176 SAVAGE SUDAN 



sense inferior whether in body or horn are exclusively 

 tawny in colour and devoid of all melanistic tendency. (2) 

 That melanism begins to appear, though co-existent with 

 the paler type, at a point some 350 or 400 miles south of 

 Khartoum say about io| North latitude; (3) That 

 the range of the blackest individuals extends from the 

 Sobat River to Lake No, or a trifle beyond that point ; 

 but that throughout this melanistic area the tawny type 

 still co-exists side by side, though the two forms, while 

 associating, appear to stand somewhat aloof from each 

 other. (4) That from Lake No westward, melanism 

 decreases and the prevalent type becomes increasingly 

 tawny, gradually merging into the so-called "Vaughan's 

 cob" of the western Bahr-el-Ghazal. The latter is 

 merely one of the regular colour-phases of the white- 

 eared cob throughout the whole of its range. 



Should these assumptions eventually prove correct, the 

 curious result follows that a species which, at the two 

 extremities of its range (only a few hundred miles), is 

 practically identical, nevertheless develops in its central 

 area a separate, or dimorphic, melanism. 



Mr Butler adds the following note: "In February 

 and March 1902, I saw on the Bahr-el-Ghazal more 

 white -eared cobs than I have ever seen since. For 

 eighty miles along that river they formed practically a 

 continuous, if scattered, herd perhaps hundreds of 

 thousands strong. All the way there was a good pro- 

 portion of black ones." 



