TUE CliVLON lM:AHL-oy«TER. 261 



on tlie Peail-Oy.ster ii.shen'es of the Gulf of Miuiaiir (16) I was in 

 Soutli Africa, and material for the exaininatiou of some of his 

 i'ojjclusions, which I was unable to liarmonise with my own 

 <)l)sei-vations made prior to my departure from England, was not 

 available. 



Since my letuiJi J have made use of all available material— 

 which is somewhat scanty ; and while it is insufficient to enable 

 nie to propound, at the present monient, a working hypothesis as 

 to the true cause or causes of the formation of Ceylon pei^irls, 

 J think I have been able to show that the Cestode theoi-y 

 enunciated by Hei'dman, which lias formed the basis of the 

 .somewhat meagre experiments which have been pi'osecuted in 

 Ceylon since his return to England, and which even seems to 

 liave Jed to definite regulations elsewhere *, rests on quite 

 insufficient evidence, and that, if the problem of the cause of 

 J'earl-Pioduction in Margaritifera vulgaris is to be solved, and ii 

 scheme for increasing the productivity of the Oysters evolved, a 

 fi'esh start will have to be made. 



The work that still remains to be done will centre around the 

 causes which lead to the development of the epidermal sacs in which 

 all peai'Ls are formed — fine pearls and seed-pearl.s, " muscle "-pefirls 

 and "cA'st ''-pearls (or, as 1 prefer to call them, "parenchyma "- 

 pearls), and the mechanism which controls tlie secietion of 

 conchyolin and the deposition therein of carbonate of lime. In 

 fact, I. am led back to the pi-inciples eniniciated by me in 1902 

 (25), that the essential element in pearl-formation is the pearl-sac, 

 !iud not the nucleus, and that it is by a study of the causes whicli 

 lead to the development of the former that the problem of tlie 

 origin of pearls is to be solved. 



Some material for these furthei- investigations has just reached 

 me as I write this introduction, and more is promised, but, owing 

 to the difficulties and delays which may occui-, 1 now publish 

 my researches on the structure of the shell, and of pearls and their 

 pseudo-nuclei and nuclei, witliout attempting to deal with the 

 origin of the pearl-sac. 



1 take this opportunity of expressing my thanks to the Ceylon 

 Company of Pearl Fishers, Ltd., for purchasing, on my behalf, 

 pearls in Colombo to be used in these inv'estigations; to Professor 

 Raphael Dubois, for pearls from MagariUfera vulgaris from the 

 Mediterranean; to Prof. W. K. Dunstan, F.R.S., for allowing me 

 to make use of material in the Imperial Institute; to Mr. J. 

 Calcott Gaskin, Assistant Political Agent at Bahrein, Persian 

 (4ulf, for sending me, in 1903, a number of preserved specimens 

 of the Lingah shell (.1/. vulgaris), some oi which contained pearls; 



* Rules for Lower liuniia under tho Burma Fislu-ries Act, 1905. liulcs 64 and 67, 

 which prohibited the ca])ture of Balistes and Trijgou in the Pearl Fishery districts, 

 and required thein, if accidentally causrht, to 1r' returned to the sea, appear to have 

 lieen inspired by tlio Cestode theory. 'I'liese rules were cancelled in 190!). It may 

 be remarked that the Pearl-Oyster of Hurnia (the ilcrp;ui shell of commerce) is not 

 the same species as the L'eylon Pearl-Oyster, .1/. cK/i/div's Schumacher, but is tlie 

 treat Mother-of- Pearl Oyster, 21. inarima Jameson. 



