



Centimeters 



Figure 244. — Diagram of the excretory system of C. rirginica based on examination of a series of transverse sections. 

 Viewed from the anterior side. Gonads and their ducts, blood vessels, and blood sinuses are not shown. The peri- 

 cardium wall is dissected and pulled down. A — auricle; a. a. — anterior aorta; Ad.M. — adductor muscle; a. 1.1. — 

 anterior left limb; a.r.l. — anterior right limb; ef.v. — efferent vein; i.r.p. — internephridial passage; 1. neph. — left 

 nephridium; p. 1.1. — posterior left limb; p. r.l.— -posterior right limb; r.d. — renal duct; r. neph. — right nephridium; 

 res. — reservoir; r.g.v. — reno-gonadial vestibule; r.p.c. — reno-pericardial canal; r.p.o. — rono-pericardial opening; 

 V — ventricle; v.g. — visceral ganglion. 



by numerous branching and twisted tubules lined 

 with excretory cells. 



Much of the posterior limb of the kidney is 

 occupied by a wide vesicle or reservoir (fig. 245, 

 R.) for the storage of urine. A short renal duct 

 (fig. 244, r.d., and fig. 247) leads from the reservoir 

 to the outside and opens into the reno-gonadial 

 vestibule, a shallow indentation on the surface of 

 the pyloric caecum, behind the opening of the 

 gonad (fig. 247). Numerous anastomosing tubules 

 of the nephridia form a spongy tissue which ex- 

 tends into the visceral mass (fig. 248). Odhner 

 (1912) pointed out that regardless of the apparent 



complexity of the nephridia, it is always possible 

 to distinguish the two limbs or branches of the 

 excretory system. 



Topography and relationship of the excretory 

 and reproductive systems vary greatly within the 

 class of bivalves. Certain topographical features, 

 however, remain constant. One of them is the 

 position of the renal opening in relation to the cere- 

 bro-visceral connective. Lacaze-Duthiers (1855), 

 one of the early students of molluscan anatomy, 

 pointed out that the renal opening (also called 

 "ncphroprokt") is always located beyond the 

 cerebro-visceral connective. Pelseneer (1891) at- 



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FISH AND WILDLIFE SERVICE 



