1921] Metcalf: Genitalia of Male Syrphide 17 
C 
(11). Place on the slide a drop of 
glycerine jelly, melted by gentle heat 
and 
~I 
iD: 
(11). Place on the slide a drop of 
Canada balsam, dissolved in pure 
acetone and 
with a brush or needle, quickly transfer the specimen to it. Under the microscope 
make sure the parts are spread to the best advantage and arrange them in the 
position desired. 
(12). Now quickly place the slide 
on a small piece of ice, if available, or 
allow to cool, in the meantime exam- 
ining carefully to see that the parts 
remain in the desired position until 
the jelly has consolidated enough to 
hold it. 
(12). Maintain them in position 
until the rapid evaporation of the 
acetone leaves the balsam firm enough 
to hold it. If necessary to change 
the position, a little fresh acetone- 
balsam can be added as many times 
as necessary to soften the balsam. 
When firmly set and covered with 
balsam, the slide may be allowed 
to harden in a place free from dust 
for a day or so, or one may at once— 
(13). Place around the specimen several pieces of a crushed glass slide, or 
glass beads, of a proper size to just keep the cover from crushing the mount, and 
then: 
€ 
(14). Add some more of the liquid 
jelly, and finally a cover glass. Chill 
thoroughly and set aside until wanted. 
When the specimen has been studied 
in this position, it can readily be 
changed by gently heating and 
manipulating under the cover glass 
with a fine needle. 
D 
(14). Adda little fresh balsam and 
finally a cover glass. If it is neces- 
sary to change the position of the 
object, the cover must be removed by 
soaking the slide in xylol or acetone, 
rearranging and remounting. 
While the above procedure may appear rather complicated, it may be noted 
that by a simple short cut, one may prepare a mount of the genitalia in a very 
short time, as follows: 
Relax the specimen with hot water; boil the postabdomen in caustic potash 
solution tntil clear; and then mount in either a drop of water, in glycerine, or in 
glycerine jelly. 
THE MALE GENITALIA. 
By genitalia is meant the group of appendages at the caudal end 
of the abdomen, surrounding the genital and anal orifices* of male 
and female insects. Their dominant functions are the reproductive 
ones of mating, oviposition, etc., but they are also involved to some 
extent in defaecation and sensation. 
These organs appear to consist primitively of four pairs of append- 
ages (Newell"). The most prolonged and voluminous debate has 
ensued regarding the homology, and morphological composition of 
these appendages and the primitive numbers of the urites to which 
they belong. The evidence appears convincing that they are entirely 
homologous with the thoracic or ambulatory appendages. And, 
according to the concensus of opinion of morphologists, these four 
*The term is more strictly limited to the genital appendages. In this family, 
however, the cerci are so intimately associated with the other appendages that 
they are, throughout this paper, treated as a part of the genitalia. 
