Microns 



200 



Figure 246. — Longitudinal section through the reno- 

 pericardial opening and reno-pericardial canal, which 

 connects the inner part of the kidney with the auricle 

 in C. virginica. Part of the auricle at upper left and the 

 adjacent portion of the kidney at lower right. Bouin, 

 heniatoxylin-eosin . 



The epithelium of the reno-pericardial passage 

 and of the renal duct is ciliated (fig. 246 and fig. 



247). 



PHYSIOLOGY 



No comprehensive account of the biochemical 

 and physiological processes of excretion in bivalves 

 can be written at present because of the inadequate 

 state of our knowledge, however, a review is 

 possible. 



During the past three-cjuarters of the century 

 many studies have been made of the function of 

 the organ of Bojanus and of the role of the peri- 

 cardial glands. Most of these investigations were 

 carried on for gastropods, cephalopods, and fresh- 

 water mussels. The reader is referred to the review 



of this subject found in the papers of Marchal, 

 1889; Letellier, 1889; Cuenot, 1900; Fosse, 1913; 

 Turchini, 1923; Delaunay, 1924, 1931, 1934; 

 Spitzer, 1937; and Franc, 1960. Very little work 

 has been done, however, witli marine bivalves and 

 particularly with oysters for wliich physiological 

 studies of the excretory system present consider- 

 able technical difficulties. The nephridial organs 

 of oysters do not form a sharply outlined unit. 

 They are surrounded by delicate and loose connec- 

 tive tissue which contains numerous blood vessels 

 with very thin walls and spacious sinuses. Con- 

 sequently, it is very difficult to obtain a sample 

 of the liquid from the various parts of the kidney 

 system without contaminating it with blood or 

 with the sea water which surrounds the organ. 

 Such difficulties are not encountered in the studies 

 of land snails and cephalopods. 



An experimental approach to the study of the 

 function of nephridia was made by Grobben 

 (1888), Kowalevsky (1890), and Emeljanenko 

 (1910) wlio injected various dyes in the foot, 

 mantle, or visceral mass of the mollusk. It was 

 shown by this method that the excretory organs 

 of bivalves excrete indigo-carmine and that 

 ammonia carmine injected in physiological solu- 

 tion is concentrated in the pericardial glands. 

 In Ostrea the carminates are concentrated in the 

 walls of the auricles, while in Peden maximus 

 they are spread throughout the connective tissue 

 (Cuenot, 1900). 



Attempts to determine the rate of filtration of 

 fluid into tlie pericardium of fresh-water Unionidae 

 were made by Turchini (1923) and Picken (1937). 

 Picken studied the hydrostatic and colloid osmotic 

 pressm-e of the body fluid. He supposed, probably 

 correctly, that the pericardial fluid is a filtrate of 

 the blood througli the wall of the heart. His 

 observation that the pericardial fluid of Anodonta 

 is isotonic with blood seems to support this view. 



On the basis of the experiments by these authors 

 and by Robertson (1949, 1953), the following 

 course of mine formation may be visualized: The 

 blood is filtered through the wall of the heart into 

 the pericurthum, and this fluid, together with the 

 secretion of the pericardial glands, passes through 

 the reno-pericardial opening into the nephridial 

 tubes. The secretion from the tubules is added to 

 the liquid. Its final composition wifl depend on 

 how far and how rapidly the secretion and possibly 

 the reabsorption of certain constituents proceed 

 in the secretory epithelium. 



274 



FISH AND WILDLIFE SERVICE 



