544 



THE POPULAR SCIENCE MONTHLY 



Free Pearls from the Abalone. The central pearl large and valuable. 

 From the collection of C. B. Linton. 



centuries. As related in ancient folk-lore, the pearl-oyster, rising to 

 the surface of the sea in the early morning, opens wide the valves of its 

 shell, so that dew-drops may fall within. Under the influence of the 

 air and warm sunshine lustrous pearls develop from these glistening 

 drops of dew. The pearls are white when the weather is fair, hut dark 

 if it is cloudy. This belief was held from the first to the fifteenth 

 centuries, when the theory was advanced that the eggs of the pearl- 

 oyster serve as nuclei for pearls. About the middle of the sixteenth 

 century Eondelet concluded that pearls form from diseased concretions, 

 and then, in 1600, Anselmus de Boot demonstrated that they are made 

 of the same substance as the shell. Eeaumur, in 1717; showed by aid 

 of the microscope that the pearl is composed of concentric layers of 



