It should be known that the pearl-bearing oyster of the Indian Ocean is only remotely related to the edible variety of America and Europe. It is the _Margaritifera vulgaris_, claimed to belong to the animal kingdom, and not to the fish family, and is never eaten. The eminent marine biologist in the service of the Ceylon government, Professor Hornell, F. L. S., who intimately knows the habits of the pearl-oyster of the East, advances two interesting if not startling premises. One is that the pearl is produced as a consequence of the presence of dead bodies of a diminutive parasitical tapeworm which commonly affects the Ceylon bivalve. The living tapeworm does not induce pearl formation. The popular belief has been that the pearl was formed by secretions of nacre deposited upon a grain of sand or other foreign particle drawn within the oyster through its contact with the sea's bottom. The other Hornell assertion is that the oyster goeth and cometh at its pleasure; that it is mobile and competent to travel miles in a few weeks. [Illustration: MAP OF THE GULF OF MANAR, "THE SEA ABOUNDING IN PEARLS"] Scientists have long been aware that the pearl shell-fish possesses locomotive powers, which it uses when in quest of food or protection, and to escape impure localities. During the Dutch occupation of Ceylon, for example, there was a period of several years when the oysters' boycott of the Manar banks was virtually unanimous. It is an accepted fact that pearls are excretions of superimposed concentric _laminae_ of a peculiarly fine and dense substance, consisting in major part of carbonate of lime. Linnaeus, believing in the possibility of producing pearls by artifice, suggested the collecting of mussels, piercing holes in their shells to produce a wound, and bedding them for five or six years to give pearls time to grow. The Swedish government succeeded in producing pearls of a sort by this process; but as they were of trifling value, the experiments were discontinued.