184 Wisco7isin Academy of Sciences^ Arts, and Letters. 



part of the abyssal fauna is descended from littoral forms which 

 have gradually moved into deep water, and have been modified 

 to suit their new environment. All the abyssal fauna of the 

 Swiss lakes is supposed to be of this character. 



What I have said thus far applies almost exclusively to lakes 

 of the temperate zones, for it is there that lakes exist in the 

 greatest numbers, and it is upon such lakes that most of the 

 work of investigation has been done. But there are lakes in 

 warmer climates, and we may expect that a thorough study of 

 them will give us much that is new and interesting. A striking 

 example of the extraordinary interest that may be attached to 

 such lakes as Lake Tanganyika in Africa. Some years ago it 

 was reported that a jelly fish was abundant in its waters. This 

 excited the curiosity of zoologists, for the medusa is a marine 

 form, and very rarely is found in fresh water, the most noted 

 case being of the one found in the basin in Kegent's Park, which 

 is supposed to have been brought with plants from some tropical 

 country. The medusa of Tanganyika is one of four jelly fish 

 known to live in fresh water, and the other examples are very 

 rare. A special expedition was organized to make an explora- 

 tion of Lake Tanganyika, and although this work was very im- 

 perfectly done, the results appear to be of great interest. Along 

 with the ordinarv lacustrine fresh-water fauna there is a fauna 

 of marine origin, but this marine fauna is not closely related to 

 modern forms. It does, apparently, closely resemble Jurassic 

 forms. Indeed, it is said that were some of the forms referred 

 to a paleontologist, he would not hesitate to say that they be- 

 longed to Jurassic times. Have we here, then, a "fauna relicta" 

 which dates back to Jurassic times ? It is too early to answer 

 this question with any certainty, both because of our imperfect 

 knowledge of the fauna of Lake Tanganyika, and because of our 

 great ignorance of the geology of that part of Africa. But the 

 mere possibility that this may be true is startling, and should 

 incite scientists to a thorough study of the fauna and flora of 

 Lake Tanganyika and the other lakes of Central Africa. So far 

 as explorations have gone this "halolimnic" fauna as it has been 

 named, is peculiar to Lake Tanganyika, but we may expect to 

 find more or less of it in other lakes. 



