The wall of the heart in Insects is of mesoblastic origin, and develops from paired rudiments derived from that peripheral part of each mesoblastic band which unites the somatic to the splanchnic layer.
These lie in the perivisceral space, between the somatic and splanchnic layers of the mesoblast, and on the sides of the abdomen.
The muscular coat of the alimentary canal is contributed by the splanchnic layer of the mesoblast.
The second chief function of the splanchnic and somatic mesoderm is the production of the serous membrane investing the body cavity and its contents from the mesothelium lining the primitive coelom.
In the dorsal median line both somatic and splanchnic mesoderm become continuous with each other and with the axial mesoderm (Fig.
The connective tissue of the splanchnic mesoderm appears as an intermediate layer uniting the epithelial lining and the muscular walls.
We can now distinguish the serous lining membrane of the abdominal cavity, derived from the mesothelium of the splanchnic and somatic mesoderm as the peritoneum.
Both the somatic and the splanchnic leaf of the mesoderm consist at first solely of a layer of flattened epithelial cells, the mesothelium.
The entodermal tube and the surrounding splanchnic mesoderm forming the intestinal canal is attached along its dorsal surface to the axial mesoderm of the dorsal mid-line.
This epithelial tube is covered from without by the splanchnic mesoderm.
At the time when the heart can first be made out and before it has begun to beat, it has the form of an oval sack with delicate walls separated from the mesenteron by a layer of splanchnic mesoblast.
The inner layer may be called the splanchnic mesoblast in spite of the absence of an intestine.
The splanchnic mesoblast follows the hypoblast in its growth, and gives rise to the connective tissue and muscular parts of the walls of the alimentary tract.
The mesoblast, though at first very thin, soon exhibits a differentiation into a splanchnic and somatic layer--though the two do not become distinctly separated by a body cavity.
The splanchnic mesoblast is, according to Metschnikoff, formed independently of the somites, but this point requires further observation.
Not only so, but there is at first no marked division into a somatic and splanchnic layer with an intervening body cavity.
This mesoblastic wall is sharply separated from the muscular wall outside, which is also formed of splanchnic mesoblast.
The cavity of the outgrowths forms the body cavity, and the walls of the outgrowths the somatic and splanchnic layers of mesoblast (fig.
The splanchnic layer of the head cavity gives rise to the musculature of the oesophagus.
In Clepsine the mesoblastic bands are stated by Kowalevsky to become split into somatic and splanchnic layers, between which are placed the so-called lateral sinuses.
One of them forms part of the body wall and is known as the somatic mesoblast, the other forms part of the wall of the viscera and is known as the splanchnic mesoblast.
Such are what have been called the Invertebrate animals, which are consequently, in accordance with their physiological signification, Splanchnic or Tegumentary animals.
The splanchnic or visceral teeth obviously rank lower than the membral teeth.
The more irritable the nerves are, by so much the more animal does the vegetable organism, or the splanchnic system, therefore become; so much the less is it produced on the mass.
The liver excretes the product which results from the splanchnic circulation; the systemic circulation has its organ also, but one which does not secrete a special, but general product.
Now, as these tegumentary formations, being surrounded in the higher animals by flesh, were thus viscera, so may the vegetative nerves be called also Visceral or Splanchnic nerves.
The splanchnic or visceral nerves are also distinguished from the animal by their being in a constant state of tension, and hence keeping the processes of their system in constant repair.
Thus the secernent organ of the general circulation must belong to the sexual system, and perform in it that which the liver, or in other words the reverse of the lungs, has done in the splanchnic circulation.
The three last divisions may be called visceral or splanchnic bones; and then we have tegumentary, splanchnic, and nerve-bones.
Prostitution is here accepted and viewed with no serious disfavor, but the prostitute herself is, nevertheless, treated with contempt.
Let us halt at the origin of the splanchnic and take a look.
It shews the general features of the layers during the stage, more especially the differentiation of somatic and splanchnic layers of the mesoblast.
Early formed band of muscles from the splanchnic layer of the muscle-plates.
The globulin has a paralysing influence on the heart, the vasomotor centres, the peripheral ends of the splanchnic nerves, as well as on the respiratory centres of both warm and cold-blooded animals.
The diarrh[oe]a and hyperaemia of the internal abdominal organs have been referred to a paralysis of the splanchnic nerves, but Esser considers them due to an irritation of the ganglia in the intestinal walls.
In my former volume on the Lepadidae, I quite misunderstood the course of these splanchnic nerves.
The great pair of splanchnic nerves springing from its under side, are here actually twice as large as the circa-[oe]sophageal chord.
The pair of great splanchnic nerves above alluded to, which arise from the anterior and dorsal surface of the infra-[oe]sophageal ganglion, are in Pl.
I have called the nerves (dd, ee) splanchnic and supra-splanchnic, from their course and apparent function in supplying the viscera.
Separate Spigelian lobe from stomach, and look for vagus nerve descending by oesophagus, solar plexus around the superior mesenteric artery, and thrown up very distinctly by the purple vena cava inferior beneath, and the splanchnic nerve.
In the parietal region a cavity has now appeared in part of the trunk between the splanchnic and somatic layers of the mesoblast (Plate 36, fig.
The proctodaeum is surrounded by a great mass of splanchnic mesoblast.
