GRADATION OF SPECIES. 187 



slightly grey on the back, and that between these 

 nearly white animals and those of the dark grey 

 Ovis fannini type, every grade of coloration is 

 to be found. 



I am inclined to think that when a series of 

 specimens of the wild sheep from every moun- 

 tain range in Alaska, the Yukon territory and 

 Northern British Columbia has been procured, 

 it will be found that Ovis kenaiensis — pure 

 white all over — ^grades into Ovis cZaiZz-— pure 

 white with a black tail — Ovis dalli into Ovis 

 fannini, and Ovis fannini into Ovis stonei. 



Furthermore, I think that it will be proved 

 that all these races of shee^D inhabiting the 

 mountain ranges of the extreme north-western 

 portion of the North American Continent, are 

 far more nearly related to Ovis nivicola, the 

 Asiatic race of wild sheep inhabiting Kam- 

 chatka, than they are to the rocky mountain 

 bighorn {Ovis canadensis) and its near allies, 

 Ovis nelsoni and Ovis mexicanus. These latter 

 are probably the descendants of a species of 

 wild sheep, which came from Asia into North 

 America, at an earlier period of the world's 



