492 THE PEARL FISHERIES OF CEYLON. 



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

 Distomnm somateria% 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 C^eylon j^earl oyster 

 there are several different kinds of worms commonly occurring as 

 ])arasites, and we shall, I think, be able to show in our final rej^ort that 

 Cestodes, Trematodes, and Nematodes are all concerned in pearl 

 formation. 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. Honiell 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 (Balistes mitis) which 

 frequents the peai-1 banks and preys npou the oysters. We have not 

 yet succeeded in finding the adult, l)ut it will jjrobabiy prove to infest 

 the sharks or other large Elasmobranchii wliich devour T^alistes. 



It is only due to my excellent assistant, JVfr. Jauses Iforuell, to state 

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

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

 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 para- 

 sites are not only widely distributed over the Manaar baidvs, but also 

 on other parts of tlie coast of Ceylon. Mr. Hornell has found Balistes 

 Avith its Cestode parasite both at Trincomalie and at Galle, and the 

 sharks also occur 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, mnch to find out in rc^o'ard to all these 

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

 perity of the jiearl tishei'ies. Mi-, irornell and I are still in the mid- 

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

 nary statement of results which may have to be coi'rected, and I hope 

 will be considerably extended in our final re}K)rt. 



It is interesting to note that the Ceylon (Government Ciazette of 

 December '22 last announced a pearl fishery to conmience on Febru- 

 ary 22, during which the following l)anks Avould be fished: The 

 Southeast Cheval Paar, estimated to have 41) million oysters; the 

 East Cheval Paar, Avith 11 millions; the Northeast Cheval Paar, 

 Avith 13 millions; the Periya Paar Kerrai, Avith S uiillion — making in 

 all over 80 million oysters. 



That fishery is now in pi'ogress, Mr. llornell is attending it, and 



