S. Yoshida 
581 
receptacle, possesses a nearly uniform diameter of 0-05 mm. The 
seminal receptacle measures 0-09 mm., and the proximal part of the 
vagina gradually narrows from the seminal receptacle to the point 
where it joins the oviduct. The entire length of the vagina is surrounded 
by a single layer of cells with distinct nuclei. 
The oviduct (PI. XXIII, figs. 16 and 17, 0) begins with the so-called 
“egg-swallower” (PI. XXIII, figs. 17 and 19, E) which is continuous 
with the middle portion of the ovary ventro-posteriorly. The “egg- 
swallower” is a remarkable organ, shaped like .a sphere flattened 
antero-posteriorly; its lumen is spacious and its muscular wall is very 
well developed; the radial muscular fibres are the most highly developed. 
Just outside the muscular wall, the “egg-swallower” is surrounded by 
a thick layer of distinctly nucleated cells (PI. XXIII, fig. 19). The 
oviduct, which follows, runs dorso-ventrally in a pronounced curve 
within the. medio-posterior part of segment. The width of the oviduct 
is 0'035 mm. proximally, and it gradually broadens distally, its end 
measuring 0-05 mm.; it narrows again at its junction with the vagina. 
The lumen of the oviduct also widens gradually from the proximal to 
the distal end. The wall of the oviduct consists of a homogeneous 
membrane and two layers (inner thicker and outer thinner) of distinctly 
nucleated cells; the innermost membranous layer of the wall is provided 
with minute spinules projecting backward into the cavity. In the 
outer thinner layer the cell boundaries are not conspicuous. 
The shell gland (PI. XXIII, figs. 16 and 17, 8D) is spherical or 
somewhat flattened in shape, measuring 0-2 to 0-14 mm.; it is situated 
medio-dorsally, posteriorly in each segment; it is composed of spindle- 
shaped cells with well-defined nuclei which are readily seen under a 
moderate magnification. At its centre the shell gland receives the yolk 
duct coming from the ventral side. 
The yolk duct has a diameter of 0-007 mm. and bifurcates at the 
point where it passes across the middle of the ovary, the branches of the 
duct proceeding right and left to unite with the yolk glands which are 
situated just outside the excretory canal on each side of body (PI. XXIII, 
fig. 16, D). The yolk cells are very small, measuring 0-0011—0-0013 mm. 
in diameter. By the smallness of the yolk cells we can easily distinguish 
them from the ovarian eggs although both of them look alike. 
The ovary (PI. XXII, figs. 16 and 17, K) is irregularly lobed, situated 
in the posterior part of body, spreading from the median plane to the 
lateral excretory canals. It lies mainly on the ventral side of the seg¬ 
ment, but it extends out to the dorsal, thus occupying an extensive 
38—2 
