149 
Variations in Uropoda. By A. D. Michael, 
wliich extends about half-way along the edge on each side ; thence 
nearly to what may be called the toe of the shoe it is continued by a 
much thinner bar, which, however, is not absolutely joined to the 
thicker. The whole space inclosed by this framework is filled by 
a moderately thick lamina of chitinized tissue, having the concavo- 
convex form before described. This lamina is transparent and colour- 
less, but is not flexible ; it retains its shape permanently, and a 
transverse section of the perigynum shows this most distinctly. The 
dorsal side of the lamina is smooth ; the ventral side is thickly covered 
with spines of moderate length. When the organ is seen from the 
dorsal side the proximal ends of these spines are seen through the 
transparent material, giving a dotted appearance. 
Bound the chitinous bar at the upper edge of the heel of the 
perigynum is fitted a piece of clear colourless chitin (figs. 3, 4, cld), 
and it is here that the upper edge of the neck of the vagina rests 
upon, and is attached to the perigynum ; the thin projecting portion 
of the heel of the perigynum actually enters the opening of the neck 
of the vagina (fig. 6). 
A powerful fasciculus of muscles (figs. 2, 8, 5, 11, &c., is 
inserted in the chitinous framework on each side of the heel of the 
perigynum just after it has curved round and become lateral ; these 
muscles arise from the dorsal surface, and serve to draw the heel of 
the perigynum upward. 
The thin membranous walls of the vestibule, although attached 
all round the perigynum, do not in all parts run simply from that 
edge to the genital aperture ; round the toe of the perigynum they 
make a large fold (figs. 2, 3, /), which, to continue the former homely 
simile, looks like the toe of a larger slipper projecting beyond the 
shoe. 
Bound the edge of rather more than the anterior half of the peri- 
gynum extends a membranous vandyked border (figs. 2, 3, 4, 7, &c., 
fr), the proximal edge of which is attached to the ventral side of the 
framework, while the whole of the remainder stands free inside the 
vestibule. This border is very conspicuous in stained dissections, as 
it takes stain readily ; but 1 cannot at all suggest what is its office. 
Two paired accessory glands (figs. 1, 2, ag) discharge close to 
the mouth of the vagina ; they are sac-like organs of even diameter 
throughout, the diameter being small compared to the length ; about 
the middle they are bent nearly at a right angle. 
Having now described the whole of the parts, it remains to indi- 
cate what it appears to me is their action. Firstly, when the recep- 
taculum seminis is being filled, and at ordinary times if the genital 
plate be opened, the heel of the perigynum would rest against the 
opening of the neck of the vagina, its spines probably interlocking 
with some spines which exist round the neck, and thus spermatozoa 
and foreign substances would be completely excluded. When it is 
necessary that spermatozoa should enter, then the action of the 
