Aquatic Oligochaeta from Japan and China. 91 
about or slightly above the middle of the height of the latter, piercing its wall ob- 
liquely. The lining of the vas consists of heavily ciliated cubical cells. 
The atrium is a cylindrical chamber, -08 mm. in diameter, which lies obliquely 
in segment xi; its hinder end, directed posteriorly and dorsalwards, reaches nearly 
to the dorsal parietes ; its lower and anterior end narrows gradually at first, and then 
suddenly, to become the ejaculatory duct. The whole of the atrium is enclosed 
within the mass of prostatic cells, with the exception sometimes of the blind end, 
which may be bare. The blind end as far down as the entrance of the vas deferens 
is lined by high ciliated epithehum ; in the remaining portion the cells are non-ciliated , 
clearer than higher up, with a more densely staining cytoplasm (eosin). There is a 
granular coagulum in the lumen. 
The paratrium is also a more or less cylindrical chamber, -06 mm. in diameter, 
lying roughly parallel to the atrium, and like it enclosed in the prostatic mass. Its 
lower end is the narrower,— two- thirds the diameter of its upper portion; it is continued 
below into theparatrial duct, which joins the ejaculatory duct shortly after the latter 
has entered the coelomic chamber. Its epithelium varies in character from cubical 
to low columnar; it is not cihated. The lumen contains a homogeneous coagulum. 
The paratrial duct, with a small or even potential lumen, has a thickness of 30-40 m, 
is lined by a non-ciHated epithelium, with deeply staining nuclei, and has a strong 
muscular investment. 
The ejaculatory duct is enclosed in its whole length in the "coelomic chamber" 
(figs. 4, 5), a sac with muscular walls, ovoid in general form, which is implanted on 
the ventral body- wall and reaches to about half the height of the body ; the mass of 
prostatic cells impinges on or gets an attachment to the upper part of the sac. The 
duct is suspended in the sac by a stout band of muscular fibres, — not only the band but 
also the individual fibres are stout ; the suspensory band and the fibres of the sac-wall 
are continuous with a vertical strand which passes upwards through the segment and 
is attached to the dorsal body- wall. The duct winds considerably in the upper part 
of the coelomic sac; it has a non-ciliated cubical epithelial lining and a prominent 
muscular coat; its diameter, 40 ix at first, diminishes further down to about 27 /x. 
The "prostatic cells," which have a close histological resemblance to the 
"pharyngeal gland cells," do not seem to be more than applied to the organs they 
surround; they thus represent an overgrowth of peritoneal cells, and do not discharge 
into any part of the lumen of the male deferent apparatus. The whole, with the 
organs contained within it, constitutes a bulky irregular mass which takes up a large 
part of the segment. 
The projecting portion of the penis (fig. 5) is shown by sections to be as it 
appears in entire specimens, hollow and bladder-like; its covering epithelium is short, 
not columnar like that of the general surface of the body ; it contains a central tube, 
the continuation of the ejaculatory duct, which opens at its free extremity. The 
space included between its outer wall and the duct which runs through its centre is 
a portion of the coelom continuous with that included in the coelomic sac ; and the 
function of the sac is apparently, by the contraction of its muscular waH, to produce 
