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 Papilionidz tells 
exactly the same tale. Thus :— 
Sumatra has... 21 species 
Borneo ,,... 30 4, 
Sumatra ,... 21, 
Java ee, oe 
Borneo ,,...30  , 
Java gow 28° & 
i 20 sp. common to both islands; 
} 11 sp. common to both islands ; 
i 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 
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