blasto-, blast-, -blast, -blastic
(Greek: germ, bud; shoot, formative cell or layer; of or pertaining to an embryonic or germinal stage of development)
blastoderm, blastodermic, blastodermatic
The germinal skin or membrane surrounding the yolk in the impregnated living ovum, and constituting the superficial layer of the embryo in its earliest condition. It divides into two and afterwards three layers of cells (the epiblast, mesoblast, and hypoblast, from one or other of which all the parts of the new animal are developed.