22 PROCKEDIXGS OY THE 



recount again the early history of this discovery, but the Linnean 

 Society may care to be reminded that the first in this country to 

 connect Trematode parasites with pearls in mussels was one of 

 our Fellows, Eobert Garner, whose paper on the subject will be 

 found in our Journal for 1871 ; and I may add that still earlier 

 in the last century another of our Fellows, Dr. E. P. Kelaart, 

 accounted for pearls in the Ceylon Pearl-Oyster by the presence of 

 platyhelminthian worms. 



Coming now to more recent work, especially during the last 

 four or five years, we must examine the matter more minutely. 

 The recent activity in this subject originated in France, and we 

 associate with the investigations there the names of our Foreign 

 Member Giard, of Dubois, Boutan, and iSeurat, Giard had 

 ascribed pearl-formation in the case of Donax and other Lamelli- 

 branchs to a Distomid worm, which he supposed to be a species 

 of Brachycoelium, but has since identified as Distomum constrictum, 

 Mehlis ; when Dubois, in 1901, visited a mussel-bed, near Billiers 

 (Morbihan) on the south coast of Brittany, which was kno^RTi to 

 be rich in pearls, and attributed the pearl-production to the 

 presence of a Trematode larva which he named Distommn mar- 

 garitartim. The next year, H. Lyster Jameson followed with a 

 more detailed account of the relation existing between the pearls 

 in Mytilus edulis and the Distomid larvse, which he, like others, 

 found, and which he identifies as belonging to the species Distomum 

 (Brachycoelium) somaterio}, the same subgenus as Giard had found 

 in Donax some years before. Jameson's observations were made 

 first at Billiers, the locality where Dubois had worked, and partly 

 nt the Lancashire Sea-Fisheries Laboratory of Piel in the BarroM' 

 Channel. Dubois published a further note* in January 1903, by 

 way of establishing his claim to have first made known the 

 dependence of the pearls at Billiers upon the Distomid larva. In 

 regard to the identification of the species of Trematode involved, 

 Odhner has recently shown that Jameson's larval stages and his 

 sexually mature form cannot belong to the same species, and that 

 both belong to the genus Gymno])haUus. 



The adult, according to Odhner t, is GymnapJialhis somatericf. 

 (Levinsen), and the larval form which causes the pearl-formation 

 in Mytilus belongs to Gymnophallus bursicola, Odhner. Li a still 

 more recent paper J Liihe also refers Jameson's stages to difi:'erent 

 species of Gymnophallus, but considers it probable that the one 

 causing the pearl-formation in the mussel is a distinct species 

 which must be called Gymnophallus margaritarum (Dubois). 

 Jameson's work may be said to have established quite clearly, if 

 any doubt previously remained, that in our common marine mussel 

 Trematodes are the parasites concerned in pearl-formation. 



There are, however, two points which were left in a somewhat 



* C. R. Acad. Sci. Jan. 19, 1903. 



t Fauna Arctica, iv. 2, p. 291 (1905). 



J ' Ueber die Entstehung der Perlen.' 



