MOLLUSCA. 169 



nexioii of the oyster with tlie pearl is one of the interesting 

 circumstances connected with its history. Moore, with his 

 usual felicity, has referred to the Eastern fable of 



" That rain from the sky 



That turns into pearls as it falls in the sea." 



The real facts, as at present known, are scarcely less won- 

 derful. The shell is pierced by some woim, and the oyster 

 deposits the " nacre," or mother-of-pearl, on the perforated 

 part; or grains of sand or gravel gain admission into the 

 substance of the mantle, and become encrusted by a similar 

 deposit. This would appear to be, in many instances, the 

 origin of the pearls, so highly prized, and still so eagerly 

 sought for. The Eomans were extravagantly load of these 

 ornaments, Avhicli they ranked Jiext 

 to the diamond, and are said to have 

 given almost incredible prices for 

 them. "Julius Ctesar presented 

 Servilia, the mother of M. Bnitus, 

 with a pearl worth £48,417 IO5. ; 

 and Cleopatra, at a feast with 

 Antony, of which Pliny has given 

 a long and interesting account, 

 swallowed one dissolved in vinegar 

 of the value of £80,729 3s. 4c?." 

 Such statements are generally re- „. ,^„ „ 



'' ■' Fig. 160. — Pkarl Oyster. 



garded by naturalists 01 the present 



day with distrust, as exaggerated or eiToneous. 



The shell (Avicula marcjaritacea. Fig. 160) from wliicii 

 the greater number of pearls and the largest quantity of 

 mothur-of-pearl is obtained, is not an oyster strictly so called, 

 but belongs to an allied genus. It is not our intention to 

 enter into any history of the pearl fisheries of Ceylon or the 

 Persian Gulf, which annually give employment to some 

 hundreds of boats and many thousand men. But we would 

 mention, that a very exaggerated idea prevails as to the 

 length of time a pearl-diver is in the habit of staying under 

 water. The usual period on the Aripo banks, is stated by 

 Captain Steuart, to be 53 to 57 seconds; when paid for the 



