250 
Psyche 
[September 
cavities and convexities of the wing, the author compared 
their dispositions in dragon-flies and may-flies, and came 
to the conclusion that they are very similar in venation 
as well as in the alternation of concavities and convexities. 
Unfortunately this author, following the erroneous concep- 
tion of Adolf ( 1 ) concerning the different origins of “convex” 
and “concave” veins in the first stage of the “fan” type of 
wing and the disappearance in other insects of a series 
of “concave” veins, came to an incorrect homologization of 
the veins of the two groups mentioned with those of other 
insects. Thus the cubitus of Ephemerids (and dragon- 
flies) he indicates by the number viii, which in other 
insects corresponds to Ai ; the median by number vii, which 
corresponds to the cubitus, etc. Denouncing the earlier 
views of Adolf, Comstock and Needham also did not attach 
any importance to the similarity in the wing venation be- 
tween the may-flies and dragon-flies, which was observed 
by Redtenbach. 
It always seemed to me very risky to depend upon Com- 
stock’s and Needham’s ontogenetic method for the explana- 
tion of the homology and evolution of venation. When 
we study the tracheation of nymphs and pupae we study 
at the same time the ontogeny of tracheation, but not vena- 
tion at all, because veins are vessel-like forms in which 
the blood circulates and into which nerves and usually 
tracheae often enter; but there can exist veins without 
tracheae. On the other hand, the thinner tracheae which we 
observe in the nymphs and young imagines of dragon-flies 
and nymphs of may-flies go through the wing and outside 
of veins in great numbers and often do not connect the 
neighboring veins, but the ones lying far apart. As to 
the formation of veins, although it was previously supposed 
that they were formed originally by the tracheae, more re- 
cent investigations have shown, especially in rather primi- 
tive groups [see, for example, the work of Marshall (17) 
on the development of the wings of the Trichoptera], that 
in the wing anlage the venation is formed before the 
tracheae pierce through. Comstock and Needham sup- 
posed that the tracheation in the wing of a pupa and nymph 
reflects the primitive state of venation. Therefore one would 
suppose that in the forms with a venation which resembles 
i 
