242 THE AMERICAN NATURALIST. (VOL. XXXII. 
costal trachea is preserved for only a short distance; the sub- 
costal trachea extends far beyond the end of the forming vein; 
and for a considerable part of its course is within the light band 
that is to form the radius; the radial sector has been reduced 
to two branches; and only three branches of the media remain. 
The most striking features of this wing are the coalescence of 
media and cubitus, which is shown by the two trachez being 
R R, R 
Fic. 13. — Psocus, wings of an adult. 
closely parallel for a considerable distance within a single vein, 
and the zigzag course of media, which is easily determined by 
following the course of the medial trachea. Neither of these 
features is so well marked in the less mature wing. The first 
anal vein coalesces with cubitus at the base. The second anal 
vein has moved nearer to the margin of the wing. And the 
third anal trachea is no longer visible. 
The wings of the adult are represented by Fig. 13. A 
remarkable feature of these wings is that, although they are 
braced in every direction, there is not a single cross-vein pres- 
ent, except an arculus which is formed of the base of the media; 
the bracing is accomplished by the zigzag courses of the prin- 
