296 MASTICATORY APPARATUS. 



termed Pedicellariae is totally unknown. Some 

 writers think they are an integral part of the Echinus, 

 others describe them as distinct and parasitic animals. 

 There is good reason to believe that the former will 

 eventually be proved to be the correct explanation 

 of the matter. 



Its masticatory apparatus is not the least wonder- 

 ful portion of the Sea-Urchin. The teeth, five in 

 number, which may frequently be seen protruding 

 from the mouth, are of extreme hardness, and of 

 seemingly disproportionate length. They are not 

 fixed in sockets as ours are, or they would be speedily 

 worn away by their action on the shelled mollusca 

 upon which the animal feeds, but fresh substance 

 is added to each tooth as fast as it is worn away 

 by use, as in the case of many gnawing animals. 

 ' In order to allow of such an arrangement, as well 

 as to provide for the movements of the teeth, 

 jaws are provided, which are situated in the in- 

 terior of the shell, and these jaws, from their great 

 complexity and unique structure, form perhaps the 

 most admirable masticating instrument met with in 

 the animal kingdom. The entire apparatus removed 

 from the shell consists of the following parts. There 

 are five long teeth, each of which is enclosed in a 

 triangular bony piece, that for the sake of brevity 

 we will call jaws. The five jaws are united together 

 by various muscles, so as to form a pentagonal 

 pyramid, having its apex in contact with the oval 



