216 



COMPARATIVE ANATOMY 



CHAP. 



A relation between the nephridial and genital systems similar 

 to that found in the Annelida exists in the Sohnogastrida?, the 

 nephridia functioning as ducts for the genital products, the latter 

 passing from the hermaphrodite gland (genital chamber of the ccelom) 

 into the pericardium. 



In a few Lamdlibranchia, Diotocardia, and in the Scapliopoda, there 

 is a relation between the genital glands and the nephridia, the former 

 opening into the latter ; so that a certain part of the nephridium 

 functions not only as renal or urinary duct, but also as efferent genital 

 duct. In all Diotocardia, it is the right nephridium which functions as 

 genital duct. In the Monotocardia, in which the right nephridium of 

 the Diotocardiii has atrophied as such, its duct persists as genital duct. 

 In all other Molluscs the genital ducts are entirely distinct from the 

 urinary passages. 



A. Amphineura. 



The kidneys of the Solcnocjastridw and the Chitonidcc differ greatly from one 

 another in structure. 



1. In the Sole nogasfr idee, two canals spring from the pericardium, embrace the 

 hind-gut, and open into the cloaca beneath it through a common terminal portion 



52 1 



11 



FIG. 179. Paramenia impexa. Posterior end of the body ; the integument must be supposed 

 to be removed on the right side, and also a piece of the wall of the right nephridium ; diagram (after 

 Pruvot). 1, Integument; 2, ovarial portion of the hermaphrodite gland ; 3, testicular portion of 

 the same, near the point where the latter opens into the pericardium (4) ; 5, glandular appendage 

 of the right nephridium ; 6, dorsal commissure of the pleurovisceral cords ; 7, organ called the 

 sensory bud ; 8, aperture of the hind-gut into the cloaca; 9, gill; 10, cloaca; 11, common aper- 

 ture of the nephridia into the cloaca : 12, lower portion of the nephridium ; 13, upper portion of 

 the right nephridium, which opens above into the pericardium ; 14, hind-gut. 



(Fig, 179). These canals function as ducts for the genital products. It is also 

 certain that they correspond morphologically with the kidneys of other Molluscs, 

 even though their excretory activity has not been proved. They are covered with 

 an extraordinarily deep epithelium of long filiform glandular cells. 



In some Solcnogastridce, an accessory gland opens into each nephridial canal. 



2. In the Chitonidce, the strongly-developed paired nephridia function exclusively 

 as excretory organs. 



Each nephridium (Fig. 180) consists of a wide canal shaped like a long Y, 



