XXVI INTRODUCTION. 



wise so dissimilar as the HepialidcR and the Micropterygidx^ 

 into a distinct Sub-order because there is a small lobe project- 

 ing backwards from the base of the fore-wings, instead of a 

 frenulum on the hind-wings, and because the hind-wings are 

 furnished with as many nervures as the fore-wings. 



It is now becoming usual to number the nervures of the 

 fore-wings from below upwards, in the manner adopted on the 

 Continent ; and it will therefore be well to explain this system 

 more fully, and to compare it with the system which we have 

 been using in the present work. 



To begin at the lower part of the wing, then the sub- 

 median (or internal) nervures are numbered la, ib, if, c. ; 

 the median nervules, 2, 3, and 4; the discoidal nervules, 5 

 and 6 ; the branches of the sub-costal, 7 to 1 1 ; and the costal 

 nervure, 12. On the hind-wings the branches of the sub-costal 

 nervure (or the upper discoidal, and the sub-costal, if we regard 

 them in this light) are numbered 6 and 7, and the costal ner- 

 vure, 8. But as some of these nervures (especially no. 5) are 

 frequently absent, this system may easily lead to ambiguity. 



Several attempts have been made to work out the homo- 

 logies of the nervures of the wings in the different Orders of 

 Insects, but hitherto without any great success. The origin of 

 the various Orders lies too far back, and the development of the 

 wings has proceeded along such diverging lines that it is diffi- 

 cult to compare them satisfactorily. Thus, Prof. Comstock, in 

 his "Manual for the Study of Insects" (Ithaca, N.Y., 1895), 

 has attempted to trace out these analogies ; and he numbers 

 the nervures from above downwards, according to the following 

 system : 



I. Costa. 



II. Sub-costa. [Costal nervure.] 



III. Radius. [Subccstal nervure; and branches numbered 

 ill. i to III. 5.] 



