PRODUCTION OF THE PEARL. 



271 



PEARL-OYSTER. 



a natural product, and an integral portion of the shell, 

 the pearl is the result of accident ; and while in one mol- 

 lusc you may find fifty, 

 sixty, or seventy of these 

 beautiful gems, in another 

 of the same species and the 

 same variety you may not 

 find above one or two. 

 And why] Because the 

 pearl is the result of the 

 avicula's effort to remedy 

 an injury it has sustained 

 by some fracture of its 

 shell or by the intrusion of 

 some foreign body. 



If an avicula be wounded in any part of its substance, 

 if some perforating animal work through its shell, or 

 some hard, angular body, such as a grain of sand, force 

 its way between the valves, the mollusc, unable to re- 

 move the cause of offence, proceeds to cover it with its 

 secretion. This is deposited in thin films, one upon the 

 other, and overlying each other without the slightest pre- 

 tence to regularity; and as the animal grows, so does the 

 secreted nacre, or pearl, increase in size and iridescence. 



The Chinese have turned to advantage this exquisite 

 arrangement of Nature. They keep a species of fresh- 

 water mussel, the Unio Hyria, in tanks; and between 

 the shell and mantle of the mollusc they introduce either 

 small leaden shot or tiny spherical fragments of mother- 

 of-pearl. In due time they are regularly coated with the 

 nacreous secretion, and assume the appearance of pearls 

 naturally produced. 



(502) 



