THE 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 problem of increasing and 
rendering more reliable the supply of pearl-oysters and pearls. 
(3) Proresson Herpman’s Conciustons on Peart-ForMmarion, 
Professor Herdman distinguishes several causes of pearl- 
formation, though only two of these are regarded as of sufficient 
frequency to have economic importance, viz. Cestodes, causing the 
majority of “cyst-pearls,” and “ caleospherules,” 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 true 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 pearls are 
valued for the true pearl that can often be dissected out of them, 
whereas blisters are used as substitutes for pearls where the 
imperfect side can be concealed in the setting, e. gy. 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 within closed 
epithelial sacs like the others, but lie in pockets or ampulle of the 
epidermis,” and on p. 146 of the same part speaks of blisters as 
‘pearls of an inferior quality,” but I cannot help feeling that, in 
scientific terminology 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 form the nuclei of pearls under exceptional circumstances. 
In the whole of their observations they have only records 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 
[7] 
