GEOGRAPHICAL DISTRIBUTION. 261 



thirty species, or less than four tenths of one per 

 cent of the family, are found in the Old World, 

 and of the American species ninety-seven per 

 cent are confined to the tropics. Only six hum- 

 ming-birds, and similarly but seven Erycinids, are 

 known within the limits of the United States. 



All the families of butterflies are infinitely rich- 

 er in specific forms within the tropics than in the 

 temperate zones, and the Gossamer- winged butter- 

 flies and the Skippers much more richly in the 

 New than in the Old World. The highest fam- 

 ily, or Brush-footed butterflies, is perhaps more 

 numerous than any of the others, and though, like 

 them, it reaches its maximum of development 

 within the tropics, its numerical superiority is 

 most evident in temperate zones, and especially in 

 the north temperate region of the Old World, 

 where its numbers equal those of all the other 

 families combined. 



In this respect we shall find a great difference 

 between the European and the eastern North 

 American butterflies. Writers, in comparing the 

 insects of these two regions, have usually called 

 attention to their similarity ; and since these 

 regions are embraced between the same isothermal 

 lines and nourish the same cereals, we should 

 naturally look for a great resemblance. But if 

 we omit from each the extreme southern species 

 we shall find, first, that eastern America is poorer 



