^^^'^ THE NEW EVOLUTION '^^'^ 



takes place as rapidly, or almost as rapidly, as it does 

 in other butterflies. 



In very many butterflies mating takes place, or may 

 take place, as soon as the wings are dry. In some 

 species the males may be seen fluttering about the 

 female chrysalids. In a few hair-streaks the full 

 grown caterpillars exhibit strong sex attraction, and 

 commonly form their chrysalids in pairs, a smaller 

 male just behind a larger female. 



Reviewing the peculiarities of species as just given 

 we cannot fail to sense a temporary equilibrium. 

 Some species are held in narrow bounds by the opera- 

 tion of internal or external forces. They vary only 

 very slightly, or their geographical range is very 

 limited. Others in one portion of their range are 

 held in narrow bounds, but elsewhere are very vari- 

 able. This variation may be correlated with a shift- 

 ing of the bounds between which life is possible from 

 season to season or from one region to another, or it 

 may be correlated with a local separation of the limits 

 between which the species can exist. 



The most striking feature of this variation which 

 we see within the species is that it is wholly, mainly, 

 or at least largely, discontinuous, that is, the several 

 forms do not intergrade, or if they do intergrade, 

 inter grades are rare. A striking example of the com- 

 plete absence of intergrades between very different 

 alternative forms is seen in our common eastern angle- 

 wings. Parents of one form will produce the same 

 form, or the other form, or both forms, but never 

 intergrades. 



[14^] 



