PEARLS. 273 



of a certain juice had formed^ and would have continued 

 to form, a coat or layer of peculiar tint, the vessel 

 that conveyed the juice had ruptured and occasioned a 

 small deposit, Avhich, gradually becoming hard, retained 

 the colour of the shell. Of this the structure of the pearl, 

 and the shell itself, is a convincing proof; for the silver- or 

 pearl-coloured part of the Pearl Mussel is formed of strata 

 lying one upon another; and the reddish portion, of a 

 multitude of small, short, close, cylindrical fibres; which 

 peculiarity of texture is also discoverable in the difl'erent- 

 coloured pearls of the Mussels of Provence. 



The intrusion of some heterogeneous substance, such as 

 particles of sand, into the stomach of the animal, frequently 

 produces these curious extravasations. M. Reaumur ele- 

 gantly terms them the nuclei, or primary causes, of the for- 

 mation of each valuable gem; as the sagacious animals 

 cover them from time to time with exudations of pearly 

 matter, in order to obviate the disagreeable friction which 

 they necessarily occasion ; and these exudations, as already 

 noticed, form several regular lamellee, resembling different 

 strata of bezoars, though considerably thinner, and more 

 delicate in their construction. Loose pearls are often found 

 within the shelly covering of the Mytilus : when this is the 



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