202 
AERIAL AND TERRESTRIAL DIPTERA 
The terrestrial MycetopJiilidae and the aerial Cecidomyiidae offer 
in their general appearance a complete contrast, although pliylo- 
genetically they are rather closely allied. 
Among the aerial family Tipulidae, the apterous Chionea, with 
its stunted antennae and stout legs, affords a very instructive 
example of a terrestrial and pedestrian Tipulid. 
The Nemocera anomala , which I consider as ancestral forms, are 
often provided with holoptic heads in the male (differing in this 
from the Nemocera vera , where such heads never occur). This 
seems to prove that holopticism among Diptera is a character of 
very old standing. The males of Bibio are holoptic and aerial. 
Plecia (including Penthetria) is more terrestrial in its habits, and 
therefore shows a minimum of holopticism in the male (sometimes 
distinctly separated eyes), and, in agreement with this character, 
the wings are often reduced in size. It has been noticed that 
among fossil remains different forms of Pleciae abound, while a 
true fossil Bibio has not been discovered yet. This may be due to 
the aerial habits of the male Bibio , which saved it from sub¬ 
mersion. 
In the Simuliidae the male is holoptic and aerial; the female 
dichoptic and terrestrial, and shows a peculiar development and 
activity of the legs (130, 1892, p. 452, footnote). This is a singular 
instance of a disseverance of sexes. The males swarm and dance 
high in the air; the females occur in myriads on riversides, and 
torment men, cattle, and horses. It is not astonishing at all that 
Sclionbauer (1795), author of a monograph of the celebrated 
“ Columbatcz ” Simuliuw i, never met with a male of this species, and 
mistook some females for it. Skuse’s statement, that in Australia 
Simuliae seem to be “ rare and local ” (130, 1892, p. 454), requires 
confirmation. Prof. L. C. Miall (“Aquatic Insects,” p. 188,1895) 
says just the contrary: “ Simulium have greatly annoyed certain 
Australian exploring expeditions.” 
Bhyphus has an holoptic male, but in his American relatives, 
Lobogaster Philippi and Olbiogaster O. S., the male is dichoptic. 
As we have no data about the life-habits of the last two genera, 
we do not know how far this difference of structure corresponds 
to a difference of life-habit. 
