198 Address to the British Association 



also in the western part of Central America), he tells us, 

 rivers flow partly through savannahs, where they have under- 

 mined the light tufaceous soil, forming deep beds with high 

 precipitous banks. According to Professor Wagner, individual 

 beetles from the highlands have thus been isolated, and in 

 no longer time than has been required by the rivers to 

 undermine the loose soil of the savannah, have given rise to 

 a distinct species markedly different in form and colour. It 

 is to similar causes — migration and complete isolation — that 

 he traces the formation of distinct races of men : a formation 

 he deems no longer possible, while the wide diffusion of 

 mankind renders more and more difficult the evolution of 

 new species of animals of any kind. 



Instances which appear to support this view will readily 

 suggest themselves to the naturalist — instances, that is, of 

 forms which are both peculiar in structure and remote and 

 isolated as to their habitat.^ Thus, for example, even in the 

 group which structurally most resembles us, we have the 

 Orang confined to very limited tracts in Borneo and Sumatra, 

 and the Gorilla to a small portion of Western Africa. The 

 Proboscis Monkey is found nowhere but in Borneo, while the 

 singular ape named ' Roxellana ' (from its wonderfully ' tip- 

 tilted ' nose) is confined to the lofty and isolated mountains 

 of Moupin in Thibet. The very peculiar black ape . {Cyno- 

 pithecus) is limited to Celebes and Batchian, while the Baboon, 

 which has the baboon character of muzzle most developed, 

 was found at the extreme south of the African continent. 



Again, if we take the group of Lemur-like animals 

 (Lemuroidea) as having had their home and starting-point 



^ Isolation, it ought to be remembered, may take place as the result not 

 only of changes in inorganic nature (such as the formation of islands, and the 

 excavation of river-beds), but also by the presence of enemies in intermediate 

 tracts, by the circumstance that the food of the species is found only in 

 certain restricted localities, and by whatever other causes determine the 

 extinction of a species in a given place. 



