TRANSFORMATIONS OF BUFFALO GNATS. 5 
Fourth stage. — The eggs are fully as large as those newly laid on 
grass blades, of the same triangular form, very dense, the shell very 
strong, and not differing from eggs just laid, with the exception that 
occasionally they may be slightly smaller. (PI. I, fig. 4.) 
Fifth stage. — One or two large eggs are usually left in the ovaries 
near the oviduct, and the rest of the ovary is entirely filled with the 
typical round eggs of the first stage. This stage is found after 
adults have finished ovipositing, and also in specimens taken actually 
engorging, concerning which more will be said later. (PL I, fig. 5.) 
The Genitalia of the Male. 
PL II, figs. U5. 
The structure of the genitalia of the male shows remarkably con- 
stant specific characters. Their systematic value may be seen from 
the striking differences in the illustration. The determination of 
the species based on color alone is at best unsatisfactory owing to the 
amount of variation in individuals of the same species and fading 
of color in dry mounted specimens. The appearance of the structure 
of the genitalia does not change when the specimens are preserved in 
alcohol, and in dried specimens the original shape can be completely 
restored by the following method: 
The last segment of the abdomen of the male after being re- 
moved with sharp scalpel or needle is placed in 6 per cent potassium 
hydroxid (KOH) and left until the soft parts are removed, the 
chitinous portions remaining intact. The material is then washed 
with water, run through alcohol in the usual way up to 100 per 
cent, transferred to xylol, and mounted in balsam, so as to give a 
direct caudal view as shown in Plate II, figures 1-5. Some of the 
European species have been studied in regard to the genitalia of the 
males by Liindstrom, but nothing has been done so far on American 
species. 
The segments to which the organs of the genital armature are 
attached are collectively designated under the name hypopygium. 
The most prominent organs of the hypopygium are the two claspers 
(c c) and the basal pieces to which they are attached. The claspers 
may be either large, fingerlike, as in S. venustum, or greatly reduced 
and somewhat hook shaped as in S. bracteatum. They sometimes 
bear a spine at the distal end as in S. venustum, a single chitinous 
fingerlike process as in S. bracteatum, or three or four such processes 
as in S. vittatum. The basal pieces (6, b) to which the claspers are 
articulated are divided by a suture near the base. They are very 
large in S. bracteatum and are reduced in S. venustum. The relation 
between the size of the claspers and basal pieces seems to be very 
