Note 2613 — BOOK IX. THE NATURAL HISTORY OF FISHES.

The pearl itself, Cuvier says, is nothing else but an extravasation, so to say, of the juices, whose duty it is to line the interior of the shell, to thicken and so amplify it; and consequently, it is produced by a malady. It is possible, he says, for them to be found in all shell-fish; but they have no beauty in them, unless the interior of the shell, the nacre, or, as we call it, the mother of pearl, is lustrous and beautiful itself. Hence it is, that the finest of them come from the east, and are furnished by the kind of bivalve, called by Linnæus, “Mytilus margaritiferus,” which has the most beautiful mother of pearl in the interior that is known. The parts of the Indian sea which are mentioned by Pliny, are those in which the pearl oyster is still found in the greatest abundance.