INTRODUCTION. 



Commencing with the costa, we first find a single nervure 

 (a) running from the base, and entering the costa. It is called 

 the costal nervure, and differs much in length in different 

 Butterflies. It is never branched at the extremity, but some- 

 times, as in the genus Archonias, in the Pieridce, the first sub- 

 costal nervule unites with it. The costal nervure is much more 

 strongly developed on the hind- wings than on the fore-wings; 

 and at the base of the hind-wings it throws up a short branch 

 in many of the larger Butterflies (not shown in our figure) 

 which, v hen present, often encloses a space at the base of the 

 wing. This nervure is called the " pre-costal nervure." 



Next to the costal nervure comes the sub-costal nervure, 

 which is generally five-branched on the fore-wings (^. i, 2, 3, 4, 

 5). These are sometimes called branches of the sub-costal ner- 

 vure, and sometimes sub-costal nervules. As already mentioned, 

 the first sub-costal nervule sometimes unites with the costal 

 nervure towards its extremity. There are generally five sub- 

 costal nervules on the fore-wings, but in many genera of Butter- 

 flies there are only fcur, and sometimes only three. The 

 position where these nervules branch off, their curvature, and 

 the points at which they enter the costa, or the neighbourhood 

 of the apex of the wing, are of great importance in the classifi, 

 cation of genera. The first two, or the first three, are often 

 sub-parallel ; in Synchloe^ the first two approximate so much 

 that they are sometimes united in the middle. On the hind- 

 wings the sub-costal nervure divides into two branches only. 



Under the sub-costal nervure is a wide open space usually 

 extending from the base to the middle of the wing, or even 

 further. This is called the discoidal cell (AD), and from it two 

 nervules run to the hind-margin on the fore-wings, and one on 

 the hind-wings. These are called radial or discoidal nervules 

 (cc\ and are distinguished as the first and second, or the upper 

 and lower. The upper radial nervule is sometimes united to the 



