$60 MOTIONS OF INSECTS. 
of whose bodies, as well as the shape and circumstances 
of their wings, is different. First are the slender flies— 
the gnats, gnat-like flies, and crane-flies (Tipulide). ‘The 
bodies of these are light, their wings narrow, and their 
legs long, and they have no winglets. Next are those 
whose bodies, though slender, are more weighty—the 
Asilide, Conopside, &c.; these have larger wings, shorter 
legs, and very minute and sometimes even obsolete wing- 
lets. Lastly come the flies, the Muscide, and their af- 
finities, whose bodies being short, thick, and often very 
heavy, are furnished not only with proportionate wings 
and shorter legs, but also with conspicuous winglets. 
From these comparative differences and distinctions, we 
may conjecture in the first place—since the lightest 
bodies are furnished with the longest legs, and the 
heaviest with the shortest—that the legs act as poisers 
and rudders, that keep them steady while they fly, and 
assist them in directing their course? ; and in the next— 
since the winglets are largest in the heaviest bodies, and 
altogether wanting in the lightest—that one of their prin- 
cipal uses is to assist the wings when the insect is flying. 
The flight of the Tipulidan genera is very various. 
Sometimes, as I have observed, they fly up and down 
with a zig-zag course ; at others in vertical curves of small 
diameter, like some birds; at others, again, in horizontal 
curves :—all these lines they describe with a kind of 
skipping motion. Sometimes they would seem to flit in 
every possible way—upwards, downwards, athwart, ob- 
liquely, and sometimes almost in circles. The common 
* To those that frequent meadows and pastures (Tipula oleracea, 
L. &c.) they are also useful, as I have before observed, as stilts, to 
enable them to walk over the grass. Reaum. v. Prof. i. ¢. iii. f. 10. 
