276 DR. H. LYSTER JAMESON ON 
In this connection an observation made by Dr. Willey (49) 
is very significant. Dr. Willey says :-— 
“« A remarkable fact, indicating the subtle dependence of 
the pearl-producing molluscs upon their environment, is that 
whereas the most ‘valuable pearls, called cyst-pearls by Prof. 
Herdman, are formed about a parasite as their centre or 
nucleus, yet the presence of these parasites in great numbers 
does not necessarily predetermine the formation of pearls. 
Pearl-oysters at Trincomalee may be heavily infected with 
the parasites without yielding pearls. It may be said that 
the parasitic infection and the pearl-disease are two separate 
phenomena, the latter proceeding from the former under 
certain conditions which are realised in the Gulf of Manaar. 
Whether these exact conditions can be reproduced elsewhere 
is one of the main problems before the Company. In the 
same way the cultivation of the oysters and the multipli- 
cation of pearls are two separate operations, the latter 
proceeding from the former in response to cer tain conditions 
affording the suitable stimulus. Conditions may favour the 
bivalves, but not their parasites; or they may favour both 
hosts and parasites, but not the production of pearls.” 
(c) Professor Herdman’s statement on p. 17 of Part V. of his 
Report that Mytilus pearls (which he examined in order to be 
able to correlate his work with mine) differed from Ceylon pearls 
in ‘the large size of the nucleus in the pearl (where a nucleus is 
present) and its characters, which are quite different from those of 
the encysted parasites in the Ceylon Pearl-Oyster.” Now the 
nucleus of a Mytilus pearl is generally about 0-5 mm. in diameter— 
the size of the Trematode when contracted into a sphere. As the 
Ceylon Cestode-parasite measures roughly from 0°5 to 1 mm, in 
diameter, the nucleus of a Ceylon pearl, if composed of its 
calcified remains, should if anything be larger, rather than 
smaller, than that of a Mytilus pearl. And the characters of the 
nucleus should not differ greatly—the dark opaque yellowish or 
brownish substance formed by the decomposition and subsequent 
calcification of the parenchymatous and muscular tissues of 
a Trematode should not differ materially in appearance from the 
analogous remains of a dead Cestode. 
For purposes of comparison I figure below (text-fig. 33, A & B) 
a Trematode pearl from Mytilus, from Foulney, Lancashire 
(Preparation CIIT). A shows the pearl decalcified and examined 
entire in oil of cloves, B shows the nucleus in section. In both 
cases the foreign nature of the nucleus is obvious, quite apart 
from the fact that in this preparation its Trematode character is 
quite clear (which would, of course, not be the case where 
decomposition had advanced considerably before calcification 
commenced). The characters of this nucleus are quite different 
from those of the pseudo-nuclei of Ceylon pearls figured in the 
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