J. Johnstone 
407 
cirrus sac, while the other branch penetrates the sac and passes 
backwards as the vagina. When the cirrus is evaginated it appears 
to proceed from the summit of the papilla—the genital pit being then 
turned inside out—and both vas deferens and vagina then open into 
everted cirrus. Tlie wall of the vagina is thickest nearest to the 
genital opening and consists of a structureless membrane bearing nuclei 
on its outer surface with some muscle fibres running mostly in a 
longitudinal dii’ection, though some are also transverse and oblique. 
The vagina runs back nearly in the middle line of the proglottis towards 
the space between the anterior lobes of the ovary—but it is not nearly 
so much convoluted as the uterine canal. Near the ovary and 
approximately in the mid line of the segment it enlarges considerably 
to form the receptaculum seminis. In the immature proglottis this 
dilated part of the vagina may be empty, but in segments approaching 
sexual maturity (in the female organs) all the canal, and particularly 
the dilated receptaculum, contain spermatozoa received from the same 
proglottis by self-fertilisation, or from another by copulation. The wall 
of the receptaculum is much thinner than that of the rest of the 
vaginal tract, being, of course, only a dilated part of the latter. 
Near the median part of the ovary, and beyond the receptaculum, the 
vagina decreases considerably in diameter and its wall becomes much 
thicker. There is now a thick basement membrane with close, but 
rather irregular layers of nuclei on the inner and outer surfaces. The 
duct passes either over or under the median ovarian bridge and just 
posterior to the latter its calibre diminishes very suddenly and from its 
extreme posterior boundary a small tube takes origin. This is the canalis 
seminalis. It has a thick wall consisting of very dense fibres running 
circularly or obliquely. It runs very nearly at right angles to the 
former direction of the vagina and joins the oviduct very close to the 
junction of the latter with the vitelline duct. It is so difficult to be 
sure that it always enters the oviduct between the ovary and the 
junction of the vitelline duct that I am constrained to conclude that 
there may be some variation in the precise order in which these three 
ducts become connected Avith each other. 
The vitellaria. These glands are represented in the diagram. Text- 
fig. 8, where they are shown in transverse section ; and in Pis. XXI and 
XXIV, figs. 10-11, where they are represented only at the margins of 
the proglottis. They form a layer which is roughly concentric to the 
integument; and which is interrupted only at the region immediately 
round the genital papilla and lies between the layer of subcuticular 
