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THE POPULAR SCIENCE MONTHLY. 



gle (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 ex- 

 tent 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 represent- 

 atives 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 re- 

 mains the same, 

 and the modifica- 

 tions bear only 

 upon one or the 

 other of their con- 

 stituent elements. 

 Thus in the mole- 

 cricket the legs of 

 the first pair are 

 adapted to digging 

 the ground (D) ; 

 those of the pray- 

 ing 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 tro- 

 chanter, 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 



Fig. 13. Different Forms of Legs. 



