CONCLUSIONS. 237 



exchange of individuals from one island to another were taking place. If this 

 has taken place in the past, it should be occurring still; and the fact that it does 

 not occur now is good proof that this method of dispersal has never played a 

 part of any importance in the past. A very few species have been carried about 

 fortuitously, — whether by human agency or otherwise, it is impossible to know, 

 — but this has been the exception and not the rule. The West Indian fauna is 

 obviously one which has descended from species which formerly ranged over great 

 areas of land which, in connection with each other at various times, as well as 

 with the mainland of Central and South America, have gone to make up the area 

 we may call Antillea. 



