Proceedings of the Linnean Society of London - University Library

24 PBOCEEDINGS OF THE
The view that the pearl is produced as a calcuhiswas originated
bv Eeaumur in 1717, followed bj Bohadsc-h in 1761, Mas supported
by Meckel and by Pagenstecher nearly a century later, and again
by Dr, George Harley in 1889. I agree with Giard that a
considerable resemblance between the pearl and an animal
calculus is compatible with the parasitic theory. Calculi commonly
form around a nucleus, and many parasites are known
to hare calcified cysts deposited over them. Some pearls, not the
best, are probably formed as calculus-like growths independently
of vermean parasites. Even when the parasite is present, the
pearl is produced by the mollusean host, and not by the parasite,
and so has been justly compared by more than one writer to an
animal gall.
It is commonly thought that the Italian naturalist F. de
Filippi originated in 1854 the view that the nucleus of the pearl
is really organic, being an encapsuled parasite. But Giard has
recently reminded us that Eondeletius propounded the same view
in 1558, and that ages before that Androstheues, who had
travelled in the East, is reported by Athena3us to have compared
the developing pearls in the oyster to the Cestode larvae in pork.
This, in the absence of microscopic examination, can scarcely be
regarded as a scientific demonstration ; but it was, at least, a very
happy guess, for one of the first facts Mr. Hornell and I were able to
determine in connection with the Ceylon pearl oyster in the spring
of 1902, was that the Orient pearl in the Gulf of Manaar is
deposited around the young larva of a Cestode,
Coming to actual identifications in comparatively recent times,
we find that Filippi's pearl- parasite in Amdonta cygnea was the
Trematode Distovnim duplicatum, v. Baer. Eobert Garner, in our
own Journal (Zool. vol. xi. 1871, p. 426) records " Distomes " from
both freshwater and marine mussels ; and Giard attributes the
origin of pearls in Donax and Tellina to a species of Brachy-
coeliwn—all cases of Trematoda. Several investigators since
(such as Dubois and Jameson) have found the same to be true
of the pearl-production in Mytilus edidis and in various other
Pelecvpoda.
Other observations, more recently, have shown Cestoda to be
the worms concerned in the production of the Orient pearl ; but
I do not go further into that matter on the present occasion, as
my purpose is to remind you of the historic connection between
Linnaeus and pearl-production.
Most of the attempts * at artificial margarosis—the production
of pearls by stimulation of tlie mollusc—have been based upon the
belief that the nucleus of the natural pearl is an inorganic particle.
The "grain-of-sand" theory was supported by Eedi and many other
early naturalists, and is the view that has been most generally
* There is also the other suggested method— by infection with the parasite
which I hope to discuss on another occasion.
—