
1905.] Anatomy of the Tsetse-fly (Glossina palpalis). 545. 
show the other parts of the generative system ; further, the individual tubes. 
are much thicker, and when stained and mounted, they take up the stain 
very deeply and appear very opaque. There can be no doubt that these: 
glands serve for the nourishment of the larva in the uterus. 
The uterus (U¢.) is a large thimble-shaped organ attached to the body-- 
wall by a number of muscles. Two retractors (retr. ut.) run forwards. 
from the proximal end. There are two pairs of protractors, one dorsal, the: 
other ventral; the former (pro. wt.) start from the sides of the uterus and. 
pass backwards to a pair of chitinous plates (Ch. 1) at the posterior end of the. 
body. The wall of the uterus is beset by a very large number of small. 
tracheal tubes (not shown in the figure), and is thick in the non-gravid 
condition, but becomes thinner when stretched by the growth of the contained 
larva. In all gravid uteri that I have seen, the two papille at the hinder: 
end of the larva cause a bulge in the lower end of the uterus (fig. 6, Z.). 
When the larva reaches a certain size, the rings of its segments become plainly 
visible through the wall of the uterus; they could not be seen in the uterus. 
drawn in fig. 6, but in another, slightly larger, they could be seen distinctly. 
The vagina (fig. 6, Vag.) is a broad tube, considerably longer in the non- 
gravid than in the gravid condition, with a pair of dilator muscles (m. vag.),. 
which are attached right and left just below its junction with the uterus, and 
pass outwards to be attached to the anterior margin of the tergum of the ~ 
seventh abdominal segment. The vagina widens out slightly as it approaches. 
the vulva (V.), which is a crescentic, transversely elongated aperture, separated 
from the anus by a small chitinous plate (Ch. 2), one of a pair from which two: 
muscles (m. v.) arise and pass outwards to be attached to the seventh tergum,,. 
a little way behind the attachment of the vaginal muscles already mentioned. 
These muscles probably act as dilators of the vaginal aperture, and the five. 
pairs of muscles described in the preceding lines are to be regarded as con-. 
stituting the mechanism of parturition. 
4. The Vascular System consists of the heart, in the abdomen, and its. 
continuation, the thoracic aorta, in the thorax. 
The heart occupies the five anterior segments of the abdomen, and is. 
situated dorsally immediately below the plates of the terga. It is so 
imbedded in the fat-body and pericardial tissue that not much can be made 
out of its structure by dissection alone, and examination of it mounted as a 
preparation for the microsccpe is necessary. It can then be seen to have five 
chambers, each with a pair of ostia and a pair of alary muscles, corresponding 
to the segments in which it lies. The alary muscles pass out at right angles 
to the axis of the heart, and can be traced through the fat-body to their 
attachments at the external lateral margins of the tergal plates. 
