i 3 4 THE TANGANYIKA PROBLEM. 



two Tanganyika expeditions. It will be unnecessary 

 in the present work to consider the mammalian, reptilian, 

 and amphibian vertebrates, as they are similar to those 

 contained in other African lakes, and are already quite well 

 known ; consequently, we may proceed at once to examine 

 the remaining inhabitants of the lake. In roughly surveying 

 the whole field, perhaps the most striking fact is that nearly 

 half the total number of species representing the population 

 of Tanganyika should be made up of different kinds of 

 Teleostian fishes. A fish-fauna with ioo species or there- 

 abouts, in a fresh-water lake, is extraordinary anywhere ; but 

 it is doubly strange when, as in the case of Tanganyika, we 

 find that 76 out of the 87 species which have actually been 

 discovered and described in the lake, are endemic forms ; 

 that is to say, they occur, so far as is at present known, 

 nowhere else in the world. The majority of the fishes in 

 Tanganyika are, in fact, endemic, and when we consider 

 the profusion of species which is present, this fact is 

 extremely interesting and suggestive in itself. Consider 

 for a moment in comparison the fish-fauna of Lake 

 Mwero : up to the present, only 14 species have been found 

 in it ; so also in Nyassa we find that there have been 

 recorded 41 species of fishes, in Rudolf only sixteen. 

 These facts point in themselves to what is from other 

 considerations unquestionable, i.e., that Tanganyika has 

 been practically isolated and undisturbed for, at any rate, 

 a considerable time, and the extraordinarily large number 

 of endemic forms present, can only be viewed either as the 

 result of the formation and multiplication of species through 

 natural selection and other similar causes, in the lake itself, 

 or as a survival in this lake of some old fauna which was 

 rich in such types of fishes. The 87 species of Tanganyika 

 fishes are divided among the following nine families : — 



