The morula of most animals further changes into a Blastula, a hollow ball filled with fluid, the wall being formed by a single layer of cells, the blastoderm or germinal layer.
That part of blastoderm where the hypoblast appears like a small disk on the inner face of the epibladst.
Of, pertaining to, or designating, that condition of the ovum in which there are three primary germinal layers, or in which the blastoderm splits into three layers.
The innermost layer of theblastoderm and the structures derived from it; the hypoblast; the entoblast.
The inner, or visceral, one of the two lamell\'91 into which the vertebrate blastoderm divides on either side of the notochord, and from which the walls of the enteric canal and the umbilical vesicle are developed.
The outer, or parietal, one of the two lamell\'91 into which the vertebrate blastoderm divides on either side of the notochord, and from which the walls of the body and the amnion are developed.
Then the Blastodermturned in his place and said:--"Why?
The Blastoderm reached out to the table, took up one paper, and jumped as if something had stung him.
We carried the Blastoderm across, in the pouring rain, to his quarters, and the Doctor gave him bromide of potassium to make him sleep.
Two days later, the Blastoderm found his tongue again.
This blastoderm is a simple, completely closed vesicle, the internal cavity of which is entirely full of food-yelk.
The blastoderm is already for the most part two-layered (b).
At last the internal cavity disappears altogether, the inner side of the blastoderm (that which lines the depression) coming to lie close on the outer side.
The fission theory--the fission of a single blastoderm to make a composite monster--is supported by Wolff, J.
An Experimental Examination into the | 154 | Growth of the Blastoderm of the Chick" | | Proc.
The relation between the unfertilised egg and the blastoderm which arises from it is not made altogether clear by Schwann.
The first of these differentiations in time is the formation of the germ-layers, which takes place by a splitting or separation of the blastoderm into a series of superimposed lamellæ.
Round the nucleus of the egg appears a Niederschlag or precipitate which is the rudiment of the blastoderm (p.
According to his account the cells of the blastoderm are formed actually in the ovum.
Valentin[250] appears to have seen cells in cartilage and epithelium even before Henle, and to have observed cells in the blastoderm of the chick.
Von Baer had already hinted at this homology in the second volume of his Entwickelungsgeschichte (1837), where he says with reference to the separation of the blastoderm of the chick into two layers.
Surface view of blastoderm of Pristiurus hardened in chromic acid.
Longitudinal section through a blastoderm at the time of the first appearance of the embryonic rim, and before the formation of the medullary groove.
Longitudinal section through the axial line of the primitive streak, and the part of the blastoderm in front of it, of an embryo duck with a well-developed primitive streak.
Portion of posterior end of a blastoderm of stage B, shewing the formation of cells around the nuclei of the yolk.
The nuclei of the blastoderm have been inaccurately rendered by the artist.
Longitudinal section of a blastodermat the first appearance of the segmentation cavity.
Longitudinal section of blastoderm of same stage as fig.
Portion of same blastoderm highly magnified, to shew the characters of the nuclei of the yolk n' and the nuclei in the cells of the blastoderm.
Section through blastodermwith well-developed primitive streak, shewing an exceptionally deep slit-like primitive groove.
Sections through the blastoderm before the appearance of primitive streak.
The thickened edge of the blastoderm is indicated by a darker shading.
Small portion of the blastoderm and the subjacent yolk of an embryo at the time of the first appearance of the medullary groove x 300.
The cells at the embryonic end of the blastoderm have been made rather too large.
It appears that the polar body is here preserved for an exceptional period, and its presence can still be proved when the blastoderm has been formed, and sometimes when development is even further advanced.
Why does the multiplication of cells in every part of the blastoderm take place with the exact amount of energy and rapidity necessary to produce the various elevations, folds, invaginations, etc.
Elsewhere in the blastoderm they are distinctly separate.
From the blastula stage to that of the early gastrula, the changes have been but slight; the blastoderm has greatly flattened out as its margins grow downward, leaving the segmentation cavity apparent.
The rim of the blastoderm has become thickened as the 'germ-ring'; and immediately in front of the dorsal lip of the blastopore its thickening marks the appearance of the embryo.
Aside from the question of periblast, the growth of the blastoderm appears not unlike that of the sturgeon.
The ovulation is closely like that of certain of the rays and sharks: the eggs are large, the segmentation is distinctly shark-like; the circular blastoderm overgrows the yolk in an elasmobranchian manner.
On either side of the ventral plate a fold of the blastoderm arises, and these folds grow towards each other beneath the chorion.
On the future ventral side of the embryo (and therefore on the concave surface of the egg) the cells of the blastoderm become columnar, and here is formed the so-called ventral plate, the first indication of the embryo.
Of course, with regard to all morphogenesis which goes on *immediately* from the blastoderm, the potency of the blastoderm is restricted as much as are the potencies of the germ layers.
The inner, or visceral, one of the two lamellæ into which the vertebrate blastoderm divides on either side of the notochord, and from which the walls of the enteric canal and the umbilical vesicle are developed.
The outer, or parietal, one of the two lamellæ into which the vertebrate blastoderm divides on either side of the notochord, and from which the walls of the body and the amnion are developed.
The embryo is invaginated into the yolk, but the surface edges of the blastoderm do not close over, so that a groove or pore puts the insunken space that represents the amniotic cavity into communication with the outside.
Escherich (1901), after a new research on the embryology of the muscid Diptera, claims that the fore and hind endodermal rudiments arise from the blastoderm by invagination, and are from their origin distinct from the mesoderm.
The embryo of a moth, a dragon-fly or a bug is invaginated into the yolk at the head end, the portion of the blastoderm necessarily pushed in with it forming the amnion.
