MOLLUSCA. 21 



of watching some of the mollusks which are vege- 

 table 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 mol- 

 lusks which have only an opening, have a supply 

 of food brought to them by the continued move- 

 ment 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 compare 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 a soft lump of flesh, and has no ap- 

 pearance of a head. 



Teacher. Many of the mollusks, like the 

 oyster, have no 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 

 without heads. 



Teacher. The former are called mollusca 

 cephala from the Greek K<paXy (kephale) a head ; 

 the latter, mollusca acephala from the Greek 



