610 Mr. D. Sharp and Mr. F. Muir on the Comparative 
appears to be an organ admirably adapted for this purpose, 
and its occurrence and reoccurrence in so many isolated 
forms is, to say the least, highly suggestive. Hven in cases 
where there is no true flagellum, it may well be the case 
that the functional orifice of the male (not to be confounded 
with our “ median orifice”) is applied to the orifice of the 
spermatheca. See on this point our figures 58 and 63. 
Certainty as to this point can only be obtained by 
repeated observations of the genital tube during its func- 
tional activity, and as to this we have been able to make 
but few observations. 
In Rhagonycha fulva $ the sac is large and rounded, 
with three pairs of diverticula along the posterior surface, 
and a large patch of strong spines on the ventral side 
(fig. 237a, a); the duct opens between the most dorsal pair 
of diverticula. During copulation this sac distends the 
uterus to its own size, and the patch of spines covers the 
entrance to the oviducts, The abundance of this species 
would make it a convenient form to work out all the 
details of copulation on. 
Unfortunately the process of killing the insects causes 
the muscles that actuate the internal sac to relax or con- 
tract, and so the exact relations of the sac and the female 
parts are never fully revealed. The shape of the female 
parts does not exactly correspond to the shape of the male 
sac and all its diverticula, etc, but there is a co-relation- 
ship between them, and apparently they always take up 
the same position in any one species. Besides the direct 
evidence as to the importance of the internal sac and its 
evagination during coition there is the great mass of 
indirect evidence afforded by the complex armatures 
that are developed upon them, especially at the apex. 
In Pissodes Hopkins* calls this armature the “seminal 
valve,” but in the various examples of the different 
families that we have examined the armature does not 
function as a valve. In cases where there is no differenti- 
ated internal sac it is difficult to state how much of the 
duct is evaginated, but judging by observations made on 
certain Hydrophilidae a large amount is turned out. The 
evagination is done, at any rate in part, by blood pressure, 
and the invagination by the contraction of muscles attached 
to certain points on the internal sac and to the median 
lobe. 
* U.S. Dept. Agr. Technical Series, No, 20, part I, 1911. 
