WILD SHEEP OF ASIA AND AMERICA 297 



west, " there is no area in which the colour of the 

 sheep is uniform." 



Commenting upon this, Dr. Allen' observes 

 that "the facts of intergradation are thus forcibly 

 and clearly presented — an intergradation continuous 

 and gradual from one extreme phase to the other 

 through a vast expanse of country. The cause of 

 this extensive and gradual merging of these two 

 widely diverse colour-types of sheep is not so easily 

 demonstrable. Has it resulted from interbreeding 

 or is it due to environment ? Mr. Sheldon favours 

 the former hypothesis, but admits the possibility of 

 its having been ' produced by subtle and indeter- 

 minate changes of environment to a much greater 

 extent than the facts seem to me to warrant.' " 



In an article by Mr. George Shiras in The 

 National Geographic Magazine for May 191 2 on 

 the game animals of the Kenai Peninsula, Alaska, 

 the remarkable fact is recorded that the white sheep 

 invariably slakes its thirst by eating snow, and when 

 feeding in a well-watered pasture, always resorts 

 to a snow-patch for moisture. 



On the Asiatic side of Bering Strait the bighorn 

 is represented in Kamchatka by a race {O. c. 

 nivicola) nearly related to the thin-horned American 

 types, but with still shorter, blunter, and more 

 thickly haired ears, a shorter face, a longer coat, 

 and a comparatively small white rump-patch ; its 



' Science, New York, ser. 2, vol. xxxv. p. 105, 1912. 



