100 DKAGONFLIES [CH. IV 



wander great distances and are even known to migrate in 

 great swarms, though the object of migration is entirely 

 unknown. 



The main structure and habits of all are very similar. 

 Possessed of both simple and large compound eyes (whose 

 facets in some cases are larger upon the upper than under 

 side, the former perhaps for remote and the latter for near 

 vision) they have keen powers of sight and rely upon this 

 sense for the capture of their prey, the antennae being 

 (consequently ?) reduced. The wings are relatively large 

 and strong ; both pairs are used in flight, but there is no 

 apparatus for linking the fore and hind wing of the same 

 side together. Nevertheless, in many species, the flight is 

 remarkably bold and swift and enables these insect-hawks 

 to catch with ease the flies and other insects on which 

 they feed. The front and hind * 



wings are free from each other 1 , Wing 

 and are provided with their re- J ~TFf~ Fulcrum 

 spective elevator and depressor I M 



muscles. But they are perhaps v| | v 



i i . . . T . .. Depressor Elevator 



brought into working connection Muscle Muscle 



with each Other by means of a long Diagram to explain action 



lever present among the chitinous of wing of Dra g nfl y- 

 pieces in the body- wall at the base of the wings. 



Von Lendenfeld has described the arrangement of the 

 muscles 2 , ligaments and complicated chitinous joints con- 

 cerned in the movement of the wings. If reduced to a 

 simple plan the mechanism appears to be that of a lever 



1 Chabrier, " Vol des Insectes," Mem. d. Mus., 1822. 



2 Akad. d. Wiss. Vienna, 1881, Eft. i. 



