NO. I THE WHITE RHINOCEROS HELLER 39 



ranged from Zululand north to the mouth of the Limpopo and then 

 northward to the Zambesi above its junction with the Shire. Here in 

 its northern range the species occurred abundantly right up to the 

 south bank of the Zambesi. Westward it extended well over through 

 the Lake Ngami country to Damaraland. The species was confined in 

 its distribution to the grassy veldt country, seldom straying into the 

 mountainous districts or high plateaus. 



The distribution of this species is almost everywhere bounded bv 

 rivers both in the north of Africa and in the south. The distribution 

 of the black rhinoceros shows the same sort of geographical barriers, 

 though only locally. In the region west of the Victoria Nyanza this 

 latter species is very abundant on the south side of the Kagera River, 

 but is not known to occur on the north side of the river. The dis- 

 tribution of rhinoceroses illustrates well what a strong aversion the 

 great beasts have to crossing large streams. This aversion must be 

 due to their fear of drowning, for they are quite immune from attack 

 by aquatic animals. 



The range of the white rhinoceros shows a remarkable case of dis- 

 continuous distribution. The distance separating the northern 

 locality, Lado, from the southern, Zambesi River, is noo miles 

 approximately. There is no evidence, geological or otherwise, to 

 show when this intermediate .territory lost its square-nosed rhinoce- 

 roses or how this separation has come about. It has doubtless taken 

 place fairly recently for there has not yet elapsed sufficient time for the 

 development of specific differences in the individuals inhabiting these 

 widely separated localities. Under the stimulus of the great climatic 

 differences of the equatorial Lado and the temperate conditions of 

 South Africa, it is to be expected that differences would soon manifest 

 themselves. All the living species of rhinoceroses are, however, old 

 fixed types which change very slowly. This is well shown by the close 

 agreement of the few fossil remains of this group from the Pliocene 

 or Pleistocene of South Africa with the same structures in the exist- 

 ing species. 1 Among the existing Asiatic species we find even more 

 remarkable cases of discontinuous distribution. The Sumatran rhi- 

 noceros, Dicerorhinus sumatrensis, is known to inhabit the Asiatic 

 mainland besides the islands of Sumatra and Borneo ; while the Javan 

 rhinoceros, Rhinoceros sondiacus, shares the mainland regions with 

 the Sumatran and in addition occurs on the island of Java. 



1 Third Rep. Geol. Surv. Natal and Zululand, 1907, p. 257 ; pi. 17, 3 figs. 

 Opsiccros simplicidens, Scott, Pleistocene. Teeth indistinguishable in shape 

 or size from Diceros bicornis. 



