278 DR. WH. LYSTER JAMESON ON 
Pearls, as described by Professor Herdman and Mr. Hornell, the 
position is briefly this :— 
1) Ceylon Pearl-Oysters were found to contain large 
numbers of Cestode parasites which occurred simul- 
taneously with pearls, but which did not necessarily 
result in the formation of pearls. 
(2) The nuclei of the majority of “ cyst-pearls” were 
thought to be identified as consisting of the remains of 
these parasites, though Mr. Hornell’s figures of such 
nuclei are capable of other interpretation. 
(3) No satisfactory evidence was adduced of the Cestode 
having acquired a surrounding epidermal sac, such as is 
normally formed around the pearl-producing Trematode 
in Mytilus, though Prof. Herdman admits that this sac 
is essential for pearl-production. ‘The first stages in the 
supposed process are therefore purely hy pothetical and 
unsupported by observation, besides pre-supposing an 
abnormal departure from the parasite’s usual habit. 
The evidence in favour of the theory is mainly that the more 
highly infected the oysters are with these particular Cestodes, the 
richer they are in pearls. Thus it was observed in 1904 (Report 
ILL. p. 32) that the oysters from the North-West Cheval, besides 
being the most extensively infected with Cestode-cysts were also 
the richest in cyst-pearls. And, again, Mr. Southwell records 
(40, p. 194), that 
‘the infection of the very old oysters [with tapeworm-cysts ] 
found on the Kondatchi Paar in 1908 was remarkably low, 
and, as bearing practical proof that infection and pearl yield 
are intim: ately” connected, it is interesting to note that the 
pearl yield also was remarkably low, the valuation only 
working out at about Rs. 18 per 1,000 oysters,’ 
These facts might be explained, however, on the assumption 
that the conditions favourable to pearl-production are also favour- 
able to Cestode infection. 
Characters, Identity, and Life-Histories of the Cestode Parasites 
of Margaritifera vulgaris. 
Apparently the first announcement of the supposed relation 
between the Cestode and pearl-production was made by Prof. 
Herdman at his Royal Institution lecture on March 27th, 1903 
(14). In this he says that he and Mr, Hornell have proved so 
far “that in Ceylon the most important cause is a larval Cestode 
of the Tetrarhynehus form.” Again, in the Report of the British 
Association, Southport, 1903, p. 695, Prof. Herdman says: ‘“ The 
parasite in the case of the majority of the cyst-pearls of Ceylon 
is the larva of a Cestode which appears to be new, and will 
be described under the name of ‘ 7'etrarhynchus unionifactor’” ; 
and the pearl-inducing parasite is referred to throughout Prof. 
Tlerdman’s Report under this name. 
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