Proceedings of the Linnean Society of London - University Library

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 pearlformation,
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.