ECHINODERMATA. 



287 



I never could understand why the dental framework of the sea- 

 urchin has been called Aristotle's Lantern, for this formidable apparatus 

 resembles the front view 

 of a battery of cannon 

 more than a lantern. It 

 consists of a series of 

 pieces designated by the 

 names of compass, scythe, 

 pyramid, and plumula, 

 which it would serve no 

 useful purpose to de- 

 scribe. 



We have said that the 

 mouth of the urchin is 

 monstrous in proportion 

 to its size, and the teeth 

 of proportionate dimen- 

 sions. As these project 

 from a very formidable 

 mouth, one can easily 

 be assured of the sharp- 

 ness of their extremities 

 by intruding his fingers on them. In fact, it is nepessary that 

 these organs should be singularly powerful, because, as we shall see 

 farther on, the sea-urchin makes incisions in the solid rock with 

 them, and hollows out shelter for himself. The strong and sharp 

 teeth grow at the base in proportion as thpy are used at the points, 

 as is the case with some of the rodent mammalia. By this means 

 they are always sharp and in good condition. Five groups of power- 

 ful muscles are used to work these terrible grinders. 



To this formidable mouth is attached an oesophagus or gullet, and 

 an intestine which extends along the interior walls of the carapace, 

 describing the circumference of its principal contour. 



The regimen of the Echinidae is still imperfectly known ; neverthe- 

 less, 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 carnassiers, or 

 flesh-eaters, while others are supposed on the same evidence to be 



Fig. 117. Clypeaster rosaceus (Lamarck). 



