260 
Psyche 
[ September 
would unquestionably weaken and finally disappear. Such 
was, according to my understanding, the way in which the 
“inserted sectors” of the German authors were formed . 8 
Now, the origin of RS sometimes from M, more seldom 
from R, or its “free” origin becomes clear to us. Entering 
into the oblique angle between the convex R and M, the 
concave RS unquestionably had to become a “Schaltsector,” 
which we quite often find in the typical species of Hexa- 
genia, in some Siphlurus and others. The approach of the 
base of RS to one of the neighboring veins, e. g., to M, 
together with some small changes in the direction of the 
joining cross-vein (the cross-veins are certainly preserved) 
easily give the appearance that RS arose from M. 
The appearance of the alternation of the convex and con- 
cave vein with its result — the change of convex veins into 
“inserted sectors” 9 — had been acquired by the ancestors 
of may-flies and dragon-flies very long ago. This appear- 
ance was well expressed not only in the may-flies of the 
Permian, but also in the Carboniferous Triplosobidse, as 
becomes clear from their possession of a series of “inserted 
sectors.” The dragon-flies of the Mesozoic do not differ in 
this respect from the recent ones. The Carboniferous “Pro- 
todonata,” at least some of them, also acquired this alterna- 
tion. The plaiting was already indicated in the Palseodic- 
tyoptera and Megasecoptera but it was very seldom that the 
branches actually turned into inserted sectors, and accord- 
ing to the branches we can judge with certainty about this 
8 Woodworth, on the contrary, sees in the “independent” veins of 
the may-flies primitive structures which illustrate the process of the 
formation cf the longitudinal veins of insects. The “independent” 
veins are supposed to receive their origins from the marginal vein, 
as growths of the latter to the inside; these growths are pulled out 
towards the base and finally fuse with one of the main trunks. The 
media, according to Woodworth, was formed as an independent vein 
also, only the anal veins having a different origin, and growing from 
the base. We have no need to stop to discuss this fantastic theory; 
it contradicts all data of paleontology and comparative systematics 
(the condition in Bastoidea is unquestionably secondary!), and is 
impossible from a morphological aspect. (One cannot imagine the 
growth of veins in the membrane.) 
£ I do not exclude the possibility that some (short) intercalary 
veins of dragon-flies could develop as illustrated by Comstock (1918): 
as a result of the formation of plaiting. 
