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THE PARASITES OF THE PEARL OYSTER. 



BY 

 ARTHUR E. SHIPLEY, M.A., F.R.S., 



FELLOW AND TUTOR OF CHRIST'S COLLEGE, CAMBRIDGE, 



AND 



JAMES HORNELL, F.L.S., . 



MARINE BIOLOGIST TO THE CEYLON GOVERNMENT AND INSPECTOR OF PEARL BANKS. 



[With FOUR PLATES.] 



INTRODUCTION. 



The history of the formation of pearls in European mussels around the Cercaria of 

 Trematodes is recorded in the papers of Garner (1871), Giard (1897), Dubois (1901) 

 and others, and it has recently been re-told in more detail by Dr. H. Lyster 

 Jameson.* The main part of Dr. Jameson's own observation was directed to the 

 Leiicit/nidcndrium (Distomum) somaterice (Levinsen) of the eider-duck (Somateria 

 mottissima, Linn.) and of a scoter (Oedemia nigra, L.), the sporocyst of which he 

 states is found in Tapes decussatus, Gmel., and in the cockle, Cardium edule, L., 

 whilst the tailless Cercaria infests the mussel, Mytilus edulis, and is the centre round 

 which the small lustreless pearls of that mollusc are formed. It has been pointed out 

 since that two points are still left in an unsettled condition by Jameson's paper, 

 viz. (1) the exact mode of origin of the epithelial sac around the parasite which 

 secretes the pearl, and (2) the supposed transference of the parasite from the cockle 

 to the mussel. 



With regard to the history of the relationship of internal parasites to the pearls 

 formed in the Ceylon pearl oyster, Margaritifera vulgaris, Schum. not a true 

 oyster but a member of the AviculibvE, and so allied to the mussel, Mytilus edulis 

 we quote two short paragraphs from Professor Herdman's Introduction to the first 

 volume of this Report : 



" To Dr. Kelaart (1857 to 1859) belongs the honour 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 Kitchenmeister (1856), Mobitts (1857), 

 * 'P. Zool. Soc.,' London, 1902, p. 110. 



