INTRODUCTION. 1 I 



increase the quantity of these gems." Thus we have Kelaart, in 1859, definitely 

 stating the possibility, in the case of the Ceylon pearl oyster, of infecting other heds 

 with the larvae of the pearl-producing Platyhehninthian parasites in order to increase 

 the quantity of pearls. 



Thurston, in 1894, confirmed Kelaart's observation, finding in the tissues and 

 also in the alimentary canal of the Ceylon oyster, " larvae of some platyhelminthian 

 (flat worm)." He figures (' Madras Mus. Bull.,' I., Plate II., fig. 1) a section showing 

 two of the parasites encysted between the alimentary canal and generative tuhes. 

 Here the matter rested so far as the Ceylon pearl oyster was concerned. 



Long before, however, Garner, in 1871, had associated the production of pearls 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 mavgaritantm. H L. Jameson (1902), then followed with a more 

 detailed account of the relations between the jjearls in Mytilus and the Distomid 

 larvae, which he identifies as belonging to Distomum (Brachycoelium) somateriw 

 (Levinsen). 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 (Comptes Rendus Acad. Sci. Paris, 

 19th Jan., 1903) 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 retrouve en Bretagne en 1901. Quelques jours apres mon depart de Billiers, 

 M. Lyster Jameson, de Londres, est venu dans la merae localite et a confirme le fait 

 observe par Garner et par moi." But Jameson has done rather more than that. 

 He has shown that it is probable (his own words are " there is hardly any doubt ") 

 that the parasite causing the pearl-formation in our common Mussel (not in the 

 Ceylon pearl oyster) is the larva of Distomum somaterice, from the eider duck and 

 the scoter. He also believes that the larva inhabits Tapes or the cockle as a first 

 host before getting into the nmssel. 



We have found, as Kelaart did, that in the Ceylon pearl oyster there are several 

 different kinds of worms commonly occurring as parasites, and we shall, I think, be 

 able to show in a later section of this report that Cestodes, Trematodes, and Nematodes 

 may all be concerned in pearl-formation. Unlike the case of the European mussels, 

 however, we find that in Ceylon the most important cause is a larval Cestode of the 

 Tetrarhynchus form. We first found this larva in pearl-like cysts outside the liver 

 of pearl oysters on the Cheval Paar during the second cruise of the " Lady Havelock" 

 in February and March, 1902. Since then Mr. Hornell has traced a considerable 

 part of the life-history of this parasite, from an early free-swimming stage to a late 

 larval condition in the File-fishes (Batistes mitis and B. stellatus) which frequent the 



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