The embryo begins to develop as an elongate, thickened, ventral region of the blastoderm which is known as the ventral plate or germ band.
This fission commences by the appearance of four transverse constrictions in the anterior part of the blastoderm; by which the whole blastoderm becomes imperfectly divided into five regions, fig.
In the region of the yolk-sack proper the blastoderm is so thin that it is not easy to be quite sure that a layer of hypoblast is throughout distinct.
While the body of the embryo is gradually being moulded this patch grows till it envelopes the yolk; the growth is not uniform, but is less rapid in the immediate neighbourhood of the embryonic part of the blastoderm than elsewhere.
Older blastoderm with embryo in which hypoblast and mesoblast are distinctly formed, and in which the alimentary cavity has appeared.
At the close of segmentation the blastoderm forms a somewhat lens-shaped disc, thicker at one end than at the other; the thicker end being the embryonic end.
The relation of the yolk to the blastoderm in the Elasmobranch embryo at this stage of development very well suits the view of its homology with the yolk-cells of the Amphibian embryo.
After segmentation the blastoderm becomes divided, as in Elasmobranchii, into two layers.
The germinal wall at this stage corresponds in many respects with the granular material, forming a ring below the edge of the blastoderm in Teleostei.
The complete differentiation of the epiblast is effected by the cells of the thickened edge of the blastoderm becoming divided into two strata (fig.
Defn: That part ofblastoderm where the hypoblast appears like a small disk on the inner face of the epibladst.
Defn: The outer, or parietal, one of the two lamellæ into which the vertebrate blastoderm divides on either side of the notochord, and from which the walls of the body and the amnion are developed.
Defn: Of, pertaining to, or designating, that condition of the ovum in which there are three primary germinal layers, or in which the blastodermsplits into three layers.
Defn: The inner, or visceral, one of the two lamellæ into which the vertebrate blastoderm divides on either side of the notochord, and from which the walls of the enteric canal and the umbilical vesicle are developed.
Subsequently cells appear at numerous points on the surface, and by repeated division constitute an uniformblastoderm investing the central yolk mass.
In C the blastoderm has become divided into two layers.
At the formation of the first larval membrane the blastoderm cells separate themselves from it, except at one part on the dorsal surface.
A fold of the blastoderm arises round the edge of the ventral plate.
The blastoderm is for the most part one cell thick, but it will be noticed that, at the edge of the blastoderm adjoining the largest yolk cell, there are placed two cells underneath the edge of the blastoderm (me).
In the next stage the cells of the thickened hemisphere of the blastoderm become still more columnar; and a second area, at first connected by a whitish streak with the cumulus, makes its appearance.
Its origin is doubtful, though it is regarded by Metschnikoff as probably derived from the blastoderm and homologous with the amnion of Insects.
In all the above types, as segmentation proceeds, the protoplasm becomes more and more concentrated at the surface, and finally a superficial layer of flat blastoderm cells is completely segmented off from the yolk below (fig.
These cells join the part of the blastoderm formed by the normal segmentation of the germinal disc.
In B a number of small cells have appeared (bl) which form a blastoderm enveloping the large yolk spheres.
During the formation of the blastoderm a cellular envelope is formed round the embryo.
As the blastoderm closes over the food-yolk, two more appendages arise and these are soon followed by others (see fig.
A depression appears at the point where the blastoderm closed and internally the pro-endoderm or inner layer is differentiated into two--the endoderm proper and the mesoderm (see fig.
But it must be borne in mind that all the nucleated masses of which the blastoderm consists are in continuity with each other and with the sparse protoplasmic reticulum of the subjacent yolk.
In this manner nucleated masses of protoplasm are continually being added to the periphery of the blastodermand assisting in its growth.
From their position in reference to the center of the cell the three layers of the blastoderm are described as-- 1.
The cells of the blastoderm become aggregated at one point on the circumference of the vesicle (dorsal pole of blastosphere) forming, when viewed from above, a thickened biscuit or disk-shaped opaque area.
The thinning out of the median portion of the mesoblast of the primitive streak is shewn in a longitudinal section of a duck's blastoderm of this stage (fig.
Sections through blastoderm with a primitive streak, towards the end of the first stage.
The groove in the primitive streak may with great plausibility be regarded as the indication of a depression which would naturally be found along the line where the thickened edges of the blastoderm became united.
Sections through a blastoderm with a very young primitive streak.
There is certainly, as is very well shewn in my longitudinal sections, a thickening of the blastoderm in the caudal region, though it is not so prominent in surface views as the procephalic lobe.
Posteriorly the breadth of the streak of epiblast which buds off the cells of the primitive streak widens considerably, and in the case of the blastoderm with the earliest primitive streaks extends into the region of the area opaca.
At the junction between the primitive streak and the blastoderm is situated a passage, open at both extremities, leading from the upper surface of the blastoderm obliquely forwards to the lower.
Near the opposite end of the blastoderm is a white area, which is probably the rudiment of the procephalic lobe.
At the edge of the blastoderm which represents the blastopore mouth of Amphioxus all the layers become fused together in the anamniotic vertebrates.
This stage is an interesting one on account of the striking similarity which (apart from the amnion) exists between a section through the blastoderm of a spider and that of an insect immediately after the formation of the mesoblast.
Below this layer fresh segments were obviously being added to the blastoderm from the subjacent yolk.
There is a main venous ring round the thickened edge of the blastoderm, which is connected with the embryo by a single stem which runs along the seam where the edges of the blastoderm have coalesced.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "blastoderm" in a variety of sentences. We hope that you will now be able to make sentences using this word.
