8 
THE TANGANYIKA PROBLEM. 
wants with respect to our knowledge of the African interior, 
eventually became the definitive motive for the formation of 
the second Tanganyika expedition. 
In the organisation of this new venture, Professor Ray 
Lankester took the initiative once more, and the expedition 
was finally despatched under the auspices of a committee of 
scientific men in England, which was formed by Professor 
Ray Lankester, and consisted of himself, Sir John Kirk, Sir 
William Thiselton-Dyer, Dr. Sclater, and Mr. Boulenger, 
and I had the honour to be invited to take command of 
the exploration in the spring of 1899. 
We have in this way briefly sketched the manner in 
which our knowledge that there was a Tanganyika problem 
first arose, and we have also indicated the aspect which 
this problem presented after the first Tanganyika expedi- 
tion had returned ; but, beyond this point, it would be 
inconvenient to treat the matter from a similar historical 
point of view. It will suffice to say, that on the second 
Tanganyika expedition an immense amount of notes and 
material were acquired, filling up the obvious lacunae which 
had presented themselves in any attempt to study the problem 
up to 1899. In what follows, I have dealt with the problem 
afresh, and with all the evidence that is now available. In 
the first place, I have found it necessary to consider the 
nature of fresh-water faunas in general, and to discuss the 
probabilities with respect to the origin of certain constant 
peculiarities which these faunas are found to present. 
In the next I have dealt at some length with the physical 
geography and geology of Central Africa, especially in 
relation to the fact that all the observations which have been 
accumulated point persistently to the conclusion that the 
structure and history of this portion of the continent are 
not what have hitherto been supposed. All the physical 
