MYA MARGARITIFERA, (Encycl.) Linnæus has made a remarkable discovery relating to the generation of pearls in this fish. This must not be confounded with what is called the mother-of-pearl shell, as that belongs to another genus, is a sea-shell, and an inhabitant of the warmer countries only. The shell-fish in question is found in rivers in all the northern parts of the world; in Norway and Sweden it abounds; it is found in the rivers of the county of Tyrone in Ireland, and in those of Donegal; in Scotland, the Don is said to abound with it; and it is not unfrequent in the rivers of England. This fish will bear removal remarkably well; and it is said, that in some places they form reservoirs for the purpose of keeping it, and taking out the pearl, which, in a certain period of time, will be again renewed. From observations on the growth of these shells, and the number of their annular laminae, or scales, it is supposed the fish will attain a very great age; 50 or 60 years are imagined to be a
moderate computation. The discovery turned on a method which Linnæus found, of putting these muscels into a state of producing pearls at his pleasure; though the final effect did not take place for several years: He says, that in five or six years after the operation the pearl would have acquired the size of a vetch. We are unacquainted with the means by which he accomplished this extraordinary operation; but it was probably published at the time, and considered as important, since it is certain that the author was rewarded with a munificent premium from the States of the kingdom on this account. We regret that we cannot speak more fully on this head; but may observe, that it is probable, from a paper published many years afterwards in the Berlin Acta, that the method consisted in injuring the shell externally, perhaps by a perforation; as it has been observed, that these concretions in shell-fish are found on the inside, exactly opposite to perforations and injuries made from without by serpents and other animals.