118 THE AMERICAN NATURALIST.  [Vou. XXXIII. 
out in this place the degree of perfection that has been reached 
in the alternation of convex and concave veins. In the accom- 
panying table the names of the convex veins, those veins that 
follow the crests of ridges, are printed in Italics; while the 
names of concave veins, those veins that follow the furrows, 
are printed in Roman type. 
TABLE OF WING-VEINS OF EPHEMERIDA. 
f Costa ; E; 
Sc. Subcosta . Sc. 
R Radi : : : i : i e Ki 
: Vem’ R; =. x -e Ra 
í Yee Rra | Ven R; ; io ae 
Rs. Radial sector < Chief accessory radial vein . 1 
; Vein Ry ; . i Ry 
| Vein Ruts (ous oe 
E Vein M: : gras ee) © 
M. Pa" Mita vein Eon 
- Vein M, : : ; M, 
Vein Cu; . 2 : ; : i ; Cu; 
Cu. Cubitus f Chief accessory cubital vein. so 
Vein Cu, . . Í ; ; j Cus 
Ist A. rst Anal vein ist A 
2d A. 2d Anal vein 2d A 
3d A. 3d Anal vein 3d A 
One of the most characteristic features in the venation of 
the wings of May-flies is that the radial sector plays the part 
of a principal vein; it originates near the base of the wing; 
and, as a rule, it is detached, in the adult, from the main stem 
of the radius.! For this reason it is given the position of a 
principal vein in the table. 
If this modification be made, it will be seen that, when the 
principal veins are considered, there is a strict alternation of 
convex and concave veins; and that in the case of the forked 
veins (the radial sector, the media, and the cubitus) the prin- 
cipal branches of a vein are of the same nature as the main 
stem 
It will also be seen that this alternation of convex and con- 
cave veins exists in the distal portion of the wing. In those 
1In certain Plecoptera and Trichoptera the radial sector of ie hind wings is 
detached in a similar manner. 
