ILLUSTRATIVE OF NATURAL SELECTION. 193 



An examination of the relations of the species of 

 the adjacent islands, will thus enable us to correct 

 opinions formed from a mere consideration of their 

 relative positions. For example, looking at a map of 

 the archipelago, it is almost impossible to avoid the 

 idea that Java and Sumatra have been recently united; 

 their present proximity is so great, and they have 

 such an obvious resemblance in their volcanic struc- 

 ture. Yet there can be little doubt that this opinion 

 is erroneous, and that Sumatra has had a more recent 

 and more intimate connexion with Borneo than it has 

 had with Java. This is strikingly shown by the mam- 

 mals of these islands very few of the species of Java 

 and Sumatra being identical, while a considerable 

 number are common to Sumatra and Borneo. The 

 birds show a somewhat similar relationship ; and we 

 shall find that the distribution of the Papilionidas tells 

 exactly the same tale. Thus : 



Sumatra has... 21 species"! 



-g 30 20 sp. common to both islands; 



Sumatra ... 21 } 



j oo I S P* common to both islands ; 



Borneo ., ... 30 ] 



9 o 20 sp. common to both islands ; 



showing that both Sumatra and Java have a much 

 closer relationship to Borneo than they have to each 

 other a most singular and interesting result, when we 

 consider the wide separation of Borneo from them both, 

 and its very different structure. The evidence fur- 

 nished by a single group of insects would have had 



o 



