444 LARVAL TREMATODES OF THE NORTHUMBERLAND COAST. 



Besides moving by means of the tail the worm is very con- 

 tractile, and pushes out its oral sucker like a snout. 



This form was found inhabiting 40 per cent, of the Fenham 

 Flats specimens at the end of September, but only about 2 per 

 cent, at the end of November. This seems to indicate that 

 this species as a rule migrates into another host well before 

 the winter sets in. In the Stranraer specimens 15 per cent, 

 contained this Trematode. 



Cercaria ubiquita (see Plate IX. D and E). In the liver of 

 Pahidestrina stagnalis at Fenham Flats and Stranraer, and 

 also in the liver of Littorina rudis at Stranraer and Z. obhisata 

 at both localities, a small Trematode was found. As it 

 occurred commonly, and in three different moUusks, I shall 

 call this worm Cercaria vbiquita. It is found in oval 

 sporocysts containing many cercariae in different stages of 

 development. The sporocysts (see Plate IX. D) measure about 

 o"3 mm. or more in length, and although apparently colourless 

 when viewed alone, when crowded together have a pinkish 

 tinge. The cercaria (see Plate IX. E) measures o'i2 mm. 

 without its tail and o'2o mm. with the tail. It is transparent 

 and very active. The most conspicuous features are the 

 " stacheldrusen," i.e., large glands with long ducts opening 

 near the single spine with which the head is armed. There 

 are two ducts each side, which curve in a regular and ex- 

 ceedingly graceful way, and reach more than half way down 

 the body where the glands appear as clear masses. The inner 

 ducts are smaller, and are somewhat hidden further back, as 

 they become overlapped by the outer ones. No posterior 

 sucker could be made out, but there is a large circular oral 

 sucker armed with the spine above mentioned, and opening at 

 the extreme anterior end. A digestive apparatus is not visible, 

 but there is a clear bilobed excretory sac at the posterior end. 

 The tail is pointed and very contractile, coming off early and 

 living for a long time separately. This worm occurred in 

 8 per cent, of Paludestrina stagnalis from Fenham Flats and 

 30 per cent, from Stranraer ; in one Littorina obtusata out 



