276 DR. H. LYSTER JAMESON OX 



In this connection an observation made by Dr. Willey (49) 

 is very signiiicant. 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 certain 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 pi'oduction of pearls." 



(c) Professor Herdman's statement on p. 17 of Part Y. 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 genei"ally 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 chai-acters 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 figvire below (text-fig. 33, A & B) 

 a Trematode pearl from Mytilus, from Foulney, Lancashire 

 (Preparation CIII). 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 wovild, 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 



