THE ENTOMOLOGIST. 232] 
externo-medial bone in fig. 38, between the second branch of 
the prebrachial and the first branch of the pobrachial. In 
fig. 89 the subapical areolet is open, and the externo-medial 
bone, noticed in fig. 38, does not extend to the border, 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 
Bombylide 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 differences 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. 
FRANcis WALKER. 
