BUTTERFLIES OF MONTANA. 11 



Venation of the Wings. 



The thickened lines in the wings are termed the veins or nerves; and 

 their arrangement is described as the venation or neuration of the wings. 

 The thin spaces of the wings which are bounded by the veins are called 

 cells. When a cell is not completely surrounded by veins it is said to be 

 open. 



The wings of different insects vary greatly in structure, but they are 

 all more are less triangular in outline; they therefore have three 

 margins; the costal margin or costa (a b) ; the outer margin b, c, and 

 the inner margin c. a. The angle at the base of the costal margin and the 

 outer margin is the apex of the wing; and the angle between the outer 

 margin and the inner margin is the anal angle. 



The principal veins of the wings are, beginning with the one lying 

 on the costal margin, the costa, the subcosta, the radius, the media, the 

 cubitus, and the anal veins. The radius media, and cubitus are usually 

 branched and there may be several anal veins. 



In some insects there are the premedia a vein- lying between the 

 media and radia; and a postmedia lying between the media and the 

 cubitus. 



I Costa V Media VIII) 



II Subcosta VI Postmedia IX) 



III Radius VII Cubitus X) Anal 



IV Premedia et al) 



By referring to Figs. 7-12 these veins may easily be studied. As many 

 of the generic distinctions are based on the venation it is essential that 

 the student become thoroughly familiar with the locations and numbering 

 of veins of wings. 



