226 THE POPULAR SCIENCE MONTHLY. 



chin is remarkable as the first animal, and below mollusks and articu- 

 lates the only animal, possessing any organs for mastication. Further- 

 more, its dental apparatus is perhaps of greatest complexity in the 

 whole animal kingdom. Five triangular teeth set in as many jaws sur- 

 round the opening to the stomach, and move toward a central point. 

 They seize and divide the food which then passes between the masti- 

 cating jaws. The latter are grooved, and, aided by saliva, effectually 

 crush and grind the food. The muscles and levers necessary to effi- 

 cient action are numerous and intricate, altogether forming an appara- 

 tus entirely unique in form and principle. 



Among mollusks the gasteropods or snails, and the cephalopods, 

 which include the cuttle- and devil-fishes, have masticating organs. 

 Most snails have thousands of minute teeth on the tongue. These are, 

 however, chiefly used for procuring food by a rasping or boring mo- 

 tion. But some snails, not satisfied with lingual teeth alone, indulge 

 the absurdity of carrying powerful teeth in the stomach. The beak of 

 the cuttle-fish divides the food somewhat, but the masticating process 

 is mainly performed by a gizzard. 



Articulates have a much greater variety of masticating organs. 

 Nearly all, even some of the worms, have efficient jaws for seizing 

 food, which also serve to cut and crush the same. 



Fig. 3. Jaws and Pavement-teeth of a Rat (Mylioba(es). 



Imagine a creature with so little regard for the proprieties as to 

 chew food with its legs ! Yet the common limulus, or " horseshoe 

 crab," actually grinds the food between its thighs. However, this is 

 not so strange, when we understand that the claws of the lobster and 

 crab are simply modified legs ; and that many higher animals, the 

 squirrel and cat, for instance, use their feet in eating. 



Another group of crustaceans, the little rotifers, pound their food. 

 The lower jaw serves the purpose of an anvil upon which the food is 

 crushed by two hammers formed from the upper jaw. Lobsters and 

 crabs masticate with their horny jaws ; but they all have complete and 

 efficient sets of teeth in the gizzard-like stomach. And, when the shell 

 is cast, the teeth are also shed along with the stomach-lining. Those 



