552 
DlPTERA. 
aquatic, cannot endure drought. The gall-making Cecidomyiidce are 
a much specialised family whose larvae are in no way aquatic. 
In the Brachycera there are a good number of this aquatic or semi- 
aquatic type among the more primitive families ( Leptidce , Stratiomyidce 
and Tabanidce), but most Brachycerous larvae (Asilidce, Therevidce, etc.), 
live on land, preying on such insects as are found in rather damp but not 
very wet places such as rotting wood, bark, or in moss or earth : they 
are active, with distinct heads, the eyes are present in some species and 
absent in others, and the antennae are not so well developed as in Nemo- 
cerous larvae. There also occur in this group a large number of para¬ 
sitic larvae ( Bombyliidce ), but these, at any rate in their later stages, are 
almost incapable of motion and have no distinct head, jaws, eyes or 
antennae, though when newly-hatched the larvae may be very active. 
Among the Aschiza there is a considerable variety in the form and habits 
of the larvae ; they may be scavengers, vegetarian, predaceous, parasitic 
or commensal, and there are a small number which are aquatic [e.g., 
genus Eristalis in family Syrphidce (fig. 404)], but in spite of this variety 
in their mode of life the head is never well developed, and the eyes and 
antennae are either absent altogether or extremely small, the general 
shape approaching that of a “ maggot. ’ 5 Much the same may be said 
of the larvae of Schizophora, but in this group there is less variety in 
habit. In the section containing what are probably the older and less 
recently developed families (the “ acalyptrate muscoids ”), there are a 
few aquatic larvae (e.g., Ephydridce, Sciomyzidce) ; and of the rest very few 
if any are truly predaceous, and almost all feed on living plants or are 
scavengers or parasites. Simplification of form has here been carried 
to an extreme (PL LXVI, & figs. 424, 425), the head and sense-organs 
being reduced to the lowest possible point. The probable reason of this 
extreme simplification lies in the shelter and protection which the 
larval habits ensure : living as these larvae do, either inside plants, 
under dung and decaying matter, or as parasites in the bodies of insects 
and other animals, they have little need of any organs except those 
which enable them to eat, breathe and digest ; all else has tended to 
degenerate and disappear, leaving as residue the typical maggot, a 
creature admirably adapted to succeed in its own simple way of life. 
A word should be said here about the breathing arrangements of 
Dipterous larvae and pupae. The devices and structures which they 
