IN COLORING AND STRUCTURE. 197 



of butterflies, the differences between the sexes 

 almost invariably occur upon the upper surface, 

 and generally upon the front wing only ; it occa- 

 sionally happens that there is a slight difference 

 in the general tone of color on the under surface 

 of both sexes, corresponding to what appears 

 above. Diana is an extreme example of this ; 

 but it rarely affects the markings of the wings ; 

 these are invariably similar, almost precisely sim- 

 ilar, in both sexes, no matter what marvellous 

 pictures nature may have drawn with her colors. 

 The differences upon the upper surface, however, 

 and especially upon the front wings, are, as we 

 have seen, often conspicuous and very curious. 

 It is hardly necessary to call attention to the fact 

 that in moths the markings of the wings are 

 almost entirely confined to the upper surface, and 

 especially to that of the front wings, which in 

 these lower groups usually cover the hind wings 

 when in repose. This subject, however, will be 

 more fully discussed in the next chapter. 



Sexual dimorphism shows itself in the legs in 

 the proportional length of the different pairs in 

 the two sexes, in the special development of cer- 

 tain joints, in the appendages and clothing. The 

 appendages we will not now consider, as it will be 

 necessary, in discussing the classification of butter- 

 flies, to enter into details concerning them ; and 

 we shall then point out how striking the antigeny 



