PHYSIOLOCY OF THE INVERTEBRATA. 185 



vessels and no special pumping apparatus, for the whole body 

 is concerned in the performance of this function. " In the 

 compound Calcnfcr(it((, this motion of the coi-pusculated liuid 

 of the body cavity affects also the fluid in tliose extensions of 



Fin. 35. — CiK( ii.ATiox IN Medls.*:. 



the body cavities, through the common flesh or ccenosarc, 

 that place in communication the interiors of the various 

 members of the compound animal." 



Fig. 35 represents the circulatory system in the Mcduscc. 



The ECHINODERMATA. 



All the Ediinodcrmata are furnished with distinct organs 

 of circulation, consisting of a " heart or corresponding organ, 

 and a complicated system of vessels. This circulatory system 

 consists of two vascular rings surrounding the orifice of the 

 digestive tube. These rings are connected with each other, 

 thev emit radiatino^ ramifications, and one of them receives 

 vessels proceeding from the intestine." Such is a general 

 description of the circulatory apparatus in the Erhinodermata, 

 but since the time of Cuvier and Tiedemann " the presence 

 or absence of a blood-vascular system in the Adcridca has 

 been alternately asserted and denied." The investigations of 

 (Jreef,* Hoffmann, f and Teuscher:}: are in favour of "the 



* JIarburf/ Sitzungsberichte, 187 1-2. 

 t Xiederh'i iKJisrhes Archlv, vol. 2. 

 X Jenaincht Zvifxrhrift, vol. lo. 



