Proceedings of the Linnean Society of London - University Library

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 Lamellibranchs
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 margaritartim.
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.'