Vill 
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 isiands, 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 Indic and the Pacific, these differently 
