COLOR MUTATIONS IN MICE OF PEROMYSCUS 291 



having thought of some, at least, of the numerous hues of possible 

 experimentation which will occur so promptly to the reader. 

 In the ensuing pages the several color mutations will first 

 be discussed separately. Later, the results of crossing these 

 mutant stocks will be considered. 



THE 'YELLOW COLOR VARIETY 



The earlier history of one of the 'yellow' stocks here consid- 

 ered has been recorded in a previous paper (Sumner, '17), and 

 a description of the hair has likewise been given (Sumner, '18). 

 It is of some interest that this and five other independent out- 

 croppings of 'yellow' in our stock have all been derived from the 

 La Jolla strain of Peromyscus maniculatus gambeli. This may 

 be due in part to the fact that more of these mice have been 

 reared than those of any other local race — more, perhaps, than 

 all of the others combined — and that the chances of encounter- 

 ing such infrequent sports have thus been increased. On the 

 other hand, it should be remarked that the ancestors of the 'yel- 

 lows' were all trapped within an area of a few square miles, so 

 that the outcroppings of this character may not have been 

 wholly independent of one another. 



With the exception of a single aberrant individual,- which 

 was probably a juvenile yellow, none of this color variety have 

 been found by us among our wild stock, although we have trapped 

 at least a thousand mice of this subspecies at La Jolla. In each 

 case the yellows have appeared for the first time either in the first 

 or the second cage-born generation. We do not, however, 

 infer from this that the 'mutation' has been due to the artificial 

 conditions of captivity. The probable occurrence of at least 

 one wild yellow renders this unlikely, as also the fact that sev- 

 eral wild specimens proved to be heterozygous (according to 

 accepted standards) when mated with cage-bred yellows. 



2 Also trapped at La Jolla (Sumner, '17). 



