PHYSIOLOGY OF THE JNVERTEBRATA. 185 



vessels and no special pumping apparatus, for the whole body 

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

 6ompound Gcelenterata, this motion of the corpusculated fluid 

 of 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 various 

 members of the compound animal." 



^'^S- 35 represents the circulatory system in the Meduscc. 



The Echinodeemata. 



All the Echinodermata 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, 

 they emit radiating ramifications, and one of them receives 

 vessels proceeding from the intestine." Such is a general 

 description of the circulatory apparatus in the Echinodermata, 

 but since the time of Cuvier and Tiedemann " the presence 

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

 been alternately asserted and denied." The investigations of 

 Greef,* Hoffmann, f and Teuscher| are in favour of "the 



* Marhurg Sitxungsherichte, 187 1-2. 

 t Niederlandisches Archiv, vol. 2. 

 J Jenaische ZeiUclirift, vol. 10. 



