306 TIIE OCEAN. 



shells produce pearls of greater or less perfection ; 

 but what is known as the Pearl Oyster is the Avicula 

 margaritifera of conchologists. The interior surface 

 of the shell is covered with very thin plates, or 

 lomellce, whicli are furrowed with, microseopically 

 minute and close parallel grooves, and in this struc- 

 ture lies the property of reflecting opaline tints ; 

 a property which has been communicated to other 

 substances by mechanically impressing the surface 

 with similar grooves. In some diseased states of 

 the animal, or when the shell has received a trifling 

 injury, or some foreign body — a grain of sand, for 

 example — has found its way within the mantle, the 

 pearly secretion is poured out in great abundance 

 around the part, and, layer being imposed upon 

 layer, produces a pearl, either attached to the inner 

 surface of the shell, or loose and held merely in the 

 folds of the mantle. 



The most productive fishery is in the Persian 

 Gulf, and the finest pearls are found there: above 

 1)0,000?. sterling are sometimes realized from this 

 source in the course of two months. Those with 

 which we are most acquainted, are carried on on 

 the coasts of Coromandcl and of Ceylon ; the former 

 being in the hands of the East India Company, the 

 latter in those of the British Government. The 

 Ceylon fishery has been well described by Captain 

 Percival, the Count de Noe, and lately by Mr. Ben- 

 nett. As the banks would soon be exhausted if 

 fished every year, portions only are selected in turn, 

 while the rest remains untouched to be recruited. 

 In the month of November, the Government ap- 



