species which unquestionably have gone farthest along the road of mechanical efficiency have produced little else commendable. In this class we would place the mosquitoes and the flies; and who will say that either mosquitoes or flies have added anything to the comfort or enjoyment of the other creatures of the world?
Reviewing briefly the esthetic contributions of the major groups of insects, we find that the grasshoppers have produced a tribe of musicians; the sucking bugs have evolved the cicada; the beetles have given us the scarab, the glow-worm, and the firefly; the moths and butterflies have enriched the world with elegance and beauty; to the order of the wasps we are indebted for the honeybee. But, as for the flies, they have generated only a great multitude of files, amongst which are included some of our most obnoxious insect pests.
However, in nature study we do hot criticize; we derive our satisfaction from merely knowing things as they are. If out subject is mosquitoes and flies, we look for that which is of interest in the lives and structure of these insects.
FLIES IN GENERAL
The mosquitoes and the flies belong to the same entomological order. That which distinguishes them principally as an order of insects is the possession of only one pair of wings (Fig. ?67). Entomologists, for this reason, call the mosquitoes and files and all related insects the Diptera, a word that signifies by its Greek components "two wings." Since nearly all other winged insects have four wings, it is most probable that the ancestors of the winged insects, including the Diptera, had likewise two pairs of wings. The Diptera, therefore, are insects that have become specialized primarily during their evolution by the loss of one pair of wings.
We shall now proceed to show that the evolution of a two-winged condition from one of four wings bas been a
INSECTS
