1930 ] Wing Venation of the Odonata and Agnatha 275 
RS 4 by the branch from R or RS 3 (almost) was established, 
but I think that the formation of a stable point of supply 
at the nodus had great influence upon the process of acquir- 
ing such a tracheation. In the Anisoptera the point of 
origin of the branch in RS 4 from the trachea R is just oppo- 
site the nodus. In the region of the nodus the wing is 
certainly stronger, is much less able to bend, and is much 
less exposed to occasional deformation at its distal point. 
The trachea which arises from this place in R is naturally 
more protected at its base and therefore more able to be 
strengthened and preserved than other more distally lying 
branches from the neighboring trunks. In the Zygoptera 
RS 4 is supplied by an entirely different trachea; this is 
from RS 3 , but here also the place of origin of the trachea 
is opposite the nodus, though a little more distal. How- 
ever, one should bear in mind that in the evolution of the 
Zygoptera, there took place migration of the nodus towards 
the base, so that the separation of the point of origin of 
RS 4 and the nodus becomes clear. The difference between 
these suborders in the tracheation of RS 4 proves my sup- 
position about the original diversity and the probable 
variability of the growing secondary tracheation in the 
dragon-fly. It would be strange if in both suborders, which 
are so different on the basis of their venation, there should 
have been established a similarity of RS 4 . 
Unquestionably the tracheation is also secondary. This 
tracheation in general is similar in both suborders, but 
there are a few which are somewhat inconsistent. The 
tracheation of the wings of dragon-flies differs in general 
from that of the may-flies in its stability; but the stability 
is not so great as one would think and one encounters in 
the Anisoptera, a variation of even a serious character. I 
did not investigate these ^questions specifically; I shall 
mention only four young nymphs of iEschna sp., which 
were taken together in the fall of 1923 in a little pond 
near Lakhta; in one of these the trachese appeared to be 
anormalous in the following features : in the left fore wing 
the treachea R behind the nodus gives rise to a strong 
trunk, which at once separates again into three branches, 
entering into RS 4 , RS 3 and RS 4 . Only RS 5 is tracheated 
here from the trachea of the media. In the right hind 
