THK CEYLON PEARL OYSTER. 265 



which of necessity were somewhat cursory and superficial. The 

 result of this lack of foresight has been that the energy that ought 

 to have been concentrated on an intensive study of the pearl- 

 oyster and the mechanism of pearl-formation appears to have 

 been largely dissipated on general faunistic work, such as the 

 description of new species of crabs and tapeworms, matters which, 

 valuable as they are from the purely scientific standpoint, have 

 only a secondary bearing on the jiroblem of increasing and 

 rentlering more reliable the supply of pearl-oysters and pearls, 



(3) Professor Herdman's Conclusions on Pearl-Formation. 



Professor Herdman distinguishes several causes of pearl- 

 foi-mation, though only two of these are regarded as of sutficient 

 frequency to have economic importance, viz. Cestodes, causing the 

 majority of "cyst-pearls,"' and " calcospherules," causing "muscle- 

 pearls." I will pass over the pearly excrescences or "blisters '' on 

 the inside of the shell, due to the irritation of boring animals or 

 intruding particles of foreign matter, as these should be kept in 

 a category entirely distinct from ti'ue pearls. The latter term, 

 following my paper published in 1902 (25), I shall confine strictly 

 to bodies developed independently of the shell, which are not in 

 any way continuous with the shell, except where, owing to the 

 rupture or absorption of the intervening tissues, they may become 

 secondarily covered over with nacre continuous with the lining of 

 the shell. When this happens to a pearl it becomes an "attached 

 pearl,"' a body quite other than a blister. Attached peai'ls are 

 valued for the true pearl that can often be dissected out of them, 

 whereas blisters are used as substitutes for pea,rls where the 

 imperfect side can be concealed in the setting, e. g. in cheap 

 jewellery, rings, pins, brooches, etc. Prof. Herdman (Report I. 

 p, 10) apparently applies the name " ampullar pearls " to blisters, 

 that is to say to bodies " which are not formed withiir closed 

 epithelial sacs like the others, but lie in pockets or ampullae of the 

 epidermis," and on p. 146 of the same part speaks of blisters as 

 " pearls of an infeiior quality,'"" but I cannot help feeling tliat, in 

 scientific tenuinology at least, it is undesirable to apply the term 

 " pearl " to these bodies at all. 



Professor Herdman recognises the following causes of pearl- 

 formation in the Ceylon pearl-oyster : — 



(i.) Grains of Sand and other Foreign Particles. 



These, in the experience of Professor Herdman and Mr. Hornell, 

 only foi-m the nuclei of pearls under exceptional circumstances. 

 In the whole of their observations they have only i-ecords of three 

 such cases out of hundreds of pearls examined (Report V. pp. 4 

 & 127). They say (V. p. 28) :— 



" Probably it is only when the shell is injured, e. g., by the 

 breaking of the ' ears,' thus enabling sand to get into the 

 interior, that such particles supply the irritation that gives 



