1!M8.] N. Annandale: Tlic Inlc Lahe. 7 



ation of peat have not been the only factors that have led to the dis- 

 appearance of water from the basins. Another cause has been the eating 

 through of limestone rocks by water rendered acid by the decay of vei>e- 

 tation. The He-Ho stream makes its way down into the lower plain 

 through an ancient limestone ridge, and it is not improbable that the 

 water may have been finally drained from the upper plain by its 

 cutting through this ridge in a comparatively short time under excep- 

 tionally favourable conditions. 



It is not surprising, therefore, to find that the fauna of the Inle Lake 

 is a very highly specialised one, differing from any other aquatic fauna 

 yet discovered. The lake is merely the last, shrunken rehc of a 

 once extensive system, the connections of which may have been greatly 

 different at different periods in its history. It has, however, been 

 isolated for a considerable time, and evolution has taken place rapidly 

 and widely. To illustrate these facts the different groups of animals 

 must be considered separately, and then the whole sunnnarized. To 

 do this is the object of the present volume. 



