1877, contemporary Latin, from Greek gaster (genitive gastros) "belly" (see gastric) + Latin -ula, diminutive suffix. Related: Gastrulation.
double-walled stage of the embryo caused by invagination for the blastula; the outer level of cells may be the ectoderm in addition to inner level differentiates in to the mesoderm and endoderm
- An embryonic type featuring its source when you look at the invagination or pressing in of the wall surface of planula or blastula (the blastosphere) on one side, thus giving increase to a double-walled sac, with one orifice or mouth (the blastopore) that leads to the cavity (the archenteron) lined by the internal wall surface (the hypoblast). See Illust. under Invagination. In a far more general feeling, an ideal stage in embryonic development. See Gastraea.
- Of or related to a gastrula.
(a.) Of or regarding a gastrula.
Regarding the Echinoderms as a whole in the light of the foregoing account, we may give the following analytic summary of the characters that distinguish them from other coelomate animals: They live in salt or brackish water; a primitive bilateral symmetry is still manifest in the right and left divisions of the coelom; the middle coelomic cavities are primitively transformed into two hydrocoels communicating with the exterior indirectly through a duct or ducts of the anterior coelom; stereom, composed of crystalline carbonate of lime, is, with few exceptions, deposited by special amoebocytes in the meshes of a mesodermal stroma, chiefly in the integument; reproductive cells are derived from the endothelium, apparently of the anterior coelom; total segmentation of the ovum produces a coeloblastula and gastrula by invagination; mesenchyme is formed in the segmentation cavity by migration of cells, chiefly from the hypoblast.