No. G08] MULTIPLE FACTORS IN MICE AXlJ h'ATS 459 



degree of spotting are almost certain to be quickly recog- 

 nized. 



In mice a so-called recessive ''piebald" spotting has 

 long been known. In addition a distinctly different 

 hereditary type, commonly dominant, was recorded by 

 Miss Durham (1911), and was further investigated by the 

 writer who found it to be entirely independent in inheri- 

 tance from the "piebald" type. This ''dominant" spot- 

 ting I have called the "black-eyed white" type of spot- 

 ting. Further in 1914 a third type of spotting known as 

 "blaze," consisting primarily of a white forehead spot, 

 was reported on by the writer. This type has since been 

 found to be independent of the other two in inheritance. 

 The existence of at least three genetically distinct types 

 of spotting in mice is therefore proven. It is not the 

 purpose of this paper to generalize from this fact, but' 

 to attempt to shoir tliat ranou.^^ (jyadei^ of a sliirjle type 

 of spoffnui w,ni hr m^lurr,] infn a rmss and wa>f re- 

 apprar n, lln /■', ur hark-m.ss p. ur ration, nnt rarelip 

 hut in a f-nnsldrrahlr prnp<n1i'ni of II, r annnals ohfanted. ' 

 This is a common breeding test of segregation as com- 

 pared with contamination and of alternative as compared 

 with blending inheritance. 



The races of mice used offer for the most part extremely 

 homogeneous material. The experimental animals come 

 from closely inbred races which have undoubtedly reached 

 a degree of genetic homogeneity which would lead to defi- 

 nite results in breeding, and a clearer opportunity to 

 observe segregation if it existed. The degree of white 

 spotting in the races of piebald mice used is estimated 

 by recording the approximate per cent, of the dorsal sur- 

 face which is pigmented. This method is subject, as is any 

 system of arbitrary grades, to a certain amount of error. 

 It is, however, reasonably accurate and affords a fair 

 measure of the degree of pigmentation of any individual. 



The first experiment to be recorded is a cross involving 

 an English piebald race descended from black-eyed 

 white mice (Little, 1915). These piebalds vary in the 

 extent of dorsal pigmentation from 20 to 96 per cent. It 



