THE PEARL FISHERIES OF CEYLON. 237 



able (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 mussel. 



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

 there are several different kinds of worms commonly occurring as para- 

 sites, and we shall I think be able to show in our final report that 

 Cestodes, Trematodes and Nematodes are all concerned in pearl forma- 

 tion. Unlike the case of the European mussels, however, we find so far 

 that in Ceylon the most important cause is a larval Cestode of the 

 Tetrarhynchus form. 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 fish {Batistes mitis) which frequents the 

 pearl banks and preys upon the oysters. We have not yet succeeded in 

 finding the adult, but it will probably prove to infest the sharks or other 

 large Elasmobranchs which devour Balistes. 



It is only due to my excellent assistant, Mr. James Hornell, to 

 state that our observations on pearl formation are mainly due to him. 

 During the comparatively limited time (under three months) that I 

 had on the banks I was mainly occupied with what seemed the more 

 important question of the life-conditions of the oyster, in view of the 

 frequent depletion of particular grounds. 



It is important to note that these interesting pearl-formation 

 parasites are not only widely distributed over the Manaar banks, but 

 also on other parts of the coast of Ceylon, Mr, Hornell has found 

 Balistes with its Cestode parasite both at Trincomalie and at Galle, and 

 the sharks also occur all round the island, so that there can be no ques- 

 tion as to the probable infection of oysters grown at these or any other 

 suitable localities. 



There is still, however, much to find out in regard to all these 

 points, and other details affecting the life of the oyster and the pros- 

 perity of the pearl fisheries, Mr, Hornell and I are still in the middle 

 of our investigations, and this must be regarded as only a preliminary 

 statement of results which may have to be corrected, and I hope will 

 be considerably extended in our final report. 



It is interesting to note that the Ceylon Government Gazette, of 

 December 22 last, announced a pearl fishery, to commence on February 

 22, during which the following banks would be fished: 



The southeast Cheval Paar, estimated to have 49 million oysters. 



The East Cheval Paar, with 11 millions. 



The Northeast Cheval Paar, with 13 millions. 



The Periya Paar Kerrai, with 8 million — making in all over 80 

 million oysters. 



