Double-walled stage of the embryo succeeding the blastula

• The outer layer of cells is the ectoderm and the inner layer differentiates into the mesoderm and endoderm

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1877, Modern Latin, from Greek gaster (genitive gastros ) "stomach" (see gastric ) + Latin -ula , diminutive suffix. Related: Gastrulation .

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Planula \Plan"u*la\, n.; pl. Planul[ae] . [L., a little plane.] (Biol.) In embryonic development, a vesicle filled with fluid, formed from the morula by the divergence of its cells in such a manner as to give rise to a central space, around which the cells ...

WordNet Word definitions in WordNet
n. double-walled stage of the embryo resulting from invagination of the blastula; the outer layer of cells is the ectoderm and the inner layer differentiates into the mesoderm and endoderm [also: gastrulae (pl)]

Wiktionary Word definitions in Wiktionary
n. (context embryology English) A stage in the development of embryos of most animals consisting of a two-layered sac of ectoderm and endoderm.