368 



MOLLUSC A. 



and a posterior artery, flows into ill-defined channels, is 

 collected in a "vena cava" beneath the floor of the peri- 

 cardium, passes thence through the kidneys, where it loses 

 nitrogenous waste, to the gills, where it loses carbonic acid 

 and gains oxygen, and returns finally by the auricles to the 

 ventricle. The blood from the mantle, however, returns 

 directly to the auricles without passing through kidneys or 

 gills, but probably freed from its waste none the less. The 

 so-called "organ of Keber" consists of "pericardial glands" 



Fig. 119. — Structure of Anodonta. (After Ra.n'kin. 



aa.. Anterior adductor; c.p.g.^ cerebro-pleuml ,eanglia : St., 

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

 above which the posterior retractor of foot ; r., rectum, ending above 

 posterior adductor ; v.g., visceral ganglia with connectives (in black) 

 from cerebro pleurals ; .^., gut coiling in foot ; p.^., pedal ganglia in 

 foot, where also are seen branches of the anterior aorta and the 

 reproductive organs ; A/., labial palps behind mouth. 



on the epithelium of the pericardial cavity. They seem 

 to be connected with excretion. Many of the cells lining 

 the blood channels secrete glycogen, the principal product 

 of the Vertebrate liver. 



