The Wing Shells, Pearl Oysters and Hammer Oysters 



Other shells, whence they never move until brought up by divers. 

 These are the bivalves which for centuries have furnished the 

 precious "oriental pearls," adding constantly to the treasure 

 of kingdoms and individual collectors. 



Mother-of-pearl, the thick lining of each valve, is the de- 

 pendable product of pearl fisheries. It is secreted in annual 

 layers by glands in the mantle. There is just enough animal 

 substance in it to support the particles of lime carbonate. The 

 iridescence is due to microscopic undulations of the various layers 

 which compose it. These layers expose oblique edges to the 

 surface, and the refraction of light produces the rainbow colours. 



The best mother-of-pearl comes from healthy, full-grown 

 shells ; the finest pearls from shells distorted by crowding and 

 disease, and invaded by parasites and foreign particles. The 

 first is a natural growth; the second abnormal. A lusty, well- 

 fed mollusk, enjoying life, has a neighbour, warped, debilitated, 

 suffering, with a grain of sand rolling around in its mantle folds. 

 Coat after coat of nacre is added to this irritating foreign body 

 to lessen its injury to the tender flesh. When the diver finds it, 

 a magnificent pearl, it makes him rich. Only one shell in a 

 thousand, we are told, contains a gem of any value. So the lines 

 of Browning would do little, I fancy, to reconcile a discontented 

 pearl-diver to his hard lot: 



There are two moments in a diver's life: 

 One, when a beggar, he prepares to plunge ; 

 Then, when a prince, he rises with his pearl. 



Throughout the seas of the equatorial regions are scattered 

 pearl fisheries where thousands of people are engaged in diving 

 for the pearl-bearing mollusks. Ceylon has ten, operated under 

 government control. Nearest to us are the Panama and Lower 

 California fisheries. Four to five thousand boats manned by 

 divers work in the Persian Gulf each summer. The harvest of 

 one year in this locality alone adds to the world's wealth in gems 

 and mother-of pearl |2,ooo,ooo. This is the average, according 

 to official statistics. The shells are smaller, but of better grade 

 than those of Tahiti and of Panama. Australian fisheries pro- 

 duce small but very brilliant pearls. The Pacific Islands have 

 many fisheries, noted the world over for their gems. The most 

 famous pearls come from the Sulu Islands, Tahiti is the centre 

 from which the products of the South Pacific fisheries are ex- 



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