252 



TEXTBOOK OF ZOOLOGY 



Circulation 



The heart which is composed of a ventricle and two auricles lies 

 in the pericardium. The ventricle, a muscular organ, surrounds 

 the rectum and drives blood forward through the anterior aorta 

 and backward through the posterior aorta. Both aortae give off 

 arteries which ramify all parts of the body. Most of the returning 

 blood is carried to the kidneys by means of the vena caval vein. 

 Within the latter, nitrogenous wastes are removed, and the blood 

 then flows to the gills through afferent hranchial veins; after puri- 

 fication in the gills it is returned to the auricles by way of the 

 efferent hranchial veins. The blood is colorless and contains several 

 types of white corpuscles. 



Nervous System and Sense Organs 



Situated on each side of the esophagus is a cerehropleural gan- 

 glion, the two ganglia being connected by means of a cerebral com- 



Perlcardial wall Reno 'pericardial pore 



Post, aorta 

 Vertical ^°^^- odductor M. 1 

 water tubes \ kidney I 



txhalQnt '' ^^^^ 

 Siphon 



Ventricle \ Excretory pore 



Auricle 





Ant.aorta Liver 

 i -Stomach j Cerebral 



commisjure 



Ant .adductor 

 muscle 



Inhalant 



siphon , Qji, , 



Mantle •^'^e" \ \ 



Visceral Q. Qonad 



Labial 

 Mouth P'^'P' 



I root 



Intestine Pedal q. Cerebro pleural &. 



Fig. 144. — Internal organs of Lampsilis anodontoides. 



missure which passes above the esophagus. Each ganglion gives 

 off two nerve cords, one of which passes ventrally and posteriorly 

 to the pedal ganglion situated at the junction of the visceral mass 



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