290 R. T. GUNTHER. 
things to occur. It was possible either that the amount of 
rainfall received by the lake should be less than the amount 
of water lost by evaporation, or that it should be greater. In 
the former case the lake would have gradually become salter 
and salter, or in the latter case the excess of water would 
have overflowed the banks and the water of the lake would 
have undergone a gradual process of freshening owing to the 
salt water being slowly replaced by fresh. It is possible that 
both conditions may have obtained at various periods—indeed, 
within our time the lake has been proved to be in both states 
of quiescence and of overflow. But on the whole the condition 
of overflow must have been the rule, because at the present 
day the water of the lake is described as being “ perfectly 
potable.” 
This hypothesis of the origin of the marine fauna of Lake 
Tanganyika may or may not prove to be possible when the 
geology of the region is known. It is, at any rate in the present 
state of our ignorance, a possible explanation of the presence 
of a Medusa in the lake. Should subsequent researches prove 
its untenability, it will have served its purpose if it should 
stimulate naturalists to discover but a few facts about the past 
history of the lake or to discover within its bounds members 
of other classes of the animal kingdom with marine character- 
istics, from which a new and better theory may be deduced to 
account for the remarkable and unique marine character of 
the present fauna of Lake Tanganyika. 
BIBLIOGRAPHY. 
1. Boum, R.—Vide Martens, E. yon, and R. Bohm. 
2. Brooxs, W. K.—“ The Life-history of the Hydromeduse,” ‘Mem, 
Bost. Nat. Hist. Soc.,’ vol. iii, 1886. 
8. Brooxs, W. K.— Budding in Free Meduse,” ‘Amer. Nat.,’ p. 670, 
1880. 
4, Curzon, —.—‘ Persia and the Persian Question,’ vol. i, p. 533, 
5. Guerne, Jutes pE.—“ La Méduse du Lac Tanganyika,” ‘La Nature,’ 
24th June, 18938, pp. 51, 52, 1893, 
