Microns 



FiGUBE 262. — Cross section of the circunipallia) norve of C. virginica. Kahlo, hematoxylin-eosin. 



closely resembles the so-called brush cells (Pinsel- 

 zelle) described by Flcmniing (1SS4) in the sense 

 organs of various mollusks. Thiele (1SS9) found 

 such cells in the pallial organs of Pinna, Avicula 

 Area, Lima, and other bivalves. The epithelium 

 of the pallial organ of C. virginica consists of two 

 layers of cells: the deeper one is made of cells 

 with globular nuclei, while in the surface layer the 

 cells and their nuclei are oval-shaped (fig. 266). 

 This observation is in agreement with the descrip- 

 tions given by Thiele. The epithelial layer of the 

 pallial organs of Lima inflata and L. hians is made, 

 however, of a single layer (.Studnitz, 1931). 

 Thiele remarks that the cilia in Area noac and 



Lima are motionless. It seems reasonable to as- 

 sume that this may be true for the pallial organs 

 of oysters. Unfortunately, the location of the 

 pallial organ inside the e.xhalant chamber of the 

 gills makes it impossible to study the function of 

 the organ without inflicting serious injury to the 

 sin-rounding tissues and nerves. From the his- 

 tological picture it appears that stiff, hairlike cilia 

 on the surface transfer the stimuli to the nerve 

 endings and to the nerve trunk. Figure 266 rep- 

 resents a small section of the epithelial covering of 

 the pallial organ of C. rirgitnca e.xamined at high 

 magnification. Here the surface layer contains 

 many sensory cells recognizable by their narrow 



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