1 62 PEARLS AND PEARLING 



the shell is used to envelop the foreign object. This be- 

 ing true, the part of the shell nearest the object would 

 not receive its full share of building material and would 

 therefore become dwarfed, while the other portions of 

 the shell receiving their full shares of building material 

 must be distorted to meet the portion which has not re- 

 ceived the normal amount of material. The fine pearls 

 are found in a number of different shapes, the most 

 valuable one being the perfectly round pearl. This shape 

 appears to be the most difficult for the mussel to de- 

 velop. 



Another desirable kind is the pear pearl. These are 

 nearly always found well formed and it appears to be 

 much easier for the mollusk to roll and coat them prop- 

 erly than the round or ball pearls. The high button and 

 low button pearls are usually pressed against the nacre 

 of the shell in such a manner as to prevent perfect coat- 

 ings of nacre from being applied to all parts of the 

 pearls. 



It is probable that some of the larger button pearls 

 were once ball pearls, but on account of their increasing 

 size they finally became pressed against the shell in a 

 manner which prevented a perfect coating of nacre so 

 they became some what flattened on one side, and in 

 some instances two sides became flattened on account of 

 the pearl touching both shells of the mussel. 



There are also other pearls which resemble eggs, bar- 

 rels and other objects. 



Most of the pearls which are found in the "crippled" 



