492 THE PEARL FISHERIES OF CEYLON. 



common mussel (not in the Ceylon "pearl oyster") is the larva of 

 Distomum soniateria>. from the eider duclv and the scoter. He also 

 believes that the larva iiihahits Tapes or the cockle as a first host 

 Ix'fore jrrettinii' into the mussel. 



We have found, as Kelaarl did. that iu the Cevh)n })earl oyster 

 there are several different kinds of worms connnonly occurring as 

 ])arasites, and we shall, I think, be able to show in onr final report that 

 Cestodes, Trematodes, and Nematodes are all concerned in pearl 

 formation. TJnlike the case of the European mussels, however, we 

 find so far that in Ceylon the most important canse is a larval Cestode 

 of the Tetrai'hynchus 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 (Halistes mitis) which 

 frequents the pearl banks and ])reys upon the oysters. We have not 

 yet succeeded in finding the adult, l)ut it will probably prove to infesi 

 the sharks or other large Elasmobranchii which devour Balistes. 



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

 that our observations on pearl formation are maiidy due to him. 

 During the comparatively limited time (under three months) that 1 

 had on the banks I was mainly occuj^ied 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 2:)eai"l-formation para- 

 sites are not only widely distributed over the IVianaar banks, l)ut also 

 on other parts of the coast of Oylon. Mr. Hornell has found Balistes 

 with its Cestode ])arasite both at Trincomalie and at Galle, and the 

 sharks also occui- all around 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. PTornell and I are still in the mid- 

 dle of our investigations, and this must be regarded as only a prelimi- 

 nary 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 Covernment Gazette of 

 December 22 last announced a pearl fishery to commence on Febru- 

 ar}^ 22, during which the following banks would be fished: The 

 Southeast Cheval Paar, estimated to have -fl) 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. 



That fishery is now in progress, JNIr. Hornell is attending it, and 



