ANATOMY OF TANIA MEDLOCANELLATA, 9 
organ would no less effectually retract it and assist at its in- 
version after copulation. 
The continuation of the perforating tube of the outer bulb 
of the penis is for a short distance of the same thick mus- 
cular-walled structure as the convoluted tube within the 
bulb, and =,!,> in. in diameter, but soon this tissue thickness 
lessens and merges into the delicate wall of the spermatic 
duct. This duct or vas deferens, average diameter 71, in., 
is of great length; it is seen to form a continuous close-set 
coiling from one side of the visceral space to the other 
(fig. 1, g) extending from the bulb of the penis to the centre 
of the segment, and even occasionally prolonged beyond the 
centre to the opposite end of the visceral space. In a longi- 
tudinal section (fig. 2, /) these coils are seen to be contained 
within a special fibrous compartment of the visceral space, 
passing directly inwards from the bulb and measuring +}, in. 
in depth. ‘The wall of the vas deferens is made up of very 
fine involuntary muscular fibre cells, forming delicate wavy 
longitudinal linear markings in its substance (fig. 7, /), and 
when coloured by carmine beautifully illustrating contractile 
tubal tissue. Between the bulb of the penis and the longi- 
tudinal water-vascular canal the coiling of the tube varies 
greatly in amount, but the tube and the accompanying vagina 
in their course towards the centre of the segment always 
pass together on one or other side of the water-vascular 
canal, never on opposite sides, and this feature of relation of 
the genital passages to the water-vascular system would 
appear to distinguish the flat surfaces of each segment into 
dorsal and ventral (fig. 1, 7, m). ‘The seminal duct in its 
meanderings gives off branches and ultimately terminates 
in similar divisions which form a covering to the seminal 
glands, or in other words, the gland structure is contained 
within a cecal dilatation of the duct (fig. 8). Occasionally 
also the duct is varicose as from circumscribed internal 
distension. 
The seminal glands or testicular bodies average twenty- 
four; they are globular, oval, pear-shaped, or crescentic in 
outline, and from =}, to ~4, im. in diameter. Occasionally 
one may be seen close to the bulb of the penis, often one or 
more between the bulb and the water-vascular canal, but the 
general site is between the canal and the centre of the seg- 
ment, though occasionally passing beyond this to the other 
extreme of the visceral space (fig. 1, #’), and their presence 
under these circumstances lends a clue to the comprehension 
of those monstrosities with a genital pit on each lateral edge. 
They lie within the sheath of the seminal duct, and conse- 
