No. 566] 



SPOTTING IN MICE 



75 



Miss Durham described the appearance of dominant spot- 

 ting in addition to the recessive form which she also had 

 experimented with. Such a dominant form of spotting 

 is supposed, by Bateson, to be due to the addition of some 

 factor for restriction of pigment formation in certain 

 areas. This produces a dominant form of spotting as 

 contrasted with the recessive type, which, lie holds, is due 

 merely to the loss of the "self" factor. 



Hagedoorn (1912) gives data to show that the domi- 

 nant form of spotting occurs in mice and in addition con- 

 siders it as produced by a factor analogous to that which 

 produces the dominant "English" spotting in rabbits. 



The object of this paper is to present certain evidence 

 concerning the nature of dominant and recessive spot- 

 ting in mice ; to discuss in its light the results of the above- 

 mentioned investigations; and to criticize one additional 

 point in Hagedoorn 's work with mice. 



Experimental 

 Materials. — Among several wild mice caught during 

 the spring of 1911 was one individual with a white spot 

 or "blaze" on the forehead between the eyes. This spot 

 or "blaze" was about one quarter of an inch in length 

 and one eighth of an inch in width. This mouse, an adult 

 male, was transferred to a breeding cage and a series of 

 experiments was started to determine whether the 

 "blaze" character was inherited and, if so, in what way. 

 As at that time no adult wild females were available 

 from unrelated stock the wild "blaze" male {81) was 

 crossed with a female from a dilute brown race. In 

 many ways this dilute brown race was the best possible 

 material for such a cross. It was very closely inbred, 

 being descended from a single pair of animals, progeny of 

 which had been free from out-crossing for more than a 

 year. Further, it had never given, nor has it ever given 

 in hundreds of young, an animal with the slightest trace 

 °f a spot, even on the tail, where white bands are fre- 

 quently seen in wild mice. Besides this the race was vig- 

 orous and active and yet easy to handle. 



