n. a cavity that forms in the very early embryo as the result of gastrulation (see gastrula). In humans it forms a tubular cavity, the archenteric canal, which connects the amniotic cavity with the yolk sac. —archenteric adj.
the early embryo before the formation of *somites. It is a flat disc of tissue bounded dorsally by the amniotic cavity and ventrally by the yolk sac. The formation of the *primitive streak and *archenteron in the embryonic disc determines the orientation of the embryo, which then becomes progressively elongated.... embryonic disc
n. an early stage in the development of many animal embryos. It consists of a double-layered ball of cells formed by invagination and movement of cells in the preceding single-layered stage (blastula) in the process of gastrulation. It contains a central cavity, the *archenteron, which opens through the blastopore to the outside. True gastrulation only occurs in the embryos of amphibians and certain fish, but a similar process occurs in the embryonic disc in other vertebrates, including humans.... gastrula
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