OF THE MALAYAN REGION. 29 



conspicuous in insects, but is shown in some degree by the Papilionidse. The following 

 groups are either almost or entirely restricted to one portion of the Archipelago : — 

 Indo-Malayan Region. Austro-Malayan Region. 



A'bar-group. PriawMS-group. 



Coow-group. Ulysses-gTo\ji\>. 



il/acareMs-group (nearly). Erechtheus-^roni^. 



Paradoxa-group. 



Disshnilis-grou-p (nearly). 



Brookeanus-grouY). 



Leptocibcus (genus). 



The remaining groups, which range over the whole archipelago, are, in many cases, 

 insects of very powerfiil flight, or they frequent open places and the sea-beach, and are 

 thus more likely to get bloAvn from island to island. The fact that three such charac- 

 teristic groups as those of Priamus, TJli/sses, and Erechtheus are strictly limited to the 

 Australian region of the archipelago, Avhile five other groups are with equal strictness 

 confined to the Indian region, is a strong corroboration of that division which has been 

 founded almost entirely on the distribution of Mammalia and Birds. 



If the various Malayan islands have undergone recent changes of level, and if any of 

 them have been more closely united within the period of existing species than they are 

 now, we may expect to find indications of such changes in community of species between 

 islands now widely separated ; while those islands which have long remained isolated would 

 have had time to acquire peculiar forms by a slow and natural process of modification. 



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 structure. 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 mammals 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 shaU find that the group of insects we are 

 now treating of tells exactly the same tale. Thus : — 



Sumatra 21 sp. 1 



-n or. ^ 20 sp. common to both islands ; 



Borneo 29 sp. J ^ 



Sumatra 21 sp.l x . -. • i ^ 



-, ^„ \\± sp. common to both islands ; 



Java ill sp. I 



Borneo 29 sp. 



^», r 20 sp. common to both islands ; 

 Java 27 sp. ^ ^ 



showing that both Sumatra and Java have a much closer relationship to Borneo than 

 they have 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 



