340 
THE TANGANYIKA PROBLEM. 
ganyika, some of the Charicinidce , and most of the 
Cichlidce , as in all probability representing the now 
scattered piscine portion of the halolimnic fauna. 
In approaching this matter we must, as I have insisted 
already, bear in mind that most fishes are active, migratory 
animals, and that, once established in the fresh-waters of 
a continent at any one point, are sure to rapidly spread 
through the water-systems of the interior, which in all 
great land-masses are often, temporarily, more or less 
connected together. Yet, in spite of this, as I have 
shown in Chapter VIII., more than half the Old World’s 
species of Cichlidae are peculiar to Tanganyika at the 
present time. 
Palaeontology is as yet silent with respect to the origin 
of this group ; but it is more than probable that its 
forerunners were once widely spread in the sea, and 
from these facts it would seem that we must draw a 
conclusion similar to the inference which we might draw 
from the distribution of blow-flies we knew to have 
emanated from maggots in a piece of rotten meat in one 
of the rooms of a house. If we found a few blow-flies in 
one of the rooms of our supposed house, and in another 
more, and in another a whole swarm, we should infer that 
the rotten meat was in that particular room. And in the 
case of the Cichlid fishes, believing their forerunners to 
have been once in the sea, but finding that in the Old 
World they are now restricted to Tanganyika, and are 
distributed more and more sparsely as we radiate over 
the Old World from this lake, we must infer that the 
sea in which they used to exist must have been in the 
neighbourhood of Tanganyika. 
Considering the distribution of the families of fish which 
are now present in Tanganyika, they are all more or less 
