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THE AMERICAN NATURALIST [Vol. LIV 



spotting in the same animal lias been found by exper- 

 iment to be distinctly different. Our knowledge of the 

 hereditary factors and of the processes concerned with 

 the development of pigment in the coat is still too frag- 

 mentary for a satisfactory comparative exposition of 

 the nature and causes of white spotting. The need at 

 present appears rather to be for intensive experimental 

 studies of variations in the most favorable species in 

 which they occur. The white spotting of some species 

 also provides excellent material for the study of the 

 nature of genes with small quantitative effects either as 

 main or as modifying factors. As a contribution to these 

 ends the present report of experiments with white spot- 

 ting in mice is offered. 



In the house mouse the whole range of variability in 

 white spotting is found. At one extreme are black-eyed 

 whites, with pigment occurring only in the eyes; at the 

 other extremes are colored mice which have only a few 

 white hairs on forehead, feet, tail or belly. The appear- 

 ance of all possible intergrades between black-eyed 

 whites at one end of the scale and animals closely resem- 

 bling self at the other led Cuenot to suppose that all 

 spotted mice differed from self by a single main spotting 

 factor (P) which might be present in various conditions 

 represented by factors with minor effects which caused 

 the more apparent differences in amount of pigmented 

 areas. The finer details and intergrades of spotting he 

 regarded as purely somatic variations with no germinal 

 (hereditary) cause. Later, however, Little (1915) bred 

 spotted mice and classified all parents and offspring by 

 estimating the percentage relations between white and 

 colored spaces. He found that the " continuous" series 

 of spotted forms consisted of two main types. One of 

 these, black-eyed white, was characterized by a pelage 

 practically all white with dark eyes. The other, piebald, 

 was distinguished by the greater extent of pigmented 

 areas down to and including mice with only a few white 

 hairs dorsally and a small patch of white on the belly. 

 Another type of spotted mouse known as "blaze" and 



