Natural History of Molluscous Anwials. 249 



Art. XI. An Introduction to the Natural History of Molluscous 

 Animals. In a Series of Letters. By G. J. 



Letter 4. Benefits. 



Sir, 



So far from having, as you may suppose, estimated too highly 

 the use of molluscous animals in the economy of nature, or 

 exaggerated their importance to man, I, on the contrary, 

 feel persuaded of having understated both ; and it would have 

 been easy for a naturalist, more favourably situated for in- 

 vestigation, to have made out a much " stronger case." Your 

 future studies will soon convince you of this ; and, in the mean 

 time, the additional facts about to be detailed will prove that 

 I have by no means exhausted my subject. To proceed. 



Pearls are not, as poets have feigned, 



" rain from the sky, 

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



but they are the morbid secretions of an oyster. Several 

 species of bivalved shellfish produce them, but the greater 

 number, the finest and the largest, are procured from the 

 Meleagrina margaritifera Lamayxk ( fig. 44. «), a native of 



the sea, and of various coasts. A considerable number are 

 likewise taken from the U'nio margaritifera {b), which inha- 

 bits the rivers of Europe ; and it is singular, as remarked 

 by Humboldt *, that though several species of this genus 

 abound in the rivers of South America no pearls are ever found 

 in them 



The pearls are situated either in the body of the oyster, or 



* Personal Narrative, vol. ii. p. 282. 

 Vol. IIL— No. 13. s 



