TREMATODES OF THE NORTHUMBERLAND COAST 29 



are in the encysted stage. Unfortunately very little structure 

 could be made out in these, as they were in an early stage of 

 development, and usually only the suckers and intestine were 

 clearly seen. Although these have not been fully worked out, 

 I give figures and some measurements of them as a help to 

 future work. 



As in my previous paper, I have given provisional names 

 to the larval forms for convenience. 



Genus GYMNOPHALLUS, Odhner*. 

 Cercaria glandosa, nov. (Plate I., fig. i). I have given 

 the name glandosa to this cercaria because of the large and 

 characteristic glands in the head region. It occurs singly and 

 free in the body of its \\o'~X, Pabidestrina stagnalis. I have 

 not found it encysted, neither have I been able to find 

 any sporocysts from which, one is justified in inferring by 

 analogy, they are developed : the redia stage being probably 

 omitted as in the case of the ' Pearl Trematodes ' of the Mussel, 

 Myfilus editlis, the young cercaria (according to Jamesonj) 

 occurring in sporocysts in Cardmm edule and in Tapes 

 decussata. It seems doubtful whether the present cercaria 

 has been developed in sporocysts already in Fah/destrma 

 stagnalis, or has migrated from some other mollusk ; the latter 

 alternative is perhaps the more probable owing '\.o the small 

 number of specimens in each individual shell. So far as I 

 am aware this is the first larval Gymnophalhis found in a 

 Gastropod, all those hitherto known occurring in Pelecypods, 

 e.g., Cardhini edttle, Mytihts edulis, Tapes decussata, Saxicava 

 rngosa, Tellma tenuis, Donax vittatus, etc. - 



Cercaria glandosa is oval, and measures o'2o mm. in length 

 when at rest. It can however be much longer or much shorter 

 when moving. It is tailless; the body is covered all over with 

 small spines and is very transparent,, except in the head 

 region, where opaque glands are conspicuous. The oral sucker 



* Odhner, T. " G-ymnophalliis, cine neue Gattung' der Vogeldistomen," Centralbl. 

 f. Bakt., etc., 1900, p. 22. 



t Jameson, H. L., "On the Origin of Pearls," Proc, Zool. Soc, London, 1902, 

 p 153. 



