MOLLUSCA. 13 



the water either tentacula or expansions of the 

 skin? 



Teacher. No ; some have no such elongated 

 parts. I think you might have discovered this 

 yourselves by observing one of the animals 

 before you. 



Child. Oh yes, the oyster. Such mollusks 

 cannot move then. 



Teacher. That is not true of all, some are 

 immoveably attached to the spot where they 

 first received life ; but others have the power of 

 leaping or shifting their positions with a sudden 

 jerk, produced by rapidly shutting the two 

 pieces of their shells ; others again transport 

 themselves from one spot to another by the force 

 with which they draw in and eject the fluid in 

 which they live. Many species are furnished 

 with a kind of bladder by inflating or contract- 

 ing which they can rise or sink in the water as 

 circumstances require. Try and enumerate the 

 various means of locomotion possessed by the 

 mollusca. 



Child. Many creep by means of a fleshy 

 elongation, which is in some a foot, in others a 

 leg. In the water they swim, making their way 

 either by the serpentine movement of their 

 bodies, or by the use of tentacula. Some can 

 rise and sink in the sea, and some make a leap 

 by rapidly closing their shells, or by drawing in 

 water and suddenly forcing it out again. 



Teacher. When we study the different kinds 

 of mollusca, I shall speak to you more fully of 



