In the gastrula stage the embryo has a two-layer wall and cavity (gastrocoel) that communicates with the surrounding environment by means of an opening, the blastopore. The outer wall is called the ectoderm; the inner wall, the endoderm. They are the primordial embryonic layers. In the beginning the endoderm, and less frequently the ectoderm, also contains the material for a middle layer of tissue—the mesoderm. At the end of gastrulation, the mesoderm separates and becomes independent, and the embryo is transformed from a two-layer to a three-layer organization.

The transformation from the blastula to the gastrula takes place differently in different animals. Already at the gastrula stage, certain differences in the properties of the embryonic layers that are precursors of their morphological differentiation can be observed. The differences in structure of the embryos of different animals at this stage of development are determined both by the structure of the eggs and by the different modes of existence of the embryos. In most animals the embryo spends the gastrula stage in the egg envelope or in the mother’s body; in some hydrozoans the gastrula is a free-living larva. Sometimes the differences pertain to the most general features; for example, in the embryos of bony fish the gastrocoel is lacking, and in certain coelenterate gastrulae the blastopore is lacking. The presence of the gastrula stage (with its characteristic separation into embryonic tissues) in the development of all multicellular organisms was demonstrated by A. O. Kovalevskii and E. Metchnikoff and provided proof of the common origin of animals.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
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Segun un modo de la genesis especificamente distinto por su contenido y su meta, el modo del 'brotar', desde y por las estructuras celulares y bioquimicas de la gastrula se constituye en el caso del hombre una psique tambien especificamente distinta, la psique a un tiempo animal y humana.
In addition, embryos (20/replicate) were exposed during cleavage (0.75-2 hpf), blastula (2.25-5 hpf), gastrula (5.25-10 hpf), segmentation (10-24 hpf), or pharyngula (24-48 hpf) alone in triplicate glass beakers, and incubated in vehicle control media (0.1% DMSO) pre-and postexposure until 96 hpf.
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