gastrula

gas·tru·la   (gās'trə-lə)    n.   pl. gas·tru·las or gas·tru·lae (-lē') An embryo at the stage following the blastula, consisting of a hollow, two-layered sac of ectoderm and endoderm surrounding an archenteron that communicates with the exterior through the blastopore. [New Latin : Greek gastēr, gastr-, belly + Latin -ula, feminine diminutive suff.] gas'tru·lar (-lər) adj.

Main Entry: gas·tru·la
Pronunciation: 'gas-tr&-l&
Function: noun
Inflected Form: plural gas·tru·las or gas·tru·lae /-"lE, -"lI/
: an early metazoan embryo in which the ectoderm, mesoderm, and endoderm are established either by invagination of the blastula (asin fish and amphibians) to form a multilayered cellular cup with a blastopore opening into the archenteron or (as in reptiles, birds, and mammals) by differentiation of the upper layer of theblastodisc into the ectoderm and the lower layer into the endoderm and by the inward migration of cells through the primitive streak to form the mesoderm —compare MORULA —gas·tru·lar /-l&r/ adjective

gastrula gas·tru·la (gās'trə-lə)
n. pl. gas·tru·las or gas·tru·lae (-lē')
An embryo at the stage following the blastula, consisting of a hollow, two-layered sac of ectoderm and endoderm surrounding an archenteron that communicates with the exterior through the blastopore.

gastrula   (gās'trə-lə)  Pronunciation Key  Plural gastrulas or gastrulae (gās'trə-lē') An animal embryo at the stage following the blastula. The gastrula develops from the blastula by invagination (inpocketing), forming an inner cavity with an opening and causing the cells to be distributed into an outer layer (ectoderm) and an inner layer (endoderm). In complex animals such as vertebrates, a third layer (mesoderm) also forms. These layers later develop into the organs and tissues of the body. In vertebrates and other deuterostomes, the opening of the gastrula becomes the anus, while in protostomes (such as arthropods), it becomes the mouth. ◇ The development of an embryo from blastula to gastrula is called gastrulation. Compare blastula.

gastrula

early multicellular embryo, composed of two or more germinal layers of cells from which the various organs later derive. The gastrula develops from the hollow, single-layered ball of cells called a blastula which itself is the product of the repeated cell division, or cleavage, of a fertilized egg. This cleavage is followed by a period of development in which the most significant events are movements of cells relative to one another.

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