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A blastoderm ( germinal disc, blastodisc) is a single layer of embryonic epithelial tissue that makes up the blastula. It encloses the fluid filled blastocoel. 
Gastrulation
Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of cells), or in mammals the blastocyst is reorganized into a multilayered structure known as the gastrula. ...
follows blastoderm formation, where the tips of the blastoderm begins the formation of the ectoderm
The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from the o ...
, mesoderm
The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical Emb ...
, and endoderm.
Formation
The blastoderm is formed when the oocyte plasma membrane begins cleaving by invagination, creating multiple cells that arrange themselves into an outer sleeve to the blastocoel.In
oviparous
Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), a ...
In chicken eggs, the blastoderm represents a flat disc after embryonic fertilization. At the edge of the blastoderm is the site of active migration by most cells.{{cite book, last1=Bellairs, first1=Ruth, last2=Osmond, first2=Mark, title=Atlas of Chick Development, publisher=Atlas Press, page=15–28, edition=3
See also
*Blastodisc
The blastodisc, also called the germinal disc, is the embryo-forming part on the yolk of the egg of an animal that undergoes discoidal meroblastic cleavage. Discoidal cleavage occurs in those animals with a large proportion of yolk in their eggs, ...
*Embryology
Embryology (from Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, '' -logia'') is the branch of animal biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embryos an ...
* Cleavage
*Gastrulation
Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of cells), or in mammals the blastocyst is reorganized into a multilayered structure known as the gastrula. ...
References