198 E VOL UTION OF TO-DA Y. 



islands which were once attached to the mainland, 

 though now widely separated from it. In these 

 islands we have practically the same conditions 

 which are found in true oceanic islands with one 

 exception. During the time that these tracts of 

 land were attached to the continents they could 

 have readily been supplied with quite an abundant 

 fauna, the larger mammals having, of course, free 

 access to them. When, therefore, they were finally 

 separated from the land, it would usually happen 

 that they would contain mammals and other ani- 

 mals which are unable to cross the water. Such 

 islands are found almost always to contain mam- 

 mals, though usually they are distinct species from 

 those on the land. This fact wellnigh proves that 

 islands are peopled from the continents. Upon any 

 other supposition what possible reason can be given 

 why such islands should have their own mammals, 

 while true oceanic islands are universally without 

 them ? We thus see that Australia is to be regarded 

 as such a fragment of the continents, which was 

 separated from Asia before true mammals appeared, 

 and contains, therefore, no true mammals. 



The examples given above form no exceptional 

 cases, for they only serve to illustrate the universal 

 law regulating island life. It was by the study of 

 hundreds of islands in all sorts of situations that 

 such a law was clearly shown ; but island life every- 

 where bears out the above conclusions. Consjder- 

 ing all cases together, it has been abundantly shown 

 that the likeness of species on islands to those on 

 the mainland depends : (i) upon the former con- 



