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[September 
wing the trachea which supplies our M (M 4 of the authors) , 
appears to be free up to the very base, and arises only very 
near the trachea RS (fig. 12). The last variation is espe- 
cially interesting as indicating that the origin of the 
trachea M from the general trunk Rs + M is perhaps the 
result of a secondary fusion of the base of the trachea M 
with the base of RS. 
And so the investigation of the tracheation of the wings 
of dragon-flies and may-flies from a functional and histori- 
cal point of view leads us to the conclusion that the pecu- 
liarities were developed in connection with the acquisition 
of the characteristic features of these groups, the alterna- 
tion of convex and concave veins, and usually the change 
of convex ones into “inserted sectors.” Such features are 
characteristic of these two recent groups and the related 
fossils, Triblosoba, Protodonata (in part), some Megase- 
coptera and evidently some Palseodictyoptera. 
The study of the relation of the jugal areas to the re- 
maining part of the wing lead me in another work (7) to 
the conclusion that the Insecta Pterygota probably sepa- 
rated during the Lower Carboniferous into several branches 
which went along different lines of evolution, the Paleoptera 
(Palseodictyoptera, Megasecoptera, Agnatha, with their 
Carboniferous relatives) and the Neoptera (the remainder 
of the Pterygota, which at rest fold their wings roof-like 
over their abdomens). My study of the venation and the 
tracheation of the wings of may-flies and dragon-flies proves 
this conclusion, because according to the wings both these 
groups are similar in many ways to the Dictyoneuridse, 
Triblosoba, and the typical members of the Paleoptera. 
In conclusion, I would like to discuss one more question. 
How can one explain that out of the once rich and diverse 
group of Paleoptera, there are now existing only the Ag- 
natha and the Odonata, the other groups having died out? 
I think that in a discussion of this question we should not 
forget the structure of such an important organ as the 
wing. 
Of course the wings of recent dragon-flies are much 
more perfect than those of their remote ancestors, which 
were like the Dictyoneuridse. They have lost most of those 
veins of their ancestors which were unnecessary from a 
