. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 654 CIRCULATION. mosing vessels. The larger parts of the longi- tudinal vessels have been observed to contract and dilate; but neither a regular progressive circulation, nor a connection of the vascular with any distinct respiratory system has as yet been detected. Entosoa.—In the Entozoa, organs of circu- lation somewhat similar to those just mentioned in the Planariae have been found by Bojanus and Mehlis in the Distoma and Tristoma, and by Nordmann* in those remarkable small Entozoa inhabiting the aqueous chamber of t
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 654 CIRCULATION. mosing vessels. The larger parts of the longi- tudinal vessels have been observed to contract and dilate; but neither a regular progressive circulation, nor a connection of the vascular with any distinct respiratory system has as yet been detected. Entosoa.—In the Entozoa, organs of circu- lation somewhat similar to those just mentioned in the Planariae have been found by Bojanus and Mehlis in the Distoma and Tristoma, and by Nordmann* in those remarkable small Entozoa inhabiting the aqueous chamber of the eyes of some quadrupeds, the Diplosto- mum, and in the Diplozoon. In the first of these animals, the motion of fluid in the vas- cular system is exceedingly obscure; but in the Diplozoon (fig. 328), Nordmann saw, with Fig. Diplozoon. a high magnifying power, currents moving in opposite directions in two sets of vessels («, v) placed on each side of both limbs of the ani- mal. These vessels, termed external and in- ternal, are said to terminate posteriorly in a dilated bag, to which Nordmann gives the name of receptacle of the chyle. The organs of circulation of the Diplozoon differ, there- fore, in this respect from those of the Plamiria, to which otherwise they bear considerable si- milarity; for, in the latter animal, the vascular system appears to be entirely closed. Accord- ing to Nordmann and Ehrenberg no contrac- tions or dilatations of the vessels are visible. Acalephts.—In some of the Medusa tribe, or Acalephae, there appears to be no distinct circulatory apparatus; and we observe that in these instances, the alimentary cavity is of great extent and is often much ramified on the surface of the animal. In others there are distinct vessels with a * Micographische Bcitrago, p. 69. Berlin, 1832. circulation of fluid within them. The distri- bution of this very simple kind of vascular system was first discovered byEschscholtz, who has described its form partic
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