1922] MADRAS PEARL FISHERIES 129 



and related problems are sufficiently definite and, I believe, 

 conclusive, in the light of the most recent results obtained by 

 others, to stand by themselves as strictly conformable to the actual 

 facts. 



Pearls in the widest sense may be defined as more or less 

 rounded masses of shell substance made up of concentric layers 

 laid down around a nucleus. The shell substance may be of any 

 one of the four layers normally present in such shells as the pearl 

 oyster or two or more of these may alternate in the layers. Some 

 pearls consist wholly of periostracum ; these are brown and on 

 account of the lack of lime in their composition, they frequently 

 crack as they yield up moisture. In one example of a periostracal 

 pearl in my possession, half the sphere is coated with nacre ; had 

 the process been extended and continued, a complete coating of 

 nacre would have been deposited, converting a valueless pearl 

 into one of considerable price, but of specific gravity less than 

 normal. Periostracal pearls are formed invariably in or close to 

 the edge of the mantle, where are situated the cells normally 

 engaged in the secretion of periostracum. Nacreous pearls 

 characterize the pearl oyster, but in molluscs where the inmost 

 layer is porcellanous, pearls produced are themselves porcellanous ; 

 examples of these are the well-known pink pearls obtained from 

 the West Indian conch, Strombus gigas, the rare and beautifully 

 watered pearls produced by the chank (Turbinella pirum) in our 

 own waters, and also the lustreless white pearls sometimes found 

 in the edible oyster. Hypostracal pearls are, in my experience 

 the most numerous of all in the local pearl oyster, but they are 

 usually minute and even microscopic. They were called calcos- 

 pherules in the Ceylon Pearl Reports. They occur, when present, 

 in and around the insertion ends of the pallial and adductor 

 muscles, often in great abundance ; "nests " of 20 to 50 are not rare 

 when properly sought for. Many of these become the pseudo- 

 nuclei of nacreous seed-pearls, the real nuclei being of course the 

 nuclei of the calcospherules themselves. Not infrequently conti- 

 guous pearls of this nature fuse into a compound mass of irregular 

 shape, one form of the baroque pearl, useful to the imaginative 

 jeweller for the production of quaint pearl ornaments. One such 

 compound mass I have seen worked into the form of a mulberry 

 fruit, mounted with a spray of golden leaves. Other artists have 

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