Evolution and Taxonomy 



as are veins IV and VI in this order, and designate this one 

 as vein XI. This view is strengthened by the fact that in 

 manjf of the Microlepidoptera with broad hind wings there is 

 a prominent fold between the two convex anal veins. This 

 fold may be looked upon as the beginning of an anal vein, 

 which is as yet undeveloped, but which if developed would 

 be vein X. 



Another important feature of Redtenbacher's system is the 

 designating of the branches of a vein by Arabic indices ap- 

 pended to the Roman numeral indicating this vein. Thus 

 the branches or radius are designated as 111^, III,, III3, etc., 



(Fig- 15)- 



While I believe that 

 we are able to trace out 

 homologies between 

 the principal veins of 

 the wings of insects of 

 the different orders, I 

 do not think it prac- 

 ticable, even if possi- 

 ble, which I doubt, to 

 liomologize the branch- 

 es of the principal veins 

 beyond the limits of a 

 single order. I have 

 not, therefore, adopted 

 in all cases Redten- 

 bacher's plan of using 

 odd indices only for 

 convex branches and 

 even indices onl}- for 

 concave Ijranches. 

 This plan will be found 

 very useful in those 

 orders {e. g. , Ephemer- 

 ida) where the fan-type 



of wing has been developed ; but in other cases {e. g. , Lepidop- 

 tera) it would merely complicate the nomenclature without ad- 



FiG. 15, — Castnia. 



