V* * 



/n 



-.'^i' 



%m 











# 





Microns 



30 



Figure 60. — Large and small bundles of fibers of the tcnsiliuni of C. tirginica seen in unstained and nondecalcified 

 preparation of the material teased in glycerin. Photomicrograph. 



from circular to elliptical liiiht areas as the plane 

 of section of the fibrils becomes tangential (see 

 fig. 62). 



Sections made at risilit anoles to tlie fibrils (fig. 

 62) demonstrate a certain similarity to those of 

 the organic membranes of the aragonitic jjart of 

 the shells of mollusks and ])earls. According to 

 Gregoire, Duchateau, and Florkin (1950, 1955), 



54 



such organic membranes have a lace-like structure 

 consisting of meshes and holes of dift'erent size and 

 pattern. In tltese inxestigations by Belgian 

 biologists the material was first decalcified, and 

 the layers of organic substance then separated by 

 idtrasonic oscillation to obtain the ultrathin mem- 

 branes suitable for electron microscopy. The 

 films of the calcite-ostracum layer of the siiclls of 



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