LARVAL TREMATOCP.S OF THK NORTHUMBERLAND COASt. 44! 



MoNOSTOMUM FLAVUM, Mehlis (larval form). In the liver 

 of Palndestriim stagnalis a larval Trematode occurs in yellow 

 redise, which I ' believe to be identical with the Cercaria 

 ephemera of Siebold*'' and the Glenocercaria fiava of Diesingf , 

 which was found in Planorbis corneus. The adult worm 

 lives in different species of duck, although La Valette 

 succeeded in experimentally infecting the House-sparrow 

 with it|. The ducks known to serve as hosts are the 

 following: — Eider Duck, Somateria mollissima (L.); Velvet 

 Scoter, CEdemia fusca (L.) ; Scaup, Ftdigtila 7?ia7'ila (L.) ; the 

 Smew, Mergns albellus (L.) ; and the Red-breasted Merganser, 

 Mergus serrator. The worm occupies the trachea, oesophagus 

 and thoracic cavity. The Eider Duck is a resident on the 

 Northumberland coast, and all the others are winter visitants, 

 so any of them may easily be the final host of this cercaria 

 from Fenham Flats, which is a great feeding place for ducks 

 and other wild fowl. 



These larval Trematodes were found in November, 1906, 

 from specimens of Paludestrina stagnalis from Fenham Flats, 

 near high-water mark, in pools left uncovered by the tide. 

 The liver was full of the rediae, from which many cercariae had 

 escaped and were moving about very quickly, continually 

 lashing their tails and contracting and expanding their bodies. 

 The redia (see Plate IX. A) is pale yellow with a dark brown 

 intestine, and is furnished with a good sized anterior pharynx. 

 It is very transparent and contractile, and is somewhat 

 irregularly fusiform in shape. The enclosed cercariae are 

 easily seen through the transparent walls of the redia, which 

 may hold one or several in different stages of development. 

 The cercaria (see Plate IX. B and C) is very opaque with a 

 brownish tinge, and is speckled more or less with dark brown. 

 There are three eyes arranged in a triangle, but the most 

 anterior eye is not developed until after the others, a fact 



* " Ueber die Band- und Blasenwiu-mer," 1854, p. 18-19, fig. 1-9. 

 t " Bericlitigmigen und Zusiitze zur Revision der Cercarieen," 1858, p. 8. 

 X La Valette "Symb. ad Tremat. evolut. historiam," 1856, flde J. J. Moulini^, 

 " De la Reproduction chez les Trematodes endoparasites," 1856, p. 207. 



