428 University of California Publications in Zoology. [Vou.5 
summer visitants to the Yukon district winter by the way of an 
interior route far south of the United States, even in South 
America; while corresponding species in the Sitkan district 
move south along the Pacific Coast and winter on the Pacific 
slope of Washington, Oregon, and California. This variation 
in the shape and area of the wing appears to be, therefore, more 
obviously adaptive than the melanism. 
