580 
Cestofles from Selachians 
worm tubular (PI. XXIII, fig. 14). Such peculiar terminal segments are 
somewhat thinner than those that precede them. The flattening of 
the posterior segments may be due to the discharging of ova from 
the uterus judging from the fact that the uterine openings are very 
conspicuous, forming macroscopically visible spots ranged along the 
ventral median line. 
The cirrus openings are irregularly alternate, situated at the middle 
or a little anterior on the segments. The cirrus is frequently pro¬ 
truded from its pore; it is long, slender, and unarmed. The uterus 
openings are situated on the ventro-median line, a little anterior to 
the middle of segment. 
Internal structure. The parenchymatous tissue is very loose and 
the cuticular layer is very thin. There is no sharp line of demarcation 
between the marginal layer and central core, that is, the transverse 
muscle fibres separating the two fields are very weakly developed. 
The longitudinal muscle fibres are also not conspicuous. I have found 
a few bundles of them here and there running through the marginal 
layer in horizontal and sagittal sections, but it is difficult to find them 
in cross sections. The fact that this species varies slightly in both length 
and breadth may be explained by the feebly developed musculature. 
In the anterior immature segments, the marginal layer is tolerably 
thick measuring about one-fourth the body thickness, but in the mature 
segments the central core bulges out the marginal layer by the growth 
of the reproductive organs, especially the uterus. 
Excretory canals. As a rule there are two main excretory canals 
on each side, dorsal and ventral, running throughout the whole length 
of worm, just inside the yolk glands; the canals are small but distinct. 
Female organs. The vagina opens into the common genital cloaca 
on the antero-dorsal side of the cirrus opening. From the opening, the 
vagina proceeds inward straight in front of the cirrus pouch. Near the 
base of the pouch, the vagina rapidly widens, and bends on itself dorso- 
posteriorly along the basal end of the pouch; and passes dorsally to the 
excretory canal on the porose side to again run inward to the median 
part of the segment, where it coils on itself; ultimately it becomes the 
seminal receptacle, which lies on postero-ventral side of the segment. 
The proximal end of the seminal receptacle continues to the small 
duct, which runs dorsally over the ovary and turns again ventrally to 
unite with the oviduct coming from the ventral side. The united duct 
runs dorsally to open into the shell gland (PI. XXIII, figs. 16 and 17). 
The main portion of the vagina, between its opening and the seminal 
