354 
THE TANGANYIKA PROBLEM . 
without interest in this connection ; for the spicules of this 
genus are highly peculiar (see Chap. XV.), and are quite 
indistinguishable from the old marine genus Renieria , 
common in the Silurian epoch. There is thus obviously 
nothing in the character of the halolimnic animals which 
is opposed to the idea that they, together with the gas- 
tropods, belong to some such ancient sea-stock as the fore- 
going comparisons suggest ; while the positive ancestral 
anatomical characters possessed by the majority of the 
gastropods, by the jelly-fish and the crabs, is in exact 
accordance with this view. 
From a consideration of the matters dealt with in the 
preceding chapters, it will have been seen that along all the 
lines of investigation that have been pursued, the result 
reached is practically in every case the same. Thus an 
investigation of the geological characters of Central Africa 
showed that there was no foundation in fact for the 
Murchison hypothesis, and that there was evidence of vast 
disturbance in the region of the great lakes. It con- 
sequently showed also further, that there is no positive 
evidence of any sort or kind against the view that the 
sea at some fairly remote period may have extended as 
far as the present site of Tanganyika. The study of 
the fauna of the Great African lakes showed that there 
is a typical African fresh-water fauna common to them 
all, and that to this the peculiar halolimnic fauna of Tan- 
ganyika bears no sort of relationship, and is so to say 
superadded. So also the examination of the halolimnic 
animals themselves shows almost in every case that they 
possess the positive attributes of primitive forms, often 
directly anteceding in their structure certain modern marine 
types. In this way we arrive at the conclusion that the lake 
must have been stocked with a sea fauna very long ago ; so 
