1902.] ORIGIN OF PEARLS. 163 



These data suffice to show that in many molluscs, including 

 several of the species yielding the most valuable pearls, Trematodes 

 are one cause, if not the exclusive cause, of pearl-formation. To 

 what extent other parasites are capable of producing the same 

 eifects cannot be said at present. That the other causes to which 

 pearls have from time to time been attributed play any part is a 

 matter of the merest conjecture only, and has never, so far as I 

 know, been demonstrated by experiment or investigation. 



Possibilities of Economic AjjpUcation. 



The bearing of the facts recorded in this paper upon the 

 problem of artificially producing pearls, and so meeting the 

 difficulty presented by the increasing demand and exhausted 

 fisheries, is obvious. It was indeed with the hope of throwing 

 some light on this matter that I first took up the subject, about 

 three years ago. The key to the realizing of this, so often 

 regarded as an academic dream, lies obviously in the scientific 

 stvidy of the parasites which occur in the valuable forms. This 

 was pointed out exactly fifty years ago by Filippi, but has been 

 ignored by most subsequent writers. 



The life-history of the Trematodes occurring in the genus 

 Margaritifera probably agrees in the more essential points with 

 those of other Digenea. Their adult stages may reasonably be 

 expected to occur in the organisms that eat the pearl-oysters, 

 notably such fishes as Balistes, while the first host will almost 

 certainly be some mollusc occurring on the pearl-banks or shelling- 

 grounds. 



Having ascertained the first host, there is no reason why 

 infection should not be performed by placing young pearl-oysters 

 in company with it in more easily accessible waters. To attempt 

 to establish the cultivation of pearl-oysters on new gi'ounds 

 without also cultivating and infecting the first host of the 

 parasite wovild be futile. Needless to say, such methods of 

 artificially promoting natural infection would be incomparably 

 superior to any method of pearl-production by ojyeration on the 

 individual oyster, as millions of examples could be treated by the 

 former method, while tens were being operated upon. 



It is obvious from my Brighton experiment that infection can 

 be induced in Mytilus, and I can see no reason to doubt that, in a 

 couple of years, these Mytili will contain pearls, resulting from 

 that artificially induced pathological condition. 



Literature. 



1712. Mery. — Remarques faites sur la Moule des Estangs. Hist. 



de I'Acad. Roy. des Sciences, Paris, Annee 1710 : Mem. 



pp. 408-426. 

 1717. REAUMUR. — Observations sm- la Ooquillage appelle Pinne 



Marine ou Nacre de Perle. Mem. de TAcacl. Roy. des 



Sciences, Paris, 1717, pp. 177-194, pis. v. & vi. 



