134 
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 : — 
o o 
