I conjecture that Linnæus alluded to this art in his writings so early as the year 1746, or long before he ever thought of keeping it a secret. The passage I mean is in the sixth edition of his Systema Naturæ, where he says, “Margarita. Testæ excrescentia latere interiore, dum exterius latus perforatur[772].” I once told him that I had discovered his secret in his own works; but he seemed to be displeased, did not inquire after the passage, and changed the discourse. That pearls are produced when the shells have been pierced or injured in a certain manner, is highly probable, and has been in modern times often remarked[773]. It appears also, that the animal has the power of sometimes filling up such openings with a calcareous substance, which it deposits in them. This substance assumes the figure of the orifice, and the animal particles it contains give it its brightness and lustre[774]. Pearl-fishers have long known that mussels, the shells of which are rough and irregular, or which exhibit marks of violence, commonly contain pearls, though they are found also in others in which the same appearances are not observed[775]. I am perfectly aware that some experiments made by piercing the shells of mussels, have been unsuccessful[776]; but this does not prove that it is impossible to procure pearls in that manner. Those who made them did not perhaps pierce the proper part of the shell; perhaps they made the orifice so large that it weakened the animal; and they may not have chosen the fittest season of the year. The strongest objection however which can be made on this subject, is the undeniable truth that the proper valuable pearls are not found adhering to the shell, but in the body only; and that therefore those calcareous balls which fill up holes, cannot be perfect pearls. But from the words of Linnæus above-quoted, I am led to conjecture, that he only made a hole in the shell without piercing it quite through. Linnæus also may have done some injury to the animal itself when it opened its shell; for it is certain that testaceous animals are strong-lived, and can easily sustain any violence. It appears by the Transactions of the Swedish Academy, that some have been of opinion that shell-fish might be made to produce pearls by a particular kind of nourishment; and Lister[777] thinks that these excrescences would be more abundant, were the mussels placed in water impregnated with calcareous matter; but Professor Linnæus seems certain that his father employed none of these methods.