I^RESH-WATER MUSSEL 



451 



the mussel tides over the winter. In other bivalves other 

 functions are ascribed to the crystalline style, which is 

 thought to aid in digestion, both mechanically, for by 

 rotating it stirs the food, and chemically, for it contains a 

 starch-splitting enzyme. Wandering amcEboid cells play 



Fig. 256. — Structure of Anodonta. — After Rankin. 



a.a., Anterior adductor ; c.p.g., cerebro-pleural ganglia ; St., 

 stomach ; v., ventricle, with an auricle opening into it ; k., 

 kidney, above which is the posterior retractor of the foot ; 

 r., rectum ending above posterior adductor ; v.g., visceral 

 ganglia with connectives (in black) from cerebro-pleurals ; g., 

 gut coiling in foot ; p.g., pedal ganglia in foot, where also are 

 seen branches of the anterior aorta and the reproductive 

 organs ; l.p., labial palps behind mouth.-- At the posterior end 

 the exhalant (upper) and inhalant (lower) apertures are seen. 



a large part in digestion and absorption. The intestine, 

 which has in part a folded wall like that of the earthworm, 

 coils about in the foot, ascends to the pericardium, passes 

 through the ventricle of the heart, and ends above the 

 posterior adductor at the exhalant orifice. 



Vascular system. — The heart lies in the middle line on 

 the dorsal surface, within a portion of the body cavity called 



