10 CEYLON PEARL OYSTER REPORT. 



gain access to the interior, that such inorganic particles supply the irritation which 

 gives rise to pearl formation. 



Pearls of another class are found in the muscular tissue of the animal, usually in 

 the levators of the foot, and in the palpar region, hut also frequently in the pallial 

 insertions, rarely at the insertions of the retractor and adductor muscles. These 

 muscle-pearls have no organic nuclei. They seem to start as minute calcareous 

 concretions (" calcospherules ") in the tissue, and the centre is sometimes crystalline. 

 They may be extraordinarily abundant. At the insertion of one levator muscle, 

 23 small pearls were counted with the eye, while under the microscope 170 additional 

 tiny spherules were found to be present. 



The best pearls, however, the " cyst " or " orient " pearls, lie in the thin muscular 

 margin of the mantle, or in the thick white lateral part over the stomach and liver, 

 or even, secondarily, free in a cavity of the bod v. 



Consequently, as we shall show in the section of the Report dealing with pearl- 

 formation, Ave can classify these pearls from the biological point of view into three 

 sets : (a.) " Ampullar-pearls " which are not formed within closed epithelial sacs 

 like the others, but lie in pockets or ampulla? of the epidermis. The nuclei may lie 

 sand-grains or any other foreign particles introduced through breaking or perforation 

 of the shell, (b.) "Muscle-pearls"' formed around calcospherules at or near the 

 insertions of the muscles, (c.) '"Cyst-pearls" where concentric layers of nacre are 

 deposited on cysts containing parasitic worms in the connective-tissue of the mantle. 



The majority of the fine pearls found in the soft tissues of the body of the Ceylon 

 oyster contain, in our experience, the more or less easily recognisable remains of 

 Platyhelminthian parasites (especially the young larva of the Cestode Tetrarhynchus), 

 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 

 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" (Comptes Rendus Acad. Sci. Paris, 14th Oct., 1901). 



To Dr. Kelaart (1857-59) belongs the honour of having first connected 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 

 Kuchenmeister (1856), Mobius (1857), and others extended the discovery to other 

 pearl-producing oysters, and to other parasites ; but it is possible that Kelaart 

 knew nothing of these papers, and that he made his discovery in regard 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 Circaria, 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 



