} 
1941] Male Diptera 85 
ship between the members of this series, but the modifica- 
tions exhibited by such a fly as the one shown in Fig. 22, in 
which the sixth segment remains unaffected by the latero- 
version of the seventh sternite 7s (and by the inversion of 
the eighth sternite 8s) would indicate that Calobata is a 
member of a series quite different from that to which the 
above mentioned flies belong, and the trends exhibited by 
these flies should be of considerable value for arranging 
them according to their natural affinities, although I do not 
know of any attempt to utilize the sclerites of this region of 
the body for such a purpose. 
In this connection it may be remarked that the modifica- 
tional trends exhibited by a Dolichopodid fly such as Argyra 
(shown in Fig. 23) seem to foreshadow many of the modi- 
fications later occurring in certain Cyclorrapha, just as the 
antennae of certain Dolichopodidas approach those of the 
typical Cyclorrhapha, and these facts may indicate that the 
Dolichopodidae are much nearer to the ancestors of the 
Cyclorrhapha than is commonly supposed to be the case. 
In like manner, the modificational trends exhibited by 
such Syrphidae as Paragus (shown in Fig. 9) seem to fore- 
shadow the modifications later occurring in certain higher 
Cyclorrhapha. Thus the lateroverted seventh sternite, 7s, 
unites with the inverted eighth sternite, 8s, in Paragus 
(Fig. 9) as it does in Hylemya (Fig. 20) , for example. The 
sixth sternite, 6s, is asymmetrical and is strongly latero- 
verted in Paragus (Fig. 9), as it is in Hylemya (Fig. 20 — 
compare also Fig. 7), and the fifth sternite labelled 5s in 
Fig. 9 of Paragus is deeply emarginated posteriorly, divid- 
ing the fifth sternite into widely separated parts which sug- 
gest the origin of the condition exhibited by Hylemya (Fig. 
20) , in which a deep posterior cleft divides the fifth sternite 
into the posteriorly projecting copulatory lobes labelled 1 in 
Fig. 20. These and many other facts suggest that the 
Syrphidae represent the ancestors of certain other Cyclor- 
rhapha as nearly as any known forms; and the Syrphidae 
furnish the most useful clues for determining the homologies 
of the genital structures of the higher Cyclorrhapha, as will 
be shown later. 
Before discussing the homologies of the genital forceps of 
the lower Diptera a brief statement may be made concerning 
