A434 WILLIAM NICOLL. 
inner layer of well-marked annular muscle-fibres and an 
outer layer of less distinct longitudinal fibres. The lumen is 
lined by a rather thick cuticularised epithelium. In addition, 
however, to the two intrinsic muscle layers there are numerous 
other stout muscle-fibres passing from the ductus to the wall 
of the cirrus-pouch. These run more or less obliquely, but 
on eversion of the ductus they are drawn nearly parallel to 
it. ‘lo explain this peculiar condition of the ductus it seems 
necessary to consider that these extrinsic muscle-fibres exert 
the most important action in retracting the ductus from its 
everted position and that on account of their direction they 
cause it to fold up instead of winding on itself. What action 
the intrinsic longitudinal fibres take or why the eventual 
result should be so different from that most frequently 
observed are questions not easy to determine. No mention 
is made of such a condition by Looss in the case Br. 
palliatum. His figure (Pl. XXIII, fig. 8) represents the 
ductus as a slightly tortuous tube of uniform calibre, widen- 
ing somewhat suddenly as it passes backwards and surrounded 
by a closely packed mass of gland-cells (Anhangsdriisen). 
‘he condition is therefore totally different from that in 
Br. oblongum, and it is a curious fact that two so closely 
related species should present such an important feature of 
difference. Cells which stain deeply (gland-cells or myoblasts) 
are certainly present around the ductus, but they are com- 
paratively few in number and scattered in the midst of 
looser tissue. 
That the terminal part of the ductus functions as an 
exsertile cirrus there can be no doubt, for in one of my 
specimens I found it extended about ‘06 mm. beyond the 
genital aperture (i. e. about *2 mm. from the male aperture). 
In that case the anterior folds of the ductus were straightened 
out, but the posterior folds remained, so that while the anterior 
part became a tube of uniform calibre, the posterior part 
remained in the condition above described. 
The histological structure of the pars prostatica and vesi- 
cula seminalis does not differ from that in Br. palliatum, 
