96 
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 imoculation 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 larvee as nuclei of pearls, which we 
made upon the Ceylon Pearl-Oyster in 1902, has been 
corroborated by M. G. Seurat, working imdependently in 
his laboratory at Rikitea 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 certamly 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. Boutan+ shows that fine pearls do not really differ from 
nacre-pearls, smce 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. 
+ Comptes rendus, Acad. Sci., 14th Dec., 1903, p. 1073. 
