Proceedings of the Linnean Society of London - University Library

LI^NEA^' sociExr of london. 21
Seychelles, has undoubtedly been, would be creditable to any
Society ; and when that exploration is a biological one, dealing
with land plants and marine algae as well as with deep-sea animals,
and with general problems of distribution and association and
habitat such as concern both sides of our house, it is difficult to
see what Society could more appropriately undertake the task than
our own. The Sladen Trust has made a financial offer to our
Council which will meet half the expenses of tlie publication, and
we may look forward to receiving as Fellows a special series of
about six extra volumes of our ' Transactions ' devoted to the
Fauna and Flora of the Indian Ocean.
Committees appointed by the Council are now deliberating on
such important matters as Zoological Nomenclature, the destiny
of the AVallichiau Herbarium, and the form of our Publications
subjects of interest to all of us.
This review of some of the chief events of the Session will
perhaps serve to show that the Linnean Society is still performing
important functions in the advancement of Natural Science ; and
that your Council has its hands full of interesting work requiring
careful attention.
In my Addi*ess last year I chose for some further remai-ks the
historic connection between the production of artificial pearls and
the great Linnaeus, whose reputed birthday we commemorate at
this Anniversary Meeting ; and that enabled me to treat bi'iefly
of one side of the interesting biological process known as " pearlformation."
I propose on the present occasion to complete the
subject, so far as I am able, by discussing briefly the other methods
of pearl-formation apparently unknown to Linnaeus.
I pointed out last j^ear that " there are three main methods which
have been advanced as explaining the formation of pearls ; and,
as is so often the case where there are several competing theories,
it cannot be said that one only is correct and of universal appli-
cation, and that the others are quite erroneous. The three I refer
to are:—(1) the grain-of-sand irritation; (2) the pathological
secretion ; and (3) the stimulation caused by the presence of a
parasitic worm, which acts as a nucleus around which an epithelial
sac deposits successive layers of pearly material." I discussed
sufficiently on that occasion the grain-of-sand theory, both as
accounting for some pearls in Nature, and also in its application
to the artificial pearls produced by Linn^us from the fresh-water
mussels in Sweden. It may be tliat there is a future before such
semi-artificial methods. If so, I am convinced that tlie process
will consist essentially in pushing in before the inorganic nucleus
a portion of the nacre-secreting ectoderm covering the mantle, so
as to form an epithelial sac in which the pearl will be produced.
But this method occurs rarely in Nature ; and I now pass to the
process of pearl-production which is stimulated by a parasitic
worm, and which results in the finest Orient pearls. I shall not
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