774 THE AMERICAN NATURALIST. [VoL. XXXII. 
II. THE SUPPRESSION OF THE DICHOTOMOUS BRANCHING OF VEINS. 
In the more highly specialized of the many-veined insect 
wings there exists a type of branching which is very different 
from that of our hypothetical primitive type. An exafnination 
of Fig. 57, which represents this type, will show that in every 
case the forked veins are branched dichotomously, while in 
the many-veined wings the more characteristic type of branch- 
ing results in the formation of pectinate veins; this pecti- 
nate type of branching is well shown by the radial sector of 
Corydalis (Fig. 54). 
The prevalence of the pectinate type of branching in the 
many-veined wings has been, doubtless, the greatest obstacle 
Fic. 57. — Hypothetical type. 
to a recognition of the homologies of the branches of the forked 
veins in such wings. Our hypothetical type was first worked 
out by a study of the few-veined wings; but it was a long time 
after that was accomplished before we saw that the pectinate 
type of branching had been derived from the same type. The 
most potent factor in reaching this conclusion was the fact that 
in some of the many-veined insects the dichotomous type of 
branching has been preserved. Good illustrations of this can 
be seen in the neuropterous genus Sialis (Fig. 55), while 
equally good examples of the pectinate type are presented by 
the closely allied genera Chauliodes and Corydalis (Figs. 53, 54). 
The changes that take place in the development of the pecti- 
nate type of venation from the dichotomous type are of two 
