has part has part has_part develops from develops from existence starts during existence ends during blastoderm cell hypoblast (generic) blastula stage gastrula stage embryonic structure epiblast (generic) blastodisc blastoderm germinal membrane Wikipedia:Blastoderm A layer of cells formed at one pole of macrolecithal eggs such as the yolky egg of birds. The yolk prevents the division from taking place through the egg, resulting in meroblastic cleavage during the many cleavage divisions. At the animal pole (containing less yolk than the vegetal pole), the zygote divides and subdivides, forming the blastoderm, which gradually spreads around the yolk and forms the embryo. The blastoderm is composed of two layers, the epiblast and the hypoblast, which enclose the fluid-filled blastocoel cavity. UBERON:0004750 ZFA:0001176 BTO:0000126 AAO:0000042 TAO:0001176 membrana germinativa MESH:D001756