OEGAXS OF MASTICATION. 



185 



the mouth of those animals that feed on solid substances, 

 which serve for cutting or bruising the food into small frag- 

 before it Fig. 189. 



is Swallowed ; Aorta . Thoracic duct. Lymphatic glands. 



and, in many of 

 lower ani- 

 mals, these or- 

 v the only 

 hard portions of 

 the body. This 

 process of subdi- 

 viding or chew- 

 ing the food is 

 termed mastica- 



335. Begin- 

 ning witli the 

 radiata, we find 

 the apparatus 

 for mastication 

 partaking of the 

 like ar- 

 rangement 

 which character- 

 izes those animals. Thus, in the Scutella (fig. 190), we have a 

 pentagon composed of five triangular jaws, converging at their 

 summits towards a central aperture corresponding to the 

 mouth, each one bearing a plate or tooth, like a knife-blade, 

 fitted by one edge into a cleft. The five jaws move towards 

 the centre, and pierce or cut the objects which come between 

 them. In some of the sea-urchins, Echinidce, this apparatus, 

 which has been called Aristotle's lantern (fig. 191), consists of 

 Fig. 190. Fig. 191. 



Roots of 



the chy- 



liferona 



vessels. 



-- Intestine. 



Mesenteiy 



