PEARL PRODUCTION. 13 



pared with our results from Piel. He associates the occurrence of pearl-bearing 

 mussels in St. Andrews Bay with the presence of large numbers of parasites in the 

 wild ducks that feed upon these mussels ; and suggests that possibly other birds, 

 such as the oyster-catcher, may be found to harbour the same parasites. 



Professor R. Dubois, whose former observations had been made in Morbihan, has 

 since turned his attention to the Mediterranean coast. He found that the southern 

 French mussel {Mytilus gallo-provincialis) forms pearls caused by another Distomid, 

 distinct from that of Brittany. He then worked at the acclimatisation of a true 

 oriental pearl oyster (" pintadine ") in French waters and the artificial production 

 of pearls.* He brought the pearl oysters from the Gulf of Gabes, in South Tunis, 

 to the marine laboratory at Sfax, and caused them to multiply and increase in size. 

 The pearls produced in Tunis are small and very rare it is necessary to open 1,200 

 to 1,500 oysters to find one pearl; but Dubois tells us t that by placing them on 

 ground where Mytilus gallo-provincialis becomes infested with pearls and parasites, 

 he very easily provoked the production of fine pearls in the "pintadine" to such 

 an extent that three successive individuals opened contained each two little pearls. 

 This, if corroborated, is a remarkable circumstance from several points of view. 

 First, it will, if it proves a success, be a striking verification of what Kelaart 

 in Ceylon, fifty years ago, declared might be done. Secondly, if the "pintadine" 

 in question is really the same species as the Ceylon pearl oyster (Giard considers 

 that it is not), it is curious that a Distomid parasite should prove to be so efficacious 

 in setting up pearl- formation, since we have found that in the Gulf of Manaar the 

 pearl-parasite is a Cestode larva. Thirdly, it is remarkable that the parasite of the 

 Mytilus should transfer itself so readily to a new host belonging to a distinct family. 



It is this last paper by Dubois that has given rise to various more or less 

 exaggerated or even erroneous statements in the public Press, such as that the 

 pearl-oyster must be infected with a microscopic germ in order to render it pearl- 

 producing ; or even that inoculation with a serum causes the oyster to produce 

 artificial pearls. The parasite that causes the irritation is, as has been known for many 

 years, not a " germ," and still less a " serum," but a worm which is visible to the eye 

 a worm which in Mytilus seems to be usually a Trematode, and in the Ceylon pearl 

 oyster (Margaritifera vulgaris), according to our observations, is certainly a Cestode. 



According to an interesting note by Professor Giard,J the discovery of Cestode 

 larvae as nuclei of pearls, which we had made upon the Ceylon pearl oyster in 1902, 

 was shortly afterwards corroborated by Dr. L. G. Seurat, working independently 

 in bis laboratory at Rikitea in the Island of Mangareva (Gambier Archipelago). 

 The oyster on which Sburat worked was Margaritifera margaritifera, var. cumingi, 



* CuMBA had, however, in lSD'J, introduced the same mollusc on the South Coast of Italy, and 

 experimented there in artificial pearl-formation. 



t 'Comptes Rendu- A.cad. Sci.,' October 19, 1903, p. 611. 



J -Comptes Rendus Soc. Biol. Paris,' November 6, 1'JOo, lv., p. 1222. 



