the genus Ypthima 8 
judgment as a factor in doubtful cases, and the final 
appeal which it affords in cases of difference. There is 
no universal test character, however, and as with all 
others, so sexual characters sometimes fail. It not 
unfrequently happens that several species have so nearly 
the same form of structure that there is no sufficient 
difference to have specific value in doubtful cases (e.g., Y. 
sakra, Doherty, and persimilis) ; in other cases, however, 
no two species are alike, and the widest variation within 
generic limits allows definite specific hmitation. A few 
remarks on the means adopted for the utilisation of these 
characters will serve to show that there is no reason why 
their study in the Lepidoptera should not be extended. 
All that is really necessary in the way of manipulation 
is to separate the parts and gum them in suitable posi- 
tions on pieces of card, which may be pinned in the 
cabinet by the side of the insect. This is best accom- 
plished by first removing the apex of the abdomen 
entire, an operation which, if neatly performed, detracts 
but little from the appearance of the specimen. ‘The 
parts to be preserved are, first, the tegumen, a more or 
less saddle-shaped piece, which terminates the abdomen 
above; this should be fixed on the card by its proximal 
edge, as this position greatly facilitates the examination 
of its inner side, which is sometimes armed with large 
hooks, as in many Lycenide ; second, the two clasps 
which form the lower boundary of the anal aperture—as 
these are symmetrical paired organs, it is better to fix 
one of them on the card with its convex side uppermost, 
and the other in the reverse position ; third, the wdeagus, 
a single chitinous piece occupying a subcentral position 
in the anal aperture, and having muscular attachments 
to both the tegumen and the clasps; the form of the 
free portion of this organ sometimes furnishes a dis- 
tinctive character when the others fail. As we are 
dealing with the subject from the systematic point of 
view and not that of the anatomist, the preservation of 
the other parts is merely a matter of taste. The method 
of mounting here advocated has the advantage that any 
number of specimens may be compared under a variety 
of aspects, and a similar aspect secured in each case. 
Those entomologists who work with the microscope will 
probably prefer to mount the genitalia as transparencies, 
either as ordinary microscopic slides, or according to the 
B2 
