“Pearl shells in Norway do breed in sweet waters: their shells are like mussels but larger: the fish is like an oyster, it produces clusters of eggs: these, when ripe, are cast out and become like those that cast them: but sometimes it appears that one or two of these eggs stick fast to the side of the matrix and are not voided with the rest. These are fed by the oyster against her will, and they do grow, according to the length of time, into pearls of different bigness, and do imprint a mark both on fish and shell by the situation conform to its figure.” The eminent surgeon, Sir Everard Home, unaware of the letter of Sandius, arrived at the same conclusion independently. He writes that this, “the richest jewel in a monarch’s crown which cannot be imitated by any art of man, either in beauty of form or brilliancy of lustre is the abortive egg of an oyster enveloped in its own nacre.” Darwin (Economy of Vegetation) writes that pearls are formed “like those calcareous productions of crabs known by the name of ‘crabs’ eyes’ which are always near the stomach of the creature. In both cases the substance is probably a natural provision either for the reparation or enlargement of the shell.” [Illustration: Small Necklet of Perfect Oriental Pearls Kelsey I. Newman Collection ] Mr. Kelaart in his reports to the Government of Ceylon (1857-1859), seems to be the first to allude to the part played by parasites in the production of pearls in tropical seas. The researches of Professors Herdman and Hornel confirmed the deductions of Kelaart that the larva of a Cestoid was the identified pearl parasite. Monsieur Seurat, the French naturalist, who made a long study of the pearl oyster of the Pacific, was also convinced that pearl formation was caused by a parasite. Whatever the cause of the irritability which brings into action the nacreous secretion of the tortured oyster, it is evident that the protective process is a long one. The pearl culture industry of the Chinese and Japanese has shown that it takes twelve months for the irritant to be covered with a coat of a tenth of a millimetre. A new layer is formed over the old one about once a year. Pearlers say that an oyster must be at least four years old before pearls begin to form properly, and that it does not mature for from 7 to 9 years. The beautiful lustre of the pearl Sir Everard Home held to arise from a central cell of bright nacre, the diaphanous substance admitting the light rays. “Upon taking a split pearl,” he writes, “and putting a candle behind the cell, the surface of the pearl became immediately illuminated; and upon mounting one with coloured foil behind the cell, and by putting a candle behind the foil, the outer convex surface became universally of a beautiful pink colour.” The examination of a half pearl will show the concentric formation which is like an onion, and the process called “skinning” is often resorted to in the endeavour to gain