The discovery of the parasitic origin of pearls was extended to the pearl-oysters and to other parasites by Küchenmeister[57] in 1856, by Möbius[58] in 1857, and by several other investigators. Prominent among these were E. F. Kelaart and his assistant Humbert, who, in 1859[59] disclosed the important relation which the presence of vermean parasites bears to the origin of pearls in the Ceylon oysters. These naturalists found “in addition to the Filaria and Cercaria, three other parasitical worms infesting the viscera and other parts of the pearl-oyster. We both agree that these worms play an important part in the formation of pearls.” Dr. Kelaart likewise found eggs from the ovarium of the oyster coated with nacre and forming pearls, and also suggested that the silicious internal skeletons of microscopic diatoms might possibly permeate the mantle and become the nuclei of pearls. Unfortunately, Dr. Kelaart’s investigations were terminated by his death a few months thereafter. In 1871, Garner ascribed the occurrence of pearls in the common English mussel (_Mytilus edulis_) to the presence of distomid larvæ.[60] Giard,[61] and other French zoölogists, made similar discoveries in the case of Donax and some other bivalves. In 1901, Raphael Dubois confirmed the observations of Garner, associating the production of pearls in the edible mussels on the French coasts with the presence of larvæ of a parasite, to which he gave the name of _Distomum margaritarum_, and boldly announced: “La plus belle perle n’est donc, en définitive, que le brillant sarcophage d’un ver.”[62] Prof. H. L. Jameson, in 1902, disclosed the relation which exists between pearls in English mussels (_Mytilus_) and the larvæ of _Distomum somateriæ_.[63] The life history of this trematode, as revealed by Dr. Jameson, is especially interesting from a biological standpoint, since it is entertained by three hosts at different times: the first host is a member of the duck family; the second is the Tapes clam (_Tapes decussatus_), or perhaps the common cockle (_Cardium edule_), which incloses the first larval stage, and the third is the edible mussel, in which the second larval stage of the parasite stimulates the formation of pearls. At the Brighton Aquarium and the Fish Hatchery at Kiel, Dr. Jameson claims to have succeeded in artificially inoculating perfectly healthy mussels with these parasites by associating them with infested mollusks, and thereby producing small pearls.