Trematode Parasites of British Birds. 250 



distinct membrane. It is situated in the long axis of the 

 body; broad posteriorly, tapering gradually forwards. 



There is some resemblance between this species and 

 Distomuin Muehlingi. They are about the same size and 

 their ova are equal, but apart from the questionable presence 

 of a genital sucker in D. Muehlingi. it displays the f<dlowing 

 differences : — The outline of the bcdy is constricted in the 

 middle ; the (Esophagus is much longer ; the yolk-glands do 

 not extend in front of the ventral sucker, but are more 

 voluminous posteriorly, uniting between the testes, which 

 are some distance apart; the ovary is rounded; the vesieula 

 seminalis is not voluminous ; and the ova are few, 



Tocotrema lingua (Crepl.). 



1 have already frequently referred to this species and to 

 Jagerskiold's excellent note on it *. It is a very common 

 parasite of the herring- gull, its favourite habitat being the 

 anterior end of the intestine, particularly the duodenum. 

 In addition a new host, Alca tor da, must be mentioned. 

 Only one bird of this species was examined, and it yielded 

 but a single example of the parasite, so that its occurrence 

 may be no more than casual. It is a small specimen about 

 1 mm. long, with few ova, but it is undoubtedly identical wiih 

 the specimens from the herring-gnll. 



The numerous specimens from Lams argentatus show a 

 remarkable uniformity in size. The length varies from 

 I'o mm. to 18 mm., while the maximum breadth is rather 

 less than ^ of the length, and occurs usually in the anterior 

 part of the body, giving the outline the familiar tongue- 

 shape. Occasionally the anterior part is more tapering. 

 The cuticular scales cover only the anterior part of the body, 

 but they extend somewhat further back than Jagerskiold 

 represents them. The oral sucker has a diameter of '{)7o- 

 •085 mm., and the ventral sucker appears to be nearly of the 

 same size, although it is ditlicult to measure the latter owing 

 to the absence of a limiting membrane. The pharynx 

 measures 'UG x '015 mm., and the short prcpharynx is about 

 \ as long. The oesophagus is extremely short (Ol-'OG mm.), 

 being not more than ._,•- of the body-length. Jjigcrskiold's 

 statement that it never exceeds \ of the body-lengtii seems 

 to be an oversight, for it never in any circumstances 

 approaches near that length, and in his figure, which is quite 

 correct, it is not more than ^q. It is thus much shorter than 

 that of T. jejunum or Distoimim Muehlingi. 



* Bergens Mus. Aarbog, 1898, no. ii. 



