78 



John Henry Comstock 



vin 



of the Geo- 

 faint indica- 

 of costa ex- 



backwards and become consolidated with the subcosta. A 

 good iUustration of this is presented by the European genus 

 Zygcena (Fig. 19). Here the costa and subcosta are distinct 

 for a considerable distance, but become united into a single 

 vein. 



It will be observed that the basal portion of costa extends 



like a cross vein and forms a 

 strong support for the frenulum. 

 This part of costa is sometimes 

 preserved when the remaining 

 part is wanting. See figure of 

 Castnia (Fig. 15;. 

 In most genera 

 metridse there is a 

 tion of a remnant 

 tending from the humeral angle, 

 at the base of the frenulum, to 

 the subcosta, which is strongl)' 

 angulated The same thing is 

 shown in Eiiphanessa, (Figs. 

 20, 21), which is probably a 

 Geometrid genus. 

 In many of the Psychidse a remnant of costa is preserved 

 (Figs. 22, 23). Here subcosta and radius are united for a 

 considerable distance ; then they separate and subcosta soon 

 becomes joined to costa for a short distance. In Figure 23 I 

 have represented what I believe to be the course of these 

 three veins, slightly separating them where they are coalesced. 



That part of subcosta that lies between its 

 separation from radius and its union with 

 costa appears like an oblique cross vein ; and 

 had the short spur that represents the termi- 

 nal part of costa been lacking, its true nature 

 would not have been suspected. Does not 

 this arrangement of the veins in the Psychidse 

 afford an explanation of the origin of the so- 

 called intercostal vein which is characteristic of 

 the Sphingidae ? See Figure 24. In many butterflies the base 



Fig. 20.- 



VHi 



Euphanessa. 



Fig. 21. — Hu- 

 meral angle of 

 hind wing of 

 Euphenessa. 



