ECHINID. 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 Echinide appear to be certain 
flattened vesicles in the form of very delicate laminz, 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 dranchie, 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 
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