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Transactions of the Society. 
muscles would expel a sufficient number from tlie receptaculum, 
and tlie action of the muscles would raise the heel of the peri- 
gynum and allow the opening of the neck of the vagina to be entered. 
Again, when oviposition is to take place, the large egg would be 
forced from the vagina through the neck, the powerful muscles 
would raise the perigynum, carrying the top of the neck of the vagina 
wdth it ; the opposed muscles would at the same time draw down 
the lower edge. Thus the neck of the vagina would be drawn from 
what may be termed its four corners and its opening widely expanded, 
while it would also be somewhat drav/n away from the lower part of 
the heel of the perigynum. The egg would thus be allowed to pass 
through the neck of the vagina into the vestibule, slipping under the 
heel of the perigynum. From the vestibule it would reach the exterior 
through the genital aperture. 
Ur 02 ) 0 da vegetans. 
The female genital organs in this species are on the whole of the 
same type as those of U. ovcdis, but there are some very marked and 
singular differences. Fig. 12 will show that the central ovaries and 
oviducts are again of the usual form, and present little variety ; the 
vagina also is similar in construction, but it is larger in proportion 
and more elliptical than the corresponding part in U. ovalis. The 
neck of the vagina is even more tightly constricted than in the last- 
named species, but the actual mouth of the organ is more expanded, 
and is not closed by the heel of the perigynum, as in U. ovalis. The 
apparent reason for this will be seen shortly. The perigynum exists 
in the present species, and considerably resembles that described above. 
In this case, however, the chitinous bar round the heel is very thin 
and delicate, the stronger portion of the framework being the anterior 
lateral ; this consists, not of a rod, but of a blade on edge (on each 
side). The concavo-convex form is not nearly so marked, the organ 
being nearly flat in transverse section, nor does the heel curve in the 
manner shown in fig. 5 ; it is much more suddenly bent upward at an 
angle, and there is not any narrow portion projecting backward into 
the vagina. On the contrary, the top curls over slightly in a forward 
direction (fig. 12, Ac.). The spines on the ventral surface of the 
perigynum are confined, in this species, to the heel ; they are shorter 
than, and very different in form from those of U. ovalis ; they are 
chitinous points, generally united at their bases into little transverse 
lines of three or four, each group standing well apart from the next. 
They remind me of the teeth on the radula of some Gasteropods ; 
they are represented in fig. 18. The flexible walls of the vestibule 
are attached all round the edge of the perigynum, as in U. ovalis, but 
there is not any vandyked border at the juncture, nor anything sub- 
stituted for it ; nor is there any great fold of the membranous wall, 
such as / in fig. 3. 
The first great difference between the two species which is noticed 
is the entire absence in U. vegetans of the large azygous receptaculum 
