151 
Variations in Uropoda. By A. D. Michael. 
seminis found in TJ. ovalis ; further examination shows that its place 
is supplied hy two very small paired organs of a totally different 
form (fig. 21, and figs. 12, 13, 14, rs). They greatly resemble the 
corresponding organs of Musca domestica, as figured by Stein, and 
each consists of a quite small elliptical sac, which is placed at the 
distal end of a long narrow tubular peduncle, which is slightly con- 
stricted at regular intervals near the sac, so as to present a somewhat 
moniliform appearance. The peduncle has a larger diameter at its 
distal end than at the proximal, where it arises from the upper side 
of the expanded neck of the vagina. It is probably because of this 
position of the entrance to the receptacula seminis that the mouth of 
the vagina is not closed by the perigynum, as in Uropoda ovalis, the 
closing of the entrance to the vagina being apparently effected in U. 
vegetans by the tighter constriction of the neck. When the organs 
are dissected out, the receptacula seminis appear dark and chitinized, 
although the peduncle is comparatively light and transparent; if, 
however, the sac be torn, and its contents expelled by pressure, it 
will then be found that the apparent darkness and opacity arise from 
the receptaculum being (in all specimens which I have dissected) so 
densely crowded with spermatozoa that they form a solid mass, which 
may be pressed out and retain its elliptical shape ; a drop of liquid, or 
a little disturbance with a fine hair, will, however, soon resolve the 
mass into its constituent parts, viz. spermatozoa, such as those repre- 
sented by fig. 20. When the spermatozoa have been expelled the 
walls of the receptaculum are nearly transparent and smooth ; while 
they are still contained in it the organ looks granular, from the closely 
packed spermatozoa showing through the walls. 
There are two paired accessory glands in this species, as in TJ, 
ovalis, which discharge into the vestibule near to the mouth of the 
vagina, hut instead of being sausage-shaped they are almost globular ; 
their walls are thin and transparent, and have a few straight wrinkles 
arranged in a radiating manner ; an extremely short duct leads from 
them to the vestibule. The glands of TJ. ovalis have generally been 
charged with secreted material when I have found them, while the 
more vesicle-hke organs of TJ. vegetans have invariably been entirely 
empty. 1 fancy, however, that in consequence of the shortness and 
openness of the ducts their contents escape during dissection. 
The accessory glands and the corner of the mouth of the vagina are 
supported on each side of the body by a singularly shaped chitinous 
piece, which is not present in TJ. ovalis, and which I will call the 
“ sigmoid piece ” ; it is an S-shaped lamina, varying in width in 
different parts, and twisted also in a direction at right angles to the 
plane of the S, so that it becomes screw-like. It is difficult to give 
an idea of it in words ; ij; will probably he understood better from 
figs. 13, 15, 17, si. The edge of the sigmoid piece is attached, at one 
place, to the lateral body-wall ; the duct of the accessory gland dis- 
charges along the hollow formed by the lower turn of the S ; the end 
of the upper turn supports the mouth of the vagina. 
