No. 376. THE WINGS OF INSECTS. 2 
45 
sector two-branched and the vein as a whole three-branched, as 
in Nemoura and in Psocus. But in these cases the intermediate 
branch of the radius arises from the posterior one of the three; 
in Cicada, on the other hand, the intermediate branch arises 
from the anterior one of the three (Fig. 14). 
It was not till we succeeded in obtaining a very young nymph 
of Cicada that this question was definitely settled. In the fore 
wing of this nymph (Fig. 15) the radial trachea is five-branched; 
and the only departure from the typical mode of branching is 
Fic. 15.— Cicada, fore wing, young nymph. 
that the branch which corresponds to vein Æ: coalesces for a 
short distance with the one corresponding to the anterior half 
of the radial sector. 
It will be observed that in this part of the wing the subcostal 
trachea closely approaches the radial. This crowding of the 
radial trachea by the subcostal is doubtless the explanation of 
the pushing outward of the point of separation of the trachea 
Rr and of the complete atrophy of this trachea in the later 
stages of this insect, which results in the non-development of 
vein Ax. 
We have discussed this matter at some length, not merely to 
show the close correspondence of the tracheation of the wing 
of the young nymph to our hypothetical type, but also to point 
out the course by which has been reached one of the most 
characteristic features of the venation of the wings of Hemip- 
tera, that is, the complete absence of vein Ax. 
