420 THE AMERICAN NATURALIST. [VoL. XXXII. 
portion of the media (M) being V-shaped. No trace of the 
second branch of the cubitus remains ; and vein Cz: appears as 
a short cross-vein, extending to the anal furrow near the middle 
of its course. But the most striking modification of all is 
exhibited by vein M4 ; the tip of this vein in its migration 
towards the base of the wing has passed over an arc of nearly 
180°, so that now it extends from the point where it separates 
from vein M, directly towards the base of the wing, and joins 
the medio-cubital cross-vein. 
X. THE TRACHEATION OF THE WINGS OF HYMENOPTERA. 
In our studies of the wings of the more generalized insects 
we found a close correlation between the venation and the 
tracheation of the wings. It can be accepted as a firmly 
established fact that the courses of the wing-veins of primitive 
insects were determined by the courses of preéxisting tracheze. 
And one of the principal objects of the present investigation 
was to endeavor to settle certain questions regarding the homol- 
ogies of wing-veins by a study of the trachez that precede 
these veins. 
The importance of this method of study has been well shown 
by the results which we have obtained. But we also found 
that in the Trichoptera! there is little correlation between the 
venation and the tracheation of the wings, a remarkable reduc- 
tion of the wing-trachez having taken place. A similar reduc- 
tion of the trachez of the wings exists in most families of 
Diptera; and even when a large proportion of the trachez are 
retained, as in certain Asilids, they afford little aid in the 
determining of the homologies of the wing-veins. For this 
reason we omitted a discussion of the tracheation of the wings 
of Diptera. Again, in the Hymenoptera we find that the 
courses of the trachez cannot be depended upon for determin- 
ing the homologies of the wing-veins. But here, in the more 
generalized members of the order, we find a very complete 
system of wing-trachez ; and it is, therefore, incumbent on us 
either to point out the correspondence between the tracheæ 
1 American Naturalist, vol. xxxii, April, 1898, p. 256. 
