from 0.20 to 0.50 seems to indicate that the 

 difi'erences are not significant. The authors' 

 conclusion can not, therefore, be accepted without 

 further confirmation. 



The relative significance of the nephi-idia, peri- 

 cardial glands, and phagocytes in excretion can 

 not be evaluated at present. The three different 

 systems probably supplement one another by 

 eliminating different waste products. Histo- 

 chemical studies show, for instance, that phago- 

 cytes play the major role in the accumulation, 

 storage, and discharge of u'on and copper. Un- 

 doubtedly the phagocytes heavily loaded with dark 

 granules contain other substances besides heavy 

 metals which are discarded by the organism. On 

 the other hand, other tissues also are involved in 

 the process of excretion. For instance, the epi- 

 thelia of the gills, of the edge of the mantle, and of 

 the labial palps under certain conditions store 

 iron. My observations on ('. rirginica indicate 

 that iron is excreted by the epithelium of the 

 mantle, and vStauber (1950) found that India ink 

 injected into the ventricle is distributed by the 

 phagocytes to all parts of the organism and is 

 eliminated through the epithelium of the alimen- 

 tary tract, digestive diverticula, palps, mantle, and 

 pericardium. Nephi-idia and shell-forming parts 

 of the mantle are not, however, the routes of 

 migTation of these cells. Observations made by 

 Kowalevsky (1890) and Cuenot (1900) showed that 

 if a mollusk with pericardial glands is injected 

 with a mixtm-e of indigo carmine and ammonia 

 carmine, the latter is concentrated in the cells of 

 the pericardial glands, while the indigo goes into 

 the nephridia. These separations lead some in- 

 vestigators to designate the different cells as 

 "carmineathrocytes" and "indigoathi-ocytes" 

 (Strohl, 1924), terms which have not been accepted 

 by biologists. The affinity of these cells to special 

 dyes does not necessarily indicate that they par- 

 ticipate in the normal process of excretion. 



Pigmentation may be considered as a certain 

 phase of excretion. Green oysters of Long 

 Island Somid develop dark gi-een pigment as the 

 result of absorption and storage of copper by the 

 phagocytes (Galtsoff and Whipple, 19.31 ). Schiedt 

 (1904) considered that the development of black 

 pigment in the mantle of oysters exposed to strong 

 illumination is also a product of excretion. His 

 finding was not in agreement with the observa- 

 tions of Faussek (1899) on pigmentation on the 

 mantle of Mytilus with partially removed shells. 



Excretion through diapedesis is undoubtedly of 

 great importance to the mollusk, but its exact 

 role is not fully understood. 



BIBLIOGRAPHY 



Baldwin, Ernest. 



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BOJANUS, L. 



1819. Sendschreiben an den Herrn Chevalier G. de 

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1938. Sur la degradation des substances d'origine 

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1900. L'e.xcretion chez les MoUusques. Archives de 

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10, pp. 695-724. 

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1910. tJber die Ausscheidung von Farbstoffen durch 



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1S99. tJber die Ab'agerung des Pigmente- bei 



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FeRNAU, WlLHELM. 



1914. Die Niere von Anodonta celknsis Schrot. Teil 



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FiNGERMAN, MiLTON, and Laurence D. Fairbanks. 



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Florkin, Marcel, and Ren£ Houet. 



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THE EXCRETORY SYSTEM 



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