274 DR. H. LYSTER JAMESOX OX 



Jiedia-stHge of a IVematode, confirms my original idea of it 



being a larval Trematode — an idea formed when first I saw 



it in March 1902" [i.e. the Oestode larva in Margaritifera 



vulgaris]. " Other facts point to the same conclusion, aiid I 



lia.ve 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 sliall henceforth 



refer to it under the cognomen of Distomum (?) Tnm'gariti- 



factor, n. sp., the specific name having reference to the fact 



that it is the inducing caiise in the production of ' fine ' 



pearls." 



Mr. Hornell anticipated that asexual reproduction would be 



found to occur in the Cestode parasites of Margaritifera vidgaris 



also, and this has since proved to be the case. 



An expurgated edition of the above report wa.s published in 

 1906 (22), whicli, 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 formally withdrawn), the name ^'■Distomutn mar garitif actor ^ n.sp.,'"' 

 cancelled with a stroke, still figuring in the lithographed plate 

 (Annexure II.). 



As explained below (p. 345) I have been unable to confirm tlie 

 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 repi'oduction 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 Placana 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 i,he black-lipped Pearl-Oyster 

 of the Gambler Archipelago (^Margaritifera inargaritifera var. 

 camingii Reeve) peaid-formation was due to the presence of a 

 parasite, figui'es of which were given, and which Prof. Giard 

 referred to a genus near to Cyatli-O-phyUns [C i/athocephalus ?] 

 Kessl. or Acrohothrium Olsson. 



Subsequently Seurat found the adult of this worm in the 

 Eagle Ray {Aetobatis narinari Euphr.) in the spiral intestine, and 

 na,med it Tijlocephalum margaritiferce (36). The a,dult, which is 

 figured by Seurat (37), is quite a minute worm, not exceeding 

 4 mm. 



The scolex occurs in cysts, similar to those occurring in the 

 Ceylon Pearl-Oyster, and multiple cysts (perhaps foi'med by bud- 

 ding of the larva as in the Placuna parasites) occur also. Seiu'at 



