70 



THE BUTTERFLY. 



of a butterfly's wing beggar all description and 

 outwit imagination, the framework of the gauze 

 on which nature has set the mosaic is of the very 

 simplest kind ; in only one group (Heliconii) 

 does it show any aberration and surprise us by 

 odd turns and unexpected meanderings of the 



veins ; and this is 

 the one group of 

 butterflies in 

 whose wings we 

 find large patches 

 of membrane de- 

 void of scales. 



The normal 

 number of veins 

 in the wings of 

 insects is six, dis- 

 posed to a certain 

 extent in pairs 

 [Fig. 74]; the 

 middle pair usu- 



FIG. 74. Veins of the wing in Danaie Plexip- ally branch to a 

 pus, nat. size. 



greater extent 



than the others, and support most of the mem- 

 brane of the wing. In butterflies the foremost 

 vein is always absent, and very commonly also 

 the hindmost, so that there are only five (often 

 only four) principal veins, rather inappropriately 

 designated costal, subcostal, median, submedian, 



