THE ANATOMY OF PLEUROTOMARIA BEYRTCHII. 259 



The left characteristically forms the papillary sac, and alone 

 (save in Patella) coniniunicates with the pericardium: this 

 organ is not truly excretory, but serves as a reserve organ, 

 and only removes foreign matter by phngocytosis : thus if in- 

 soluble powder-like carmine be injected into the body it is 

 removed by phagocytes which discharge through the papil- 

 lary sac (Pelseneer ^) . This left kidney has also a peculiar and 

 characteristic blood-supply, being directly connected with 

 the auricle or auricles (Perrier, op. cit.), and thus receives 

 arterial blood. 



The right kidney, on the other hand, is very large, and 

 characteristically situated between the pericardium and 

 stomach, being also at times extended below the former into 

 the anterior part of the hEemocoele. This kidney, which 

 receives the venous blood on its way to the gills, is the true 

 excretory organ, since it alone removes the soluble waste 

 products. The right kidney further serves to transmit the 

 genital products, its duct being frequently modified and 

 glandular in this connection. 



In the adult Monotocardian a single kidney alone is present. 

 The position occupied by this gland is somewhat intermediate 

 between that of the two seen in the Diotocardia, being placed 

 in the majority between the pericardium and stomach. It 

 opens normally (where no secondary ureter is developed) 

 by a slit-like orifice between the rectum and gill near 

 the posterior limit of the mantle-cavity, much as does the 

 left kidney of the Diotocardia, and it further resembles that 

 organ in the fact that its cavity communicates with the peri- 

 cardium ; but at the same time it is a true kidney, and func- 

 tions like the right kidney of the Diotocardia. Closely 

 pressed between this organ and the pericardium is a glandular 

 mass, often spoken of as the renal gland ; the last organ has 

 the peculiar blood-supply found in the papillary sac of the 

 Diotocardia, which it further resembles in function (Perrier). 

 We see, then, that the kidneys of these two great sub- 



' " Les reins, les glandes geiiitales, et leurs conduits dans les Mollusques," 

 ' Zool. Anz./ Bd. xix, 1896. 



