原腸胚

(1)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

(2)胞胚の陥入によって、胎児が二重の壁で囲まれる段階

(3)外側の細胞層は外胚葉で、内側の細胞層は中胚葉と内胚葉に分化する