1921] Metcalf: Genitalia of Male Syrphide HD 
sufficient. A reliable test is to leave them in the moist jar until a wing or leg can 
be moved without breaking. 
The relaxation can be accomplished almost instantly if necessary by applying 
boiling water in a small camel’s-hair brush directly to the parts, or by plying a 
tiny jet of steam against the genitalia, or even by dropping the specimen briefly in 
boiling water. Owing to the greater injury to the colors and vestiture of the 
specimens likely to be caused by these methods, I prefer the moist chamber. 
For the same reason it is important to leave the specimens in the relaxing jar. 
only so long as is necessary to accomplish the purpose. 
(3). The fresh or relaxed and pinned specimen is then held ventral side up, 
by the left hand under the dissecting microscope, while with a fine needle the 
retracted genitalia are pried or drawn out of the cavity formed by the invagination 
of the terminal segments at the ventro-caudal extremity of the abdomen. I have 
found by removing the metal stage of the binocular and placing a microscope 
slide across to bisect the field of vision that the tip of the abdomen can be rested 
against the edge of the slide and the parts pried out most easily. Any elevated, 
sharp edge at the middle of the field so that the head of the pin is not in the way, 
will do as well. With properly relaxed specimens, and a little care, one can 
remove these genital segments and leave the rest of the specimen in almost perfect 
condition for cabinet purposes. Of course, if one does not care for the specimen, 
it will suffice to simply clip off the tip of the abdomen a little beyond the middle 
with a fine scissors. Or, indeed, the whole of specimens not needed for the cabinet 
may with great interest and profit be carried through the successive stages, thus 
revealing many features of the chitinous structure not readily made out from 
uncleared specimens. 
Before severing the genital segments it is well to study the relations of the 
modified segments (postabdomen) to the unmodified segments (praeabdomen), 
noting any variation in number of segments involved or characteristics of length, 
shape, size and arrangement of these parts. It is also well at this point, to make 
an examination, descriptions and preliminary sketches of the separated, opaque 
parts, since in this condition certain features are better revealed than in the cleared 
preparation. Indeed if several specimens of the same species are available, it is 
advisable at this point to preserve one without clearing, using for the purpose 
small gelatine capsules which are securely sealed by closing and thrusting on to 
the pin bearing the insect itself. This also affords a precaution against being 
misled by any possible artifact due to subsequent treatment. 
(4). A duplicate of the serial number (in carbon ink on a tiny slip of paper 
and thoroughly dried) is now placed, together with the detached genital segments, 
in a container for treating with caustic potash. For this purpose I use small shell 
vials or test tubes, about 8 x 70 mm., that have had a part of the bottom removed 
by means of a diamond point, or by heating the bottom in a gas jet and blowing 
out the molten glass. This bottom is then replaced by a plug of cotton. Sections 
of glass tubing may be used, but I prefer the vials, as the partial shelf of glass 
prevents the cotton plug from dropping out. With this arrangement the specimens 
can be passed rapidly through the remaining treatment without the necessity 
of once touching the parts themselves. It is only necessary to raise the vial 
until the liquid has drained out through the cotton bottom, rinse it with a few 
dropper-fulls of fresh liquid, and then place it in the next reagent, which will rise 
and promptly envelop the specimen. 
By the use of these small containers it is convenient to carry through the 
subsequent operations a considerable number of specimens at a time without any 
danger of loosing them or separating the parts from their key numbers. 
When the desired number of vials, each with its genitalia and serial number, 
(from a dozen, or less, to a hundred, as the case may be), have been prepared in 
this way, they are placed in a shallow dish with straight sides or cross partitions, 
to keep them upright; and into the dish is poured an aqueous solution of caustic 
potash, 10 to 15% strength, sufficient to bring the solution to a depth of a half 
inch or an inch in each vial. They are then allowed to remain in this condition, 
occasionally raising and lowering the vials to bring in a fresh supply of caustic, 
until the parts are almost transparent. The length of time required for this again 
