THE CEYLON PEARL-OYSTER. 261 
on the Pearl-Oyster fisheries of the Gulf of Manaar (16) I was in 
South Africa, and material for the examination of some of his 
conclusions, which I was unable to harmonise with my own 
observations made prior te my departure from England, was not 
available, 
Since my return I have made use of all available material 
which is somewhat scanty ; and while it is insufficient to enable 
me to propound, at the present moment, a working hypothesis as 
to the true cause or causes of the formation of Ceylon pearls, 
I think I have been able to show that the Cestode theory 
enunciated by Herdman, which has formed the basis of the 
somewhat meagre experiments which have been prosecuted in 
Ceylon since his return to England, and which even seems to my, , , 
have led to definite regulations elsewhere*, rests on quite iAiFigion of 7 
insufficient evidence, and that, if the problem of the cause of Secon} 
Pearl-Production in Margaritifera vulgaris is to be solved, and a. 
scheme for increasing the productivity of the Oysters evolved, a 
fresh 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 saes in which 
all pearls are formed—fine pearls and seed-pearls, “‘ muscle ”-pearls 
and ‘“eyst”-pearls (or, as | prefer to call them, “parenchyma’”’- 
pearls), and the mechanism which controls the secretion ot 
conchyolin and the deposition therein of carbonate of lime. In 
fact, I ain led back to the principles enunciated by me in 1902 
(25), that the essential element in pearl-formation is the pearl-sac, 
aud not the nucleus, and that it is by a study of the causes which 
lead to the development of the former that the problem of the 
origin of pearls is to be solved. 
Some material for these further investigations has just reached 
me as I] write this introduction, and more 1s promised, but, owing 
to the difficulties and delays which may occur, 1 now publish 
my researches on the structure of the shell, and of pearls and their 
pseudo-nuclei and nuclei, without attempting to deal with the 
origin of the pearl-sac. 
I take this opportunity of expressing my thanks to the Ceylon 
Company of Pearl Fishers, Ltd., for purchasing, ou my behalf, 
pearls in Colombo to be used in these investigations ; to Professor 
Raphael Dubois, for pearls from JMagaritifera vulgaris from the 
Mediterranean; to Prof. W. R. Dunstan, F.R.S., for allowing me 
to make use of material in the Lnperial Institute; to Mr. J. 
Calcott Gaskin, Assistant Political Agent at Bahrein, Persian 
Gulf, for sending me, in 1903, a number of preserved specimens 
of the Lingah shell (.W/. vulgaris), some of which contained pearls ; 

, 
Ass 
* Rules for Lower Burma under the Burma Fisheries Act, 1905. Rules 64 and 67, 
which prohibited the capture of Balistes and Trygon inthe Pearl Fishery districts, 
and required them, if accidentally caught, to be returned to the sea, appear to have 
heen inspired by the Cestode theory. ‘These rules were cancelled in 1909. It may 
be remarked that the Pearl-Oyster of Burma (the Mergui shell of commerce) is not 
the same species as the Ceylon Pearl-Oyster, WZ. vulgaris Schumacher, but is the 
ereat Mother-of-Pearl Oyster, IZ. maxima Jameson. 
re 
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