PEARL PRODUCTION. 15 



of the oyster." Tin's " Filaria " may possibly be either the Ascaris or the 

 Cheiracanthus which we have found, and which are described as new species by 

 SHIPLEY and HORNELL ; or it may possibly be the elongated, later stage of the 

 Tetrarhynclms larva which also occurs. 



Finally, at the end of KE LA ART'S last Report (1859) occurs the remarkable passage 

 where, in speaking of the corroborative observations of Mons. A. HUMBERT, he said : 

 " We both agree that these worms play an important part in the formation of pearls ; 

 and it may yet be found possible to infect oysters in other beds with these worms, 

 and thus increase the quantity of these gems." As we stated in the Introduction to 

 this work (Part L, p. 7, 1903), "Dr. KELAART'S short reports show that he was 

 tackling the problems in a scientific manner, and his researches were incomplete at 

 the time of his sudden death."* We may take these observations as our point of 

 departure. THURSTON, in 1894, however, confirmed KELAART, finding in the tissues 

 and also in the alimentary canal of the oyster " larvae of some platyhelminthian (flat 

 worm) " ; but he was able to add little beyond figuring (" Madras Museum Bulletin," 

 L, Plate ii., fig. 1) a section showing two of the parasites encysted between the 

 alimentary canal and the gonads. Here the matter practically rested so far as actual 

 investigation of the Ceylon pearl oyster was concerned, until we found the Cestode 

 larvae in association with pearls in the tissues during our cniises in the "Lady Havelock " 

 in the Gulf of Manaar, in February and March, 1902. It was about March 6th (see 

 " Narrative," p. 70, in Part L), when cutting up oysters from the western part of the 

 Cheval Paar, that we first became convinced that the opaque white globular larvae we 

 were finding encysted in the liver belonged to Cestode worms. Subsequent work 

 showed us that some of them at least were referable to the genus Tetrarhynchus, 

 and the various stages that we were able to find up to the spring of 1904 were 

 described by SHIPLEY and HORNELL in Part II., p. 79. 



Since then large numbers of pearl oysters from various paars in the Gulf of Manaar 

 have been examined by us in the field and in the laboratory, and although many 

 small pearls and many parasites have been found, it is apparently very difficult indeed 

 to hit upon a stage showing the commencement of the pearl- formation, or any evidence 

 bearing on the entrance of the parasite into the mollusc. 



The youngest stages in the life-history of Tetrarhynchus are still unknown, and it 

 is still uncertain whether the free-swimming larvae found on Muttuvaratu Paar really 

 belong to this life-history. They have calcareous corpuscles and an indication of an 

 invaginated head, and are almost certainly young Cestodes. We reproduce here 

 (fig. 1) four of the figures of this presumed youngest stage, given by SHIPLEY and 

 HORNELL, and are unable to add anything to their statement (loc. cit., p. 86) : " On 

 the whole we think it probable that this larva is the first stage in the life-history of 

 the pearl-forming organism," &c. 



* When in medical attendance on General LOCKYER. Both the General and the Doctor died in the 

 Red Sea, in 1859. 



