THE PEARL OYSTER. 255 



valves or in the fleshy part of the mollusc. Between nacre and 

 pearls, therefore, there is only the difference of the form of deposition. 

 Fig. 165 represents the pearl oyster with calcareous concretions in 

 various states of progress. 



The finest pearls solidified drops of dew, as the Orientals term 

 them in the language of poetry are secretions supposed to be the 

 result of disease in the animal. The matter, in place of being spread 

 over the surface of the valves in their beds, is condensed either on the 

 centre of the valves or in the interior of the organ, and forms a more 

 or less rounded body. The pearls, when deposited on the valves, are 

 generally adherent ; those which originate in the body of the animal 

 are always free. Generally we find some small foreign body in their 

 centre which has served as a nucleus to the concretion, the body 

 being perhaps a sterile egg of the mollusc, the egg of a fish, a 

 rounded animalcule, a grain of sand even, round which has been 

 deposited in concentric layers the beautiful and much-prized gem. 



The Chinese, and other Eastern nations, are said to turn this fact in 

 the natural history of bivalves to practical use .in making pearls and 

 cameos. By introducing into the mantle of the mollusc, or into the 

 interior of a living valve, a round grain of sand, glass, or metal, they 

 induce a deposit which in time yields a pearl, in the one case free, 

 and in the other adhering to the shell. In some cases they are said 

 to be produced in whole chaplets by the insertion of grains of quartz 

 connected by a string into the mantle of a species of Symphynota ; 

 in other cases, a dozen enamelled figures of Buddha seated have been 

 produced by inserting small plates of embossed metal in the valves of 

 the same species. 



The pearls are very small at first ; they increase by annual layers 

 deposited on the original nucleus, their brilliancy and shade of colour 

 varying with that of the nacre from which they are produced. Some- 

 times they are diaphanous, silky, lustrous, and more or less irides- 

 cent ; occasionally they turn out dull, obscure, and even smoky. 



The pearl oyster is met with in very different latitudes ; they are 

 found in the Persian Gulf, on the Arabian coast, and in Japan, in 

 the American seas, and on the shores of California, and in the islands 

 of the South Sea ; but the most important fisheries are found in the 

 Bay of Bengal, Ceylon, and other parts of the Indian Ocean. The 



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