270 On the Trematode Parasites of British Birds. 



already been recorded from Oidemia nigral but this is, I 

 believe, the first time that P. brevicolle has been met with in the 

 scoters. The most recent note on the species is by Braun"^, 

 in the course of which he criticises Mueller's observations f. 

 My specimens are small, 1*7'1-3'41 mm. long with a breadth 

 of •35-'54 mm. They are somewhat cylindrical anteriorly, 

 more flattened posteriorly, agreeing in this respect with 

 Braun's specimens. The posterior end is usually rather 

 blunt. With regard to the length of the neck (distance 

 between centres of suckers, as I take it) my specimens are 

 apparently much more extended than those of Mueller or 

 Braun, for I find the proportion to be nearly constantly ^ of 

 the body-length, certainly never less than \, and in young 

 examples much more. The constriction behind the ventral 

 sucker is not a mere narrowing in the breadth, but is usually 

 accompanied by distinct transverse annulation of the cuticle. 

 The breadth here is only about half that at the widest part 

 of tlie body. The oral sucker is slightly larger than the 

 ventral. The latter is, as Braun says, usually deeper, 

 although in extension of the anterior part of the body the 

 oral sucker may be quite as deep. There is practically no 

 prepharynx. The pharynx is almost globular, measuring 

 •14-*21 X ■12-22 mm. ; it is thus somewhat larger than 

 Braun has it. He is correct in saying that the oesophagus 

 is extremely short, the bifurcation taking place almost im- 

 mediately behind the pharynx. 



The testes are contiguous or very nearly so, and the 

 posterior is most often but not invariably the larger. With 

 regard to the ova, there seem to be great variations in size, 

 although when the large size of the ova is taken into con- 

 sideration the variation is not excessive. The observations 

 of Mueller and Braun show an apparent discrepancy; the 

 former gives the dimensions as •12-'13x "l mm., the latter 

 •104 X 08 mm. This difference must result from the fact 

 that Mueller had only measured the larger ova and Braun 

 the smaller. W^ith the view to explain this difficulty I 

 measured the ova in upwards of 30 examples, and find the 

 limits in length to be •100-"124 mm., and in breadth -062- 

 '078 mm. These limits do not represent isolated examples, 

 for all sizes between them were observed. The average 

 figures are -1118 x -0685 mm., but this does not imply that 

 such a size is commoner than others. From this it is obvious 

 that Mueller's figures, which are at best a rough approxima- 



* Zool. Jahrb. Syst. xvi. pp. 12-13, pi. i. fig. 9. 

 t Arch. Naturg. Ixiii. p. 19, pi. iii. fig. 2. 



