94 PEOCEEDINGS OE THE 



since I came out here I have had no chance to continue my 

 pearl-work." 



From this it seems clear that Dr. Jameson would now agree 

 with his critics (such as Boutau) ; and in fact I take it that all 

 who are working on the subject are now agreed that the epithelium 

 of the sac secreting the pearl must be derived, directly or indirectly, 

 from the nacre-secreting ectoderm covering the outside of the 

 mantle. 



To return to the French investigators, Dubois, whose first 

 observations were made in Brittany (1901), has since turned his 

 attention to the Meditei'ranean Coast. He there finds that the 

 Southern French Mussel {Mytilus gaUo-jJrovlneialis) forms pearls 

 caused by another species of Distomid. He then worked at the 

 acclimatization 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 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 1200 to 1500 oysters to find one pearl ; but 

 Dubois telis us (C. E. 19 Oct. 1903, p. Gil) 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 when he said — " It may yet be found possible to 

 infect oysters in other beds with these worms, and thus increase 

 the quantity of tliese gems," 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 Mr. Hornell and I found that, in the Gulf of 

 Manaar, the pearl-parasite is a Cestode larva. Thirdly, it is 

 remarkable that the parasite of the Myiilvs 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 Mr. Hornell's and my 

 observations, is certainly a Cestode. 



