from The American Heritage® Dictionary of the English Language, 4th Edition
- n. See blastula.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A blastula
from the GNU version of the Collaborative International Dictionary of English
- n. The hollow globe or sphere formed by the arrangement of the blastomeres on the periphery of an impregnated ovum.
from The Century Dictionary and Cyclopedia
- n. In embryology: A hollow sphere (vesicular morula) composed of a single layer of blastomeres or derivative cells, inclosing a central cavity or blastocœle.
- n. By Haeckel restricted to the germ-vesicle, vesicular embryo, or blastodermic vesicle of the Mammalia, which follows after gastrulation, and is called by him a gastrocystis, or intestinal germ-vesicle. Also called blastula.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. early stage of an embryo produced by cleavage of an ovum; a liquid-filled sphere whose wall is composed of a single layer of cells; during this stage (about eight days after fertilization) implantation in the wall of the uterus occurs
Sorry, no etymologies found.
At first the cells present the appearance of a bunch of grapes or the grains of a mulberry, the morula stage; the growth proceeds rapidly, a cavity forms itself inside and the blastosphere stage is reached.
We naturally assume, from what we have learnt, that the next stages will be the formation of a hollow blastosphere, invagination, a gastrula forming mesoblast by hollow outgrowths from the archenteron, and so on.
The blastosphere of the frog is like what the blastosphere of amphioxus would be, if the future hypoblast cells were enormously larger through their protoplasm being diluted with yolk.
And so segmentation (= cleavage) proceeds, and, at last, a hollow sphere, the blastosphere (Figure 4) is formed, with a segmentation cavity (s.c.).
This is the blastosphere, shown diagrammatically in Figure 4, and of which an internal view, rather truer to the facts of the case as regards shape, is given as Figure 5.
There is no open invagination of an archenteron in the fowl, as in the frog --, the gastrula, like the blastosphere, stage is also masked.
This stage is shown in section in the lower figure of Figure 1. b.d., the blastoderm, is from this point of view, a part of the ripped and flattened blastosphere, spread out on the yolk; s.c. is the segmentation cavity, and y. the yolk.
In such types (e.g., amphioxus) a part of the blastosphere wall is tucked into the rest, and a gastrula formed by this process of invagination.
If we compare this with the typical blastosphere of the lower type, we see that it is, as it were, flattened out on the yolk.
In this process a portion of the blastosphere wall is the tucked into the rest, as indicated by the arrow, so that a two-layered sack is formed.