from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. the outer layer of the blastoderm; the ectoderm or epiblast
from the GNU version of the Collaborative International Dictionary of English
- n. The outer layer of the blastoderm; the epiblast; the ectoderm.
- n. The outer envelope of a cell; the cell wall.
from The Century Dictionary and Cyclopedia
- n. In biology, the outermost recognizable structure of a cell; a cell-wall, in any way distinguished from mesoblast or other more interior structures. The ectoblast is to a cell what the epiblast is to a more complex organism.
- n. In embryology, the outer primary layer in the embryo of any metazoan animal; the epiblast; the ectoderm. See cut under blastocæle.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the outer germ layer that develops into skin and nervous tissue
Sorry, no etymologies found.
The former is often also called the ectoblast, or epiblast, and the latter the endoblast, or hypoblast.
The entire ectoderm arises from the first, second and third micromere quartets (collectively, the 'ectoblast').
When the mesoblast has become thus infinitely subdivided into hundreds of minute spheres, the ectoblast bursts, and the new generations of cells thus set free collect in that part of the egg where the embryonic disk is to arise.
This process goes on till all the cells are so filled by the mesoblast, with its myriad brood of cells, that the outer sac or ectoblast becomes a mere halo around it.
In this form, he says, the progaster is already developed, and its wall is differentiated for the first time into an animal or dermal layer (ectoblast), and into a vegetative or intestinal layer (hypoblast).
But in all other animals the ovum first grows into two primary layers, the outer or animal layer (the ectoderm, epiblast, or ectoblast), and the inner or vegetal layer (the entoderm, hypoblast, or endoblast); and from these the tissues and organs are formed.
B longitudinal section through the axis, g primitive-gut cavity, a primitive mouth-aperture, i inner cell-layer (entoderm, endoblast, gut-layer), e external cell-layer (outer germinal layer, ectoderm, ectoblast, or skin-layer).
(B) Schematic showing ontogeny of ectoblast cell distributions relative to the secondary axis.
Oppositely, the vegetal extremities of the ectoblast
LR1, and that the progress of epiboly over the next three or four hours coincides with mitotic quiescence of the ectoblast.