124 Mittheil. d. Münchener Ent. Ver. 1881. 
bristles (in certain families) aets as a screen in front of the haltere etc. 
Hence the persistency of the certain bristles in the same places, not 
only through the immense divisions of the Calyptrata and Acalyptrata, 
but even among more distant families, like Asilidae and Dolichopodi- 
dae ; hence also the possibility of a uniform terminology. 
Still, this hypothesis of Macquart’s does not explain how certain 
families can exist without any macrochaetae at all. The integuments 
of a Syrphus are apparently not harder than those of a Tachina, and 
yet they are unprotected by bristles? — The explanation may per- 
haps be found in the mode of flight of the different groups of diptera., 
In examining the list of the Diptera eremochaeta, ıt will be noticed 
that most of the families belonging to them possess the power of 
regulating the momentum of their flight, which involves the faculty 
of poising themselves in the air. Observe the flight of a Syrphus, 
the cautious way in which he turns round a solid object and repea- 
tedly touches it with the tip of his tarsi, without alighting, and compare 
it to the headlong flight of a Calliphora. The most bristly of all the 
diptera and the least cautions in their flight are the Calyptrata, those 
very flies which €. C. Sprengel, in his „Das entdeckte Geheimniss der 
“Natur, 1793“, called the stupid lies (die dummen Fliegen), for their 
clumsiness, their inability to discover honey in flowers and the ease 
with which they are deceived by odors and appearances. Stratiomyi- 
dae, Tabanidae, Bombylidae, Syrphidae, all have the power of poising, 
and all belong to the eremochaeta. 'Therevidae and Empidae, who 
also have that power, are provided with only very few macrochaetae. 
Without following out this suggestion at present, I will connect 
it with another generalization and recommend both to the attention 
of observers, That faculty of poising seems, for some as yet unknown 
reason, to be connected with contiguous eyes in the male sex. Most of the 
above-named families of Diptera eremochaeta, which possess that fa- 
culty (Tabanidae, Bombylidae*), Syrphidae ete.) have Aoloptie males 
(as I will call them for brevity's sake). The .Diptera chaetophora 
hardly ever have holoptic males (even among the Orthorhapha, as the 
Asilidae and Dolichopodidae) ; the only exceptions, as far as I remember, 
*) An exception among the Bombylidae is Toxophora, which has some 
conspieuous macrochaetae, and the male of which is, nevertheless, holoptie, 
