120 POPULAR CONCHOLOGY. 



animal ; they are found deposited in the most 

 fleshy parts, particularly within and around 

 the adductor muscle, and are said to be occa- 

 sioned by the overcharge of those glands whose 

 function it is to secrete the nacrous fluid des- 

 tined for the internal lining of the shell. When 

 the animal is thus diseased, this beautiful 

 iridescent fluid is very irregularly discharged, 

 being also deposited upon the inner surface of 

 the shell in little excrescences ; these are often 

 detached, and form articles of commerce as 

 pearls of inferior value, the former being con- 

 sidered more precious, both on account of their 

 rotundity of form and the clearness and beauty 

 of their complexion."* 



Excellent imitations of pearls have been 

 made with hollow glass globules, the inside of 

 which is covered with a liquid called pearl 

 essence, and then filled with white wax: 

 the essence is composed of the silver-coloured 

 particles which adhere to the scales of the 

 Bleak fish, and was first applied to this purpose, 

 by a Frenchman named Jacquin, early in the 



* Reeve's Con. Sys. 



