2o PEARLS AND PEARLING 



small lumps of mother-of-pearl covered by the secretions 

 of the mollusk. Then again they appear to be due to an 

 irritation caused by the introduction of some foreign ob- 

 ject. All these objects gradually become coated with 

 layers of nacre. 



These are found in a large variety of forms ; but 

 never assume the perfect shape of any of the styles of 

 the fine pearls. 



In this chapter, therefore, we shall give our attention 

 mostly to the study of the formations that are only found 

 in or near the mantle at the posterior or thin end of the 

 shell. 



As the pearl has been known for so many centuries, it 

 is quite probable that its origin was a much debated ques- 

 tion in ancient times ; yet the old historians have not re- 

 corded anything more than a few far-fetched stories that 

 are referred to as legends and that do not offer any 

 reasonable theories as to the origin of this brilliant 

 jewel. 



For more than 350 years the best scientists have been 

 studying the origin of the pearl. Their efforts have re- 

 sulted in many theories which differ widely and all are 

 interesting. Our first record is that of the experience of 

 Rondelet in 1554. He considered pearls to be concre- 

 tions due to disease, like the calculi of mammals. In the 

 sixteenth and seventeenth centuries some writers regarded 

 pearls as the eggs of the mollusk. In 1826 a scientist 

 named Home advanced a similar theory, stating that 

 pearls were formed around eggs that had failed to be ex- 

 pelled by the oviduct. 



