1930 ] Wing Venation of the Odonata and Agnatha 257 
Cu 2 of the Ephemerids CuA and CuP. The similarity with 
the dragon-flies seems to confirm it, but their palaeontologi- 
cal data do not assert this with certainty, and I indicate 
these branches so far by different symbols. 
In groups with the curve of Cu 2 present Ai also has a 
more or less considerable curvature. Often the descending 
segment of Cu fuses entirely with the original of Ai, a 
condition which we encounter in some Palingeniidae (Ana- 
genesia, Plethogenesia) , or otherwise disappears (Camp- 
surus, Polymitarcys, et al). Ordinarily A x forms distally 
a series of branches directed posteriorly. It usually also 
has an upward curvature. A 2 arises either in the middle 
of Ai and A 3 , or very close to Ai; usually it curves back- 
wards soon after, and becomes short, and only in Baetiscidse 
does it run parallel to the straight Ai. A 3 is still shorter, 
but often has more branches ; in Bsetisca its first branch is 
parallel to A 2 . From the distal part of these (A 3 ) lead 
a few weak anal veins, but more often the latter lose their 
independence, and come in contact with A 3 in different 
ways. 
In groups which have the tendency to a final reduction 
of the hind wings, the cubito-anal regions of the fore wings 
grow, take the place of the disappearing hind wings in 
function, and correspondingly elongate and distribute the 
anal branches in accordance with the mechanical needs 
(Csenidse, Bsetidse, Leptophlebiidse) . The anal veins pre- 
serve the more original bow-shaped form in the hind wings, 
but quickly weaken towards the base. 
Now let us turn to the question of concave and convex 
veins, and to their relation to the veins in the wings of 
may-flies. In 1880 Adolf noted the fact that in the wings 
of may-flies the concave ones, like valleys, alternate with 
the convex, as longitudinal ridges. In the bottom of val- 
leys and on the peaks of ridges are the adjoining longitudi- 
nal veins. Adolf regarded this alternation as very impor- 
tant. According to his understanding the “convex” and 
the “concave” veins have entirely different origins, signifi- 
cance and destinations. He thought that the original wings 
differed in the possession of a more regular alternation of 
the numerous convex and concave veins and that the wings 
