Vol. 1.] Woodworth.—Wing Veins of Insects. 49 



The fact that there are three kinds of pigmentation and 

 that these may occur in ahriost any combination as regards 

 their relative distinctness, affords abundant opportunity for 

 apparent differences in structure. One can commonly trace 

 on a single wing, sometimes in a single vein, a large num1)er 

 of variations in pigmentation. Interesting examples of this 

 are very common in the wings of the higher flies and of beetles. 



A very careful study of the pigmentation of the veins sup- 

 posed by different authors to represent different types of veins 

 has failed to reveal a single constant item of difference in any 

 case when a sufiiciently large number of wings were studied. 

 The pigmentation of the same vein differs in many cases 

 according to the size of the wing, indicating that perhaps the 

 size of the vein cavity may have something to do with the 

 amount or character of pigmentation. However this may be, 

 it is safe to say that there is no evidence that the pigmenta- 

 tion indicates in any case differences of structure by which 

 types of veins may be differentiated. 



There still remains for consideration that class of so-called 

 veins which are represented on the wing either by the arrange- 

 ment of the surface hairs, by the disturbance of the color pat- 

 tern, or by folds in the membrane. 



Hairs usually occupy a very definite position in relation to 

 veins. Usually the surface over the vein is either devoid of 

 hairs, or possesses one or several rows of them regularly 

 arranged, often of a larger size than those on the membrane, 

 and sometimes of a peculiar structure. Whenever there are 

 on the surface of the membrane rows of hairs similar in struc- 

 ture and arrangement to those on the veins, their position is 

 always such that if a vein were to replace them, it would not 

 be considered anomalous in position. The very common pres- 

 ence of hairs on veins, except such as have been just described, 

 gives very good grounds for thinking that they could not be 

 produced except over cavities like the vein cavities, and there- 

 fore that they represent veins either suppressed or not yet 

 perfected. 



The pattern on a wing, whether due to coloration of the 

 membrane, or, as in Lepidoptera, to the presence of colored 

 scales, often shows a very distinct irregularity where a vein 

 crosses a spot or band. This is conspicuously evident in the 

 bands along the outer margin of the wing in most Lepidoptera. 

 4— V 



