44 
Fig. V. 
The Trematode from the foot of the mussel is the encysted 
cercaria of Echinostomum secundum Nicoll, which in the adult state 
inhabits the Oyster Catcher and certain gulls.* It is very common 
at Budle in the foot of both the mussel and cockle, but especially 
in the former, where almost every specimen is infected. It is 
fairly common at Holy Island, and was found in one specimen from 
the Tweed. In those examined from Blyfch, Amble, and Alnmoutk 
it was not present. I believe I have found the previous stage in 
the common periwinkle Littorina littorca , where in about two per 
cent, of these mollusks from Budle I found the liver full of orange 
rediae, containing tailed cercariae which agree closely with the 
encysted forms.! I had hoped to make experiments as to the 
* Nicoll. Ann. and Mag. Nat. Hist., Jan., 1906, p. 148, and June, 1906, p. 313. 
+ Northumberland Fisheries Report for 1905, p. 100. 
