1930] Wing Venation of the Odonata, and Agnatha 251 
especially closely the scheme of the original venation, 
we should expect a particularly complete parallelism of 
the tracheation with the venation. But this is not so. 
In Hydropsyche, which is a small caddis-fly with extremely 
primitive venation, Comstock and Needham found a com- 
plete unconformity of the tracheation with the venation, 
which they interpret without regard for the direction of 
the trachea. These authors are obliged to do the same 
with the Hymenoptera and Diptera. Why should we rely 
so blindly upon the tracheation in case of dragon-flies and 
Ephemerids and ignore the data of paleontology, which 
proves the close relation of venation in contemporary repre- 
sentatives of dragon-flies and may-flies with that of the 
Palseodictyoptera (in the case of the Ephemerids, through 
the Carboniferous Triplosoba Handl.) ? Such a “concep- 
tion” is all the more unacceptable because the theory of 
Comstock and Needham encounters serious contradictions 
within the groups themselves. The crossing of the media 
which arises from R by means of the trachea RS takes 
place only in the Anisoptera; this does not appear in the 
Zygoptera, and the trachea of the corresponding vein arises 
from the branch M. We have no proofs that the latter 
condition developed from the former. As to the Aniso- 
zygoptera, in view of their very close relationship to the 
Agrionidse (through the Lestinse), one can suppose that 
in them the trachea RS of the authors arises from the 
media of the authors. A very diverse and changeable 
tracheation of nymphs of may-flies gives us still less right 
to conclude that they have such a crossing, that their com- 
plicated vein below R is M, etc. 
My investigation of the relation of the venation to the 
tracheation has led me to the conclusion that the formation 
of venation occurred under the influence of causes of me- 
chanical character; the tracheation, adapting itself to the 
newly formed distribution of veins, often changed in a 
most original way; therefore, one can judge the venation 
by such an “indirect”* representation of it only with ut- 
most care. 
In view of these facts I decided that in investigating the 
venation of dragon-flies and may-flies, as well as of other 
groups, to turn first to the comparative study of the vena- 
