Longitudinal section through a blastoderm after the layer of cells has disappeared from the floor of the segmentation cavity.
One of the chief points to be noticed in their distribution is the fact that they form almost a complete layer under the floor of the segmentation cavity.
The engraver has not accurately copied my original drawings in respect to the structure of the segmentation furrows.
Formative cells at the bottom of the segmentation cavity are seen at b.
Longitudinal section of a blastoderm at the first appearance of the segmentation cavity.
It illustrates the same points as the previous section, but in addition shews the formation of the rudiments of the vertebral bodies (Vr) which are seen to have the same segmentation as the muscle-plates.
The section is intended to illustrate the fact that the nuclei form a layer in the yolk under the floor of the segmentation cavity.
It is intended to illustrate the growth of the embryonic rim and the disappearance of the segmentation cavity.
Section parallel with the long axis of the embryo through a blastoderm, in which the floor of the segmentation cavity is not yet covered by a complete layer of cells.
All this is reversed on the Red River of the North.
Such was his intention--for in a few moments he was seen to raise the gun to his shoulder, and take aim.
The segmentation of the nucleus was first noticed in the United States and at the Cape of Good Hope, September 30.
The mass of cells undergoes segmentation corresponding with the outersegmentation of the embryo, and a pair of cavities--the coelomic pouches (fig.
The first segmentation of the ventral plate is not, however, very definite, and the segmentation does not make its appearance simultaneously throughout the whole length of the plate; the anterior parts are segmented before the posterior.
The nervous system is ectodermal in origin, and is developed and segmented to a large extent in connexion with the outer part of the body, so that it affords important evidence as to the segmentation thereof.
In the cockroach embryo, before the segmentationof the germ-band has begun, the primitive germ-cells can be recognized at the hinder end of the mesoderm, from whose ordinary cells they can be distinguished by their larger size.
One of the smaller cells, or blastomeres, resulting from the complete segmentation of a telolecithal ovum.
In the gastrula stage, the segmentation cavity in which the mesoblast is formed lies between the entoblast and ectoblast.
To divide or separate into parts in growth; to undergo segmentation, or cleavage, as in thesegmentation of the ovum.
Sponges produce eggs and spermatozoa, and the egg when fertilized undergoessegmentation to form a ciliated embryo.
The segmentation of the body, too, is not readily seen in the upper surface on account of the thick felt-like covering of hairs, but is at once apparent when the creature has been turned over to expose the ventral side.
The relations of the arcualia to the segmentation of the body, as shown by myotomes and spinal nerves, is somewhat obscure.
The segmentation is complete; one side of the hollow blastosphere invaginates and forms a gastrula.
The segmentation is of the mesoblast to begin with, and appears later behind the mouth, the part anterior to this becoming the prostomium of the adult.
This coelom is lined by peritoneal cells and is divided into a series of metameres by septa which correspond to the segmentation of the body, the arrangement being thus precisely like that of typical Chaetopoda.
Eventually it breaks down by segmentation or by swelling up into a gelatinous mass.
It may happen, too, particularly in the sarcinæ, that segmentation is not complete, and that the elements are larger than in any other class of cocci.
As development proceeds, the body of the nauplius elongates, and indications of segmentation begin to appear in its posterior part.
A remarkable feature found only in the Stomatopoda is the reappearance ofsegmentation in the anterior part of the cephalic region.
Segmentation is usually of the superficial or centrolecithal type.
Segmentation is complete and unequal, producing macromeres and micromeres marked by differences in the size and in yolk-contents.
I have been able to photograph these successive stages of the segmentation of the chromatin just as I have those of the achromatin spindle" (Fig.
As a consequence of this superficial concentration we get segmentation of the vitellus, with the production of a morula.
We are able to produce by diffusion not only the achromatin spindle, but also the segmentation of the chromatin, and the division of the nucleus.
It may be objected that segmentation is also produced by a solution which is isotonic with sea water.
The segmentation is influenced by very slight currents of diffusion, and I have many preparations showing the segmentation regularly distributed in various ways along radial diffusion lines.
The extremely slow movements of diffusion thus produced would be very favourable to the action of the cohesive force on the particles in suspension, and hence to the segmentation of the egg.
If the preparation is preserved for several hours longer, we may see the cells formed by segmentation unite around the circumference so as to form a hollow bag corresponding to a gastrula, as shown in Fig.
Finally the segmentation becomes complete, and the preparation presents a muriform appearance, looking in fact something like a mulberry (Fig.
Opisthosoma without trace of separate terga and sterna, the segmentation merely represented posteriorly by slight integumental folds and the sterna of the 1st and 2nd somites by the opercular plates of the pulmonary sacs.
Trilobite so far as its segmentation and trilobation are concerned.
