MOLLUSCA. 21 



vegetable feeders, you can tell me how they 

 manage. 



Child. The snail feeds upon vegetables, it 

 crawls upon its fleshy foot till it reaches a plant, 

 and then gnaws it with its jaws. 



Teacher. The animal feeders stretch out 

 their proboscis and catch hold of their prey, and 

 some grasp it with their tentacula, and thus 

 bring it within reach of their mouths. Those 

 mollusks which have only an opening, have a 

 supply of food brought to them by the continued 

 movement of the waves and the flowing of the 

 tides, and you must remember my telling you 

 of some who ingeniously increase this supply by 

 creating an eddy in the water. I have brought 

 you an oyster and a snail, and wish you to com- 

 pare them together, and tell me what appears to 

 you to be the most striking difference between 

 the two. 



Child. The snail has a head, but the oyster 

 is only as oft lump of flesh, and has no appear- 

 ance of a head. 



Teacher. Many of the mollusks like the 

 oyster, have no obviously distinct head. This 

 circumstance has led naturalists to divide these 

 animals into two great classes. How should 

 you think they are distinguished ? 



Child. One class contains those mollusks 

 which have heads ; the other, those which are 

 destitute of heads. 



Teacher. The former are called mollusca 

 cephala from the Greek /ce^aXj (kephale) a head; 

 the latter, mollusca acephala from the Greek 



