Nos. 618-619] INHERITANCE IN PEROMYSCUS 



291 



Not only are the larger color differences which distin- 

 guish these main races heritable, but certain lesser differ- 

 ences which distinguish narrowly localized sub-races have 

 been shown to be genetic characters. In a recent paper 

 (1917) I discussed an aberrant colony of "rubidas" in- 

 habiting an isolated sand-spit fronting on the ocean. 15 

 The evidence for the inheritance of these peculiarities of 

 color may now be stated somewhat more strongly than 

 was done in that paper. Upon preparing the skins of the 

 three Q l members of this sub-race, born and reared at La 

 Jolla, it was found that all three were of the aberrant 



As regards differences relating to the measurable parts, 

 certain preliminary explanations are necessary. It was 

 early found that the cage-born mice depart from the 

 wild type in certain rather striking respects. They are, 

 on the average, considerably smaller than the latter, and 

 have tails, feet and ears which are shorter not only abso- 

 lutely but relatively. In extreme cases these malforma- 

 tions may fitly be termed deformities. Not rarely, too, 

 the dorsal tail-stripe becomes so diffuse that definite out- 

 lines can no longer be distinguished. Measurements re- 

 veal the fact that this stripe becomes narrower, on the 

 average, in the cage-born animals. Furthermore, the fer- 

 tility of the captive generations is greatly reduced. 



These abnormal characteristics resulting from captiv- 

 ity are manifested much more strongly by the Eureka 

 race than by the desert one, or by the race which is native 

 to this locality (La Jolla). In fact, my original stock of 

 rubidus, consisting of over a hundred animals of the wild 

 generation, has dwindled down to one male and six fe- 

 males in the C 3 generation. In contrast to this, no diffi- 



