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Of or pertaining to a gastrula.

The process of invagination, in embryonic development, by which a gastrula is formed.

Applied to a gastrula when the blastorope does not entirely up.

The primitive enteron or undifferentiated digestive sac of a gastrula or other embryo. See Illust. under Invagination.

irst stages of their individual evolution pass through a two-layered structural stage, or gastrula form, must have descended. This idea constitutes the Gastræa theory of Haeckel. See Gastrula.

ectoblast and entoblast, which form respectively the outer covering and inner wall of the gastrula. A third layer of cells, the mesoblast, which is formed later and lies between these two, is sometimes included. -- Germinal membrane. (Biol.) Same as Blastoderm. -- Germinal spot (Biol.), the nucleolus of the ovum. --…

f multicellular organisms, from the same embryonic systems into which the secondary unit (gastrula or plant enbryo) differentiates.

arrange themselves as an envelope; an embryonic form intermediate between the morula and gastrula. Sometimes used as synonymous with gastrula.

the cells in segmentation or cleavage of the ovum; the cavity of the blastosphere. In the gastrula stage, the segmentation cavity in which the mesoblast is formed lies between the entoblast and ectoblast. See Illust. of Invagination. -- Segmentation nucleus (Biol.), the body formed by fusion of the male and female pro…

he stomach and heart; the abdominal appendages are large, and bear the gills. Called also Gastrula, Stomatopoda, and Squilloidea.