It exhibits frequent changes of form, the reticulum vanishes, its membrane becomes gradually absorbed, its outline indented and indistinct, and finally its contents become to a certain extent confounded with the vitellus (fig.
The yolk is contained in the meshes of this reticulum in the manner already described for other ova.
The masses form the basis for the new nuclei, and become reconverted into an ordinary nuclear reticulum after repeating, in the reverse order, the changes of form undergone by the reticulum previous to its division.
The protoplasmic reticulum of the embryonic germinal vesicle may in some instances be retained till the ovum is nearly ripe, but usually assumes a very granular form.
The germs or cells which give rise to the vermiform embryos originate endogenously in the protoplasmic reticulum of the axial hypoblast cell.
In it are a number of loose oval cells, which soon become stellate, and form a mesoblastic reticulum connecting the body wall and central cells of the embryo, which may now be spoken of as hypoblast.
In the germinal vesicles of very young ova the reticulum is often absent.
The psalterium is sharply constricted off from the reticulum and is an elongated chamber showing little trace of the longitudinal ridges characteristic of this region; it opens directly into the relatively small abomasum.
Further, we find that thereticulum within the nucleus is made up of two very different parts.
Like the latter, it is made of fibres, which form a reticulum (Fig.
One portion is apparently identical with the reticulum of the cell substance (Fig.
Within the meshes of this thread or reticulum there is found a liquid, perfectly clear and transparent, to whose presence the liquid character of the protoplasm is due (Fig.
In this way the nerve trunks are developed--by a gathering up, so to speak, of the fibres of the reticulum into bundles.
These structures arise from the mesoblastic reticulum already described (Sedgwick, Quart.
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.
Then follows an exudation of a serous fluid at one or more points in the papule, the meshes of the reticulumbeing so stretched and torn that small chambers are formed filled with the liquid exudate containing granules.
The fibrous network resembles the reticulum of a lymphatic gland, and nuclei are often found at those points where the fibres are united.
The giant-cells, the epithelioid cells, and the well-characterized reticulum appear as the tubercle increases in age.
The neighboring epithelia become granular, divested of their cement envelope, and transformed into protoplasmic clusters still connected with the living reticulum by slender threads.
In this fibrous reticulumare many spindle-shaped and a few rounded cells.
There is, in brief, a liquefaction of the glue-giving basis-substance, which makes visible the reticulum of living matter formerly hidden within it.
One of the most interesting points in Klein's paper, as well as in those of Heitzmann and Eimer, is the demonstration of a connection between the reticulum of the nucleus and fibres in the body of the cell.
There is a special layer of protoplasm surrounding the nucleus, while the remainder of the protoplasm consists of a reticulum holding together the yolk-spherules.
Its contents are rendered granular by reagents though quite clear when fresh, and the reticulum of the earlier stages is sometimes with difficulty to be made out, though in other instances fairly clear.
A reticulum is very conspicuous in the germinal vesicle in the freshly formed ova, but becomes much less so in older ova, and assumes, moreover, a granular appearance.
The absence of thereticulum does not, of course, mean that the substance capable of forming a reticulum is absent, but merely that it does not assume a particular arrangement.
The contents are clear but traversed by a very distinct and deeply staining reticulum of fibres connected with the several nucleoli which are usually present and situated close to the membrane.
The protoplasm of the cells composing it forms a loose reticulum with a fair number of oval or rounded nuclei, with their long axis for the most part parallel to the lower surface of the epithelium.
The second stomach or reticulum is also deeply grooved.
From this bag (the paunch) in the act of rumination a certain portion of the food is ejected into the second chamber, which is termed the reticulum (i.
After the remasticated food has reached the manyplies, the groove in the reticulum is pushed open by a fresh bolus, and so the process is repeated until the food consumed has all passed on towards the abomasum or true digestive stomach.
These balls are found most frequently in the reticulumor second stomach (Pl.
In the types in which the notochord persists in the adult the mesh-work becomes highly complicated, and then forms a peculiar reticulum filled with gelatinous material, the spaces in which do not indicate the outlines of definite cells (figs.
Cell membrane Cytoplasm Chromatin Mitochondrion Nucleolus Endoplasmic reticulum Nucleus Nuclear membrane The basic structure of a cell is shown in Figure 2.
This membranous network is called the endoplasmic reticulum and is distinct from the mitochondria, which are membranous organelles (little organs) structurally independent of other components of the cytoplasm.
For instance, the red cells of the blood do not have a nucleus, and in other cells the endoplasmic reticulum is at a minimum.
The reticulumis the smallest, with a capacity of about one-half gallon.
Cattle may suffer from traumatic pericarditis caused by sharp, pointed, foreign bodies passing through the wall of the reticulum and penetrating the pericardial sack.
