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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.

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.

The embryo in the early stage following the blastula, characterized by morphogenetic cell movements, cell differentiation, and the formation of the three germ layers.

The embryo in the stage of development following the blastula, consisting of a sac with double wall. endoderm and ectoderm, the cavity being the archenteron. See cut in the next column.

The cup- or basin shaped structure formed by invagination of a blastula.

That early embryonic stage which follows the blastula.

Syn. : germ cup. The blastoderm at the period of its development when it consists of a double-walled bag formed by its invagination, so that its cavity is the primitive alimentary canal.