No. 391.] THE WINGS OF INSECTS. 581 
in all other insects we have studied, the two groups are con- 
nected and the media is either joined to the cubito-anal group 
or arises from the transverse basal trachea. No one will hesitate 
to believe that the Plecoptera and the Blattidze are the ones 
more likely to have retained the more primitive structure. 
(2) We have previously shown?! that in a Cicada nymph one- 
third grown the medial trachea springs from the transverse basal 
trachea midway between the radial and the cubital trachez, while 
in the grown nymph it has reached the cubital trachea. In most 
insects of which we have had nymphs of various ages we have 
observed the same direction of migration; never any migration 
in the opposite direction. 
From this it follows that, in arranging the orders of winged 
insects in an ascending series, if we take into account only the 
structure of the wings, the Plecoptera should be placed first ; for 
this order, as a whole, retains the primitive condition of the 
basal connections of the wing trachez. Next to this in degree 
of divergence from the primitive wing type stand the Orthop- 
tera, with the Blattidz the lowest of the series of orthopterous 
families ; for in this family alone is the primitive condition of 
the basal connections of the wing trachez retained. 
In this connection attention should be called to the striking 
similarity of the anal area of the hind wings in the Orthoptera 
and in the Plecoptera ; in both cases the fanlike portion is sup- 
ported by the second and third anal veins, while the first anal 
vein remains simple. 
An understanding of the nature of the changes that are tak- 
ing place in the basal connections of the wing trachez renders 
this region of the wing a very instructive one. Let us examine 
again the figures herewith given: In the wing of a cockroach, 
represented by Fig. 80, the primitive type is retained, the medial 
trachea is a member of the costo-radial group, and there is no 
transverse basal trachea; while in the wings represented by 
Fig. 74 the basal trachea is well developed, and the medial 
trachea has begun its migration toward the cubito-anal group, 
but it still arises from the basal trachea. In all other forms 
here figured the base of the medial trachea has nearly or quite 
1 American Naturalist, vol. xxxii, p. 249. 
