the Pearl Oyster and on the Production of Pearls, 91 



Taking these facts into consideration, Dr. Kelaart advises the 

 application of various restrictions to the fishery, the nature of 

 vs^hich w^ill suggest themselves readily enough to most naturalists, 

 and at the same time recommends the employment of ordinary 

 oyster-dredges for removing the mollusks from the banks ; being 

 unattached, they would of course easily be brought up by the 

 dredge. The small oysters brought up might be returned im- 

 mediately to the bank, or kept to be transferred to some other 

 suitable locality. By this means he thinks the numerous salt- 

 water lakes of the Ceylonese coast, such as those of Calpentyn, 

 Puttam, Batticaloa and Hambantotte, might easily be stocked 

 with this Pearl Oyster, when they would yield a handsome 

 revenue to the Government. To test the feasibility of this pro- 

 position our author has already removed about 1200 middle- 

 sized oysters, obtained from the water of the Tamblegam fishery, 

 to Yard Cove in Trincomalee Harbour, where the muddy bottom 

 promises to be suitable for breeding them. 



Production and Structure of Pearls. 



" There are pearls,'' says Mobius, " which, like the shells in 

 which they were formed, consist of three difi*erent systems of 

 layers, — only that these are superposed in a reversed order. Iii 

 the shell, the nacreous layer forms the innermost coat ; in the 

 pearl, on the contrary, it constitutes the shining outer coat ; so 

 that the pearl, as it were, only represents a reversed pearly shell, 

 and consequently possesses all the chemical and physical pro- 

 perties of the latter, except those for which it is indebted to its 

 round form.'' Under these circumstances the qualities of the 

 pearl must necessarily depend to a very great extent upon those 

 of the shell in which it is produced ; and the analysis of the 

 nacreous layers of difiierent shells shows a sufficient diversity of 

 composition to account for the different qualities of the pearls 

 produced from them. Thus, according to Schlossberger, the 

 nacreous layer of the Common Oyster contains 94* 7-98*2 per 

 cent, of carbonate of lime with only 0"8-2*2 per cent, of nitro- 

 genous organic matter ; whilst the same layer in the true Pearl 

 Oyster contains, as found by Ulex, only 87*6 per cent, of car- 

 bonate of lime, and the amount of organic matter rises to 11*8 

 per cent., or more than five times the largest quantity found by 

 Schlossberger in the Common Oyster. The latter also contains 

 0'8-3'l per cent, of other earthy salts wanting in the Pearl 

 Oyster, which, however, contains 0*6 per cent, of chloride of 

 sodium. It is to this large amount of organic matter that the 

 true pearls are indebted for their hardness, which is considerably 

 greater than that of crystals of carbonate of lime; and the same 



