As the blastoderm closes over the food-yolk, two more appendages arise and these are soon followed by others (see fig. 28).
He it was who introduced the terms "Keimhaut" (blastoderm) and "Keimblatt" (germ-layer).
After segmentation the blastoderm becomes divided, as in Elasmobranchii, into two layers.
About two-thirds of the yolk have been enveloped by the blastoderm.
From this region the mesoblast spreads as a continuous sheet to the sides and posterior part of the blastoderm.
There is one point to be noticed in the shape of the blastoderm as a whole.
The whole anterior part of the blastoderm becomes at the same time gradually constricted off from the yolk.
The points of similarity are— The swollen edge of the blastoderm.
It is more completely pinched off from the blastoderm than in the last described embryo.
It should be constituted as if formed of the fused edges of the blastoderm.
blastoderm blas·to·derm (blās'tə-dûrm') or blas·to·der·ma (blās'tə-dûr'mə)
The layer of cells formed by the cleavage of a fertilized mammalian egg, which later divides into the three germ layers from which the embryo develops. Also called germinal membrane, germ membrane.