156 Journal New York Entomological Society. [Voi. v. 
veins are the residuary legatees of the branches of the Media, and the 
determining cause as to which shall succeed to the odd or middle branch 
lies in the habit of the insect in flight. The strengthening of the Ra¬ 
dius implies a more sailing, that of the Cubitus a more hovering flight, 
with quicker up and down movement as in the Hawk Moths. Comstock 
distinctly regards the crossvein as established after base of Media has 
disappeared to hold the branches. I do not. The crossvein appears to 
me a residue which is next attacked after the base of Media has been 
absorbed. If the middle branch refuses to follow either Radius or Cu¬ 
bitus it falls away by want of a base of supply, as in Lycczna and Hes¬ 
peria. (See “Evolution and Taxonomy,” p. 70.) The axiom ex¬ 
pressed by me i The amount of the absorption is the measure of the 
specialization , is intended to embody the leading principle which is to 
guide our pterogostic studies.* In the Pieridae alone have I found 
both positions of IV2 expressed. While in Leptidia the position on 
secondaries is cubital, in all the rest of the genera it is radial. I follow 
Comstock’s general view in considering this as here indicating dichot¬ 
omy of descent and establish upon it a subfamily division. 
To summarize the principal openings through which I have tried to 
carry the working theory of the evolution of the wings beyond what had 
been previously attained: 
1 . I try to shew that the suppression of the Media is the result of a 
continuous movement which, after absorbing the connection of the sys¬ 
tem with the base of the wing and thoracic sources of supply, next dis¬ 
integrates the crossvein and distributes the branches between Radius and 
Cubitus. It is probable that the crossvein is an old character, an 
adapted survival of a former system of crossveins. 
2. That that part of the crossvein closing the cell, and lying between 
the median branches and either Radius or Cubitus, becomes functionally 
the base of the branches in their new auxiliary position after the disin¬ 
tegration of the central or connecting portion of the crossvein. Its 
former morphological character as a portion of the crossvein becomes 
gradually lost, the angles rounded off. 
3. The absorption of the radius branches is sporadic on different 
lines of descent and is a reminiscent action of the absorption on the 
secondaries which has here already generally fully taken place and been 
* The inequality of the specializing movement has been recognized by mein 
various places: Die Saturniden, 11, etc. The correlation of flight with the portion 
of the middle branch of Media is endeavored to be established by me in the “ Tag- 
falter,” etc., pp. 4 and 5. 
