W. Nicoll 
245 
pars prostatica is considerably shorter and the prostatic cells much fewer 
in number. The pseudo-cirrus pouch, however, is distinctly longer, 
being somewhat cylindrical instead of globular. The posterior end is 
slightly inflated. The genital aperture lies immediately over the 
intestinal bifurcation. 
The two foregoing species present not a few features of considerable 
taxonomic interest. They obviously belong to the small group of forms, 
inhabiting the stomach, of which Derogenes various is the- best known 
example. Hemipera differs from all the forms which may be included 
in this group by reason of the structure of its cirrus pouch, which 
contains not only the ductus ejaculatorius but also the pars prostatica. 
In all other members the latter is free. It presents the further 
peculiarity of having the testes situated behind tlie ovary. In this 
respect it resembles Liocerca, to which it is probably more closely allied 
than to any other genus. 
Derogenoides, on the other hand, is a typical member of the group 
with a free pars prostatica and the testes in front of the ovary. It bears, 
indeed, a very close resemblance to Derogenes. The somewhat different 
structure of the terminal male organs, however, together with the 
more anterior position of the ventral sucker and the genital glands and 
the characteristically shaped eggs, appear sufficient grounds for excluding 
it from this genus. 
The systematic position of Derogenes has for long been a difficulty. 
It was included in the family Hemiuridae by Ltihe (1901) and its 
^ somewhat isolated position in this family was recognised by Odhner 
(1904) who suggested that a separate sub-family would probably be 
required for its reception. On the other hand, Looss (1907) definitely 
excluded it from this family. There can be little doubt, however, of its 
Hemiurid affinities. Its whole structure, apart from the absence of an 
appendix, gives evidence of this and there appears no very strong reason 
why it should for the preseiit be excluded from this family. At the 
same time it displays considerable affinity with the Syncoeliinae and 
the inclusion of Derogenes within the Hemiuridae would necessitate 
the inclusion of this sub-family as well. Odhner (1911), indeed, has 
advocated the advisability of this step, including Derogenes actually 
within the sub-family Syncoeliinae. He extends the family moreover 
to include the Accacoeliinae and the group of which Hirudinella 
clavata is the chief representative. In this reconstructed family Looss’s 
Hemiuridae takes the position of a sub-family. 
In view of the great variety of structure which occurs in these 
forms Odhner’s arguments in favour of a wider conception of the family 
16—2 
