« 
THE CEYLON PEARL-OYSTER. ale 
and then nacre, which, at places, showed the characters of 
“ sranular repair-nacre,” 
Text-fig. 38. 

Margaritifera margaritifera Linneus (Black-lipped Mother-of-Pearl Oyster). 
Part of an artificially produced blister. pr, prismatic layer ; Sér., horizontal 
dividing membrane of conchyolin in same; nae., nacre; rep.nac., granular 
repair-nacre. (Preparation VIII.) 
Pl. XL. fig. 29, from the “repair-membrane” formed by 
M. vulgaris over a hole in the shell (umbonal region), shows the 
same substance at é7.' passing over on the one hand into columnar 
repair-substance, on the other into nacre. The same substance 
is seen at dr. 
Pl. XLI. fig. 30 (rep.nac.) shows the same substance, secreted 
at the point of junction of two pearls (from one of Dr. Kelaart’s 
specimens of JZ, 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 
distinetly columnar structure, indicating a transition to the 
columnar repair-substance ; such a transition is still more obvious 
in Pl. XL. fig. 29. 
The same granular repair-nacre is seen in Pl. XXXYV. fig. 9, 
Pl. XXXVIL. fig. 15, and Pl. XX XVIII. fig. 18, surrounding the 
central cavities of ‘ muscle-pearls,” where unduly rapid secretion 
might well be expected, and in Pl. XX XIX. fig. 23, where a 
hypostracum-pearl (‘“ calcospherule,” Herdman) is in process 
[53] 
