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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 ioj 0 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 “Vaughans 
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.” 
