450 LARVAL TREMATODES OF THE NORTHUMBERLAND COAST. 



It is a curious fact that there should be two cercariae so 

 very much alike, but apart from the measurements the 

 difference in the rediae would prove them to be different 

 species. In what I believe to be the first stage of E. secundum 

 in Littorina littorea the rediae are bright orange, with a con- 

 spicuous brownish red intestine; in those from Paludestrina 

 stagnalis the rediae are pale yellow or colourless, and have no 

 conspicuous intestine. In the Turnstone Strepsilas interpres 

 from Beadnell I have found a species of Echinostomum (see 

 Plate XII.) which is almost certainly the adult of the cercaria 

 described above, young forms almost exactly corresponding 

 to it being found in the intestine along with the adult forms. 

 Unfortunately the spines could not be exactly made out, as the 

 specimens were not quite fresh. Although this worm does 

 not agree fully with the description of Distotmitn leptosomum 

 in every particular, yet I believe it to be this species, possibly 

 a variety. The worm has a broadly heart-shaped head 

 surrounded by spines. A small anterior sucker is followed by 

 a short tube and a thick-lipped pharynx, this leads to a 

 straight intestine bifurcating just above the large ventral 

 sucker. Excretory tubes begin in the head, are very much 

 branched, and end in the excretory pore at the extremity of 

 the body. Two large oval testes are plainly seen at the 

 posterior part, one in front of the other, a rather dense ovary 

 in front of these, and a twisting oviduct full of clear oval eggs. 

 The vitteline glands are dense and take up the greater part of 

 the body. The genital aperture is just above the ventral 

 sucker, the penis sac and vesicula seminalis being plainly 

 seen. The body is covered with spines for about two-thirds 

 of the way down, and the further back these go the more con- 

 spicuous they become, forming transverse lines. The worm 

 is much longer than those described by Villot, but beyond the 

 ventral sucker it is usual for the species of Echinostomum to 

 elongate greatly. A more serious difference is the position of 

 the ventral sucker, which is situated much further down than 

 is shown in Villot's figures ; and this is also the case with the 

 cercaria above described. 



