No. 378.] THE WINGS OF INSECTS. 42I 
and the wing-veins, or to demonstrate that such a correspond- 
ence does not exist. 
In the introductory article of this series,! in discussing the 
figures of the wings of a nymph of Nemoura, we called atten- 
tion to the fact that the tracheæ in the wings of that insect 
extend in straight lines or in gentle curves, while in some cases 
the corresponding veins are much more angular; and we 
offered the following explanation of this phenomenon: 
It is evident from this that in the perfecting of a wing as an organ of 
flight the position of a vein in the adult may become quite different from 
that of the corresponding trachea of the immature form. In other words, 
although there is no doubt that the courses of the principal wing-veins of 
a A ACO COIL 
Fre. 46 — Wings of a pupa of Tremex. 
primitive insects were determined by the position of the principal trachee of 
the wings, the wing-veins have been more or less modified to meet the needs 
of adult life; while at the same time the trachez of the immature wing, serv- 
ing the purpose of respiration, and lying more or less free within the wing- 
Sac, have not been forced to follow closely the changes in the cuticular 
thickenings of that sac. 
In the Hymenoptera, as we have shown, the courses of the 
branches of the forked veins, in those forms where they have 
been preserved, have been so modified that these branches 
extend more or less transversely, making sharp angles with the 
main stems. It is not strange, therefore, that the tracheæ of 
the wings of the pupa lying free within the wing-sac, have not 
followed these changes. 
1 American Naturalist, vol. xxxii, January, 1898, p. 47. 
