74 Johri Henry Comstock 



dia, where a remnant of the base of media still persists, vein 

 Vj is merely connected with vein III by a cross vein. But 

 in Adoneta, where the base of media of the hind wings is lost, 

 vein Vj has become consolidated with vein III for a consider- 

 able distance. It is obvious that in these respects, the loss of 

 the base of media and the extent of the coalescence of veins 

 III and V2, Adoneta is the more highly specialized of the two 

 genera. 



It often happens that after the abortion of the base of media 

 the discal cell is traversed by a more or less distinct line or 

 scar indicating the former position of this part of the vein. 

 This scar is indicated in the accompanying figure of the 

 wings of Eacles (Fig 18) by dotted lines. 



It will be observed that the branches of media are not con- 

 tinuous with the branches of this scar. There has been a 

 migration of the proximal end of the remaining portion of 

 each branch towards the vein from which it gets its supply of 

 air. Frequently there remain short stumps, projecting into 

 the discal cell from the discal cross vein, and continuous 

 with the scar, at the points where the branches formerlj' 

 emerged from the discal cell. These are indicated hy the 

 arrows in Figure 13, and are also shown in Figure 18. It 

 will be readily seen that the extent to which this migration 

 of the base of a branch has gone will serve as an indication of 

 the degree of divergence of the form from a primitive type.* 



In connection with this part of the discussion a few words 

 regarding the nature of the so called discal vein are appropri- 

 ate. It is evident that this is not a single cross vein extend- 

 ing from radius to cubitus ; but it is made up of several distinct 

 elements, and these elements may differ in different genera. 

 There is a cross vein between radius and the first branch of 

 media, and another between the third branch of media and 

 cubitus (Figs. 16, 18, c. v., c. v.). These extremes of the 

 series forming the discal vein, however, have the appearance 

 in many cases of being parts of longitudinal veins (Fig. iS) ; 



*I wish here to acknowledj^e the assistance of Miss Clelia D. 

 Mosher, who, while a student in my laboratory at Palo Alto, first 

 worked out the relation of these stumps to the branches of media. 



