THE INHERITANCE OF FAMILY TRAITS 29 



PURE 



Fig. 9. — Distribution of pure blue eyes among Scottish boys. About 15 

 per cent of all boys have blue eyes. The relative density is indicated by depth 

 jf shading as indicated in the key at the left. A very high density (21 to 24 

 per cent) occurs in the lower Spey Valley in the northwest. This is the region 

 )f the Norse invasion which brought in much protoplasm that was defective 

 n pigmentation. The highest density (over 24 per cent) exists in the coal and 

 ron districts of East Lanarkshire and "this is probably due to the Irish immi- 

 jrants." J. Gray, 1907. 



