PROBLEMS TO BE SOLVED, 



297 



One problem that might be solved by means of a great 

 aquarium is the Pearl problem. " What is a Pearl ] " has 

 been often asked. But it is a question which no man has yet 

 been able to answer. Some say that these gems are the result 

 of disease in the animal, whUe others maintain the pearl to be 

 produced by the introduction of some foreign substance into the 

 ^hell. Having studied the question a little, more especially as 

 concerns the Scottish pearl, I have come to the conclusion that 

 the production of the pearl is quite accidental, and that, as has 

 been asserted by some writers on the subject, it is not a result 

 of a hereditary kind. There is no special breed of mussels that 



produces the pearl. The above drawings of Scottish pearl shells 

 are very accurate, and give a good idea of the style of mussel 

 which produces the most beautiful gem of Scotland. Practised 

 collectors always select deformed or " wrinkled " shells as being 

 more likely to contain pearls than those of a smooth surface. 

 Scottish pearls have become scarce of late, owing to their 

 having been so largely fished for ten years ago — another proof 



