79 



the first anal vein. It is represented in Figure 2 by a dotted 

 line. 



If this structure were always of the form that it bears in 

 flies it would not be termed a vein, but in many moths it is 

 thickened and appears like the true veins; it is, therefore, 

 termed a vein. 



Note. — The anal furrow is of very great use in determining the 

 homologies of wing-veins. Except in very highly specialized insects 

 it is easily observed and makes a good starting point in working out 

 the structure of a difficult wing. 



Anal veins. — The anal furrow divides the wing into two 

 areas, which may be termed the preanal area and the anal 

 area. The anal area, that part of the wing caudad of the 

 anal furrow, is usually transversed by one or more simple 

 veins ; these are termed the anal veins. The anal veins are 

 often designated as the first anal vein, the second anal vein, 

 etc. It should be remembered that in numbering the anal 

 veins the anal furrow is counted as the first anal vei?i. 



Premedia and postmedia. — 

 In the May-flies there appears 

 to be a distinct, branched vein 

 between radius and media ; 

 this has been termed the pre- 

 media (Fig. 3, IV). There 

 also appears to be in May-flies 

 a distinct, branched vein be- 

 tween media and cubitus ; 

 this has been termed the post- 

 media (Fig. 3, VI). 



Numbering of wing- 

 veins. — It is often more con- 

 venient to refer to the wing- 

 veins by numbers than by the 



names that have been applied to them. The system of 

 numbering the veins that we have adopted is illustrated by 



Fig. 3. — Wings of a May-fly, Hexagenia. 



