1922] 



MADRAS PEARL FISHERIES 



133 



nuclei of periostracal-like substance derived from the oyster's own 

 tissues. The former class comprises, according to my investigations, 

 the majority of the larger cyst-pearls, the latter of the smaller ones 

 of this description which, as I have indicated above, constitute 

 by far the larger proportion of cyst-pearls. This conclusion to 



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Fig. 11. A. and B. are two nuclei obtained from Ceylon Orient pearls by decalcification. 

 In each a portion of the inmost conchyolin layers is shown. In A. some of the 

 minute calcareous granules seen in Fig. 9 are observable, while B. shows the collar 

 and proboscis (face view) of this larva very distinctly. C. is the enlarged appear- 

 ance of the pearl that enclosed nucleus B ; note its resemblance in form to the 

 outline of the spherical larva shown in D. (cf. Fig. 9-A). 



our local researches disposes satisfactorily of certain objections 

 levelled at the cestode theory and places the latter in its proper 

 perspective; we see that cestode larvae, though less frequently the 

 cause of pearl formation than was at first believed, are nevertheless 

 the most important factor in the production of the larger and finer of 

 orient pearls and therefore of supreme importance from the economic 

 and commercial view point. Let us now see how pearl formation 

 proceeds {a) in cyst pearls formed around intrusive foreign bodies, 

 {b) in those with a fragment of periostracum as nucleus, and lastly 

 (c) in muscle pearls. 



