274 DR. H. LYSTER JAMESON ON 
Redia-stage of a Trematode, confirms my original idea of it 
being a ee al Trematode—an idea formed miben first I saw 
it in March 1902” |2.e. the Cestode larva in Margaritifera 
vulgaris|. “ Other facts point to the same conclusion, and | 
have now no doubt on the subject. The genus to which it 
belongs is still doubtful, but as it is inconvenient not to have 
a name whereby to make mention of it, I shall henceforth 
refer to it under the cognomen of Distomum (¢) margariti- 
factor, n. sp., the specific name having reference to the fact 
that it is the inducing cause in the production of ‘ fine’ 
pearls.” 
‘Mr. Hornell anticipated that asexual reproduction would be 
found to occur in the Cestode parasites of Margaritifera vulgaris 
also, and this has since proved to be the case. 
An expurgated edition of the above report was published in 
1906 (22), which, however, bore the same date, June 15, 1905, as 
the Sessional Paper. In this the statements as to the supposed 
Trematode nature of the parasite were suppressed (though not 
formally withdrawn), the name “Distomum margaritifactor, n.sp.,” 
cancelled with a stroke, still figuring in the lithographed plate 
(Annexure IT.). 
As explained below (p. 345) I have been unable to confirm the 
presence of Cestodes in the centres of Placuna pearls from Ceylon, 
any more than I can find them in the pearls of Margaritifera 
vulgaris. 
In 1907 Dr. A. Willey (48) confirmed and extended Mr. Hornell’s 
observations on the endogenous reproduction of the Placuna 
Cestode. 
Mr. Southwell discovered (39, p. 173) that endogenous asexual 
reproduction or budding, similar to that described by Hornell and 
Willey in the parasite of Placuna occurs occasionally in the Cestode 
parasites of the Pearl-Oyster. He only observed the occurrence 
twice, in November 1906 and January 1909—in each case a single 
endogen was found. 
In 1903 the late Professor A. Giard (10) announced that 
M. L. G. Seurat believed that in the black-lipped Pearl-Oyster 
of the Gambier Archipelago (Margaritifera margaritifera var. 
cumingii Reeve) pearl-formation was due to the presence of a 
parasite, figures of which were given, and which Prof. Giard 
referred to a genus near to Cyathophyllus [| Cyathocephalus ?| 
Kessl. or Acr -obothr ium Olsson. 
Subsequently Seurat found the adult of this worm in the 
Eagle Ray (Aétobatis narinari Kuphr.) in the spiral intestine, and 
named it Tylocephalum margaritifere (36). The adult, which is 
figured by Seurat (37), is quite a minute worm, not exceeding 
4 mm. 
The scolex occurs in eysts, similar to those occurring in the 
Jeylon Pearl-Oyster, and multiple cysts (perhaps for med | by bud- 
ding of the larva as in the Placwna eee) occur also, Seurat 
[16] 
