Evolution and Taxo7iomy 



59 



Fig. 8. — Necymylacris 

 heros. 



These subcostal veins resemble ver}' closely in form and ar- 

 rangement the group of veins lying behind the cubitus, the 

 anal veins. In fact a longitudinal line drawn through the 

 center of the wing divides it into two nearly similar halves. 



It will be readily seen that this 

 type of wing is poorly fitted for active 

 flight ; the costal edge lacking the 

 strength necessary for this purpose. 

 In fact the arrangement of the veins 

 approximates that of the covering 

 piece of a tracheal gill figured above 

 (Fig. i), or that of the lateral ap- 

 pendages of the prothorax of Litkomaniis (Fig. 2). 



In Necymylacris heros (Fig. 8, II) we see the beginning of 

 a strengthening of the subcostal area. One of the subcostal 

 veins, the hindermost, becomes the principal vein of this area; 

 and most of the other subcostal veins have become consoli- 

 dated with this one, so as to appear to be branches of it. The 

 subcostal area is also relatively much narrower. 



In EctoblattiJia lesqiiereuxii (Fig. 

 9) the tendencjr of the many sub- 

 co.stal veins to become consolidated 

 into a single strong vein with branch- 

 es extending to the costa is carried 

 much farther ; and the narrowing 

 of the subcostal area is also more 

 marked. 

 The step from the form of the subcosta in Ectoblattina to 

 that presented by many modern insects is not a great one, as 

 for example, that of the fore wing of Corydalis. 



It is probable that correlated with the lengthening and nar- 

 rowing of the subcostal area in these paleozoic insects a 

 thickening of the costal edge of the wing took place, thus 

 forming the costal vein. As I have been able to study only 

 figures of these paleozoic remains, I am unable to decide at 

 what point in the development of the wing a distinct costal 

 vein was formed. It was probabl)' very early ; for Mr. Scudder 

 states that in the paleozoic insects the six principal veins 



Fig. 9. — Ectoblattina 

 lesquereuxii. 



