CLASS ASTEEOIDEA. 



261 



like the incisors of a rodent, are constantly renewed. These 

 are worked by thirty-five powerful muscles the wbol 

 apparatus being known as "Aristotle's lantern."' 



CLASS III. ASTEROIDEA. 



General Characteristics. The Asteroids (star-like) 

 have five or more radiating arms, which contain portion* 



Fig. UU1. 



Astenas, Star-fish. 



of the viscera. Their mouth and locomotive suckers are on 

 the lower side the former without teeth, digestion being 

 performed by the animal's -turning its stomach out of its 



* Some species, like the Key-hole Urchin, are singularly modified from the typical 

 forms, and are hence called Irregular Echinoids. 



