170 JOURNAL, R.A.S. (CEYLON). [VOL. XVI. 



The pearls produced by the above five species are of every 

 shade of colour, from the pale golden pearl of Northern 

 Australia to the lustrous black gem of the Bay of Panama. 

 Those most generally admired however, and which command 

 the highest prices, are of almost transparent whiteness, 

 with a slightly azure reflection. They are known as the 

 " pearls of the Orient," and are produced by the pearl 

 oyster (M. fucata) of the Gulf of Mannar. 



Nature and Formation of Pearls. 



It will be necessary for us to pause here for a moment to 

 consider what is up to the present time known of the nature 

 and formation of pearls, in order that this discussion may 

 have a sound basis. 



Pearls are an excretion of super-imposed concentric 



lamina} of a peculiarly fine and dense nacreous substance 



consisting of membrane and carbonate of lime. The question 



of their origin has a special attraction for the zoologist, 



since it still forms one of the unsolved problems of Science. 



Pliny held the belief that they were drops of dew or rain 



which fell into the shells when opened by the animals and 



were then altered by some power of the mollusc into pearls. 



This view obtained all over the East, and — strange to say — 



Columbus found the same belief popular among the natives 



of Mexico. Moore thus alludes to it in his poem " Peri and 



the Pearl":— 



" And precious the tear as that rain from the sky 

 Which turns into pearls as it falls in the sea." 



At the present day it is popularly supposed that all pearls 

 have for a nucleus a grain of sand which has become coated 

 with nacre by the animal ; but this is simply a conjecture 

 which has gradually become regarded as a fact. As a 

 general rule, it is some organic substance, which behaves in 

 the same way as epidermis when treated with certain 

 chemical re-agents. In some districts one kind of nucleus 

 seems to be more common than another, and this is how the 

 different results obtained by observers in different localities 



