Tremalode Parasites of British Birds. 253 



the middle line. It is thus not entirely in front of the 

 ventral sucker, with which it is contiguous. Its long axis 

 is obliquely transverse and the ductus ejaculatorius issues 

 from its left end and passes round in front of the ventral 

 sucker in almost direct course to the genital body. The 

 testes are situated as in the preceding species. The ovary is 

 a regularly ovoid body, with its long axis transverse and 

 slightly depressed towards the middle line. It is on the 

 level of the posterior border of the ventral sucker and is 

 thus further back than in »S/>. excel/ens. From it the uterus 

 passes down the middle of the body towards the left side ; 

 it then runs round the posterior edge of the body to the 

 right side, where it forms a few convolutions. Pursuing a 

 transverse zigzag course it returns to the left side, almost 

 reaching the outer edge of the body, whence it bends back 

 ajiain and passes forward to the genital sucker. Its topo- 

 graphy is thus entirely different from that in Sp. excellens. 

 In addition the ova are almost colourless or of a very dull 

 hue. They measure •020-"025 X'()10-'01 2 mm. I'he uterus 

 is of very limited extent and does not extend in front of the 

 testes. The yolk-glands can thus be easily made out. They 

 occupy the usual position ventral to and a little behind the 

 testes. In an immature specimen their lobed structure can 

 be distinctly seen. In Sp. simile Jiigerskiold figures six 

 lobes on each side. Odhner corrects this to eight for both 

 Sp. simile and Sp. pygniceum. In Sp. feriaiuui, however, 

 there seem to be seven lobes on the left side and eight on 

 the right. Should this be the normal condition it would 

 be analogous to that in some of the Heniiuridai, in which 

 there are three lobes or tubes on the left and four on the 

 right. The arrangement of the lobes is characteristic and 

 apparently fairly constant. In each groiip there is a central 

 lobe of roughly quadrilateral outline ; the sides of this form, 

 as it were, facets into which the other lobes fit. The latter 

 are all of quadrilateral or wedge-shaped outline, broadest at 

 their distal ends, with rounded corners. The anterior face 

 of the central lobe and each of the lateral faces accommo- 

 dates a single lobe, while behind there are three lobes in 

 the left vitellarium and four in the right. I have obserxed 

 the odd number of lobes on the left side in all the specimens 

 examined, but it is possible that an additional lobe may 

 be obscured. From Odhner's figure there appears to he 

 no such regular formation of the lobes in Sp. pi/f/fiueifin. 

 Jiigerskiold * represents a regular arrangement, but there is 

 no central lobe. 



* Centralbl. f. Baktcr. xxvii. p. 7;?3, fig. 1. 



