No. 615] INHERITANCE IN PEBOMYSCTS 



183 



entire ranges of both the races (Fig. 2). In this ease 

 there would be no real boundary between the two groups, 

 and indeed the recognition of two subspecies, rather than 

 one or three, would be quite an arbitrary procedure. 



Finally, there might be a condition, less easy to repre- 

 sent by diagrams, in which neither race was completely 

 homogeneous, each being subject to considerable local 

 variation within its own territory. Such loeal differences 

 might or might not tend to be graduated as indicated in 

 Fig. 2. Or, there might be some degree of gradation with 

 respect to certain characters (e. g., pigmentation), but 

 not with respect to others (e. g., length of appendages). 

 In such circumstances, the recognition of two "subspe- 

 cies" would depend upon the fact that the population of 

 each of the respective territories was relatively uniform, 

 and the changes encountered at the boundary relative!}! 

 abrupt. 



I am not .vet in a position to say with certainty which of 

 these possibilities is realized in the case of the species with 

 which I am dealing {Peromyscus maulrulatus) . but I 

 already have some strong evidence that the third one most 

 nearly represents the actual state of arairs. As regards 

 depth of pigmentation, we certainly find something ap- 

 proaching a graded series as we pass from the interior 

 desert regions of California toward the coast, or as we 

 pass from the coast of southern California, northward 

 into successively more humid regions, as far as Alaska. 

 But here we are dealing with a number of "subspecies." 

 I have grounds for believing, however, that similar gra- 

 dations occur within areas conventionally assigned to 

 single subspecies. 



Other questions of high theoretic importance relate to 

 the nature of the animals inhabiting the so-called "areas 

 of intergradation." Does this intermediate population 

 manifest a complete blending of all the subspecific char- 

 acters, or does it consist of a mixture of individuals, sev- 

 erally exhibiting the respective racial characters in a 

 fairly pure state, or may there be a mosaic condition more 



