No. 635] 



WHITE SPOTTING IN MICE 



467 



characterized only by a small white spot between the 

 eyes was also removed from the continuous series by 

 the work of Little (1917). This variation was apparently 

 heritable, although subect to some variability in expres- 

 sion. Two types of piebald spotting, one with more and 

 one with less white were likewise indicated in Little's 

 data. He regarded these differences as possibly due to 

 two distinct modifying factors of the piebald gene. In 

 addition, crosses of black-eyed white with self-colored 

 mice had produced two new spotted types, one with more 

 and one with less white. The continuous series of 

 spotted forms has thus been broken up on the basis of 

 amount and distribution of spotting into a large number 

 of fairly distinct types, two of them due to genes the in- 

 heritance of which is known. The process of resolution 

 has not reached its end yet, for a great deal of variabil- 

 ity exists within the various types, and the resolution of 

 these variations into still more sub-types is possible. 

 The specific objects of this study are to redefine the 

 ranges of the main types of spotting in the light of in- 

 creased data; (2) to find out, if possible, whether the 

 conditions of spotting in the sub-types are due to dif- 

 ferent combinations of the main genes or to distinct 

 genes which modify the expression of the main genes. 



spectively as black-eyed white and piebald. Little at 

 first described black-eyed whites as spotted mice which 

 were 95 per cent, or more white dorsally, later extending 

 this limit to include mice which are 80 per cent, or more 

 white dorsallv. Certain yellow black-eyed whites were 

 described by Little (1917) as exhibiting as little as 60 

 per cent, of white in the dorsal surface. Evidence will 

 be presented later to show that the range of black-eyed 



Piebalds are much darker, i.e., have less white spot- 

 ting than black-eyed whites. The piebalds born in my 

 experiments have, with one or two exceptions, been less 

 than 50 per cent, white dorsally with belly spotting rang- 



