THE PEARL OYSTER. 923 



tion, and the nucleus of the Pearl, if of organic matter, 

 after having been the cause of infinite annoyance to its 

 unfortunate captor, is returned to the place from whence 



it came. 



It may be urged that the layers of shell enveloping 

 the Pearl or blister are laid equally upon the top of it and 

 at the sides, and that an unnatural excrescence would still 

 remain on the inner surface of the shell, long after the 

 original cause of it has passed away ; but this is not so. 

 It must be remembered that the laws of development by 

 which creatures are adapted to cope with the surrounding 

 conditions and difficulties of their existence are as appli- 

 cable to an oyster as to any other form of life, and the 

 same power that taught the oyster to protect itself against 

 the inveterate attacks of its enemy, the " borer," by in- 

 creasing the thickness of its shell at the point of danger, 

 might also teach it to rid itself of an uncomfortable tenant 

 in its bed, by exactly the reverse process. 



Pearls, when of extraordinary beauty, size, or bril- 

 liancy, will sell for sums which appear extravagant in pro- 

 portion to what is given for ordinary specimens. The 

 reason for this is obvious, for no sooner is one of surpas- 

 sing beauty in the market than it is removed from the 

 common category, and the price will depend more upon 

 the fancy of the purchaser than any system of valuation. 



The larger, the smoother, the rounder and brighter 

 the Pearl, the more it is prized. The lustre of Pearl shells 

 and Pearls is owing to their formation of regular, very thin 

 laminae, or layers of two very different substances ; one of 

 these is lime, which is opaque, the other is animal matter, 

 which is transparent. Thus, the real colour of the one 

 being pure white, and the other devoid of colour, the light 

 is divided into different tints at the surfaces of the plates 



