36 



NORTH AMERICAN DIPTERA. 



it is alone present and the pul villi are wanting (see 

 Bibionidse, fig. 7a). 



Fig. 11. Male genitalia. 1, Tipulidse [Diotrepha)\ 2 TipulitUe 

 [Atarba);-$, Tipulidae (indet.)i 4. Culicidae {Aedes); 5 Dolichopodi- 



dae (/Jo/ic/io/>i/s)\ 6. A>ili<la± [Astltts). 



ABDOMEN. 



The abdomen is composed of a variable number cf seg- 

 ments, m6re or less closely fused together. The normal 

 number for insects, nine, are rarely all visible (the Tip- 

 ulidae are examples). They are counted from the base 

 on the upper side. In not a few cases the first two are 

 so closely fused together, and the first one abbreviated, 

 that the nomenclature leaves some doubt in themiud oi 

 the student. The upper part of the abdomen may be es- 

 pecially indicated by the word dorsum, but in general, the 



