blaste'ma

The bioplasm of the develop- 122 ing embryo. [Gr., blastema, bud, from blastein, to sprout.] blas'ticle. nucleus. See vitelline nucleus under blas'tid. A small clear space in a segment of a fecundated ovum, the precursor of the nucleus. blasto-. Combining form of Gr., blastos, sprout, germ; used as a prefix in compound words to signify of, or pertaining to, a germ or bud. blas'tocele. The central cavity of a blaslow.] tula. [Gr., blastos, sprout, -fkoile, holblas'to chyle. The clear or shiny liquid of the blastodermic vesicle. [Gr., blastos, sprout, + chylos, juice.] blastocyst. The germinal vesicle. [Gr., blastos, sprout, + kystis, bag, from kye in, to contain.] blas'toderm. The germinal, or blastodermic membrane, or vesicle; a membranous bag formed in the fecundated ovum, consisting of segmentation spherules (blastomeres) pre ed away from the center by the accumulation of blastochyle; the rudimentary structure from which the embryo is formed. At first it is a simple layer; after the formation of the primitive streak, it consists of two layers, the epiblast (ectoderm) externally and the hypoblast (entoderm) internally; after the formation of the medullary plates and the notochord, a third layer, the mesoblast (mesoderm), forms between the two. See epiblast, hypoblast, and mesoblast. bilaminar b. The b. at that stage in which it consists of two layers, before the formation of the mesoblast. discoid b. See disco gastrula. _ tri laminar b. The b. at that stage in which it consists of three layers, the epiblast, the hypoblast, and the mesoblast. [Gr., blastos, sprout, + derma, skin.] blasto'ma.