noun.
The layer of cells that develops on the surface of the yolk in an avian or reptilian egg and gives rise to the germinal disk from which the embryo develops.
noun.
The layer of cells formed by the cleavage of a fertilized mammalian egg. It later divides into the three germ layers from which the embryo develops.
The Century Dictionary and Cyclopedia
noun.
In embryology, the primitive membrane or layer of cells resulting from the subdivision of the germ (the segmentation of the vitellus or yolk).
the GNU version of the Collaborative International Dictionary of English
noun.
the early embryo developing from a blastodisc, after the blastocoel has formed.
noun.
in an insect embryo, the layer of cells that surrounds the internal mass of the yolk.