THE INDIAN OCEAN. 347 



mould thread by thread ; a glutinous fluid being 

 secreted in a long groove or canal formed by the 

 foot, which in the air rapidly acquires solidity. 

 \Vlien complete, the united threads form, as observed 

 above, a cable, projecting through an opening in 

 the back of the shell, and adhering by the other 

 extremity to the rock so firmly as to resist the 

 agitation of the sea, and so tough as to be severed 

 only by an axe. Marsden mentions one which was 

 more than three feet three inches long, and two 

 feet one inch wide : and specimens have been seen 

 which had attained the enormous length of four feet. 

 They are sometimes taken, when not adhering, by 

 thrusting a long bamboo between the open valves, 

 which immediately close firmly, and they are dragged 

 out. Tlie substance of the shell is perfectly white, 

 several inches thick ; it is worked by the natives 

 into arm-rings, and by European artists is made to 

 receive a polish equal to the finest statuary marble. 



l*earls, whose exquisite beauty has made them 

 celebrated from the earliest ages, are well known to 

 be marine productions ; and as the shores of the 

 Indian Ocean yield the finest specimens, I may here 

 say a word of the fishery for them. IMany bivalve 

 shells produce pearls of greater or less perfection ; 

 but what is known as the Pearl Oyster is the Avi'cuJa 

 margaritifera of conchologists. The interior surface 

 of the shell is covered with very thin plates, or 

 lamella, which are furrowed with microscopically 

 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 



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