422 THE AMERICAN NATURALIST. (VoL. XXXII. 
Fig. 46 represents the wings of a pupa of Tremex; and Fig. 
47, the fore wing of a pupa of Apis. In both cases the main 
tracheze extend in nearly direct lines from the base of the wing 
to near its outer margin. This fact alone would indicate that 
the needs of respiration. of the pupa, rather than the flight 
function of the adult wing, has been the important factor in 
determining the courses of these trachez. 
A comparison of the fore wing of Tremex with that of Apis 
shows a remarkable difference in tracheation. In Tremex 
vein Æ, is traversed by a branch of the radial trachea (X); 
while in Apis the radial trachea is not branched, and the 
trachea traversing vein X, arises from the cubital trachea (Cu). 
When this fact was first observed it was thought that the 
See EO RAI” 
Iga 
Fic. 47. — Fore wing of a pupa of Apis. 
trachea of the radial sector in Apis had become transferred 
from the radial trachea to the cubital. We were not greatly 
surprised at this phenomenon, for a similar switching of tracheze 
is common in those Lepidoptera in which the branches of the 
media become joined to the adjacent veins. 
It was found, however, that this is not the explanation of 
the change. An examination of the wings of young pupz of the 
honey-bee revealed the fact that in this insect the laying out 
of the wing venation precedes the tracheation of the wing. 
After the wing-veins reach that stage of development in which 
they appear as pale bands, the tracheze grow out from the base 
of the wing into them. Fig. 48 represents the wings of a pupa 
taken at a stage which illustrates this pushing out of the 
trachez into the previously formed wing-veins. 
It is obvious that trachez developed in this way will follow 
the paths offering the least resistance to their progress; and 
