62 THE HALL OF SHELLS. 



" Another theory has been that pearls were 

 always the result of a grain of sand or some 

 irritating substance entering the shell ; the ani- 

 mal, unable to discharge it, converted it into a 

 pearl. Hence we are told : 



" Learn from yon Orient shell to love thy foe, 

 And strew with pearls the hand that brings thee woe. 



This is beautifully suggestive, yet seems to 

 be only half the story. While irritating sub- 

 stances are known to be covered by Tiacre it is 

 believed all pearls are not the result of irrita- 

 tion, but are secreted by the moUusk and held 

 ready to be dissolved by powerful acids, which 

 are also of the animal's secretion, for spreading 

 over openings made in their shells by the borer. 



" Injured shells are often found with their 

 points of irritation covered with thin lamina- 

 tions of this nacreous matter. 



" Pearl fishers, tell us the little pearl maker 

 is, sometimes at least, able to expel his jewel 

 at will, and often does so when captured ; un- 

 derstanding this, the fisher places his hand over 

 the shell so as to close its valves or secure the 

 pearl if ejected. 



" After possessing himself of all the pearls 

 in old mussels — the old being the most produc- 

 tive — the gatherer sometimes deposits the mol- 



