ECHINIDJZ. 283 



from the presence of shells, fragments of corals, crustaceans, and 

 even other Echinodermata in their intestinal tube, it is to be inferred 

 that a certain number of them at least are carnivores, or flesh-eaters, 

 while others are supposed on the same evidence to be vegetarians. 

 The organs of respiration of the Echinidae appear to be certain 

 flattened vesicles in the form of very delicate laminae, which adhere 

 to the internal surface of the walls of the body, and float freely in the 



Fig. 117. Skeleton and Masticating Apparatus of Clypeaster rosaceus. 



liquid with which the visceral cavity is filled. These organs, known 

 as the internal branchia, are in communication with the central canal 

 and ambulacral tubes. The heart is spindle-shaped, tapering above, 

 swelling out below. There are two distinct vascular systems, one 

 intestinal, the other cutaneous. 



The nervous system consists of a ring, which surrounds the gullet, 

 and is placed at a short distance from the mouth. In this ring the 

 nervous trunks have their origin. In reference to the senses, we may 

 observe that that of touch is highly developed. Certain forms called 



