38. How do oysters produce pearls? 



Pearls are produced by a type of oyster more closely related to 

 mussels than to the common edible oyster. These gems are formed by 

 a foreign substance, such as a grain of sand, which accidentally enters 

 the shell. The oyster attempts to reduce the irritation by depositing suc- 

 cessive layers of nacreous material around the foreign body. 



The most valuable pearls are obtained from oysters taken near Ceylon 

 and in the Persian Gulf. It is believed that the nucleus of these pearls is 

 a tapeworm egg. 



Cultivated pearls are produced by inserting particles in pearl oysters. 

 It takes 3 to 5 years for an oyster to produce a pearl; if sea conditions 

 are not right during the entire period, the oyster may yield only a 

 worthless lump of calcium. Under the best conditions, only 60 percent 

 of cultivated oysters live to yield pearls and only 2 to 3 percent produce 

 gem quality pearls. 



There are many legends and stories about pearls. The ancient Greeks 

 believed that pearls were created when lightning struck the sea. 



Miller, Robert C. 



The Sea, Random House, 1966. 

 U. S. Naval Oceanographic Office 



Science and the Sea, Washington, D. C, 1967. 



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