STUDIES ON THE DIGENETIC TREMATODES. 433 
longitudinal fibres of the cirrus-pouch and vagina. The 
cirrus-pouch (fig. 7) is a pear-shaped or ovoid structure 
extending backwards nearly as far as the posterior border of 
the ventral sucker. It thus reaches further back than in any 
other species of the genus. At its posterior end it approaches 
the dorsal surface of the body, and is separated from the 
ventral sucker by the uterus. Its maximum diameter is ‘5 
mm. The longitudinal muscle-fibres of its wall have a 
diameter of -002—004 mm., and are separated by spaces of 
‘001—004 mm. The annular fibres are much finer, ‘0Q04—002 
mm., with intervening spaces of ‘0007-0015 mm. The 
vesicula seminalis is of large size and occupies the greater 
part of the cirrus-pouch. Its length is about *8 mm., but 
it displays numerous dilatations and convolutions. Its 
diameter varies from ‘16 mm. to*28 mm. At its anterior end 
its wall is slightly invaginated into the pars prostatica, which 
is a short S-shaped tube with a diameter of 066 mm. The 
prostatic cells are comparatively few and are entirely confined 
to the space around the pars prostatica. The cells are oval, 
with a long diameter of ‘012 mm. and nuclei of -0035—004 
mm. diameter. Amongst the prostatic cells there are a few 
larger cells measuring ‘019 mm., which do not stain so deeply 
and have faintly-staining, round nuclei measuring ‘0062 mm. 
At its anterior end the pars prostatica passes into a widely 
dilated ductus ejaculatorius, which presents a rather unusual 
condition. In its retracted state, instead of being convoluted 
or wound upon itself, as is the case in many species, it is 
crnmpled up (concertina-fashion). In sections it presents a 
grating-lke appearance (fig. 7), the lumen being alternately 
contracted and expanded. The crumpling, however, is not 
by any means irregular, fairly equal spaces being maintained 
between the folds.! The structure of the wall of the ductus 
does not differ from that commonly met with, there being an 
‘A somewhat similar condition appears to exist in Distomum 
alacre Lss., according to Looss’s short description of that species 
(‘Centralbl. f. Bakter., Abth. 1, vol. xxix, p. 401). In the genera 
Fellodistomum and Steringop horus an analogous condition exists, 
but in these the ductus is very short. 
