1 78 THE AMERICAN NATURALIST [Vol. XL VII 



eordingly be capable of indefinite expansion without 

 constant remodeling. 



I favor Morgan's further suggestion that as new forms 

 arise through recombination of simple " mutations" these 

 be described, so far as possible, in terms of the simple 

 mutations composing them. This principle is clearly 

 illustrated in the names chosen by Morgan for the eye 

 color series of Drosophila. It is surprising how little 

 change this system necessitates in the common names 

 with which we are already familiar, for example, in the 

 mouse-color series. 



The color mutations 9 of mice with which I am person- 

 ally familiar number seven. If all of these are independ- 

 ent, i. e., not "coupled" or "associated," there should be 

 theoretically possible 127 different combinations involv- 

 ing one or more of them. A considerable proportion of 

 these combinations has been produced in my laboratory 

 in the course of the last twelve years, the earlier and 

 simpler ones by Dr. G. M. Allen or myself, the later and 

 more complex ones by Mr. Little, who has in press an 

 extensive paper dealing with his investigations. I shall 

 deal with the series as known up to 1909. The historical 

 order of appearance of the mutations is now unknown; 

 I shall place them in the alphabetical order of the sym- 

 bols used. It is also unknown whether each of them arose 

 directly from the wild type. More probably they did not, 

 but experiment shows that they might have done so, since 

 each behaves in crosses as if it had a distinct and inde- 

 pendent basis in the germ-plasm. 



Wild Type and its Seven Mutations 



1. Wild = gray. 



2. a = albino (transmitting gray in crosses). 



3. b = black. 



4. c = cinnamon. 



5. d= dilute. 



of DeVries. 



