CLASS ASTEROIDEA. 



261 



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

 are Worked by thirty-five powerful muscles— the whole 

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



CLASS III. ASTEROIDEA. 



General Characteristics.— The Asteroids (star-like) 

 have five or more radiating arms, which contain portions 



Fig. M7. 



AMenas,, Star-flsh. 



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 epeciep, like the Key-hole Urchin, are singularly modified from the typical 

 forms, a..d are hence called Irregnlar EchinoidB. 



