Their origin and formation. 1 1 7 



dissolution, and the nucleus of the Pearl, if of 

 inorganic matter, after having been the cause of 

 infinite annoyance to its unfortunate captor, is 

 returned to the place from whence it came. In 

 Fig. 4, p. 95, we have a representation of the 

 oyster shell after the Pearl has been passed through 

 the substance. 



It may be urged that the layers of shell enve- 

 loping the Pearl or blister, are laid equally upon 

 the top of it and at the sides ; and that an un- 

 natural 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 

 applicable to an oyster as to any other form of life, 

 and the same power that taught the oyster to pro- 

 tect itself against the inveterate attacks of its enemy, 

 the " borer," by increasing 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. 



