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.
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.
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.
The central part of theblastosphere is called the segmentation cavity or blastocoel.
In the former type the mesoblast and hypoblast are formed either from cells budded off from the outer cells of the blastosphere or from the solid inner mass of cells; while the outer ciliated cells become the epiblast.
In Barrois' type the inner ends of the cells of the blastosphereare stated to fuse into a kind of syncytium.
During the segmentation growth is very rapid, and eventually there is formed a blastosphere many times larger than the original ovum.
This stage nearly completes the segmentation: in the next one, the cells of the poles of the blastosphere increase in number, and the cells of the greater part of the blastosphere become columnar and ciliated, (fig.
The segmentation results in the formation of a single-walled blastosphere with a large central cavity (fig.
There is a regular segmentation resulting in the formation of a blastosphere with a central segmentation cavity.
The blastosphere is converted by invagination into a gastrula (fig.
One-half of the blastosphere may be pushed in towards the other half.
When the segmentation is regular, and results in the formation of a blastosphere, the epiblast and hypoblast are usually differentiated from the uniform cells forming the wall of the blastosphere in one of the two following ways.
In the type observed by Metschnikoff (Intoshia gigas) the ova undergo a regular segmentation, resulting in the formation of a blastosphere in which an inner layer is subsequently formed by delamination.
The segmentation is regular and leads to the formation of a blastosphere with a large segmentation cavity.
The cells of the blastosphere may divide themselves by a process of concentric splitting into two layers (fig.
From the above description the following general conclusions may be drawn:-- (1) The blastosphere stage is followed by a gastrula stage.
Invagination, the infolding of a layer of cells, as, for instance, in the transformation of a blastosphere into a gastrula, xvii.
The conditions for the origin of the blastosphere come into existence only by the process of segmentation, and it is only by its capacity to divide that the egg contains the conditions for blastosphere formation.
Plainly, the blastosphere cannot be pre-existing as a structure of particles in the fertilised nucleus; there cannot be blastosphere determinants.
The blastosphere determines the orientation of the gastrula, and so forth.
At one side the single layer of cells, of which the wall of the blastosphere is composed, begins to bend inwards, just as a dimple forms in a hollow india-rubber ball if a pin-prick allow some of the contained air to escape.
A limit is set to increase in the size of a blastosphere by the nature of the material of its walls.
Blastosphere stage with hypoblast spheres becoming budded into the central cavity.
Delamination where the segmented ovum has the form of a blastosphere in the cells of which the protoplasm is differentiated into an inner and an outer part.
By a subsequent process the inner parts of the cells become separated from the outer, and the walls of the blastosphere are so divided into two distinct layers (fig.
The blastosphere resulting from the segmentation first becomes flattened on one side, and the cells on the flatter side become more columnar (fig.
One side of theblastosphere next becomes invaginated, and during the process the embryo becomes ciliated, and commences to rotate.
When the segmentation results in the formation of a blastosphere, one half of the blastosphere may be pushed in towards the opposite half, and a gastrula be thus produced (fig.
E) the embryo consists of a blastosphere formed of a single layer of cells enclosing a large segmentation cavity.
This process consists of a concentric splitting of the cells of the blastosphere into an outer layer (epiblast) and an inner layer (hypoblast).
The cells of the lower half of the blastosphere are slightly larger than those of the upper half.
Both the blastosphere and gastrula often swim freely by flagella.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "blastosphere" in a variety of sentences. We hope that you will now be able to make sentences using this word.
