2 2 The Form of Insects 



Beetles and Bugs. Among insects which habitually 

 walk, run, or swim, the prothorax is usually 

 distinct from the other segments. It may project 

 backwards over them, as in many Water-bugs, or 

 over the hind-body as well as in certain small Grass- 

 hoppers. In many Beetles it is ornamented with 

 strong curving spines. But in insects which are 

 specially adapted for powerful flight, such as Dragon- 

 flies, Moths, or Flies, the prothorax is reduced and 

 the segments of the fore-body become, to a great 

 extent, fused together, so as to build up a firm 

 capsule for the attachment of the strong wing- 

 muscles. In Ants, Bees, and other insects related to 

 them, not only are the three usual segments of the 

 fore-body fused together, but the first segment of the 

 hind-body (fig. 1 8 n) is also united with them ; the 

 fore-body of these insects is known as an alitrmik. 

 The most extreme variation is to be observed in the 

 outward shape of the fore-body in different groups of 

 insects. Paired erectile plates (^patagici) are borne on 

 the prothorax in Moths, and small plates {tegiila) at the 

 base of the fore-wing on the mesothorax in Moths, 

 Sawflies (fig. 1 8 /), Bees, and other insects (2). 



Legs. — Each segment of the fore-body bears a pair 

 of legs. In this restriction of the locomotive limbs 

 to six, insects show the highest specialisation of all 

 arthropods. In the Cockroach, the front, middle, 

 and hind legs are closely similar to each other, the 

 size of the limbs increasing from before backwards 

 (fig. 19). Each has a large conical basal segment, 

 the haunch {coxa), which, in the cockroach, is remark- 

 ably large, taking up much of the space occupied in 

 other insects by the side region of the fore-body. 

 Jointed with the haunch is a small evenly bent seg- 

 ment, the trochanter. Then follows the principal 

 segment of the leg, the thigh {femur), elongate, and 



