78 



THE AMERICAN NATURALIST [Vol. XLVIII 



dominant "English" spotting in rabbits but also agrees 

 that, in the case of mice, there is no criterion to enable one 

 to distinguish somatically between the dominant and re- 

 cessive forms. This, of course, is not the case in rabbits 

 where the "English" pattern differs visibly from the 

 "Dutch" spotting, which Hurst (1905) found to be re- 

 cessive to self. Bateson also considers that the case of 

 dominant spotting in mice, reported by Miss Durham, is 

 the result of a different spotting factor from that pro- 

 ducing recessive spotting. 



In terms of the presence and absence hypothesis this 

 means that the dominant form possesses a factor for re- 

 striction of pigmentation ivhich self forms lack. This 

 fact becomes of interest when Miss Durham's experi- 

 mental results are closely examined. 



In the race which gave rise to the dominant spotting 

 the following conditions are seen. 



A sooty yellow spotted mouse of unknown origin was 

 crossed with a black-eyed white (spotted) animal (of 

 At lee's strain). Among other progeny was obtained a 

 black-eyed white mouse with "agouti ears." This 

 mouse, No. 21 (spotted), was crossed with an albino (car- 

 rying chocolate), No. 35, and gave among its progeny No. 

 69, a black self mouse. This black animal, No. 69 was 

 crossed with an albino (carrying chocolate), No. 34, and 

 from these two individuals came the dominant spotted 



Now inasmuch as No. 34 and No. 35, the albinos, were 

 not supposed to carry spotting, the dominant spotting 

 must be considered- as probably coming from No. 69, a 

 black self animal. We know that this animal must carry 

 spotting as a recessive character since its parent, No. 21, 

 was spotted. 



If, therefore, this animal was the progenitor of the 

 dominant spotted race, and if he carried a recessive spot- 

 ting, as it seems certain he did, we must suppose that one 

 of three things has happened to the recessive spotting 

 which he carried. 



