516 DR. W. A. CUNNINGTON ON THE 



it is not easy to px-ononnce, l^ut I incline to the view that at the 

 present time the disproportion --if any — is not great*. It is 

 perhaps the smaller lakes which ha.ve been less fully explored, 

 and from them, therefore, new records might be expected, 

 although their smaller size does not offer the same occasion for 

 other organisms to come to light. The larger lakes, more 

 thoroughly, but still incompletely explored, may well from their 

 very vastness contain a number of forms which have never yet 

 been observed or collected, On the whole then, while recog- 

 nising that future investigations will probably add considerably 

 to the records from the individual lakes, there is reason to believe 

 that a comparative survey of the forms at present known will 

 afford a relatively true conception of the actual state of affairs. 



It is not so easy as might at first sight appear, to give complete 

 and satisfactory lists of the animals known to inhabit the lakes 

 in question. I do not refer only to the difficulties of synonymy, 

 though these are by no means inconsiderable, particularly where 

 the Mollusca are concerned. There is also the difficulty of 

 deciding which forms should be regarded as true aquatics, since 

 there axe of necessity a number of types which are on the bordei- 

 line. While in some groups the question does not arise, in 

 others it is clearly impossible to draw a hard and fast distinction 

 between aquatic and non-aquatic species. Thus in making a 

 decision in individual cases, as was necessary for the purposes of 

 this paper, I may have excluded forms which some think should 

 have been included and vice versa. For example, I have deliber- 

 ately excluded all reference to the Aves, although the lakes are 

 well stocked with water-fowl, and similarly I omit the group 

 Insecta, notwithstanding the presence of water beetles and 

 insect larvse. Certain Oniscidaj were in the collections which I 

 brought from Nyasa and Tanganyika, the specimens having been 

 obtained from the lake shore. These truly terrestrial Isopods 

 are likewise omitted from the systematic portion of the paper, as 

 are also certain of the Oligochaete worms. All these types, while 

 moisture-loving, are obviously not to be associated with individual 

 lakes, and their precise distribution cannot have the significance 

 which attaches to the distribution of strictly aquatic species. 



There is finally the problem of deciding whether forms recorded 

 from the neighbourhood, but not actually from the waters of a 

 particular lake, are to be reckoned as belonging to that lake's 

 fauna or not. This becomes, in a sense, a matter of special 

 importance when a species is described as endemic f. Should a 

 species, for instance, be regarded as peculiar to a certain lake 



* As concerns Nyasa, tlie collections of Fiilleborn do not come only from tlie Like 

 itself, but also from adjacent ponds, swamps, and rivers. Resjarded in this light, 

 Nyasa has been more thoroughly investigated than the other lakes, where records 

 from the surrounding neighbourliood are almost unknown. 



t It is necessary to explain that I u^^e this word deliberately in the sense of 

 peculiar to a locality, i. e. not found elsewhere. While tlie word is often used with 

 this siguiticance in works on geographical distribution, its meaning is a little 

 ambiguous, and it is desirable to make the matter quite clear. 



