1898] CLASSIFICATION OF THE DAY BUTTERFLIES 91 



logically this base must be traced to the cross- vein, physiologically 

 it becomes an active portion of the branch in its new attachment. 

 All the angles of the former joining of the branch to the cross-vein, 

 soften and at length depart. Sometimes the upper branch of the 

 media is not content with this union, but becomes so greatly absorbed 

 by the radius as to be emitted from the lower stationary branch 

 of the latter, vein III5, beyond the cell, i.e., in the Pieridae and 

 Nemeobiidae. 



In the meantime what becomes of the middle branch of the 

 media, vein IVg ? It, in its turn, yields to the attraction of either 

 radius or cubitus and saves itself, ensures its perpetuity by attaching 

 itself to one of these two controlling svstems of the wincf, the cross- 

 vein which formed its base changing its relations in the same 

 manner above described. If vein IV2 stayed where it was, at the 

 centre of the cross-vein, we see that it becomes eventually destroyed, 

 as in the Lycaeni-Hesperiadae. Saving itself, in either direction, up 

 or down, it becomes preserved as a functional vein. No better 

 instance of this can be cited than that offered by the common 

 ' Skipper,' Augiadcs sylvanus.. On its forewiugs, vein IVg, still 

 keeping central, has succeeded in retaining its connection with the 

 cubitus after the disintegration of the cross-vein above its original 

 point of issuance ; and this through a transformation of the lower 

 part of the cross-vein, which latter has now assumed function and 

 appearance of the true base of the branch, here bending the base of 

 the branch down towards the cubitus. On the hindwings vein IVj 

 has failed to retain its connection, the source of supply has given 

 out with the disintegration of the cross-vein, and in consequence this 

 middle branch of the media has almost entirely vanished, through 

 degeneration, from the surface of the wing. 



To resume, the cross-vein eventually entirely melts away between 

 IY2 and IV3, or between IV^ and IVg, as the case may be, and the 

 cell opens. In this state of affairs the media, as a system, has dis- 

 appeared. Its first base, at the root of the wing, first went, and its 

 second, artificial base, the cross-vein, now goes by the board. The 

 two surviving primary veins, the radius and cubitus, become its 

 residuary legatees and receive a larger or smaller share as they have 

 induced the odd, middle branch of the three, vein IV2, to join their 

 respective systems. This process is unequally expressed in the 

 wings of all the various forms of the lepidoptera. The movement 

 is not regular, seems arrested in a number of genera at certain 

 points, but it is always displayed in the day butterflies, of which I 

 am now especially writing, and the amount of its progress is the 

 evident gauge of the specialisation of the butterfly in this direction. 

 I have called this the first direction because it seems to be more 

 important, more susceptible of use in classification, by reason of tlie 



