REMARKS ON DR. PEARSON'S REVIEW. 127 



£1 ,000. With regard to overfishing there is not the shghtest 

 doubt that this took place during the Company's regime, as 

 indeed it has done at every fishery, but if Dr. Pearson's 

 interpretation of our current work is correct, this could not 

 have mattered, since any spat liberated by oysters which 

 might have been left for breeding purposes would have been 

 carried away, a conclusion with which I entirely disagree. 



Pearl Production. 

 I made the first attempt to ascertain the exact nature of 

 fche parasites contained in the globular cysts found scattered 

 about in the tissues of the oyster, by the only method possible, 

 viz. , by feeding experiments. Various fish were fed on oysters 

 containing the cysts. The fish were first treated with castor 

 oil and male fern extract in order to get rid, if possible, of any 

 parasites already present in their intestines. A test examina- 

 tion of a dosed ray indicated that the purgative had been 

 fairly effective. After the other fish had been feeding on 

 oysters for several weeks, they were killed and carefully 

 examined. Large numbers of Tetrarhynchus unionifactor 

 (the pearl-inducing worm) were found. Other cestodes were 

 also found, viz., Tetrarhynchus herdmani, Phyllobothroides 

 hutsoni,. and Phyllobothroides kerkhami. In my reports 

 {Ceylon Marine Biological Eeports, Parts IV. and V.) I pointed 

 out that the experiment was not absolutely conclusive, but 

 that there was every reason to believe that T. unionifactor 

 was the adult of the pearl-inducing worm, and that other 

 species found as a result of the feeding experiments were 

 parasites already present in the intestines of the fish when the 

 experiment was begun, and which the purgative had failed 

 to dislodge. The strength of the evidence lay in the fact that 

 T. unionifactor was obtained on 6o^^ occasions, and that in all 

 other rays examined from the open sea, and which had not been 

 fed on oj^sters, no specimens of this species had been obtained, 

 although Tetrarhynchus herdmani, Phyllobothroides hutsoni, 

 and Phyllobothroides kerkhami were common. The circum- 

 stantial evidence is as strong as it could well be. Every 

 feeding experiment is always open to the objection that unless 

 the animal to be fed on larval cestodes is actually killed and 

 examined, anj^ critic can say that the adult parasite was already 



