



Microns 



200 



Figure 265. — Sagittal section of the pallial organ of C. virgiiuca. Long ciliated cells rest on semiglobular protuberance 

 of connective tissue richly supplied with blood vessels and ramifications of the posterior pallial nerve. Kahle, 

 hemato.xylin-eosin. 



mechanical disturbance in the surrounding water. 

 A final answer to the enigma of the pallial organ 

 must await results of physiological studies which 

 so far have not been undertaken. 



A different type of pallial sense organ of the 

 spat of 0. edulis was described by Cole (1938), 

 who found a thin-walled spherical and pigmented 

 sac projecting from the inside mantle sin-face 



near its border, about one-third of the length of 

 the free edge from the mouth. The cavity of 

 the sac contains a comparatively large non- 

 calcareous and nonsiliceous concretion which 

 stains visibly with eosin. There are no cilia inside 

 the sac, which is covered by very attenuated 

 cpithelimn. Cole remarks that the organ is 

 suitably constructed and in a favorable position 



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FISH AND WILDLIFE SERVICE 



