90 H. H. COLLINS 



secondary sexual feather, and not a feather of the juvenile type. 

 After that all further regenerations are of the sexually differen- 

 tiated feather" (p. 144). 



I have occasionally noticed the premature appearance of post- 

 juvenal pelage without operation in young mice which had lost a 

 patch of hair before the time of the regular moult, or in places 

 where apparently the juvenal hair had failed to appear. 



In the course of his rather extensive studies of the regeneration 

 of hair in rabbits, Schultz describes certain phenomena, similar 

 to those which I have found to occur in mice. 



For example, he found after shaving large patches on the dorsal 

 and ventral surfaces of an adult black and tan rabbit that 

 restoration was accomplished quickly on the ventral surface, 

 while the depilated region on the dorsum, with the exception of a 

 few 'hair islands,' remained bare for a year after the operation. 

 On the other hand, when the pelage was plucked out, restoration 

 w^as found to occur promptly at all seasons of the year and in 

 animals of different ages. 



As already pointed out in my account of the regeneration of 

 adult pelages,^ the conditions are quite similar in the case of 

 Peromyscus. In both animals the activation of the hair follicles 

 is more readily accomplished when the mechanical stimulus is 

 added to the effects of temperature upon the exposed skin. 



Schultz regards the appearance of 'hair islands' as due to 

 differences in the peripheral blood supply. Furthermore, he sees 

 in this phenomenon an evanescent manifestation of the mottled 

 color pattern, as seen, for example, in dappled gray horses. 



Another of Schultz' experiments may be briefly mentioned 

 because of its general bearing on his theory of animal coloration. 

 In the Himalayan rabbit, according to his account, when white 

 fur was plucked out it was replaced by black, although this 

 color is normally limited to the feet, ears, and muzzle. The 

 capacity for pigment formation seemed to be general and markings 

 could be produced at will on parts of the body where they never 

 occur in nature. In the^course of his experiments, it became 



' See page 87 above. 



