22 



ANIMAL LIFE PAST AND PKESENT. 



Butterflies and Moths readily distinguishes the Lepi- 

 doptera from all other insects, and likewise suggests 

 that they form a much specialised modification of the 

 class. Still greater specialisation as regards their 

 organs of flight is, however, presented by the Flies and 



Gnats, constituting the 

 order Diptera, in which 

 while the front pair of 

 wings are large and mem- 

 branous, or hairy, the 

 second pair are reduced 

 to small, drumstick-like 

 processes termed balan- 

 cers, or halteres, which 

 are of no sort of use in 

 flight, and are typical 

 rudimentary organs. The 

 specialisation of the wing- 

 structure in this group 

 is, therefore, exactly the 

 opposite of what occurs 

 among the Beetles, where, 

 as we have already seen, 

 it is the first pair of 



wings which takes no part in flight. In the Cicadas 

 and Bugs (Fig. 9), constituting the order Ehynchota, 

 the wings, when present, are four in number, but the 

 first pair may be converted into horny wing-covers, 

 as in the Beetles. Like those of the next order, 

 all the members of this group differ from the insects 



FIG. 9. Enlarged view of a Flying Bug, 

 with the wings closed. 



