REPRESENTATIVE SPECIES. 93 



Tiicre are three explanations which might be 

 oft'erecl. First, we could assume that in all species 

 whose areas are discontinuous variation may have 

 reached its limits, but this to my mind seems 

 utterly opposed to ail the teachings of nature. 

 Secondly, the fact that the individuals in each 

 special locality or area remain homogeneous may 

 be due to their having not been isolated sufficient 

 time for any divergence of character to arise. It 

 is possible that the area of distribution has becom.e 

 discontinuous within recent time, and that provided 

 the same conditions prevail for a long period 

 variation will eventually assert itself, and end in 

 j)artial or complete segregation. Thirdly, these 

 curious cases are always open to the objection that 

 the species may ultimately be discovered in the 

 intervening area, although in many cases this con- 

 tingency is certainly a remote, if not an impossible 

 one. 



