]52 
Transactions of the Society. 
Uropoda cassidea. 
I had only one specimen of this large and well-marked species 
to dissect, so that I was not able to carry on investigations nearly as 
satisfactorily as I was in the cases of the two species treated of above ; 
it was, however, plain that considerable differences existed between 
the vestibule and surrounding organs of U. cassidea and those of any 
of the other species which I have dissected. The perigynum exists, 
and is large and conspicuous, but it consists of an almost flat plate, 
which is entirely surrounded by a broad chitinous band (fig. 22), 
nearly elliptical as regards its exterior margin, but retaining a little 
of the shoe-shape on its inner edge. The anterior part of the outer 
edge has a few large serrations projecting from it. The flexible wall 
of the vestibule is attached round the edge of the perigynum, as in 
the other species. The neck of the vagina is short, but is surrounded 
by a very powerful ring-muscle; the vagina itself is large, and is 
drawn out in a more or less triangular extension on each side, at the 
apex of which triangle the oviduct enters. In the single specimen 
which I had I was not able to detect any receptaculum semiuis or 
accessory glands. 
It now only remains to offer a possible explanation of the very 
considerable differences between the I'orms of the vestibule in all these 
species and that of the same organ in TJ. Krameri. In my paper on 
that species in this J ournal * I suggested that the parts appeared 
eminently fitted to strip the shell from the egg as it emerged, and I 
called attention to the fact that the eggs found in the part of the 
oviduct near the vagina, in all cases which I had observed, contained 
larvae fully, or nearly fully, developed ; and in most cases apparently 
ready to emerge. It therefore seemed probable that the larva did 
emerge from the egg at the moment of oviposition, and that the 
vestibule removed the shell of the egg from it ; cr, at all events, that 
this was the course at some periods of the year. In the species treated 
of in this paper the vestibule does not seem nearly as well fitted to 
perform this office as in TJ. Krameri, and it is an interesting fact 
that, although the eggs in the lower part of the oviduct had appa- 
rently attained their full size, and yolk-division had proceeded to some 
extent, yet not in one single instance among all my numerous dissec- 
tions was there the least sign of a formed, or partially formed, ^larva 
in the egg. This may possibly be due to some difference of season or 
other cause, but the time of year did not differ much from that of the 
former investigation, the present being in August and September, the 
former in July and August ; it seems probable, therefore, that in the 
species now considered the larva does not emerge from the egg until 
longer after its dei^osition, and this may well account for the differ- 
ences in the structure of the vestibule. 
Loc. cit. 
