PEARL PRODUCTION, 17 



represented one is certainly a species of Tetrarhynchus (Rhynchobothriiis), and another 

 is probably the same genus or may possibly belong to Cyathocephalus, Kessler 

 (= Aerobothrium, Olsson), characterised by the unarmed head and the terminal 

 circular bothrium. 



Seurat, writing in 1906,* states that in the case of the pearl oysters (Margariti- 

 fera margaritifera, var. cumingi, Reeve) of the Gambier Archipelago the numerous 

 encysted parasites scattered through various parts of the body branchiae, mantle, 

 heart, liver, &c. are the scolices of Cestodes " appartenant aux genres Cyathophyllus 

 [Cyathocephalus'f] ou Acrohothrium." 



In a letter received on February 28th, M. Seurat gives as his latest opinion 

 " L'adulte du Cestode qui produit les perles a Mangareva vit dans la raie-aigle ; je me 

 propose de l'appeler Aphanobothrium, n.g., margaritiferce, genre voisin des Cyatlio- 

 cephalus, Kessler." Finally, in a further letter (March 8th), he says: " Je crois 

 pouvoir ranger le Cestode margaritifera dans le genre Tylocephalum, Linton, et ne 

 pas avoir a creer de nouveau genre. Ce sera done le Tylocephalum margaritiferce. 

 Hab. scolex Margaritifera cumingi, Reeve. Hab. adulte Intestin spiral de 

 .Jitobatis narinari, Euphr."J 



We agree at least with Seurat that the parasites are Cestodes, and that is clearly 

 the first point to establish. 



In order to be able to co-relate our work with that of Dr. Jameson and make a 

 comparison between the Ceylon specimens and those from European seas where the 

 parasite is a Trematode, we obtained material from the pearhbearing mussels 

 (Mytilus edulis) at Piel, on the Lancashire coast, the same locality where 

 Dr. Jameson worked. Figs. 1 to 12 on Plate I. show the condition of affairs in this 

 material ; and the chief points of contrast with the Ceylon pearls are : 



(1) The distinctness of the pearl-sac (figs. 8, 10, 11). 



(2) 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. 



We agree entirely with Jameson, of course, that the organism in the Mytilus 

 pearls is a Distomid, and the marked difference that we find in our own preparations 

 of the two cases (Mytilus and Margaritifera) confirms us in our belief that the 

 Ceylon parasite cannot be a Trematode. 



* " La Nacre et les Perles en Oceanie Franchise," par M. L. G. Seurat, Charge de mission a Tahiti, in 

 ' Compte Rendu des Trav. Premiere reunion internat. d'Agronomie Coloniale ' : Alcan, Paris, p. 308. 



t Seurat writes " I'l/athophylhts," hut surely that must be intended for Cyathocephalus. 



J Since published in ' C.R. Acad, des Sci.,' 26 Mars, 1906, p. 801. 



We are indebted to our friend Mr. Andrew Scott, A.L.S., Resident Naturalist at the Piel Marine 

 Laboratory, for the help he has kindly given us in this matter ; and to Mr. T. SOUTHWELL, in the 

 Liverpool Laboratory, for assistance in the preparation of many specimens. 



D 



