176 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



It is this last paper by Dubois that has given rise 

 ^o 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 

 Mr. Hornell's and my observations, is certainly a Cestode. 



According to an interesting note by Prof. Giard* the 

 discovery of Cestode larvae as nuclei of pearls, which we 

 made upon the Ceylon Pearl-Oyster in 1902, has been 

 corroborated by M. G. Seurat, working independently in 

 his laboratory at Eikitea in the island of Mangareva 

 (Gambier Archipelago). The oyster on which Seurat 

 worked was a Meleagrina, and the Cestode parasite found 

 is, according to Giard, an Acrobothrium, or some allied 

 form. It is possible that some of our Ceylon Pearl-Oyster 

 parasites may also belong to the genus Acrobothrium, 

 although others 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 production 

 of pearls is not yet justified by the facts. Last of all M- 

 L. Boutant shows that fine pearls do not really differ from 

 nacre-pearls, since both are secreted from open or closed 

 epithelial sacs, derived from the epidermis ; and Giard 



* Comptes rendus, Soc. Biol., Paris, 6th Nov., 1903, lv., p. 1222. 

 f Comptes rendus, Acad. Sci., 14th Dec, 1903, p. 1073. 



