1930 ] Wing Venation of the Odonata and Agnatha 269 
by such means and which was one of the first to lose 
its own trachea, is RS 4 (=1 Morgan) ; that is the vein 
which has no normal tracheation in Odonata, where 
it receives the trachea either from RS 3 (Zygoptera) 
or from R (Anisoptera) . Furthermore, the convex vein 
between RS 4 and RS 4 is tracheated (almost exclusively) in 
the same way. Tracheae which go into M and R are often 
very weak also, or even vanish entirely (especially in M), 
and in such a way these veins adopt a secondary tracheation 
^rom the branches of the neighboring trunks. The inter- 
calary vein in Cu 4 is similarly tracheated, sometimes A 4 
also. If we compare such characteristics of tracheation 
with the characteristics of venation, then without effort we 
shall notice the fact that the first veins to lose their own 
trachea and begin to be tracheated by small branches from 
neighboring trunks are all veins which were made 
“inserted” (independent, intercalary, Shaltsectors, etc.), 
— that is, which lost their origins. Such veins as far as 
known are almost always convex veins. Furthermore, in 
the more primitive species groups as Bsetoidea, but also 
Siphloneuridse and a few Ephemeridse, the tracheae which 
go into M and R, that is already into the main but exclu- 
sively convex veins, are weakened and eventually disappear. 
We have said above that because of this loss and even by 
the weakening, of trachea as in the case of R and M, which 
penetrate into the vein through the base, this vein begins to 
be tracheated by small branches from the neighboring 
tracheal lines. The tracheation of such “inserted” veins is, 
however, very diverse, because branches penetrate into it 
not only from neighboring systems but also from trunks 
which lie further away anteriorly and posteriorly. Such 
small branches must quite often go a long way around 
before they come into the necessary vein. Quite often some 
small tracheal branches, which are derived from the neigh- 
boring trunks as well as the trunks placed further away, 
become a great deal stronger than others, and accept the 
chief burden of tracheation; in such cases one- -or the other 
part, and sometimes most of the small tracheal branches, 
are subject to reduction. Finally, not rarely there are cases 
when only one trachea receives the repossession and tra- 
cheates almost entirely a given vein (a certain part of the 
