H. A. Baylis 407 
marking the junction of the cortical and medullary parenchyme. Numerous 
very fine dorso-ventral fibres run across both cortex and medulla. 
Excretory system. Dorsal and ventral longitudinal vessels are present, both 
pursuing a very irregular and sinuous course. Both pairs of vessels are situated 
at some distance from the lateral borders of the segment (PL XXI, fig. 3, D. 
and F.). As seen in transverse sections, the dorsal vessel on either side is not 
vertically above the ventral vessel, but usually displaced a little outwardly. 
Narrow transverse vessels connect the ventral longitudinal pair at the back 
of each segment. These transverse vessels usually form a kind of ‘"delta" at 
their ends, and open by several mouths into the longitudinal canal, exactly 
as has been described for 0. rostellata by Zschokke (1905). They also, as in 
that species, often send out small side-channels along their course, forming an 
incipient network confined to the interproglottidal region. 
Genital organs. Although rudiments of genital organs, or at least of their 
ducts, appear very far forward, mature segments begin to appear very late— 
fully 200 segments from the anterior end. There are only about eight segments 
with fully-developed organs before the appearance of the uterus. The latter 
rapidly obscures the other organs, and these very soon begin to degenerate. 
In a mature segment (PI. XXI, fig. 2) the ovary (Ov.) is the most conspicu¬ 
ous organ. It is a roughly triangular mass of lobes, not distinctly divided into 
two lateral portions, as is sometimes the case in this genus. Its longest diameter 
is from 0-4 to 0*5 mm. It lies entirely on the pore side of the middle line of the 
segment. The yolk-gland (PI. XXI, figs. 2 and 3, Vit.) is irregular in shape, and 
a little smaller than the ovary. It lies obliquely behind the latter, the middle 
line of the segment just passing through it near its aporal end, so that the 
greater part of the organ is on the pore side. A small shell-gland (PL XXI, 
figs. 2 and 3, S.) is situated between the ovary and volk-gland. A coiled 
oviduct (PL XXI, fig. 3, Od.) connects the female glands and the uterus. The 
latter will be described below. 
The testes (PL XXI, figs. 2 and 3, T.) number from 60 to 70, and occupy 
the greater part of the middle field of the segment behind and at the sides of 
the female glands. A few on the aporal side even extend so far forward as to 
lie in front of the ovary. The layer of testes is only one deep, as may be seen 
in transverse sections (PL XXI, fig. 3, T.). The testes are mostly oval in out¬ 
line, their longest diameter varying from 0-075 mm. to 0-1 mm. Their long 
axis most frequently lies in a direction transverse to the length of the worm. 
The male and female ducts open at the base of a shallow muscular genital 
cloaca (PL XXI, fig. 2, Cl.). The cirrus-sac (PL XXI, figs. 2 and 3, C.S.) 
measures 0-25 mm. in length, and in thickness 0-2 mm. Its wall is very 
muscular, especially towards the outer end. The vas deferens (PL XXI, fig. 2, 
V.D.) is much coiled, especially about the middle of its course. The vagina 
(PL XXI, figs. 2 and 3, Vag.) opens into the genital cloaca behind the cirrus-sac, 
in the same horizontal plane. It is a very narrow tube, running almost straight 
towards the ovary. It does not, as in some related species, widen out at any 
