Page:Popular Science Monthly Volume 39.djvu/244

232 (of the side of the escutcheon); the summit or extremity of the elytra; and the sutural angle, formed by the line of the suture with the outer edge at the summit of the elytra.

The elytra are not always entirely horny. In the heteropterous Hemiptera, the elytra remain membranous for a considerable extent near the summit. When the two pairs of wings are alike, both are membranous, and are constituted on the same plan as the wings of the second pair in Coleoptera. Of this character are the wings of the bee, the hornet, dragon-fly, and butterfly. The wings of the last are furthermore covered with brilliantly colored scales. The wings of the Diptera (flies, gnats, etc.), with their finely reticulated nervation, present the same membranous appearance; but the second pair are wanting, the only representatives left of them being small appendages known as balancers. The legs are shaped for leaping (Fig. 13, A), for walking (B), or for swimming ( C ). Whatever may be their use, the general plan of their structure remains the same, and the modifications bear only upon one or the other of their constituent elements. Thus in the mole-cricket the legs of the first pair are adapted to digging the ground (D); those of the praying mantis (E F) are shaped like pincers; the lower leg, attached to the upper by a very supple joint, bends back upon it, as is shown in F, and forms with it a vise, the interior of which bristles with fine toothings suitable to hold captive any prey that may be taken. What it has been agreed to call the leg of an insect comprehends the coxa (a), the trochanter (b), the femur (c), the lower leg or tibia (d), and the tarsus (e). The coxa is short, and is articulated into a cavity of the epimerum called the cotyloid cavity. The trochanter, which follows it, assists the movements of the femur joint. The femur is a strong lever which, in the case of insects organized for leaping, is considerably developed in the hinder