56 Our Food Mollusks 



tinue and the mud strained out and discharged from the 

 mantle chamber instead of being taken to the mouth. 

 But an objection to closing the shell for long periods is 

 that aeration of the blood ceases when the water stops 

 flowing. It is true that some lamellibranchs may live 

 for days or weeks out of the water, when the tempera- 

 ture is low, but they seem to be injured by such treat- 

 ment, at least in the adult state. Probably for this rea- 

 son, the second plan is the one that has been adopted. 



Bivalves persist in keeping the shell open, thus allow- 

 ing water to enter the branchial chamber, even when 

 bearing mud in considerable quantity. On entering, 

 many of the suspended particles are brought in contact 

 with the inner faces of the mantle and the wall of the 

 visceral mass. Now all of the free surfaces of the 

 mantle chamber — mantle, visceral mass, and gills alike — 

 produce a sticky mucous secretion, so that particles 

 adhere to any of these surfaces that they happen to 

 touch. Let us first inquire into the disposition of those 

 that are lodged against the inner mantle wall. 



Figure 13 represents the inner surface of the mantle 

 (m) lining the left valve of the shell of the hard clam, 

 Venus. All other parts of the body have been removed. 

 If a few grains of powdered carmine or fine sand are 

 allowed to settle through the water upon a living specimen 

 prepared in this way, they may be seen to adhere to the 

 mantle wherever they touch it, and then, together with 

 the mass of mucus in which they are held, they begin to 

 move in the direction indicated by the arrows of the 

 figure. 



This movement is due to the action of cilia, lashing 

 continually in definite directions, and uncontrolled by 

 the nervous system. Everything is moved downward, 



