12 



APPLIED ENTOMOLOGY 



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farther forward. The first abdominal segment when seemingly more a 

 part of the thorax than of the abdomen is called the median segment or 

 propodeiim. 



The three pairs of legs may be quite similar, or differ widely, according 



to the uses to which they are put. In running and walking insects they 



are usually most similar; but when for example, the fore legs are used 



for capturing other insects, their form will depart greatly from that of the 



others. The jumping power of the grasshopper is 



due to the great development of its hind legs as 



compared with its others. Different types of legs 



are shown in Fig. 17. 



Whatever may be the variations in form and 

 details of the legs, all are composed of a definite 

 number of pieces or segments, connected -by hinge 

 joints so arranged that by combining the motions of 

 these, a leg can be placed in nearly any position 

 desired. 



The leg (Fig. 18) is cornposed of a coxa, a tro- 

 chanter (two in a few cases), a femur, a tibia and a 

 tarsus. The last is really not a single segment but 

 a row of from one to five, small, and on the whole 

 rather resembling each other. 



The coxa is the segment which articulates with 

 the body, frequently partly lying in a more or less 

 cup-shaped hollow of the latter. It may be short or 

 long, is generally freely movable on the body, and 

 l)owerful. The trochanter is usually small and may 

 not be visible on all sides of the leg. It is followed 

 by the femur, generally the largest and stoutest, but 

 not often the longest leg segment. The tibia is in 

 most cases quite long, more slender than the femur, 

 and often provided with downwardly projecting 

 spines or other structures which are of assistance to 

 the insect in climbing plant stems and other objects, 

 to help prevent slipping. The tarsal segments are 

 generally rather small, short, tend to be broadest at their outer ends, and 

 vary greatly in details of structure. At the end of the last a pair of 

 claws is generally found, and between them a sort of pad or cushion, the 

 pulvillus. Sometimes there are three of these, in which case the outer 

 ones are called the pulvilli and the middle one the empodium. Where 

 the tarsi are reduced to a small number of segments, only one claw may 

 be present. 



The wings are chitinous outgrowths from the body which vary much 

 in size and form in different insects. Each consists of two delicate 



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Fig. 18. — Leg of a 

 Beetle showing parts, 

 c. coxa, d, claws; /, 

 femur; s, spine or 

 spur; t^^, tarsal seg- 

 ments; th, tibia; 

 tr, trochanter. {From 

 Folsom.) 



