1903.J on the Pearl Fuheries of Ceylon. 285 



Minute grains of sand and other foreign bodies gaining access to the 

 body inside the shell, which are popularly supposed to form the 

 nuclei of pearls, only do so, in our experience, under exceptional 

 circumstances. Out of the many pearls I have decalcified, only one 

 contained in its centre what was undoubtedly a grain of sand ; and 

 from Mr. Hornell's notes taken since I left Ceylon, I quote the 

 following passage, showing that he has had a similar experience : — 



" February 16, 1903 — Ear-pearls. Of two decalcified, one from the 

 anterior ear (No. 148), proveil to have a minute quartz grain (micro, 

 preparation 26) as nucleus." 



It seems probable that it is only when the shell is injured, as, for 

 example, by the breaking off or crushing of the projecting " ears," 

 thereby enabling some fine sand to gain access to the interior, that 

 such inorganic particles supply the irritation which gives rise to 

 pearl formation. 



The majority of the pearls found free in the tissues of the body 

 of the Ceylon oyster contain, in our experience, the more or less 

 easily recognisable remains of Platyelmian parasites ; so that the 

 stimulation which causes eventually the formation of an " orient " 

 pearl is, as has been suggested by various writers in the past, due to 

 infection by a minute lowly worm, which becomes encased and dies, 

 thus justifying, in a sense, Dubois' statement that — " La plus belle 

 perle n'est done, en definitive, que le brillant sarcophage d'un ver." * 



To Dr. Kelaart (1859) belongs the honour of having first con- 

 nected the formation of pearls in the Ceylon oyster with the presence 

 of Vermean parasites. It is true that Filippi seven years before (in 

 1852), showed that the Trematode Distomum duplicatum was the 

 cause of pearl formation in the fresh-water mussel Anodonta, and 

 Kiichenmeister (1866), Moebius (1857), and others extended the 

 discovery to some of the larger pearl oysters, and to other para- 

 sites ; but it is probable that Kelaart knew nothing of these papers 

 and that he made his discovery in regar»l to the Ceylon oyster 

 quite independently. He (and the Swiss zoologist Humbert, who 

 was with him at a pearl fishery) found " in addition to the filaria 

 and cercaria, three other parasitical worms infesting the viscera and 

 other parts of the pearl oyster. 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." 



Thurston, in 1894, confirmed Kelaart's observation, finding in the 

 tissues, and also in the alimentary caual, of the Ceylon oyster, 

 " larvpe of some Platyhelminthian (flat-worm)." 



Garner (1871) associated the production of pearls both in the 

 pearl oysters and also in our common English mussel {Mytilus edulis) 

 with the presence of Distomid parasites ; Giard (1897) and other 



* Comptes Rendus, 14th Oct, 1901. 



