88 THE AMERICAN NATURALIST. (VoL. XXXII. 
The fifth principal vein is the cudztus (Cu); this vein separates 
into two branches, — cubitus-one (Cui) and cubttus-two (Cuz). 
Between the cubitus and the anal margin of the wing there 
are typically three veins; these are commonly termed the anal 
veins. We will distinguish them as the frst anal (IstA), the 
second anal (2dA), and the third anal (3?dA), respectively, the 
first anal being the one nearest to the cubitus. 
The first anal vein is generally simple; but in those orders 
where the anal area of the wing is expanded the second and 
third anal veins become separated into many branches, which 
form the supports of the fan-like portion of the wing. 
Before leaving the discussion of this hypothetical type it 
seems necessary to say a little regarding the basal connections 
of the trachez that precede the wing-veins. In what appears 
` to us to be the most generalized type, the tracheze that supply 
the wing with air arise from two distinct trunks, as shown in 
Fig. 4. The first of these trunks is a branch of the dorsal 
longitudinal trachea of the thorax; the second, of the ventral 
longitudinal trachea. This type exists in all Plecoptera that 
we have examined and in certain cockroaches; we have not 
found it elsewhere. . 
The two groups of wing-trachez thus formed may be desig- 
nated as the costo-radial group and the cubito-anal group, re- 
spectively. When the two groups are distinct, the trachea that 
precedes the media is a member of the the costo-radial group. 
In most insects there has been developed a transverse 
trachea connecting these two groups of trachez; the position 
of this transverse basal trachea of the wing is indicated in the 
figure by dotted lines. Frequently the transverse basal trachea 
is indistinguishable from the two main trunks which it connects, 
the three forming a single, continuous, transverse trachea, from 
which arise all of the wing trachez. All of the stages of this 
development have been found by us within the Orthoptera. 
When a transverse basal trachea is formed, the medial 
trachea (z.e., the trachea that precedes media) tends to migrate 
along it towards the cubito-anal group of trachez, and often 
becomes united with that group. This is well shown in certain 
Orthoptera and in the Hemiptera. In some cases the base of 
