DIPTERA. 



431 



The structure of the ovipositor is also quite distinctive, 

 being composed of two pairs of long, horny, pointed valves. 

 These are fitted for depositing the eggs in the ground, or in 

 other firm substances. 



The larvae of most species live in the ground ; and some 

 of them destroy grass and grain by gnawing the young 

 plants just below the surface of the soil. Those of other 

 species live in various situation?, as in water, in decaying 

 wood, in fungi, and even on the leaves of plants. The larvae 



xi ix VII > 



FlG. 505.— Wing of Tipula abdominalis. 



of this family have either a single pair of spiracles situated 

 at the hind end of the body, or they have two pairs, one 

 at each end of the body. The pupae are not enclosed in 

 a puparium, and bear transverse rows of hairs, bristles, or 

 spines, which enable them to work their way out from the 

 earth when about to transform. 



Crane-flies often appear in great numbers, flying over 

 meadows and pastures. But in most cases their power of 

 flight does not seem to be well developed ; for they fly 

 slowly, and only a short distance at a time. Some species, 

 however, sustain themselves in the air for long periods. 

 This is especially true of some of the smaller species ; which 

 often collect in swarms at twilight, forming a small cloud, 

 and dancing up and down like some of the midges. But 

 even with these the flight is poor compared with that of the 

 more specialized families, as the Syrphidae or the Muscidae. 

 Their ability to walk is also poor; for they use their long 

 legs awkwardly, as if they were in the way. This has sug- 

 gested the rhyme : — 



" My six long legs, all here and there, 

 Oppress my bosom with despair." 



