429 
It has long since been accepted by Zoo-geographers that in the 
latest Tertiary Sumatra, Java, Borneo and the intervening islands 
must have been interconnected by land, and must have been united 
with the peninsula of Malacca, consequently also with the Asiatic 
continent. 
Only on the basis of this assumption could the faunistie unifor- 
mity of these islands be interpreted. 
The faunistic differences, which also exist, are of two kinds. 
Some of them would have been brought about also if the vast land- 
complex that extended from the West-point of Sumatra to Macassar 
Strait — the Sunda Land of MorwNGRAAFF — had never been broken 
up into the present parts, simply on account of its vast extent and 
the difference in conditions of life as the immediate result. For others 
an explanation was found in the longer or shorter duration of the 
continuity of the now separated parts. It had been assumed, for 
instance, that Java first lost its connection with Borneo and Suma- 
tra, while Sumatra remained longest united with the Asiatic continent. 
The questions how this connection by land was brought about, 
and how it was broken up afterwards, led to various hypotheses, 
which were most often ad hoc and devised by zoologists and had no 
geological foundation. It is remarkable that we do not find among 
them what we will simply call CrorL and Prnck’s theory, in which 
Prenck set forth the influence of the pleistocene ice-period on the 
ocean-level, in a comprehensive demonstration based on figures. 
Still, this theory would have afforded a sound interpretation of the 
recent changes of land and sea, required by Zoogeography for the 
facts observed. Nevertheless up to the present day it entirely escaped 
the notice of the Zoogeographers, who were engaged in the nume- 
rous problems regarding the Indo-Australian Archipelago. 
This is all the more regrettable as, conversely, the zoogeography 
of the Archipelago could have yielded evidence to substantiate the 
validity of the Crorr-Penek theory. In its turn it could then have 
shown again that it can afford data to prove geological hypotheses, 
and thus be subservient to the geologist, who is always occupied with 
problems bearing on the younger and the youngest history of our 
earth. 
The fact that the Crour-PrNekK theory meets the requirements of 
zoogeography in a masterly way, speaks well for its validity. 
But more cogent proofs of this validity might be given by zoogeo- 
graphy: one of them I will discuss here. 
The supposed subsidence of the Java- and the South China-sea of 
70 m. must also have affected the existing riversystems. That influence 
28* 
