88 
Psyche 
[June-Sept. 
respond to the processes of the ninth tergite labelled st 
in Fig. 15 of Protoplasa, and these in turn may correspond 
to the long slender processes of the ninth tergite labelled st 
in Fig. 16 of the Ptychopterid Bittacomorpha. It is prob- 
able that such processes of the ninth tergite of the lower 
Nematocera become the articulated processes of the ninth 
tergite called surstyli, or edita, in such Cyclorrhapha as 
those shown in Figs. 8, 9, 20 and 21, etc., in which the surstyli 
are labelled st. 
The proctiger, or anus-bearing region behind the ninth 
tergite, labelled 9t in Figs. 1, 2, 4, 5, 8, etc., is apparently 
composed of the greatly reduced tenth abdominal segment, 
with which the similarly reduced, cerci-bearing, eleventh 
abdominal segment, and the anus-bearing telson, have 
united. The structures labelled ce in these figures are inter- 
preted as true cerci since they are clearly homologous with 
the cerci of female Tipulidse and female Mecoptera, etc., in 
which the structures in question are borne on a distinct, 
though greatly reduced, eleventh abdominal segment, as is 
the case with the cerci of lower insects, in which the cerci 
are appendages of the eleventh abdominal segment. 
In attempting to determine what genital structures of 
the higher Diptera shown in Figs. 19, 20, 21, etc., correspond 
to the segments of the genital forceps of the lower Diptera, 
such as those shown in Figs. 1, 2, 3, etc., it is necessary first 
to compare them with the parts in the key group Syrphidse 
(Fig. 17) which occupies a position intermediate between 
the higher and the lower Diptera, and furnishes the neces- 
sary clues for tracing the modifications met with in the 
sclerites and other structures of the higher forms. 
Starting with the lower Nematocera, in which the seg- 
ments of the genital forceps b and d are long and slender, as 
they are in the Nematocera shown in Figs. 14, 15, etc., we 
note that the segments tend to become shorter and stouter in 
the genital forceps of the Brachycera shown in Figs. 2 and 4 ; 
and in the Stratiomyid Ptecticus shown in Fig. 4, the disti- 
meres, labelled d, are broad and flat, like the distimeres 
labelled d in Fig. 17 of the Syrphid Syrphus rectus , while 
the basimeres labelled b in Fig. 4 of Ptecticus, are reduced 
and unite with the ninth sternite, as the basimeres, b, do 
in the Syrphid shown in Fig. 17. It is thus an easy matter 
