S. Yoshida 
oHo 
the spermatozoa for it functions as a seminal vesicle. On leaving the 
cirrus pouch the vas deferens is coiled many times basally to the pouch; 
its further course to the testes has not been traced in my preparations; 
the vas deferens is surrounded throughout by a cell-layer. 
Female organs. The essential parts are situated posteriorly in the 
segment. The vagina (PI. XXIII, fig. 5, F) beginning at the common 
genital cloaca, runs towards the median line along the anterior edge 
of the cirrus pouch, then bending nearly at right angles it runs back 
to in front of the shell gland where it enlarges and assumes an irregular 
shape. The narrow proximal part of vagina passes by the shell gland 
posteriorly and turns again anteriorly to open into the shell gland. 
Where it bends, it unites with the oviduct. The vaginal wall is of uniform 
thickness, and is surrounded by a cell-layer with distinct nuclei; its 
structure is best seen in sections. It is nearly uniform in diameter 
(about 0-02 mm.) throughout its length, but for the dilated portion 
lying anterior to the shell gland; the dilated portion may serve as a 
receptaculum seminis. 
The shell gland (PI. XXIII, fig. 5, sd) is spherical, with margins irregu¬ 
larly lobed, and measuring 0-064 mm. It is situated in the median 
part of the posterior region. Aiiteriorly, its canal runs forward along the 
vagina to near the middle of the segment and opens into the uterus, 
which lies longitudinally in the median field. The canal measures about 
0-009 mm. in width and is surrounded by thick masses of cells. 
The uterus (PI. XXIII, fig. 5, U), in young segments, appears as a 
mere longitudinal cell rod, containing a canal which gradually grows 
larger toward the posterior segments. In the mature segments ,the 
uterus is much distended with the ova, and ultimately it completely 
fills the available space in the segment. 
Running forward from the side of the shell gland is the yolk duct 
(PI. XXIII, fig. 5, G) which forks anteriorly to form two canals running 
laterally to the yolk glands on both sides of the segment. The yolk 
glands are situated in the lateral areas, extending dorso-ventrally 
insidedhe transverse muscle bundles, which separate the medullary field 
from the cortical; they occupy the anterior two-thirds or three-fourths 
of the segment; their arrangement is best seen in sections (PI. XXIII, 
fig. 4, D). 
The ovary (PI. XXIII, fig. 4, K) is situated posteriorly in the segment, 
its antero-lateral margins being continuous with the posterior end of 
yolk glands; it is arranged in four groups or laminae, two on each side. 
The lateral groups are placed on the dorsal and ventral side of medullary 
37—2 
