THE TANGANYIKA PROBLEM. 
337 
ence of the jelly-fish, the gymnolaematous, polyzoa, the 
prawns, the sponges and the gastropods which are peculiar 
to Tanganyika, along any of these lines. Yet these organ- 
isms are in Tanganyika, they are not elsewhere in the 
great lakes of the African continent ; they must have got 
into Tanganyika from some place or medium in which 
these sorts of animals habitually live ; and there is no 
place or medium in which these animals habitually live, 
except the sea. 
Along all the lines of enquiry which we have examined, 
the explanation of the existence of the halolimnic group 
in Tanganyika is beset with insuperable difficulties, first 
in one direction, then in another. But, if we leave all 
these hypothetical explanations entirely on one side, and 
follow the direct and simple evidence afforded as to the 
origin of the halolimnic animals, through the characters of 
these animals themselves, the whole difficulty vanishes at 
once. The jelly-fish, prawns, sponges and gastropods, etc., 
are at once perfectly intelligible, if we regard their presence, 
as in fact it is, indicative of the past extension of the sea 
into the African interior. 
We are, therefore, inexorably driven by the force of facts 
to view the halolimnic organisms of Tanganyika as having 
emanated from the sea ; or, to put the matter another 
way, the zoological characters of the halolimnic animals, 
and the facts of their distribution, show that the sea 
has been connected with Tanganyika in the past. 
That is to say, the characteristics of the halolimnic 
group throw light upon the past history of the African 
land-mass ; and I wish to be quite clearly under- 
stood in this connection. We have seen that there 
actually is no geological evidence which militates against 
the view that Tanganyika may have been connected with 
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