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1. 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.
2. 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.

blas′to·der·mat′ic (-dər-măt′ĭk), blas′to·der′mic adj.


1. (Biology) the layer of cells that surrounds the blastocoel of a blastula
2. (Biology) a flat disc of cells formed after cleavage in a heavily yolked egg, such as a bird's egg
Also called: blastodisc
ˌblastoˈdermic adj


(ˈblæs təˌdɜrm)

1. the primitive layer of cells that results from the segmentation of the ovum.
2. the layer of cells forming the wall of the blastula and in most vertebrates enclosing a cavity or a yolk mass.
blas`to•der′mic, adj.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.blastoderm - a layer of cells on the inside of the blastulablastoderm - a layer of cells on the inside of the blastula
layer - thin structure composed of a single thickness of cells
References in periodicals archive ?
Avian twinning is the result of embryonic cleavage causing identical monozygotic twins, two fertilized blastoderms within a single yolk, or two blastoderms within their own yolk (Hollander and Levi 1940, Romanoff and Romanoff 1972).
a single yolk with two blastoderms or two yolks enclosed in a single shell) could not be determined with absolute certainty.
However, the fact that the egg was within the normal range for mass, length, and width expected for the species may indicate that the twins originated from a single yolk with two blastoderms rather than two separate yolks.