262 
Psyche 
[September 
the “attempts” did not lead to the form of a typical triangle, 
died out. From here by way of another evolutionary path 
of the Zygoptera, were derived the majority of the known 
Anisozygoptera, which often cannot be told apart from the 
Zygoptera. 
Unquestionable Zygoptera and Anisoptera are known only 
as far back as the Jurassic. The form of the wings in the 
Anisoptera and still more in the primitive Archithemidse, 
resembles very much that of the wings of the Dictyoneu- 
ridse, the most primitive of the Palseodictyoptera, also the 
Spilapteridse, Triplosobidse and may-flies of the Permian. 
If these dragon-flies have remained unchanged in their 
original form and homonomous nature of wings, we have 
also the right to expect a general plan of the distribution of 
veins, because the one and the other are bound together by 
function. This we actually find takes place. In Diasta- 
tomma (Archithemidas) no nodus is to be found and Sc has 
the same aspect and same relation to R as it has in the 
majority of Dictyoneuridse and Spilapteridae. The next 
longitudinal vein after R gives rise to 3 or 4 branches ; their 
method of origin and general distribution repeats that in a 
series of Dictyoneuridae and Spilapteridae (e. g., in Steno- 
dictya, Polioptenus, Acanthodictyon, Eumecoptera and 
others), and still more of Triplosoba and the Agnatha. The 
resemblance of the Triplosobidae in the distribution of the 
branches of RS, especially to the Anisoptera, and to the 
recent may-flies is so striking and obvious, that we can 
compare vein by vein without difficulty. In the dragon-flies 
we usually find in the region of RS two groups, the basal, 
— formed by the first concave branch, as in may-flies (RS-,= 
M 3 of authors) ; and the second convex and also usually 
“inserted” branch (RS 4 =1 Morgan) ; and the distal group, 
formed by the concave RS 3 the weak convex and sometimes 
almost disappearing inserted RSo, and lastly the concave 
continuation of RS (as in may-flies and Triplosoba). After 
this complicated RS follows the simple vein which is divided 
from it at the very arculus, and which is indicated by 
Odonatologists as M 4 , but which represents M. It is still 
impossible to say whether this M corresponds to MA or MP 
of Triplosoba, and that is why we shall indicate it simply 
by the letter M. At its base M turns sharply towards R 
