TREMATODES OF THE NORTHUMBERLAND COAST 



37 



the two cases known, a Gastropod), the redia stage being 

 omitted. 



A word may be said here about the closely allied genus 

 Ma7-itrema of NicoU*. This author suggests that the two 

 cercarias C. oocysta and C. pintm discovered by mef encysted 

 in Pahidestrina stagnalis are larval stages of Trematodes 

 belonging to this genus, and it appears extremely likely that 

 this is the case. C. oocysta was found encysted in sporocysts, 

 and C. pirum had in all probability also encysted in the 

 sporocysts in which they were developed, although these were 

 not actually seen. The cysts were so packed together that it 

 is unlikely that they came from another host. Tailed forms 

 of C. oocysta were also found within the sporocysts, which 

 shows this cercaria to differ from the genus Spelotrerna in this 

 respect as well as in others. As the sporocysts of C. piruvi 

 were not found, it was impossible to ascertain whether the 

 cercariae were tailed or not. It seems rather a curious fact 

 that cercariae which have no free-swimming stage in their life 

 history, and encyst in the sporocysts, should possess tails, for 

 they can have no use for them. A similar case was observed 

 by me in a Trematode from Cai'diiim edule, tailed cercariag 

 being found in the sporocysts side by side with the encysted 

 forms J. 



A comparison of the scantily known life history of the three 

 genera Gymmophallus, Spelotrerna, and Maritrema is here 

 given in tabulated form : — 



Genus 



Gijinnophallas 



A,dult. 

 marine birds 



Encysted stage 



omitted, but 



a resting stage 



occurs in Mollusca 



Cercaria 



no tail (?) ; 

 developed in 

 sporocysts 



Redia 



omitted 



Sporocyst 

 in Mollusca 



Spelotfema „ in Crustacea no tail; 



developed 



] in sporocysts 



" 



" 



Maritrema 



" 



in sporocysts 



tailed ; 



developed in 



sporocysts 



" 



" 



* Nicoll, W., Op. cit., Ann. and Mag. Nat. Hist., 1907, p. 265. 

 t Op. cit.. Trans. Nat. Hist. Soc. Northbd., etc., N.S., Vol. I., p. 445-446. 

 % "On Three Mollusk-iufesting Trematodes," Ann. and Mag. Nat. Hist., 1907. 



