ANATOMY OF INSECTS - - EXTERNAL 



usually two branches. The anal veins (a) are typically three in 

 number, but often one or two are lost, and in other groups the 

 anal area is greatly expanded and they become many-branched. 

 Specialization by reduction in the number of veins is seen in the 

 wings of the flies, bees, and butterflies and moths, while special- 

 ization by addition is found in the wings of Orthoptera and the 

 neuropterous orders. 



In several orders the front wings are modified to form wing- 

 covers for the hind wings and are not used in flight. Thus the 

 front wings of the beetles, called elytra, are hard and horny, those of 

 the grasshoppers are 



leathery, and those 

 of the bugs are leath- 

 ery at the base, with 

 membranous tips. 



In addition to be- 

 ing organs of flight, 

 the wings sometimes 

 have other functions. 

 Thus in crickets and 

 other Orthoptera the 

 wings bear sound- 

 producing structures, 

 and the honey-bee 

 maintains the temperature of its hive by the body heat derived 

 from the incessant motion of the wings. 



Abdomen. The ten segments of the abdomen are the most dis- 

 tinct and simple of the body. The jointed appendages have been 

 almost entirely lost in adult insects, and the abdomen merely houses 

 the respiratory, digestive, and genital systems, the posterior seg- 

 ments being modified in connection with the external sexual organs. 

 In the lowest order, the Thysanura, rudimentary abdominal append- 

 ages still exist, and caterpillars and other larvae frequently bear 

 several pairs of fleshy, unsegmented prolegs, or false legs, bearing 

 a circlet of hooks at the tip. In several orders the females bear an 

 ovipositor, or egg guide, which has been developed from a speciali- 

 zation of the appendages of the seventh, eighth, and ninth seg- 

 ments, The females of many grasshoppers and crickets bear large 



FIG. 28. Wing of May-fly, showing specialization of 

 wing venation by addition of wing veins 



Lettering as in Fig. 27. (After Folsom) 



