Notes to Introduction. 
a • o 
Xlll 
grounds. The specimens should be pinned, as shown in Fig. 1, 
through the mesothorax (e), the point of the pin not projecting 
more than 2 mm. above the surface of the thorax, so as to 
allow the lens to be brought close to it during examination. 
A stiff pin (a) should then be put through the disc near the 
edge, by means of which the specimen may be pinned in the 
cabinet or store-box. When required for examination the disc 
and insect can be taken off the large pin and placed on a piece 
of thick cardboard perforated in the middle (x), to allow the 
v disc (b) to set flat, so that the object can be focussed under 
the microscope (Fig. 2). I have found that all the Gulicidae , 
except Psorojohora, Mucidus and the Megarliinus , are not at all 
brittle, and can be safely removed, as described above, without 
any damage being done. In all cases the detailed descriptions 
'3 
Fig. 2. 
Method of examining a gnat under microscope, 
x, circular hole in cardboard ; other lettering as in Fig. 1. 
given in the work have been drawn up in this way, a two-third 
power on one of Swift’s microscopes being used. 
In using the dispositions of the cross-veins, the relative 
length of the fork-cells, their stems, &c., great care must be 
taken, no relative length should be given from a museum type. 
It is surprising how the least unevenness distorts the appearance 
of the neuration. Every wing, to be accurately described, should 
be mounted flat between an ordinary glass slide and an oil 
immersion cover slip, so that no misjudgment can be made. 
By far the best way is to mount the wings dry and have them 
photographed, so that measurements can be made. 
The exact measurements are, however, valueless in some 
species, for I find (vide Cidcx 'piggiens and C. fatigans) that there 
is some considerable variation even in specimens from the same 
batch of eggs. 
For photographing the scales the wings must be mounted 
