. The physiology of the Invertebrata. water currents inthe Porifera have a circulatory function, they also performthe functions of respiration and digestion. The Ccelenterata. In these animals the blood or nutritive fluid is not con-tained in any vessels, but is free in the somatic cavity orenteroccele. This fluid is moved by the contractions of thebody, and, generally, by cilia developed on the endodermallining of the enteroccele. By this means a kind of circula-tion is constantly maintained. The movements of the bodyof the animals belonging to the Ccelenterata cause a move-ment of the corpus
. The physiology of the Invertebrata. water currents inthe Porifera have a circulatory function, they also performthe functions of respiration and digestion. The Ccelenterata. In these animals the blood or nutritive fluid is not con-tained in any vessels, but is free in the somatic cavity orenteroccele. This fluid is moved by the contractions of thebody, and, generally, by cilia developed on the endodermallining of the enteroccele. By this means a kind of circula-tion is constantly maintained. The movements of the bodyof the animals belonging to the Ccelenterata cause a move-ment of the corpusculated blood in the body cavities, a fluxand reflux, a flowing and an ebbing of the nutritive is the most general form of circulation. There are no PHYSIOLOGY OF THE JNVERTEBRATA. 185 vessels and no special pumping apparatus, for the whole bodyis concerned in the performance of this function. In the6ompound Gcelenterata, this motion of the corpusculated fluidof the body cavity affects also the fluid in those extensions of. Fig. 35.—Circulation in Medusa. the body cavities, through the common flesh or ccsnosarc,that place in communication the interiors of the variousmembers of the compound animal. ^^S- 35 represents the circulatory system in the Meduscc. The Echinodeemata. All the Echinodermata are furnished with distinct organsof circulation, consisting of a heart or corresponding organ,and a complicated system of vessels. This circulatory systemconsists of two vascular rings surrounding the orifice of thedigestive tube. These rings are connected with each other,they emit radiating ramifications, and one of them receivesvessels proceeding from the intestine. Such is a generaldescription of the circulatory apparatus in the Echinodermata,but since the time of Cuvier and Tiedemann the presenceor absence of a blood-vascular system in the Asteridea hasbeen alternately asserted and denied. The investigations ofGreef,* Hoffmann,f and Teuscher| are in favour of the * Marh
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectinverte, bookyear1892
