No. 386.] THE WINGS OF INSECTS. 123 
ized, it separates into two trunks in the thorax near the base of 
the wing (Fig. 70); from one of these arises the costo-radial 
group of tracheze, and from the other the cubito-anal group. 
Fig. 70 will serve to illustrate what may be considered the 
type of tracheation of the wings in this order. It was made 
from a study of the nymphs referred to above. The positions 
of those longitudinal veins that contained no trachez in these 
nymphs are indicated by dotted lines. 
The discussion of the venation of the wings of Ephemerida 
brings up the question of the venation of the primitive insect 
wing. For, in several of the more important papers on the 
homologies of wing-veins, it has been assumed that the wings 
of May-flies resemble closely the wings of the primitive winged 
insect. : 
The great preponderance of the many-veined type among the 
insect wings that have been found in the Carboniferous rocks 
has doubtless strengthened the quite generally accepted view 
that the primitive winged insect had many wing-veins. Thus 
Redtenbacher states : 1 
The geologically older Orthoptera and Neuroptera show a much richer 
venation than the Coleoptera, Lepidoptera, Hymenoptera, and Diptera ; 
likewise among the Rhyncota, the oldest forms, the Cicadas and the Ful- 
goridæ, possess much more numerous veins than the Hemiptera. There is 
apparently, then, no doubt that the oldest insect forms were provided, to a 
certain extent, with a superfluity of veins, and that, in the course of devel- 
opment, all the superfluous veins disappeared by reduction, and in this way 
a simple system of venation was brought about. 
But we have shown that all the existing types of insect wings 
can be derived from one in which there are but few wing-veins 
— our hypothetical type, already figured several times. The 
deviations from this type in the more generalized members of 
the greater number of the orders of insects is slight. And 
we have pointed out the ways in which it is being modified, on 
the one hand by the coalescence of veins, and on the other 
by the development of accessory veins. While this is easy 
to understand, it is very difficult to conceive how the wings of 
the Lepidoptera, Diptera, and Hymenoptera could have been 
1 Annalen des k. k. nat. Hofmuseums, Bd. i, p. 153- 
