INTRODUCTION. 



XL 



occasionally have an emarginatiou on the inner side, the upper 

 edge of which is often prolonged into a spur, v. 



i& 19. 



WINGS, alee. Figs. 1, 20—28. 



There are two pairs of wings, the fore wings, alee anteriores, fig. 

 20, and hind wings, alee posterior es, fig. 21, indifferently called pri- 

 maries and secondaries, or superiors and inferiors — sometimes rudi- 

 mentary or imperfect in the females, very seldom entirely wanting. 

 The primaries lie with their hind edge on the fore edge of the 

 secondaries, and cover the latter entirely in most of the nocturnal 

 moths when in a state of repose. The secondaries are often folded 

 together when at rest, and in that case usually have on the upper 

 edge near the root, a strong elastic, sometimes double hair or bris- 

 tle, which draws itself through a hook on the under side of the 

 primaries and serves to maintain or render more easy the expansion 

 of the secondaries. This is called the frenulum, fig. 21, fr. This 

 instrument is wanting in nearly all butterflies, which do not fold 

 the secondaries when at rest. 



The wings have three edges or margins, the anterior margin, 

 margo anterior, on the upper side, A, the interior margin, margo 

 interior, opposite the anterior, B, and the posterior margin or seam, 

 margo posterior or limbus, C, which is opposite the root of the 

 wing, basis, and binds the two other margins. The angle made 



"Fig. 20- Fig. 21. 



J? * 



al 



Bid 



