No. 376.] THE WINGS OF INSECTS. 249 
vein 4+5, separates from vein R2+3 very near the base of the 
wing, and coalesces with the media for a short distance, after 
which it traverses the wing as a separate vein. A result of this 
is that while the 1st cell R} of the fore wing lies beyond the 
nodal furrow, in the hind wing it reaches the base of the wing; 
and the rst cell Rs occupies a similar position. A study of the 
base of the hind wing of the recently emerged adult (Fig. 20) 
confirms these conclusions. 
Other features of interest in the hind wing are the following: 
The media is only three-branched as a rule, but in some speci- 
mens there is a small remnant of cell M2. The first and 
second anal veins are widely separate, and the third anal vein 
is forked. 
In the course of the development of the wing of Cicada there 
is an excellent illustration of the migration of the base of the 
medial trachea, which was referred to at the close of Chapter 
II. In the young nymph of Cicada (Fig. 15) the medial trachea 
arises from the transverse basal trachea midway between the 
radial and cubital tracheze. In the mature nymph (Fig. 14) the 
base of the medial trachea has reached the cubital trachea. 
In tracing the homologies of the tracheze of the wings, it is 
very important that this migration of the base of the medial 
trachea be kept in mind. For while in the more generalized 
forms where there is no basal transverse trachea (Plecoptera 
and certain Blattida) the medial trachea belongs to the costo- 
radial group of trachez, whenever a basal transverse trachea is 
present the medial trachea either arises from it or is a member 
of the cubito-anal group. The ontogeny of Cicada gives con- 
clusive evidence of this migration. In all mature nymphs of 
Hemiptera that we have examined the migration has taken 
place, the medial trachea being a member of the cubito-anal 
group. 
V. THE VENATION OF THE WINGS OF HETEROPTERA. 
In Cicada we found the most generalized condition of the 
wings that exists in the hemipterous insects that we have 
Studied, and it is hardly to be expected that a more generalized 
