A membrane formed by the repeated segmentation of the blastomeres.
A disk of cells (germinal disk or blastodisk) that develops on the surface of the yolk in an avian or reptilian egg from which the embryo develops; also, in mammalian embryos a disk of cells lying between the yolk sac and the amniotic cavity from which the embryo develops. From the blastoderm, the three germ layers (ectoderm, mesoderm, and endoderm) arise.
The initial membrane inside an egg that develops into the growing embryo.