n. the opening that forms as a result of invagination of the surface layer of the early embryo (*gastrula). It is very much reduced in humans, in which it gives rise to the archenteric canal (see archenteron).
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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