ANIMAL LIFE OF THE COUNTRY. 25 



themselves to it. It would then become necessary for them to gradually quit a 

 country they once inhabited. Another of these natural changes might be the springing- 

 up and outward expansion of a new species, more able and better fitted to sustain life 

 in the country, and before which the older inhabitants would have to give way. 



When conditions such as these arise, a barrier is often put across, separating the 

 area of the former distribution of the species into two or more parts, and it is 

 conditions like these which account for the finding of a small isolated detachment 

 of some species far removed from the country inhabited by the bulk of its own kind. 

 An instance of this is found with the sassaby. The main country inhabited by this 

 species is to the south of the Zambezi River. Passing northwards it is not again met 

 with till away up by Lake Bangweolo, in which locality is found a small isolated 

 settlement. 



One can hardly credit this animal with a parallel case to the Angoni Zulus. 

 That is, that, having suffered from internal strife and determined to endure no longer 

 the tyranny of their paramount chief, a number broke off from the main body and took 

 a long trek up to another country. The only feasible explanation to offer is that at 

 one time there were sassaby distributed over the whole of the intervening country 

 from Lake Bangweolo to the Zambezi, till something occurred to drive them away 

 from the large intermediate tract. As the sassaby is a plain-loving animal, a 

 reasonable theory to offer is that there were tracts of open plain at one time more 

 or less connecting their present habitats. It must then have been the thick bush, 

 which now covers this country, gradually spreading over the land that made it 

 uninhabitable to these animals. At last the only retreats left were those great, 

 open flats to the south of Bangweolo, and which are the only large, open spaces 

 in the country. 



Another explanation, but perhaps a less likely one, is that the coming of the 

 Lichtenstein's hartebeest, an animal more suited to the intervening country, was 

 the cause of the retirement of the sassaby. 



There are similar cases of this broken distribution of species in British East Africa. 

 One of these is that of the topi, an animal closely allied to the sassaby, and of very 

 similar habits. He is found plentifully in the plains of Yubaland and the open country 

 near the coast in Tanaland. Passing westwards from there he is not again met with 

 till after the Rift valley is crossed and the shores of Lake X'ictoria are approached. 



it is true that he is screened off by dense bush which almost encircles his 

 Tanaland and Yubaland habitats, but west of this bush many plains are met with 

 that might have supported him. These are probably at too great an altitude or else 

 deficient in some particular shrubs, and so do not sutHce for his needs. 



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