300 DR J. STEPHENSON ON 
less deeply, in its first part. The cells of which its wall is composed have nuclei 
which are much elongated transversely to the axis of the tube; their length may be 
as much as one-third of the circumference. The vas deferens is continued into the 
atrium, which begins in the posterior part of xi, the septum (+3) being here much 
bulged backwards. The atrium is of an elongated pyriform shape, its first part being 
the broader (90«); the lumen is at first small, or even, in transverse sections, invisible ; 
only the basal portions of the cells take the stain. The penial end of the atrium is 
narrower, the lumen is more distinct, the whole of the cells are deeply stained so 
as to obscure the nuclei. The prostate is a fairly large, somewhat spherical cellular 
mass, continuous with the wall of the atrium, to the first part of which it is attached, 
a little way beyond the end of the vas deferens. The atrium joins the penis, which 
hes in a canal directed forwards and downwards to the male aperture. This canal is 
narrow and cylindrical, wider near its external termination, contracting again, — 
however, at the actual aperture, which is situated ventrally on xi, in the position 
of the missing setal sacs. The penis itself is surrounded by a chitinous penis sheath 
lying loosely within the canal. The sheath is tubular, circular in cross section, 
narrowing gradually along its course, but expanding again and curving forwards at 
its outer end; its length is about 520s, its breadth 494 above, at its narrowest part 
28u. ‘The lower side of its expanded end terminates in a free margin; the upper side 
is curved strongly upwards and joins the wall of the penis canal (fig. 16); in the 
section there illustrated a horizontal cellular shelf projects backwards into the open 
end of the penis sheath. The sheath ends some distance above the external aperture 
of the penis canal. The vesicule seminales comprise a pair of sacs in ix, forward 
bulgings of septum ;%,, and a long single sac extending back through xi and a number 
of succeeding segments, which is essentially a backward bulging of septum +2. 
The ovaries in segment xi correspond in position to the testes; they are large, 
extending upwards at the sides of the alimentary canal, and becoming dorsal to it. The 
funnel is situated ventrally on septum +3; the ovzduct is a minute passage leading to — 
the exterior in the inter-segmental constriction between xi and xii. The ovisac extends — 
backwards in the same way as the sperm-sac. The spermathece are in segment xX; 
their external aperture is just in front of and in line with the setal sacs. At first the 
passage runs vertically ; its lumen here is narrow, and its epithelial lining consists of | 
deeply staining cubical or low columnar cells, with a cuticle on their free surface. The 
height of the epithelium soon becomes irregular, and the outline of the lumen in conse- 
quence wavy. All this first part, or duct, is invested by a strong muscular covering, 
in two layers, a longitudinal external and cireular internal; its diameter is about 80». 
After bending about, the cavity widens very considerably; the lining consists of a 
rather irregular layer of low columnar cells, and the lumen is filled with a granular 
coagulum ; the diameter of the ampulla is about 2704. There were no spermatophores. 
The diagnosis of the genus Limnodrilus, as given by MicHAELSEN (5), runs as 
follows :—‘‘ Ventrale und dorsale Biindel lediglich mit gleichartigen, gabel-spitzigen 
