FACTOR RELATIONS IN QUANTITATIVE INHERITANCE 187 



FIG. 88. Top row, a set of arbitrary grades used in the classification of hooded rats. 

 Middle and bottom rows, skins of rats graded as indicated by the numerals above each 

 skin. The animals +4, +4}^, +4%, being entirely dark above, are shown in ventral 

 view. (After Castle and Phillips.) 



