6 CEYLON PEARL OYSTER REPORT. 



used. A quantity of nacre was therefore detached from Ceylon pearl-oyster shells 

 which had been lying dry in a box at the ordinary temperature of the Museum for 

 about four years, and was handed to Dr. HERBERT E. ROAF, of the Bio-chemistry 

 Department of the University of Liverpool, who has kindly supplied us with the 

 following analysis : 



Calcium carbonate 88*79 



sulphate 4'93 



Organic matter 2*32 



Water. 2'28 



Loss (no magnesium, no phosphates, faint trace of iron) 1*68. 



From this it appears that the composition of the nacre is much more like that of 

 the pearl than HARLEY supposed, and in fact the proportions of mineral matter and 

 of water present in the two cases are practically the same if the " carbonate of lime" 

 in the older analysis may be regarded as expressing the total salts of calcium present. 

 The only notable difference remaining is the larger amount of organic matter in the 

 free pearl than in nacre. In both, the calcareous part is in the form of aragonite. 



The abnormal pearls which are formed not of nacre but of prismatic layers (calcite) 

 or of horny material may very possibly have a composition widely different from that 

 of the true orient or " cyst " pearl. 



PEARLS AND PARASITES. 



It is commonly thought that the Italian naturalist, PH. 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 RONDELETIUS propounded the 

 same view in 1558, and that ages before that ANDROSTHENES, who had travelled in 

 the East, is reported by ATHEN^ETJS to have compared the developing pearls in the 

 oyster to the Cestode larvae in " measly " 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 that we 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 of the organic nucleus in comparatively recent 

 times, we find that FILIPPI'S pearl-parasite in Anodonta cygnea was the Trematode 

 Distomum duplicatum, v. BAER; ROBERT GARNER (in 1871) records "Distomes" 

 from both fresh- water and marine mussels ; and GIARD attributes the origin of pearls 

 in Donax and Tellina to a species of Brachyccelium all these being cases of 

 Trematoda. Other naturalists have since extended the discovery to other pearl- 

 producing molluscs and to other worm parasites. To E. F. KELAART belongs the 

 honour of having first connected the formation of pearls in the Ceylon oyster with 



