196 
AERIAL AND TERRESTRIAL DIPTERA 
among them the Empidae, although the number of their macro- 
chaetae, the development and the remarkable specialization of their 
legs, and other characters, prove them to be properly pedestrian, 
have aerial habits, which bring along with them the frequent con¬ 
tact of the eyes in the males and, in some genera (as Hybos , Syne- 
ches, Cyrtoma'), even liolopticism in both sexes. Among the 
Empidae themselves, however, exceptions in the opposite, terres¬ 
trial, sense occur ( Hemerodromia, Clinocera, Tacky dr omia'), and in 
these genera dichopticism reappears in both sexes. Hilara, in this 
respect, is singular; although aerial in its habits, it is dichoptic in 
both sexes. 
Of the other families of the Energopoda, the Asilidae, so far as 
I know, are dichoptic without exception, and the Dolicliopodidae 
likewise, with rare exceptions (' Diaphorus ). 
The third superfamily of the Orthorrhapha Brachycera, the 
Eremochaeta, afford a peculiar interest, as they are entirely want¬ 
ing in macrochaetae. This want seems to be amply compensated 
by the great development of a variety of structures of the anten¬ 
nae. No other superfamily offers anything equal to it, and this 
peculiarity I have characterized as morphological restlessness ( Berl . 
Eat, Zeit., 1892, p. 427 ; 130, 1892). 
Another peculiarity of the Eremochaeta is, that they contain a 
considerable number of archaic forms. Like the Marsupialia 
among the Vertebrata, the Eremochaeta seem to represent a collec¬ 
tion of survivals of bygone zoological horizons. And this general¬ 
ization is confirmed by the fact that genera of this superfamily 
are more abundant in countries the whole fauna of which is of a 
more ancient origin than the European fauna (North America, 
Chili, Australia). 
For a detailed characterization of the Eremochaeta, I refer to 
my above-quoted paper (130, 1892). At present I shall confine 
myself to some generalizations tending to show that, although the 
great prevalence of liolopticism and the total absence of macro¬ 
chaetae make of the Eremochaeta aerial Diptera, the terrestrial and 
pedestrian tendencies which occur among some of them are indi¬ 
cated by the very same characters that distinguish terrestrial and 
pedestrian forms in other superfamilies: the reappearance of dichop- 
