HOW TO KNOW THE BUTTERFLIES 



a dense clothing of scales which hides from view 

 most of the distinguishing characteristics used in 

 the classification of beetles and other compara- 

 tively naked insects, the structure of the wings 

 presents an even larger proportion of the easily 

 available criteria for separating the order into its 

 subdivisions. 



It is essential, therefore, that the student of 

 butterflies should learn at the outset the more im- 

 portant facts regarding the structure of the wings, 

 and become familiar with the terms that have 

 been applied to the different parts of a wing. 

 Fortunately it is an easy matter to do this. 



The two pairs of wings are designated as 

 the fore wings and the hind wings respectively. 

 Some writers on butterflies term the fore wines 

 the primaries, and the hind wings the secondaries. 



The wings are more or less triangular in out- 

 line ; a wing, therefore, presents three margins : 

 the costal margin, or casta (Fig. 4, a— 8) ; the outer 

 margin (Fig. 4, b-c) ; and the inner margin 

 (Fig. 4, c-d). 



The angles limiting these margins have also 

 received names. The angle at the base of the 

 costal margin (Fig. 4, a) is the humeral angle ; 

 that between the costal margin and the outer 

 margin (Fig. 4, b) is the apex of the wing ; and 



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