516 THE BUTTERFLIES OF NEW ENGLAND. 



patterns become most complicated, where, indeed, we should naturally 

 expect that ornamentation would be least restrained by such limitations. 

 The rod-like veins of the wing are often completely concealed beneath the 

 downy covering of scales, and yet there is scarcely a spot in the wing of 

 any butterfly whose precise position is not fixed by the nearest veins. 

 This, however, is a very imperfect statement of the facts ; to consider 

 them fairly we must recall the general structure of the wings in butter- 

 flies. These consist, as explained more fully in the Introduction to this 

 work, of a thin double membrane supported by tubular rods, which extend 

 between them and diverge somewhat like the rods of a fan. In butterflies, 

 the number and distribution of the main rods or veins are essentially the 

 same in the front and hind wings, although the wings themselves diifer 

 greatly in shape. Omitting details, there is a single unbranched vein in 

 front and another behind ; while between these are two others, both 

 branched, of which the front one (the second vein of the wing) throws out 

 branches on both sides and the other only behind. This distribution of the 

 veins may, for our purpose, be considered as dividing the wing longitudi- 

 nally into four separate areas, each occupied by a distinct vein with its 

 branches. The principal diiference between the two wings is found in the 

 branches of the second vein ; in the front wing the anterior branches are 

 numerous and most of them run to the front border of the wing ; this arrange- 

 ment is plainly for greater strength, the front edge of the fore wings having 

 to bear the brunt of flight, while the front edge of the hind pair requires no 

 such special provision, these wings in flight being practically a part of the 

 front pair ; and they therefore have only a single front branch to the sec- 

 ond vein terminating on the outer margin. 



Notwithstanding these great differences, but in harmony with the fun- 

 damental idea in articulated animals that similar parts on successive rings 

 should have similar structure, the markings of the two wings harmonize 

 even to a greater extent than appears at first glance ; for although there 

 is a distinct tendency toward symmetrical repetition of markings upon the 

 front and hind wings of a butterfly, this symmetry is not absolute, being 

 subordinated to the distribution of the veins, and this again to the diverse 

 needs of the two wings. The distribution of spots on these wings may 

 therefore appear very different, when in reality tliey hold the same posi- 

 tion on both, relative to the structure. 



The number of instances in Avhich similar markings appear in the same 

 areas of the two wings, and in the same relative position in those areas, is 

 far too common to be a mere coincidence ; it is most readily traced in the 

 disposition of ocelli, which are very apt to be similar in size and perfec- 

 tion and to be situated between the same branches of homologous veins. 

 As one of a thousand examples of this kind, the peacock butterfly may 

 again be cited. On the front wing of all the butterflies of this type, the 



