212 SPOLIA ZEYLANICA. 



be accepted, extensive cultching in the pearl banks is not a feasible 

 scheme, and in the later years the Ceylon Company of Pearl Fishers, 

 who were bound under their agreement to deposit at least 500 tons 

 of cultch each year, were able to induce Government to forego that 

 stipulation. 



The work subsequent to Herdnian's reports gives very little 

 evidence that his recommendations have heen carried out seriously. 

 With the exception of cultching, which appears to be impracticable 

 on a large scale, there is little evidence to show that efforts were 

 made to seriously guard against the alleged evils of overfishing and 

 overcrowding. We have yet to learn the importance of these two 

 factors in regard to the problems which are awaiting solution. 



Peabl Production. 



In addition to their investigations upon the main problem, 

 Messrs. Herdman, Hornell, and Southwell have considerably 

 extended oui^ knowledge of the sujiposed pearl -inducing parasite. 

 Herdman and Hornell determined the Ceylon pearl to be formed 

 around the larva of a tapeworm, Tetrarhynchus unionif actor . 

 Herdman was of opinion that three hosts are probably concerned 

 in the life -history of the parasite, namely, the pearl oyster, a large 

 ray, and Balistes. While Southwell agreed as to the nature of the 

 parasite, he did not believe that three hosts were concerned ; and 

 he made two series of experiments, with the object of showing that 

 the life-cycle of the tapeworm could be completed within the pearl 

 oyster and ray without the intervention of a bony fish. This con- 

 viction apparently was not shaken when the experiments produced 

 only negative results. 



A small area of the sea bottom was enclosed by expanding metal 

 and stocked with oysters. In the 1909 experiment some 36,000 

 oysters were deposited in the enclosure, and four fish, after being 

 treated with male fern extract and castor oil, were introduced, viz., 

 Tetrodon unimaculatus , Tetrodon stellatus, Ginglymostoma concolor, 

 and Tseniura melanospilos. 



At the end of twenty-eight days the fish were killed, and an 

 examination of the gut-contents revealed the absence of any adult 

 cestodes from the two species of Tetrodon. In Ging. concolor there 

 were 51 T. unionif actor ^nd 48 Tetr. herdmam, and in Taeniura 

 melanosfilos there were 150 Tetr. herdmani. 



In 1910 a second experiment was tried. 12,000 oysters were 

 placed in the enclosure, together with the following fish : — Serranus 

 undulosus, Ginglymostoma concolor, and Trygon walga. In about 

 seven weeks' time the fish were killed, and only Ginglymostoma 

 concolor proved to have any adult cestodes. Three species were 

 represented : 38 specimens of T. unionif actor , 140 specimens of 

 Phyllobothroides hutsoni, and 9 specimens of Phyllobothroides 

 kerkhami. 



