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 com- 

 monly 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. 



