Proceedings of the Linnean Society of London - University Library

LINNEAN SOCIETY OF LONDON'. 2$
According to an interesting note by Prof. Giard *, the discovery
of Cestode larvae as nuclei of pearls, which we had made upon the
Ceylon Pearl-Oyster in 1902, was shortly afterwards corroborated
by Dr. L. G. Seurat, working independently in his Laboratory at
Eikitea in the island of Mangareva (Gambler Archipelago). The
oyster on which Seurat worked was Mavgaritifera margaritifera,
var. cumingi, Eeeve, and tlie Cestode parasite found is, according
to Giard, an Acrobothrium ( = Cifathocephahis) or some allied form.
It is possible that some of our Ceylon Pearl-Oyster parasites may
also belong to the genus C'ljathocepTialus, although most 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's claim to have
established the artificial production of pearls is not yet justified
by the facts. Last of all Boutan t 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 very properly replies a few days later t that this fact is
quite in accord with general principles, and was previously known.
M. Boutan in a letter (20th Jan. 190-1) states that he is on the
point of departure for the East in order to investigiite the matter
further. But so far as I am aware, he has as yet made no further
contribution to the subject.
In what I told you of Linnaeus and pearls last year, the pearlforming
mollusc was a freshwater mussel of the genus Unio. In
the greater part of what I have told you now of the recent investigations
on the coasts of France and England, the molluscs in
question belong to the genus Mijtilus. But the pearl-formation in
which I personally have taken most interest, and which is of the
greatest importance to the pearl-merchant, is the Ceylon Pearl-
Oyster belonging to the genus Margaritifera,—and to that I now
pass.
I desire to pay passing tribute to the work of a pioneer. It was
Dr. Kelaart who, in the Gulf of Mauaar, half a century ago, first
connected pearl-formation in a true pearl-oyster with the presence
of Termean parasites. In his ' Introductory Eeport on the
Xatural History of the Pearl-Oyster in
describing the secretion of nacre by the
Ceylon' (1857), after
mantle, he said :— " It
AviU be thus clearly understood that when a gi'ain of sand or the
larva of an insect is introduced between the mantle and shell, it
will become covered over with the pearly secretion, which, always
going on, is augmented at the part where the foreign matter lies.
This phenomenon I have detected with the aid of the microscope
in its very earliest stage."' The probability is that by " larva of
* Comptes Kendus, Soc. Biol. Paris, 6 Ifov. 1903, Iv. p. 1222.
t Comptes Rendus Acad. Sci. 14 Dec. 1903, p. 1073 ; and also Arch. Zool.
Exp.'1904.
X Comptes Rendus, Soc. Biol. Paris, 19 Dec. 1903, p. 1618.