THE FAUNA OF THE INLE LAKE. 



SUMMARY OF RESULTS. 



By N. Annandale, D.Sc, F.A.S.B., Director, 

 Zoological Survey of India. 



With Plate XXVI. 



The object of this paper is to summarize what has been said in 

 previous papers in this vokime on the biology, the geographical rela- 

 tions and the origin of the fauna of the Inle Lake. 



In the time at our disposal in the Shan States Dr. Gravely and I 

 were able to study only the macroscopic fauna and I must ignore one 

 important element, namely the plancton, which I have purposely 

 omitted from consideration. At the time of our visit to the lake, in 

 early spring, floating organisms were extremely scarce and it is 

 always necessary if the plancton of fresh water is to be examined in a 

 satisfactory manner that collections should be made at all seasons. 

 We know that many of the organisms are plastic and vary greatly 

 with temperature and the like, and I am not at all sure that descrip- 

 tions of stray samples of plancton are not liable to obscure rather than 

 to elucidate the biology of a given body of water. In another direction 

 we were able to do little — in the collection of aquatic reptiles, Batrachia 

 and the more delicate insects, mainly because we were on the lake too 

 soon after winter. 



Zones of Life in the Inle Lake. 



Three zones of life can be distinguished in the Inle Lake : — a Marginal 

 Zone, an Intermediate Zone and a Central Region. 



Marginal Zone. — This is a zone of varying width that encircles the 

 lake. It owes its most peculiar features to the fact that it is covered 

 with floating islands of dead and living plants in which the dead matter 

 is undergoing a transformation into fen-peat. The process produces 

 chemical changes in the water and also in both the chemical and the 

 physical condition of the mud at the bottom, which is black, fairly 

 coherent and often malodorous. Contamination of another kind is due 

 to the villages built at the edge of the lake and on piles in the w^ater. 

 The floating islands provide abundant cover, with the floating plants on 

 the channels between them, while the villages provide food for foul- 

 feeding animals ; but the conditions prevalent in this zone are unfavour- 

 able to the more delicate forms of life and the environment is of the palu- 

 dine rather than the lacustrine type. At the two ends of the lake, and 

 to a less extent at certain places on the western shore, the ring of floating 

 islands merges gradually into a great marsh, covered with a network 

 of natural and artificial waterways and containing numerous small 

 stagnant pools. This marsh is buried in gigantic reeds, which are burnt 



