356 INTRODUCTION TO ZOOLOGY CHAP. 



inside the pockets, jerking themselves round so that they 

 expose first one side and then another. The two com- 

 monest species are Simulium sericeum and Simulium elegans. 



This pupa is always submerged, and yet the fly 



Emergence w ] 1 j c ] 1 j s ^ o emerge from it would be iniured if 

 of Imago. & _ . , . , J , 



wetted by water. It is very difficult to observe 



the process by which this danger is surmounted. Appar- 

 ently, during the latter part of the pupal stage which lasts 

 about two weeks, air collects under the pupal skin, so that when 

 this splits, the imago rises with this air-bubble, which is 

 extended in an air-film clinging to the hairs on the surface 

 of the body of the fly, and thus all danger of drowning is 

 avoided. 1 



Family 4 : TIPDLIDAE (DADDY-LONG-LEGS OR CRANE-FLIES) 



The Tipulidae are Diptera with slander bodies, very long 

 legs, and narrow wings, which are held well above the body 

 when at rest, the second pair of modified wings or halteres 

 being unusually large. The veining of the wings is also char- 

 acteristic and 

 is rather com- 

 plex, especially 

 near the free tips 

 of the wings- 

 (Fig. 283). 



The Common 



Daddy-long-legs 



or Crane-fly. 



FIG. 283. The Spotted Crane-fly, male ( x 2). ThlS msec ^ 1S 



shown m Fig. 



283, where the typical form of body, the narrow wings, large 

 halteres, long legs, simple long antennae, and projecting palps 

 with their characteristic long terminal joint, all are clearly 

 visible. 



In all species of Tipula, the sexes can be distinguished by 



1 I have never been lucky enough to see the emergence of the imago, 

 though I have reared many. These statements are based on Verdat's 

 observations, quoted by Professor Miall. 



