THE ENTOMOLOGIST. 2Q1 



externo-raedial bone in fig. 38, between the second branch of 

 the praebrachial and the first branch of the pobrachial. In 

 fig. 39 the subapical areolet is open, and the externo-raedial 

 bone,noticed in fig. 38, does not extend to theborder,but closes 

 the discal areolet at some distance from the border. In this 

 figure there are three cubital areolets connected by means of a 

 short additional transverse bone, and the mediastinal bone is 

 apparent, so also the mediastinal areolet. In fig. 40 there is 

 an extraordinary multiplication of bones, so that the wing has 

 a dragonfly-wing appearance. The family represented in this 

 figure has its highest development in South Africa, and several 

 species of it occur in Central Asia, and among its relations it 

 is especially suggestive of heat and of dryness of soil. In 

 passing from fig. 40 to fig. 41 there is a transition from the 

 greatest activity to the greatest inactivity of flight in the 

 Diptera. The structure of the wing-bones is comparatively 

 simple in fig. 41, yet not more so than in many genera whose 

 flight is strong. In fig. 42 there is a great change in wing- 

 bone structure : some of the bones are curved forward, the 

 cubital bones do not extend to the border, the discal areolet 

 is very long, and has behind it the second pobrachial areolet; 

 the first and second cubital areolets are closed. The family 

 Bombylida) are well known by the great variety of structure 

 of their wing-bones, and by the elegance of the markings in 

 the bodies and in the wings. In some other more extensive 

 families there is a comparative sameness of wing-structure, 

 and consequently less variety of flight. 



There is much interest in observing the very numerous 

 modes of flight in the Diptera, and in comparing them with 

 the diff'erences of wing-structure by which they are occasioned. 

 When the flight is most quick or powerful there are generally 

 many wing-bones, but in some cases there is much strength 

 of wing with few bones, and much weakness of the same 

 when the bones are numerous. The bones are subservient to 

 the muscles at the base of the wing and to the structure of 

 the body, and all these are secondary to the electric currents, 

 which, when active by heat, are the means of flight, the wing- 

 bones being as conductors to them. 



Fbancis Walker. 



