VASCULAR SYSTEM. 



35i 



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

 earthworm coils about in the foot, ascends to the peri- 

 cardium, 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 



FrG. 153. — Structure of Anodonta. — After Rankin. 



«.«., Anterior adductor; c.j*.r., cerebro-pleural ganglia; st., 

 stomach ; z»., 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 aortaand the reproductive organs ; 

 l.p. } labial palps behind mouth. At the posterior end the ex- 

 halant (upper) and inhalant (lower) apertures are seen. 



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

 the pericardium, and consists of a muscular ventricle which 

 has grown round the gut and drives blood to the body, 

 and of two transparent auricles — one on each side of the 

 ventricle — which receive blood returning from the gills and 

 mantle. In bivalves the heart-beats average about twenty 

 per minute, much less than in Gasteropods. The colour- 



