96 THE FRESHWATEB MUSSEL. 



5. The course of the circulation. 



The ventricle receives arterial blood from the 

 auricles, and drives it through the arteries aU over 

 the body. The blood from the foot and viscera is 



R u ■" CO UO 



so LM 



Fig. 27. — Anodonta cygnea. Diagrammatic view from the right side. 

 The right valve of the shell, the right mantle- lobe, the right gills, 

 and the right auricle have been removed. The alimentary canal 

 has been laid open from the right side as far as the point where it 

 enters the pericardial cavity. The pericardial cavity, the ventricle, 

 and the right kidney and ureter have been laid open from the right 

 side. The longer arrow passes from the pericardial cavity through 

 the right reno -pericardial aperture into the right kidney. The 

 shorter arrow passes through the external aperture of the right 

 ureter, (a. m. m.) 



A, margia of the left valve of the shell iu which the auimal is lyin^. AA, 

 anterior adductor muscle. AM", anus. B, ligament of the shell. BD, bile- 

 duct. BD', openings of bile-ducts into stomach. C, cloacal cavity. D, sep- 

 tum between the cloacal and branchial cavities. E, tentacles bordering 

 . inhalant aperture. F, foot. G, line of fusion of inner lamellffi of right and 

 left inner gills. GO, genital aperture. H, anterior aorta. I, intestine. K, 

 kidney. L, liver LG, inner gill of left side. LM, left mantle-lobe. M, 

 mouth. W, posterior aorta. O, cesophagus. PA, posterior adductor muscle. 

 PC, pericardial cavity. PB, right posterior retractor mUsole. K, rectum 

 BG, genital gland— ovary or testis. EM, line of attachment of right lobe of 

 mantle. BP, right reno-pericardial aperture. S, stomach. SO median 

 slipra-branchial canal, lying above the inner gills. T, typhlosolc. 'xj right 

 ureter. UO, external opening of right ureter. V', cavity of ventricle ' 



