VIII 



For the rest the southern boundary of the Archipelago is 

 naturally determined by the chain of islands which reaches 

 from South New Guinea in the east, to Pulu Weh, west of 

 Sumatra. 



For practical reasons we were obliged to trace an artificial 

 northern boundary to our region, as we excluded the Philip- 

 pines but included the Sulu Archipelago, which shows a great 

 affinity with Borneo. Besides this small archipelago, the northern 

 part of our region includes all the islands, which belong to 

 the Dutch East Indies. 



Zoogeographically the part of the world, now under consi- 

 deration, forms therefore an Austro-Malay or Indo-Australian 

 transition region between the Notogaea and the so-called 

 oriental region of the Arctogaea. 



This is one cause for the wealth of the fishfauna of this 

 part of the world. The great diversity in the conditions of 

 life is another, even greater cause for its being one of the 

 richest tropical faunas of the world. Its area is far above five 

 millions of square kilometers, exceeding therefore the area of 

 Europe without Russia. It consists of numerous islands, some 

 of which are amongst the largest of the world and equal France 

 in extent. These contain great rivers and swamps, volcanic 

 ranges with mountain lakes, mountains which reach above the 

 snowline and where alpine brooks and rapid torrents are 

 abundant. Often an extensive lowland lies between these 

 mountains and the sea, and here the slowly flowing rivers 

 form swamps and widely ramified estuaries, which are under 

 the influence of the tide and contain brackish water of diverse 

 salinity. 



Other islands are mere low coral islands or reefs, which just 

 emerge above the level of the sea and scarcely yield any 

 freshwater fauna. 



As great a diversity is found in the localities, where marine 

 fishes can live. About three millions and a half of the above- 

 mentioned five millions of square kilometers are covered by 

 sea. Part of it is shallow, as the Java Sea, the bottom of which 

 consists of terrigenous mud, sand or detritus of coral. On the 

 other hand the Archipelago is characterized by deep basins 

 as the Celebes- and Banda Sea, which have depths of up to 

 6500 M. and belong to the deepest seas of the world. 



Situated between the Indie and the Pacific, these differently 



