258 
Psyche 
[September 
were similar to a fan. Redtenbach compared fully the dis- 
tribution of these veins in the may-flies and dragon-flies, 
and found a complete correspondence. Later it was shown 
(2) that the indicated representation of Adolf was incor- 
rect and perhaps this was the cause of Comstock’s and 
Needham’s paying little attention to the valuable compari- 
sons of Redtenbach. The plaiting and alternative distri- 
bution of veins along the bottoms and tops has great me- 
chanical value. The wings of the may-fly have attained 
a very high specialization. The membrane is extremely 
thin and delicate, and its veins have already adopted an 
extraordinary mechanical function and acquired the cor- 
responding structure (ribs, absence of blood, dry struc- 
ture) and their distribution also corresponds to the me- 
chanical requirements. If this thin membrane were spread 
over the veins entirely in one plane, then at the stroke of 
the wings upon the air, being so delicate and unable to 
stretch, it would break and inevitably tear. The plaiting 
gives the membrane flexible, elastic qualities. At the sharp 
resistance of air on the stroke of the wings, the latter 
can stretch sufficiently because of the plaiting at all neces- 
sary points. In the formation of this plaiting the closely 
lying veins, as in similar cases (Arthoptera) , were dis- 
tributed, some on the bottom, others on top, and their 
course, even in their details, was affected by the plaiting; 
the fundamental character of the latter, in its turn, was 
conditioned by the original distribution of veins. In that 
way the continual reciprocal action of these two structures 
took place in the course of evolution. The concave position 
among the main veins includes Sc, RS, Cu and A 2 , and then 
a series of distal branches, which alternate with the convex 
greater part of the distal sectors, Cuad 7 , Mad, RS 4 , the 
RS 3 concave, RS 2 convex ; among the smaller distal sectors, 
the larger ones also alternate. In the more primitive Pal- 
ingeniidse, Ephemeridse, Ecdyuridse and the ones near to 
them, which retain rich, thick venation in their wing, the 
greater part of the distal sectors, Cuad 7 , Mad, RS 4 , the 
branches between RS 2 and RS 3 as well as these branches 
7 Cu additional or M additional; in this way we shall designate the 
middle branches of Cu and M. 
