WINGS. 37 



venter or under part is alone thus contradistinguished, 

 The male genitalia, which in many cases are of compli- 

 cated structure, and of much value in classification, are 

 known collectively as the hypopygium^ and this term is 

 usually restricted to the male genitalia, though some- 

 times used also for the female organs. The ovipositor of 

 the female abdomen very frequently projects from the 

 abdomen, and is sometimes extremely long; its structure 

 may be characteristic of genera or families. The more 

 detailed description of the parts of both these organs it 

 is unnecessary to go into here; the}- may be studied in 

 the different families, where the} 7 often find useful appli- 

 cation in the separation of species, though rarely of 

 genera. 



Fig. 12. Wing of Tabanns. 



WINGS. 



To understand the venation or neuration of the wings 

 the student may select a common large horsefly (Taban- 

 idae). Observe near the middle of the wing directed 

 transversely, a large, oblong, five or six sided cell, sur- 

 rounded on all sides by other cells. This is the discal 

 cell and is present in nearly all flies. Somewhere on the 

 vein (fourth longitudinal}, that bounds this cell in front, 

 will be seen a short connecting vein, directed anteriorly, 



