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Updated: August 19, 2024
In general, it is certain that the greater part of the cells that compose the vessels and their contents come from the mesoderm in fact, from the gut-fibre layer; it was on this account that Baer gave the name of "vascular layer" to this visceral layer of the coeloma. But other important observers say that a part of these cells come from other germinal layers, especially from the gut-gland layer.
"If we don't catch us somebody, soon..." Out here, the needs could get truly primitive. Oxygen, water, food, repair parts for vital equipment. Cannibalism and blood-drinking could also be part of blunt necessity. Nelsen and Ramos were fortunate. Twenty miles off was a haze against the stars a cluster of small mesoderm fragments.
It seems to be true that blood-cells may be formed from the cells of the entoderm before the development of the mesoderm. In this we see clearly how a number of stellate cells proceed from the "vascular layer" and spread in all directions in the "primary body-cavity" i.e. in the spaces between the germinal layers.
But our bones and muscles and blood-vessels all come from the mesoderm by folding, plaiting, and channelling, and division of labor resulting in differentiation of structure. Of all true mesodermal structures the hydra has actually none, but in the ectodermal and entodermal cells he has the potentiality of them all.
It is incontestable that the musculature of the Vertebrates has been evolved from that of lower Invertebrates; and among these we have to consider especially the unarticulated Vermalia. They have a simple cutaneous muscular layer, developing from the mesoderm.
It would have been rough going for them to try to sleep in beds. They had lost the habit. They slept inside their new Archer Fives. Afterwards they painted their armor a dark grey, like chunks of mesoderm stone. They did likewise to the two bundles in which they wrapped their relics. They were as careful as possible to get away from the post without being observed, visually or by radar.
Maybe they thought that they would be located and picked up the gang that had robbed and dumped them had found them easily enough. But there, again, was a paradox of enormity. Bands might wait for suckers somewhere beyond Mars. Elsewhere, there could be nobody for millions of miles. They saw their first asteroid a pitted, mesoderm fragment of nickel-iron from middle-deep in the blasted planet.
In all the Craniotes the soft, indifferent cells of the mesoderm, which originally compose the skeletal plate, are afterwards converted for the most part into cartilaginous cells, and these secrete a firm and elastic intercellular substance between them, and form cartilaginous tissue.
In their more advanced mesoderm we find a few contractile longitudinal canals which force the blood through the body by their contractions; these are the first blood-vessels. Transverse section of the branchial gut. A of Balanoglossus, B of Ascidia. r branchial gut, n pharyngeal groove, asterisk ventral folds between the two.
But between the two germinal layers a mesoderm is developed, a soft mass of connective tissue, in which the organs are embedded. The Turbellaria are still represented by a number of different forms, in both fresh and sea-water. The surface is covered with ciliated epithelium, a stratum of ectodermic cells.
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