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 " pearl- 

 formation." 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 



