GENERAL ACCOUNT OF BUTTERFLIES 



the angle between the outer margin and the inner 

 margin (Fig. 4, c) is the anal angle. 



The wings are large membranous appendages, 

 which are thickened along certain lines. These 

 thickened lines are termed 

 the veins of the wing; and 

 their arrangement is de- 

 scribed as the venation of 

 the wings. 



A study of the wings of 

 all orders of winged insects 

 has shown that there is a 

 striking uniformity in the 

 more general features of the 

 venation of the wings of the 

 more generalized or "lower" 

 members of the different 

 orders; while in the more 

 specialized or "higher" 

 members of each order this generalized type of 

 venation is more or less modified. 



An investigation of the various ways in which 

 this generalized type of wing venation has been 

 modified and of the varying degrees of these 

 modifications has contributed much to our knowl- 

 edge of the relationships of the different groups 

 of insects. 



Fig. 



4. — Margins and an- 

 gles of a wing. 



