MOULT AND REGENERATION OF PELAGE IN MICE 87 



more in evidence on the dorsal surface, appeared simultaneously 

 with the new pelage on the throat and forelimbs. 



Following this partial 'restoration after the new hair had at- 

 tained its full length there were no further signs of regeneration 

 for a period varying in different individuals from one to four 

 months. Then new hair appeared at the same time on all the 

 bare spots between the 'islands,' except on the rump, where, in 

 most cases, replacement was still incomplete when the animals 

 were last examined, five months after the operation. 



Although there appears to be no subsequent growth of the 

 body hairs, which were fully grown out at the time of the opera- 

 tion, it is worthy of note that the restoration of the vibrissae is 

 accomplished by the elongation of the identical hairs which 

 were cut. Although, as previously pointed out, there are cer- 

 tain structural differences between these two types of hairs, the 

 cause of the difference in the mode of regeneration is not at all 

 evident. 



In those individuals in which the pelage was removed from 

 one side only, the mode of replacement was essentially the same. 

 Apparently, at least within these limits, there is no correlation 

 between the rate and mode of regeneration and the size of the 

 area operated upon. 



While engaged in a study of seasonal changes in color due to 

 fading, abrasion, and other causes, it seemed highly desirable to 

 be able to compare old and new pelages on opposite sides of the 

 body of the same individual. With this object in view, a series 

 of twenty adult gambeli were trapped in worn and faded pelage, 

 a few weeks prior to the autumnal moulting season. The animals 

 were etherized and the old hair was plucked out on one side only, 

 from the dorsal median line to the lateral line and from the tip 

 of the snout posteriorly to the base of the tail. Although this 

 series of experiments will be described more fully in a later paper 

 dealing with color variations, they may be briefly mentioned here 

 in connection with the topic of regeneration. 



Replacement occurred much more rapidly than in the preceding 

 series. With but one exception, complete restoration was ac- 

 complished one month from the date of the operation (fig. 15). 



