Vol. 1.] 



Woodworth. — Wing Veins of Insects. 



99 



primitive one, and the explanation of the significance of convex 

 and concave veins, ah'eady given, shows that it is not necessary 

 to derive all insects from an Ephemerid, in order to explain the 

 presence of traces of this arrangement in so many different 

 groups. 



The veins are not simply convex and concave, as the 

 accounts given would lead one to infer, but there are many 

 peculiar changes of level not easily explained. The wing of 

 Hexagenia, from which Fig. 32 was made, was mounted on a 



FIG. 32. Venation of Hexagenia bilineata. 



slide, and vertical measurements were made, by means of the 

 graduated fine adjustment screw of the microscope, at the 

 points where the veins intersected twelve equidistant lines 

 crossing the wing at right angles to the costa, to ascertain the 

 relative heights of these several points. The results are given, 

 in hundredths of millimeters, in the following table. The first 

 column is the anterior and the last the posterior marginal 

 vein; the intermediate columns represent all the veins (except 

 the minute apical independents) occurring back as far as the 

 first posterior. The first line is nearest the tip. 



Table showing the Variation in the Level of the Veins. 



4 2 7 2 6 2 6 ...._- .- - .. .. 5 



10 7 10 3 6 10 7 7 3 -. .. .. .. .. .. 8 



16 6 13 4 15 6 14 9 8 8 .. .- -. .. 6 



12 12 18 3 16 4 17 .. 4 14 1 12 4 13 .. -_ 4 



9 9 20 7 .- .- 12 .. 6 18 3 24 7 15 19 .. 11 



2 2 22 11 .. .. 19 .. 2 20 .. 18 3 9 13 24 18 



11 16 4 .. .- 28 .. 1 .. .. 15 2 7 27 22 15 

 18 5 8 4 .- .. 26 .. 8 -_ .. 25 2 _. 24 413 26 

 29 8 23 10 .. .. 4 .- 6 .. .. 22 2 -. 27 5 28 

 28 6 28 15 .. .. .. .. .- -. -. 32 3 .. 31 3 12 



26 6 26 24 .. .. .. 30 6 .. 29 14 4 



16 8 19 - -. 37 .- 9 