The superficial layer on the dorsal side is continuous with the somatic mesoblast, while the remainder pertains to the splanchnic layer.
At the present stage the splanchnic mesoblast, apart from the septa, is a delicate membrane of flattened cells (fig.
This mass of cells has now become divided into a somatic and splanchnic layer (Pl.
The origin of this lining layer I could not certainly determine, but its connection with the splanchnic mesoblast suggests that it is probably a derivative of this[314].
It may be called either the subintestinal or splanchnic vein.
The first trace of the heart becomes apparent during stage G, as a cavity between the splanchnic mesoblast and the wall of the gut immediately behind the region of the visceral clefts (Pl.
Each mesoblastic somite is formed of a distinct somatic layer closely attached to the epiblast, and a thinner and less well-marked splanchnic layer.
Along the line of insertion of each of these septa there is developed a considerable space between the somatic and splanchnic layers of mesoblast.
At the junction between the successive somites the splanchnic mesoblast on each side of the abdomen dips down into the yolk and forms a septum (Pl.
In the intervals between these venous spaces the somatic and splanchnic layers of mesoblast are in contact with each other.
The outer or somatic wall becomes very thin indeed, the splanchnic wall, on the other hand, thickens and forms a layer of several rows of elongated cells.
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.
The muscles of the appendages are formed from the ventral part of the original procoelom, just as I have argued is the case with the muscles of the splanchnic segmentation in vertebrates.
In this region, as already mentioned, the evidence of segmentation is based more clearly on the somatic than on the splanchnic segments.
These two sets of muscle-segments correspond in the vertebrate to the somatic and splanchnic segmentations.
IVth nerve and muscle lost, there must have been also seven corresponding ventral or splanchnic segments supplied by the trigeminal.
It was the stone that was an index of what has been called "the blues" or what one modern writer has dignified by the title "splanchnic neurasthenia.
Most of them are banished by frequent hearty laughter which, with its exercise of the diaphragm, tends to stimulate splanchnic blood vessels and nerves.
From thesplanchnic layer are formed (1) A great part of the voluntary muscular system.
The outer or somatic layer of the vertebral plates is formed of a single row of cells, but the inner or splanchnic layer is made up of a kernel of cells on the side of the somatic layer and an inner layer.
The splanchnic layer of the plates buds off cells to form the rudiments of the vertebral bodies which are at first segmented in the same planes as the mesoblastic somites (fig.
The arterial trunk is a branch of the dorsal aorta, and the venous trunk originally falls into the heart together with the subintestinal or splanchnic vein.
Its walls are formed ofsplanchnic mesoblast with blood-vessels, within which is a lining of hypoblast.
The undivided ventral portion gives rise to the general somatic and splanchnic mesoblast (fig.
On the formation of the lateral folds of the splanchnic walls, the two halves of the heart become carried inwards and downwards, and eventually meet on the ventral side of the throat.
The cavity of the heart may thus be described as being formed by a hollowing out of the splanchnic mesoblast, and resembles in its mode of origin that of other large vascular trunks.
According to Todaro's statements, it is replaced by a second cavity, which appears between the splanchnic and somatic layers of mesoblast, and constitutes the true body cavity.
While the true splanchnic stalk of the yolk-sack is becoming narrow, a somatic stalk connecting the amnion with the walls of the embryo is also formed, and closely envelops the stalk both of the allantois and the yolk-sack.
Thus both layers of the muscle plate are concerned in forming the great longitudinal lateral muscles, though the splanchnic layer is converted into muscles very much sooner than the somatic[245].
As there is always more or less paresis and dilatation of the large veins of the splanchnic system, a tight bandage about the abdomen is of great advantage in raising the blood pressure to the safety mark.
When the splanchnic vessels are dilated there is also a lack of proper tone to the cerebral vessels, and this may be a cause of mental weariness and neurasthenia.
The consequence is contraction of the splanchnic blood vessels, with a rise in general blood pressure.
As has been shown, arteriosclerosis of the splanchnic vessels not infrequently occurs, and an embolus or thrombus may completely occlude the superior mesenteric artery.
It is held by some authors that the great splanchnic area is capable of holding all the blood in the body and in respect of its liability to arteriosclerosis, it is second only to the aorta and coronary arteries.
Further, they have been unable to find at autopsy on man a definite association between sclerosis of the abdominal aorta and great splanchnicvessels and cardiac hypertrophy.
Among others, Janeway has shown that general arteriosclerosis without marked disease of the splanchnic vessels does not cause as a rule increase of blood pressure.
It has been shown that sclerosis of thesplanchnic vessels may be due to constant irritation of toxic products elaborated in digesting constantly enormous meals.
This I believe to be a potent cause of splanchnic arteriosclerosis with the resulting indigestion, cramp-like attacks, high blood pressure, etc.
The enormous number of such vessels in the mesentery and intestines explains the ability of the splanchnic area to accommodate the greater part of the blood in the body.
It has been stated that arteriosclerosis of the splanchnic vessels almost invariably causes high tension.
The fact that the vessels in the splanchnic area are frequently attacked by sclerotic changes means, as a rule, increase of work for the heart.
Lying face downward with a pillow under the abdomen presses the blood out of the congested splanchnic circulation.
In an erect posture the abdominal muscles tend to remain taut and to afford proper support or pressure to the abdomen, including the great splanchniccirculation of large blood-vessels.
