Ml lllmeters 



0.5 



Figure 248.— Tightly packed and twi.sted blind tubules 

 of the excretory organ of C. virginica form "spongy" 

 tissue which extends on both sides into the visceral 

 mass. Adductor muscle at upper right. Bouin, hema- 

 toxylin-eosin. 







Microns 



40 



Figure 250. — Cubical cells of the epithelium lining of the 

 inner wall of the internephridial canal of C. virginica. 

 Oil immersion. Kahle, hematoxylin-eosin. 



Microns 



40 



Figure 251. — Tall columnar cells of the lining of the tubu- 

 les of the posterior limb of C. virginica. Oil immersion. 

 Kahle, hematoxylin-eosin. 







Microns 



40 



Figure 249. — Medium-sized cylindrical epithelial cells 

 lining the lumen of the nephridial tubules of the anterior 

 limb of C. virginica. Oil immersion. Kahle, hema- 

 toxvlin-cosin. 



276 



THE WASTE PRODUCTS 



Relatively little is known about nitrogen excre- 

 tion in the oyster or in other marine bivalves. 

 As in other organisms the waste products are 

 various nitrogenous compounds. The presence of 

 a low concentration of ammonia, the principal 

 nitrogenous product of amino acid breakdown in 

 moUusks (0.051 mg. per 100 ml.) was demonstrated 

 by Florkin and Houet (1938). In the excreta of 

 the mai-ine clam {Mya arenaria) ammonia com- 

 prises 21.5 percent of the total nonprotein nitrogen 

 (Delaunay, 1924), and in Mytil%f< the figure varies 

 from traces to 10.8 percent (Spitzer, 1937). Small 

 quantities of urea amounting to 4.5 percent of the 

 nonprotein nitrogen excreted in different forms 

 were found in Mya and only traces of it in Mytilus. 

 No uric acid was found in the latter species 



FISH AND WILDLIFE SERVICE 



