Page:Popular Science Monthly Volume 63.djvu/240

236 in a sense, Dubois' statement that—'La plus belle perle n'est done, en définitive, que le brillant sarcophage d'un ver.'

To Dr. Kelaart (1859) belongs the honor of having first connected the formation of pearls in the Ceylon oyster with the presence of vermean parasites. It is true that Filippi seven years before (in 1852), showed that the Trematode Distomum duplicatum was the cause of pearl formation in the fresh-water mussel Anodonta, and Küchenmeister (1856), Moebius (1857) and others extended the discovery to some of the larger pearl oysters, and to other parasites; but it is probable that Kelaart knew nothing of these papers and that he made his discovery in regard to the Ceylon oyster quite independently. He (and the Swiss zoologist, Humbert, who was with him at a pearl fishery) 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; and it may yet be found possible to infect oysters in other beds with these worms, and thus increase the quantity of these gems."

Thurston, in 1894, confirmed Kelaart 's observation, finding in the tissues, and also in the alimentary canal, of the Ceylon oyster, 'larvæ of some Platyhelminthian (flat-worm).'

Garner (1871) associated the production of pearls both in the pearl oysters and also in our common English mussel (Mytilus edulis) with the presence of Distomid parasites; Giard (1897) and other French writers have made similar observations in the case of Donax and other Lamellibranchs; and Dubois (1901) has more recently ascribed the production of pearls in mussels on the French coast, to the presence of the larva of Distomum margaritarum. Jameson (1902) then followed with a more detailed account of the relations between the pearls in Mytilus and the Distomid larvæ, which he identifies as Distomum (Brachycælium) somateriæ (Levinson). Jameson's observations were made on mussels obtained partly at Billiers (Morbihan ), a locality at which Dubois had also worked, and partly at the Lancashire Sea-Fisheries Marine Laboratory at Piel in the Barrow Channel. Finally, Dubois has just published a further note in which, referring to the causation of pearls in Mytilus, he says (p. 178): "En somme ce que ce dernier [Garner] avait vu en Angleterre en 1871, je l'ai retrouvé en Bretagne en 1901. Quelques jours après mon départ de Billiers, M. Lyster Jameson, de Londres, est venu dans la même localité et a confirmé le fait observé par Garner et par moi." But Jameson has done rather more than that. He has shown that it is