2 9 o THE STUDY OF INSECTS 



The Costa extends along the costal margin of the wing; it usually 

 ends somewhere near the apex of the wing; in Anisopus it ends at the 

 tip of win K 4 i„ (Fig. 500). In some families it extends entirely around 

 the wing; it is then called the ambient vein. Vein Sc is simple. Vein R is 

 typically five-branched ; but the number of branches is usually reduced to 

 four or to three. Vein M is three-branched in the more generalized 

 forms. Vein Cu is two-branched. The first anal vein is usually merely a 

 concave fold jusl behind vein Cu and parallel with that vein; it is repre- 

 sented in most of the figures of wings by a dotted line. The second anal 

 vein is usually present; and sometimes the third anal vein also exists. 



One of the most marked features in the specialization of the wings 

 of Diptera is a tendency of the veins to coalesce from the margin of the 

 wing towards the base. This is illustrated by the wing of Conops (Fig. 

 499). In this genus veins R 4+5 and Mi +2 coalesce at the margin of the 

 wing; veins M 3 and Cui coalesce for nearly their entire length. The re- 

 sult of this coalescence is to cause the free part of vein M 3 to appear 

 like a cross- vein between cells M and the 1st cell M 2 . Veins Cu 2 and 

 2d A also coalesce at the margin of the wing. 



In a few genera of flies certain longitudinal veins are bent so as to 

 form a sharp angle, and from this angle a spur is developed. Thus in 

 the primitive crane-flies there is a sharp angle near the base of vein R 2+5 

 which bears a spur; in Mydas a similar spur is formed on vein R 4 (Fig. 

 549); and in Pantarbes this spur on vein R 4 is prolonged so as to form 

 a complete cross-vein dividing cell R 3 into two parts. 



TABLE OF FAMILIES OF DIPTERA 



A. Flies in which the abdomen is distinctly segmented, and the two legs of each 



thoracic segment are not widely separated. Habits various, but the adults do 



not live parasitically upon either birds or mammals. 



B. Antennae consisting of at least six distinct segments, the palpi in most cases 



of four or five segments (Nemocera). 



C. Small moth-like flies, with the body and wings densely clothed with hair 



and scales. Wing with from nine to eleven longitudinal veins but with no 



cross- veins except sometimes near the base of the wing (Fig. 506). p. 295. 



PSYCHODID^E 



CC. Flies that do not resemble small moths in appearance. 



D. Mesonotum with a more or less distinct V-shaped suture (including Tany- 



derinae, Ptychopterinas and Pipulinae). p. 293 Tipulid^e 



DO. Mesonotum without a distinct V-shaped suture. 



E. Media three-branched; ocelli present, p. 295. (In part) Anisopid^e 

 EE. Media simple, two-branched or wanting; cell M 2 not divided by a 

 cross-vein. 



F. Wing with network of fine lines, p. 304 Blepharocerid^e 



FF. Wing without network of fine lines. 



G. Margin of wings and wing-veins fringed with scales or scale-like 



hairs. (Fig. 512). p. 297 CuLlCIDiE 



GG. Wing veins with or without hairs but without fringe of scales. 

 H. Anal vein entirely wanting; vein M wanting or represented by a 



single unbranched fold. p. 301 Cecidomyid,*: 



HH. Anal vein usually present or represented by folds; vein M 

 present or represented at least by a fold which is usually 

 branched. 

 I. Ocelli present. 



J. Antennae shorter than the thorax; coxae not usually long; 



cross- vein m-cu absent or present, p. 302 Bibionid^e 



JJ. Antennae usually longer than the thorax and in many cases 

 with much elongated coxae. 



