STUDIES ON THE DIGENETIC TREMATODES. 445 
diameter of about ‘05 mm., usually runs straight back from 
the genital aperture, while the thicker part is bent on this 
either to the right or left. The diameter of the latter reaches 
a maximum of ‘09 mm. Its wall consists of the usual double 
layer of muscle-fibres, which have a diameter of about ‘0009 
mm. and are closely set. The vesicula seminalis is re- 
markable for the extent to which it is convoluted (fig. 11), 
exceeding that of Podocotyle atomon (Rud.) in this 
respect. It appears, however, to have a fairly definite 
configuration. From the end of the cirrus-pouch it passes 
forwards in a curve towards the right. It then turns 
completely on itself and bends back in an S-shaped course 
nearly to the posterior end of the pouch, where it again 
turns and runs forward almost parallel to the first part. It 
then passes into the ductus ejaculatorius, which almost 
immediately bends backward, describes a turn, passes 
forwards again, only to describe another complete turn, after 
which it runs forwards in a sinuous manner, but without 
further convolutions. The diameter of the vesicula seminalis 
is ‘(04 mm.; that of the ductus is about ‘015 mm. 
Asin Podocotyle atomon (Rud.) no well-differentiated 
pars prostatica occurs on the ductus. Around the initial part 
of the ductus, however, there is a considerable number of 
large cells which occupy the usual position of the prostatic 
cells. hey differ from the corresponding cells in Stephano- 
phiala laureata, Brachycladium oblongum and other 
species which I have examined. ‘he cell body appears to be 
very tenuous and almost invisible, but the nucleus and 
nucleolus stain very brightly. The nucleus is large and 
round, measuring ‘0068 mm., the nucleolus ‘0018 mm. They 
certainly do not lend the impression of being gland-cells, but — 
from their position they can hardly be otherwise. They are 
quite distinct from the “ Beegleitzellen” or myoblasts which 
are present in large numbers around the anterior two thirds 
of the ductus. The latter are much smaller cells, staining 
deeply and resembling the peri-vaginal cells. 
The genital aperture is situated midway between the 
