THE CEYLON PEARL-OYSTER. 



311 



anfl thou nacro, whicli, at places, showed tlie cliaracters of 

 " graiuilai' repair- uacro." 



Text- tiff. :?8. 



yep.nxLc. 



Str 



Mai-javitifera margarilifura Linna-us (Black-lii)i)ed Mot lier-of- Pearl Oyster). 

 Part of an artificially produced blister, pr., prismatic layer ; Str., hori/oiital 

 dividing membrane of coiicliyoliu in same ; nac, nacre; r ep Mac. , '^nwmhw 

 repair-nacre. (Preparation Vlll.) 



PI. XL. fig, 29, from the " repair- membrane" formed by 

 M. vuhjaris over a hole in the shell (umbonal region), shows tho 

 same substance at irJ passing over on the one hand into columnar 

 repair-substance, on the other into nacre. The same substance 

 is seen at tr. 



PL XLI. fig. 30 (rejJ.nac.) shows the same substance, secreted 

 at the point of junction of two pearls (from one of Dr. Kelaart's 

 specimens of M. vulgaris). Here it was secreted as a result 

 of disturbances following upon the fusion of the two pearls and 

 the absorption or calcification of the intervening tissues. The 

 granular repair-nacre in the preparation shows in places a 

 distinctly columnar structure, indicating a. transition to the 

 columnar repair-substance ; such a transition is still more obvious 

 in PI. XL. fig. 29. 



The same granular repair-nacre is seen in PI. XXXV. fig. 9, 

 PI. XXXVIL fig. 15, and PI. XXXVIII. fig. 18, surrounding the 

 central cavities of " muscle-pearls," where unduly rapid secretion 

 might well l)e expected, and in PI. XXXIX. fig. 23, where a 

 hypostracum- pearl (" calcospherule," Herdman) is in process 



