14 CEYLON PEARL OYSTEE REPOET. 



Reeve, and the Cestode parasite found, is, according to Giard, an Acrobothrium 

 (= Cyathocephalus) or some allied form. Some of oui>Ceylon pearl-oyster parasites 

 very closely resemble the figures given by Giard, and possibly may also belong to 

 the genus Cyathocephalus, although most of them are certainly Tetrarhynchids. 



Giard, in a further note in the same Journal (p. 1225), discusses the statements 

 that have been made in regard to " margarose artificielle," and evidently considers 

 that Dubois' claim to have established the artificial jjroduction of pearls is not 

 yet justified by the facts. About the same time, M. L. Boutan* wrote showing that 

 " fine pearls " do not really differ from " nacre-pearls," since both are secreted from 

 open or closed epithelial sacs derived from the ejudermis ; and Giard very properly 

 replied, a few days later, f that this fact is quite in accord with general principles, and 

 was previously known. M. Boutan then published a more detailed account^ giving 

 figures illustrating his point that in all cases the pearl-sac is formed by an invagination 

 of the surface of the mantle, and that it is of ectodermal origin, not mesodermal as he 

 supposed Jameson to have indicated. Finally, in a letter (January 20, 1904) to one 

 of us, he states that he is on the point of departure for the East in order to investigate 

 the matter further. The results have not yet appeared. 



CEYLON PEARLS AND PARASITES. 



Turning now to the investigations on the Ceylon pearl oyster in the Gulf of 

 Manaar, let us first recall the Avork of our predecessor, Dr. E. F. Kelaart, in the 

 same field and on the same animal nearly half a century ago. Kelaart, in 1857, in 

 his " Introductory Report on the Natural History of the Pearl Oyster of Ceylon," 

 after describing the secretion of nacre by the mantle, said : " It will be thus 

 clearly understood, that when a grain of sand or the larva of an insect is introduced 

 between the mantle and shell, it will become covered over with the pearly secretion ; 

 which, always going on, is augmented at the part where the foreign matter lies. This 

 phenomenon I have detected with the aid of the microscope, in its very earliest 

 stage." The probability is that by "larva of an insect" in this passage Kelaart 

 meant such an organism as the Cestode larva which we now find is the determining 

 cause of such pearl-formation. 



In another passage, in his " Report on the Pearl Banks of Arripo for Season 1858," 

 he says : " The presence of a worm (a species of Filaria) found in the oysters has, I 

 am positive, much to do with the formation of pearls. I would rather reserve this 

 part of my investigation for longer experience. But this much I can say at present, 

 with perfect safety : that whenever I found good pearls in a batch of oysters, I found 

 this worm and its eggs in large numbers in the liver, ovary, mantle, and other parts 



* ' Comptes Eendus Acad. Sci.,' December 14, 1903, p. 1073. 



t ' Comptes Eendus Soc. Biol. Paris,' December 19, 1903, p. 1618. 



} -'Les Perles Fines : leur Origine reelle," 'Arch. Zool. Exper.,' ser. 4, t, ii., p. 47, 1904. 



