422 
THE STUDY OF INSECTS. 
four or to three. Vein V is three-branched in the more generalized 
forms. Vein VII is two-branched. Vein VIII is usually merely a 
concave fold just behind vein VII and parallel with that vein; it is 
represented in most of the figures of wings by a dotted line. Vein IX 
is usually present; and sometimes vein XI 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 Cotiops 
(Fig. 496). In this genus veins III4+6 and Vi+a coalesce at the mar¬ 
gin of the wing; veins V* and VII, coalesce for nearly their entire 
Fig. 497.—Wing of Rhyphus. 
length. The result of this coalescence is to cause the free part of 
vein V 3 to appear like a cross-vein between cells V and the 1st cell 
V a . Veins Vila and IX 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 Protoplasa there is a sharp angle near the base of vein IIIa+» which 
bears a spur (Fig. 504, s') ; in Erax a similar spur is formed on vein 
III4 (Fig. 559, s) ; and in Pantarbes this spur on vein III4 is prolonged 
so as to form a complete cross-vein dividing cell III* into two parts 
(Fig. 564). 
TABLE FOR DETERMINING THE FAMILIES OF THE 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 more than three segments. (Note that 
a style or bristle borne by the third segment is not counted as a 
segment.) 
