STUDIES ON THE DIGENETIC TREMATODES. 4.67 
there is no doubt it invariably occurs. The posterior part is 
the smaller of the two. Hach has a length of about ‘(085 mm. ; 
the breadth, which is capable of great variation, is respec- 
tively ‘(06-11 mm. and *04—08 mm. The walls are muscular, 
and an epithelial lining with a few large nuclei can be observed. 
The pars prostatica is exceedingly well developed, and, in fact, 
occupies the largest portion of the cirrus-pouch. It has, as 
represented in Jacoby’s figure, a bulbous shape, narrowed 
somewhat at its junction with the vesicula seminalis. Its 
length is °18 mm. and greatest breadth "18 mm. Its wall is 
muscular and it is lined by a distinct epithelium with oval 
nuclei, measuring ‘0096 by ‘0057 mm. ‘The lumen is almost 
entirely filled by long string-like masses of prostatic secretion, 
which he, hke so many filaments, parallel to each other, and 
are directed out towards the ductus, into which they project. 
The prostatic cells occupy a large part of the cirrus-pouch, 
surrounding the pars prostatica and the vesicula seminalis. 
A few are also found around the ductus. Their nuclei 
measure ‘008-01 mm. Amidst the prostatic cells several 
large myoblasts or ganglion cells occur. They are distin- 
guished by their much larger nuclei (‘012 mm.) and different 
staining reaction. ‘he pars prostatica passes into a wide 
(11 mm.) ductus ejaculatorius, of comparatively short length. 
Its wall has an irregular outline, being crumpled up in some- 
what the same manner as in Brachycladium oblongum, 
but not nearly to the same extent or so regularly. At first 
sight it might be mistaken for the sinus genitalis, and it 
certainly offers a contrast to the long narrow ductus found in 
the majority of Distomids. It is doubtful if it functions as 
an eversible cirrus, but if so it evidently cannot be everted 
to any great length. It was not everted in any of my speci- 
mens, and Jacoby makes no mention of having seen it in such 
a condition. The extreme prominence of the genital papilla 
may be an adaptation to compensate for the shortness of the 
cirrus. ‘he walls of the ductus have the usual structure, but 
are unusually thick. The lining consists of a thick meta- 
morphosed epithelium easily distinguished from the cuticular 
