336 DIVISION II. ARTICULATED ANIMALS.—CLASS IV. INSECTA. 
ORDER XII. DIPTERA. 
This order comprises the two-winged flies, as its name, formed from 
the Greek words dis (two) and ptevon (wing) implies. The dipterous in- 
sects have six feet, two membranous extended wings, having beneath them 
two movable slender bodies, called balancers, which the insect moves with 
great rapidity. The use of these appendages is not known. Many of these 
insects are extremely obnoxious and hurtful both to man and beast. Some, 
however, make partial compensation by consuming decaying animal matter, 
which otherwise would infect the air. 
The life of these insects, after arriving at the final state, is very brief. 
They all undergo a complete metamorphosis, but modified in two material 
ways. The larve of many change their skin in order to undergo their trans- 
formation to pupx, and some spin a cocoon. The larvi of dipterous insects 
are destitute of feet, but some have appendages which resemble them. 
After passing through their various changes, and arriving at their perfect 
development, the Diptera spend no part of their limited life in idleness. 
They belong to every clime, and everywhere are disturbers of the peace, and 
a perpetual annoyance to all living things which are within their reach. 
“Besides their variety,” says Figuier, “and the number of their species, 
they are remarkable on account of their profusion. The myriads of flies 
which rise from our meadows, which fly in crowds around our plants, and 
around every organized substance from which life has departed, some of 
which even infest living animals, are Diptera. 
This order is divided into several families, the first of which, Wemocera, 
has the antennw, in some, composed of from fourteen to sixteen joints, and 
in others of from six or nine to twelve. The body is elongated, with the 
head small and rounded; the eyes large; the proboscis exserted, short, and 
terminated by two large lips, or extended into a beak. Many of these 
smaller Diptera often assemble in vast armies in the air, and disport them- 
selves in a kind of dance. They compose the genera Culex and Tipula. 
Cutrx. — The Gnats, Mosquitos. The body of the Gnat is long and 
cylindrical. When in a state of repose, one of its wings is crossed over the 
other. They present a charming appearance when seen through a micro- 
scope, their nervures, as well as their edges, being completely covered with 
seales, shaped like oblong plates, and finely striated longitudinally. These 
scales are also found on all the segments of the body. The antenne of the 
Gnat, particularly those of the male, have a fine, feathery appearance. 
Their eyes, covered with network, are so large that they cover nearly the 
whole of the head. 
