PEARLS. 79 
Muscle of Provence, the tints of each are precisely 
the same with those of the shell; and that each kind 
of coloured pearl is found in the corresponding 
coloured part of the shell itself; thus clearly evincing 
that where a certain juice had formed, and would 
have continued to form, a coat or layer of a 
peculiar tint, the vessel that conveyed the juice had 
become ruptured, and occasioned a small deposit, 
which hardened gradually, and 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 Muscle, is formed 
of strata lying one upon another like the coats 
of an onion; and also of the reddish part of a 
multitude of small, short, close, cylindrical fibres ; 
which peculiarity of texture is also discoverable 
in the different coloured pearls of the Muscles of 
Provence. 
The intrusion of some heterogeneous substances, 
such as particles of sand, into the stomach of the 
animal, frequently produces these curious extrava- 
tions. M. Reaumur elegantly terms them the nuclei, 
or primary causes of the formation of these valuable 
gems; 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 
