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gastrula
g a s t r u l a hex:#103;#97;#115;#116;#114;#117;#108;#97;
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- Gastrula - n. - An embryonic form having its origin in the invagination or pushing in of the wall of the planula or blastula (the blastosphere) on one side, thus giving rise to a double-walled sac, with one opening or mouth (the blastopore) which leads into the cavity (the archenteron) lined by the inner wall (the hypoblast). See Illust. under Invagination. In a more general sense, an ideal stage in embryonic development. See Gastraea.
- Gastrula - a. - Of or pertaining to a gastrula.
- Gastrulae - pl. - of Gastrula
- Gastrulation - n. - The process of invagination, in embryonic development, by which a gastrula is formed.
- Archenteron - n. - The primitive enteron or undifferentiated digestive sac of a gastrula or other embryo. See Illust. under Invagination.
- Archaeostomatous - a. - Applied to a gastrula when the blastopore does not entirely close up.
- Gastraea - n. - A primeval larval form; a double-walled sac from which, according to the hypothesis of Haeckel, man and all other animals, that in the first stages of their individual evolution pass through a two-layered structural stage, or gastrula form, must have descended. This idea constitutes the Gastraea theory of Haeckel. See Gastrula.
- Gastrulation - n. - The process of invagination, in embryonic development, by which a gastrula is formed.