MOLLUSCA. 27 



instrument is a fleshy pliable tube, terminated 

 by a round aperture, with a cartilaginous edge 

 armed with little teeth. The proboscis is sup- 

 plied with muscles, by which the animal can 

 protrude and draw it in at pleasure. Many use 

 it to pierce the shells of other mollusca, that 

 they may suck out the flesh of the inhabitant. 

 The mollusca possess also different means of 

 bringing their food to their mouths ; some make 

 use of tentacula to grasp their prey; others 

 stretch out their proboscis ; and some, you re- 

 member, insure a frequent supply of food by 

 creating an eddy in the water.* I should like 

 you now to compare the oyster and the snail 

 together, and tell me what you consider to be 

 the most striking difference between them. 



Child. The snail has a head, but the oyster 

 appears only a lump of flesh without any division 

 in its body. 



Teacher. This is the case with a large num- 

 ber of mollusca ; they have no obviously distinct 

 head. This circumstance has induced naturalists 

 to divide them into two great classes. What do 

 you think they are ? 



Child. One class would consist of those 

 animals which have heads ; the other of those 

 destitute of heads. 



Teacher. The former are called mollusca 

 ctphala, from the Greek K^aA? (kephale) a head ; 

 the latter, mollusca acephala, from the Greek a 



* The children should give a recapitulation of this account of the 

 animal. It may either be a viva voce repetition, or written on their 

 lates. 



