MOLLUSCA. 13 



parts. I think you might have discovered this 

 yourselves by observing one of the animals 

 before you, 



Child. You mean the oyster. Such mollusks 

 cannot move then. 



Teacher. That is not true of all indeed ; some 

 are immoveably attached to the spot where they 

 first received life : but others, as the common 

 scallop, 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 contracting which they can rise or 

 sink in the water as circumstances require. Try 

 and enumerate the various means of locomotion 

 possessed by mollusks. 



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 you study the different kinds 

 of mollusks, I will describe to you more fully 

 their peculiar habits. Did you ever observe, 

 when you have been on the sea-coast, numerous 



