478 THE AMERICAN NATURALIST [Vol. LIV 



cross black-eyed white by self. Further reference will 

 be made to these mice in the section on modifying factors. 

 In addition certain mice have appeared which exhibit 

 only a small white spot in the form of a " blaze ' ' of white 

 hairs between the eyes which may or may not be accom- 

 panied by a small belly spot. Such mice have proved to 

 be self in distinction from piebald since when mated inter 

 se they have produced 15 self-colored mice lacking any 

 spotting and 6 piebalds, indicating that both "blaze" 

 parents were selfs heterozygous for piebald. When 

 tested by crossing with pure piebalds, such "blaze" mice 

 have produced 55 selfs and 39 piebalds. Certain of the 

 selfs had a small white spot (always less than 10 per 

 cent.) ventrally, and it is possible that these may be pie- 

 balds. If so, the ratio of 1 self : 1 piebald may be more 

 closely approached, indicating that the small white dorsal 

 spot is a non-genetic imperfection of dominance occurring 

 in self mice heterozygous for piebald. None of the " self ' ' 

 progeny from crosses of blaze with piebald exhibit any 

 dorsal spotting. One other possibility is that the blaze 

 may be due to a separate gene either identical with or 

 similar to the gene which differentiated the blaze mice 

 reported by Little. The second or other segregating gen- 

 eration which is critical for determining this point has 

 not been. bred. Of course the term self should apply 

 properly only to mice which show no trace of white spot- 

 ting. Genetically it is the sum of the factors producing 

 the normal solid coat of the wild mouse and as such 

 should be always the same unless new mutations take 

 place or unless certain somatic variability exists uncon- 

 nected with a germinal cause. Sufficient data in the case 

 of the dorsal spotting of apparently self mice are not at 

 present available to decide between these alternatives. 

 In the case of the small belly spotting, as will be seen 

 later, the case is somewhat different. 



For convenience in reference the range of variability 

 of each of the several genotypes discussed above has 

 been placed in tabular form (Table I). All ranges ex- 

 cept that for piebald (line 3) have been drawn from ob- 



