376 



kssentialS of zoology 



Digestion 



During the activity of the clam a constant current of water is 

 maintained in the mantle cavity. Food material is circulated for- 

 ward to the mouth which lies between ciliated labial palps. Upon 

 entering the mouth, food is passed through a short esophagus into 

 the saclike stomach. Here it comes in contact with a digestive fer- 

 ment produced by the digestive gland which is discharged into 

 each side of the stomach through ducts. The crystalline style, a 

 diverticulum of the intestine, and found only in mollusks, produces 

 an enzyme mixed with the stomach content which undoubtedly 



Mantle cut frco. 



Pericardial cavity Rectum 



Auricle 



Ant. retractor 



Anterior i 

 adductor • 



Post, retractor 

 Post. adductor 

 I tx.slpbon 



Foot' 



Protractor txt. labial palp 



Left gill plate 



in. siphon 



"wffljfeii^- 



Fig. 144. — Lampsilis anodontoides with the left mantle partially removed and 



turned back to expose the underlying organs. 



facilitates the digestion of carbohydrates. The food, having been 

 mostly digested and partly absorbed in the stomach, is passed on 

 into the intestine which makes one or more loops in the foot, passes 

 through the pericardium and terminates in the anus near the dorsal 

 siphon. 



Respiration 



Respiration is carried on through two pairs of vascularized gills 

 which hang down into the mantle cavity on each side of the foot. 

 Oxygenated water drawn in through the ventral siphon is passed 

 through a rather complicated series of water tubes in the gills. 



