THE FAUNA OF THE GREAT AFRICAN 



LAKES. 



IT has been known for some years from the character of 

 the shells of the Gastropods that have been brought 

 back by travellers and missionaries from the interior of 

 Africa that the great lakes of this continent contain animals 

 which are quite unlike anything existing in the true lacus- 

 trine faunas from other quarters of the earth. At the same 

 time these lakes are so remotely inland, and so greatly ele- 

 vated above the surface of the sea, that all possibility seems 

 to be precluded of animals such as deep-water gastropods 

 and jelly-fish being either carried into them through the air 

 or making their way up the rivers which run out of them to 

 the sea. To determine the nature and affinities of these 

 animals, and to account, if possible, for their presence in the 

 great African lakes, was the object of a recent expedition 

 which I made to the interior, the ultimate destination of 

 which was Lake Tanganyika. I was, however, enabled 

 while en 7'oiite, through the exceptional facilities given to me 

 by Sir Harry Johnston, to spend some time upon, and to 

 become acquainted with, the physiographical characters and 

 the faunas of both Lake Shirwa and Nyassa. 



The discovery of the Tanganyika fresh-water jelly-fish 

 by Boehm in 1886, the character of the shells of gastropods 

 obtained by Burton and Speke, and still more those brought 

 back by the missionary Mr. Hoare from the same lake, are 

 all so remarkable in themselves that a considerable amount 

 of scientific interest has been roused concerning the real 

 nature and origin of these singular lacustrine forms. 



The mere existence of a jelly fish in Tanganyika is 

 sufficient to suggest the idea that the fauna of Tanganyika 

 must have been at some time contaminated by incursions of 

 these animals from the sea, and it is the merits of this 

 theory of marine contamination^ if I may so call it, which I 

 wish to discuss in some detail at the present time. I wish 

 more especially to call attention to the amount and character 



