primary veins; but, since the great specialty of in- sects is flight, in their evolution they have concentrated on the wings, and the different groups have tried out different styles of venation, with the result that now each is dist]nguished by some particular pattern in the arrangement of the vems and their branches. The entomologist can thus not only distinguish by their wing structure the various orders o(insects, as the Orthoptera, the dragonflies, the moths, the bees, and the flies, but in
F*ç. _ç'?. Wings of a cockroach, Periplaneta, showing the rein pattern characteristic of the roach family
many cases he can identify families and even genera. Part"?cularly ;tre the wings ol ? value to the student of fossil insects, for the bodies are so poorly preserved in most cases that without the wings the paleontologist could have made little headway in the study of insects of the past. As it is, however, much is know?a of insects of former times, and a study of their fossil remains bas con- tributed a great deal to our knowledge of this most versatile and widespread group of animais.
[841
ROACHES