From the beginning of segmentation or, in any case, very early, the outer-layer cells become marked off from the inner-layer cells.
Then sets in what is known as the segmentation or cleavage of the ovum.
The central part of the blastosphere is called the segmentationcavity or blastocoel.
The nature of partial segmentation of the yolk was first made known by Kolliker in his work on the development of the Cephalopoda in 1844, and, as has already been mentioned, the phenomena were observed by Coste in the eggs of birds.
Further researches in a vast number of animals give every reason to believe that the phenomenon of segmentation is in some shape or other the invariable precursor of embryonic formation.
The first change the zygote undergoes in all animals is what is generally called the segmentation or cleavage of the ovum.
As previously mentioned, one or more lithocysts may often be observed to be permanently prepotent over the others; and I may here observe that the segmentation experiments just described have shown the converse to be true, viz.
Besides, as we shall subsequently see, for some reason or other segmentation of a Medusa profoundly modifies the rate of its rhythm.
The obliteration of the segmentation cavity during the period when the pseudo-invagination is occurring.
The small cells at the sides of the segmentation cavity in Amphibia correspond exactly in function and position with the lower layer cells of the Elasmobranch blastoderm.
This is not due to a secondary segmentation of the vertebrae but, as I have satisfied myself by a study of the development, takes place when the vertebral bodies first become differentiated.
Cells are thus formed which are added to those resulting from the segmentation proper.
The roof of the segmentation cavity appears therefore to be entirely constituted of epiblast.
In most existing Teleostei, the ovum has become again reduced in size, but the meroblastic segmentation has been preserved.
The changes which next follow result in what has been known since Remak as the secondary segmentation of the vertebral column.
In the later stages the vertical furrows extend through the whole egg, and a segmentation cavity appears between the small and the large spheres.
The segmentation cavity thus becomes enclosed between an hypoblastic floor and an epiblastic roof several cells deep.
During segmentation there arises a layer of small superficial cells (epiblast) and a central layer of larger cells, which becomes separated from the former by a segmentation cavity, except at the pole adjoining the free end of the brood-pouch.
The same ingrowth causes the obliteration of the segmentation cavity.
The market acknowledges the segmentation of family-no longer an economic entity in its own right-and in turn accentuates it.
Segmentation of work takes place concomitant with the effort to conceive of tools appropriate to each segment in order to ensure the desired efficiency.
The segmentationof life and labor, increased mediation, and expectations of high efficiency make mass production possible.
The segmentation of work in order to reach higher efficiency is not arbitrary.
The extreme segmentation of the world, its heterogeneity, the new rhythms of change and of human experiences, the continuous decline of the ideal embodied in literacy, education included, are arguments against the possibility of such a novel.
The multiplicity of food-related experiences in our time is representative of segmentation and heterogeneity in the civilization of illiteracy.
Especially interesting is the segmentation due to the excretory organs, for the evidence distinctly shows that such excretory organs have steadily shifted more and more posteriorly during the evolution of the vertebrate.
This segmentation may receive the name of visceral or splanchnic in contradistinction to somatic, since all the muscles without exception belong to the visceral group of striated muscles.
In the vertebrate the segmentation in this region is indicated by the coelomic or head-cavities, which are cavities formed in the mesoderm of the embryo, the walls of which give origin to the striated muscles of the head.
In addition to the evidence of segmentation afforded by the body-musculature in all the higher vertebrates, similar evidence is given by the segmental arrangement of parts of the supporting tissue to form vertebrae.
Such a segmentation implies a definite series of body-segments, corresponding to the mesomeric segmentation of the vertebrate, and a definite series of appendages corresponding to the splanchnic segmentation of the vertebrate.
Many palaeontologists, looking upon segmentation as indicative of gills and gill-slits, have attempted to interpret such markings as branchial segments, regardless of their position.
His papers show that the segmentation is discoidal, and results in an oval blastodermic area lying on a large mass of yolk.
The larger of the two first-formed spheres of segmentation is always turned towards the pointed end of the egg.
Until recently it was regarded as a general rule that, by the partial segmentation of the vitellus a germinal disc was formed, and in this, corresponding to the ventral surface of the embryo, a primitive band.
Thus, in Fishes, the first changes consist in the segmentation of the vitellus and the formation of a germ, processes which are common to all classes of animals.
Much of this flow is seen to be directed into the arms along the channels determined by the segmentation of the annular rim.
The segmentationof the body is anomomeristic, there being no fixed number of somites characterizing all the forms included.
The character pointed to by all these terms is that of a ring-like segmentation of the body.
The segmentation of the body is anomomeristic in the more archaic members of each class, nomomeristic in the higher members.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "segmentation" in a variety of sentences. We hope that you will now be able to make sentences using this word.
