The next section of the alimentary tract is the stomach or mesenteron (fig.
I failed to find any trace of an anterior part of the mesenteron adjoining the stomodaeum.
In Crustacea the proctodaeum and stomodaeum, especially the former, are very long, and usually give rise to the greater part of the alimentary tract, while the mesenteron is usually short.
I must, in fact, admit that I have hitherto failed to work out satisfactorily the history of the mesenteron and its appendages.
In the Tracheata the mesenteron is always considerable, and the proctodaeum is always short.
The mesenteron has as yet hardly commenced to be developed.
From the condition of the mesenteron at this stage there can be but little doubt that it will be formed, not on the surface, but in the interior of the yolk.
A layer of epithelial cells is thus formed on the ventral side of the mesenteron which very soon becomes raised into a series of longitudinal folds, one of which in the middle line is very conspicuous.
An oral invagination on the flattened ventral side meets the mesenteron after its separation from the vaso-peritoneal vesicle.
The solid yolk in the Isopods on this view represents the primitive mesenteron of Decapods after the yolk has been absorbed by the hypoblast cells.
The glandular walls of the mesenteron are formed from the hypoblast; but the exact origin of the layer has not been thoroughly worked out in all cases.
The mesenteron is represented as a closed sack filled with yolk cells.
In Chironomus the mass of yolk external to the mesenterontakes the form of a median and two lateral streaks.
Some of the hypoblast cells adjoining the junction of the proctodaeum andmesenteron become flattened, and in the neighbourhood of these cells a lumen first appears.
The hypoblastic walls of the mesenteron appear to be formed in the first instance laterally (fig.
By this rupture themesenteron is placed in communication with the exterior by the opening at m, while at the same time the tentacles of the water-vascular ring (t) project freely to the exterior.
The forward extension of themesenteron is remarkable.
There early grow out from the walls of the mesenteron a pair of hepatic diverticula.
The lateral parts of the primitive mesenteron become constricted into four wings, two directed forwards and two backwards; these, after the yolk in them has become absorbed, constitute the liver.
The lateral parts of the dorsal side of the mesenteron similarly give rise to hepatic cylinders.
While the mesoblastic somites are becoming formed the dorsal wall of the mesenteron develops a median longitudinal fold (fig.
The front portion of the mesenteron gives rise to the oesophagus, stomach and duodenum.
The growth inwards of the dorsal wall of the mesenteron is no doubt in part a true invagination, but it seems probable that it is also due in a large measure to an actual differentiation of yolk-cells along the line of growth.
The general arrangement of the parts, at the time when the hind end of the mesenteron is first closed, is shewn in fig.
The invagination of the mesenteron has in the meantime extended very far forwards, and the segmentation cavity has become obliterated.
The communication between the stomodaeum and the mesenteron is effected comparatively early (on the 4th day in the chick), while that between the proctodaeum and mesenteron does not take place till very late (15th day in the chick).
At the time of the folding in of the hinder end of the mesenteron the splitting of the mesoblast into somatopleure and splanchnopleure has extended up to the border of the hinder division of the primitive streak.
The posterior part of the primitive respiratory division of the mesenteron becomes, in all the higher Vertebrata, the oesophagus and stomach.
The yolk-cells adjoining the opening of the mesenteron are the latest to be covered in, and on their enclosure this opening constitutes the whole of the blastopore.
The definite closing in of the mesenteron by the true hypoblast-cells commences in front and behind, and takes place last of all in the middle (fig.
The mesenteron now rapidly extends by the invagination of the cells on its dorsal side.
Between the mandibular and the hyoid, and between each of the following arches, pouches of the mesenteron push their way towards the external skin.
In the formation of the neurenteric canal, there is no free passage leading into the mesenteron from the exterior as in Amphibia (fig.
The branchial region of the mesenteron becomes established, and causes a dilatation of the anterior part of the body, and the branchial pouches grow out from the throat.
The external opening of this passage finally becomes obliterated, and the passage itself is left as a narrow diverticulum leading from the hind end of the mesenteron into the neural canal (fig.
From the mesenteron there might be pouch-like or tubular outgrowths.
This idea of an enlarged mesenteron certainly has much to commend it, and such actual evidence as exists seems in favor of rather than against it.
The main branches of the latter enter the mesenteron just behind the fifth pair of cephalic appendages.
The mesenteron and its sheath crowd so closely against the dorsal test in the anterior part of the thorax that there seems to be no room for the heart, but it must have been located beneath the sheath and above the alimentary canal.
Behind the enlarged portion, the mesenteron appears to have been of practically uniform diameter in Cryptolithus, but to have tapered posteriorly in Ceraurus and Calymene.
Melanosilpha capensis, South Africa (Harrison, 1955): All specimens of this gregarine were found in the anterior mesenteron of the host.
The gregarines were found in the anterior mesenteron but none in the hepatic caeca.
Melanosilpha capensis, South Africa (Harrison, 1955): This gregarine was found in the anterior and middle parts of the mesenteron and in the hepatic caeca.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "mesenteron" in a variety of sentences. We hope that you will now be able to make sentences using this word.
