348 DR. H. LYSTEK JAMESON OX 



It appears, in fact, as though the simultaneous presence of pearls 

 and Cestodes in the Ceylon Pearl-Oyster were a case of two parallel 

 diseases, comparable to the case of a dog infected simultaneously 

 with tapeworms and mange, or of a man suffering at the same time 

 from echinococci and scabies. And even should it be found that 

 tapeworms do sometimes form the nuclei of Ceylon pearls, an 

 explanation of the reason why this occurs in some cases only is 

 necessary. It is, of course, possible that in certain of the Ceylon 

 banks conditions may exist which cause Tylocephalwrn ludificans 

 to depart from its normal habit, and acquire an ectodermal instead 

 of a fibrous cyst ; or it might even be found that in certain banks 

 another species of Tylocephalum (or other Cestode) occurs which, 

 like the Trematode in Mytilus, normally and habitually gives rise 

 to a peai-1-sac in the tissues, and which has been confused with 

 Tylocephalum ludificans. But, in any case, peai'ls formed around 

 tapeworms, if such ever occur (and this still remains to be demon- 

 strated), must be so comparatively scarce that, from the economic 

 standpoint, the role of the tapeworm in pearl-production in 

 Margaritifera vulgaris must be unimportant. Examination of 

 such pearls from Flacuna placenta and Margaritifera margaritifera 

 var. cumingii as were obtainable failed to confirm the supposed 

 occurrence of Cestodes as their nuclei. 



(3) The shell of Margaritifera comprises in addition to the 

 hinge-ligament the same layers as those of other typical Lamelli- 

 bi-anchs, viz. a periostracum (the outermost layer of which is 

 secreted in a difi'erent manner to the remainder and is very 

 much reduced in Margaritifera), prismatic substance, nacre, and 

 hypostracum or muscle-attachment substance. 



In addition to these, certain pathological varieties of shell- 

 substance arise when the normal rhythm of secretion is disturbed, 

 the chief of which are desciubed as amoi-phous i-epair-substance 

 (which is probably simply uncalcified conchyolin), columnar repair- 

 substance, and granular repair-nacre. These substances intergrade 

 with normal nacre and prismatic substance, and with each other. 

 The peculiar characters of these substances are the chief cause of 

 the distinctive appearance of the " pseudo-nuclei " of pearls. The 

 shell-substance, except the hypostracum and the outer layer of the . 

 periostracum (and probably the ligament), is secreted in liquid 

 form, and its structure and variation may be interpreted as the 

 expression of the normal processes of the crystallisation of CaCOg 

 in a colloidal medium, modified by the periodicity of the action 

 of the shell-secreting tissues of the mantle. 



(4) The " Calcospherules," which Herdman identifies as the 

 nuclei of muscle-pearls, are not free concretions or " depositions 



Mr. Southwell in liis researches on this question ; but he thought that gentleman 

 would support him in saying that those researches had not been unsuccessful up to 

 the present, and promised to be most interesting as well as satisfactory." Mr. 

 Southwell's thoroughly frank statements of the case in his subsequent publications 

 do not appear to me to reveal anything sufficiently epoch-making, from the com- 

 mercial standpoint, to render such mystery necessary I 



