MOULT AND REGENERATION OF PELAGE IN MICE 91 



evident, so he believed, that light played an important role in the 

 production of pigment in the skin of the depilated surfaces. On 

 the margins of the depilated areas, shaded by the surrounding fur, 

 the regenerated hair was found to be white, while that in the 

 partially shaded region was less intensely pigmented than the 

 fully exposed central area. Furthermore, he describes having 

 obtained hairs of the banded or agouti type by exposing the 

 denuded skin to light at certain intervals only. 



The experiments were repeated on a number of other rodents 

 with negative results. Nevertheless, Schultz suggests that the 

 differential coloration of the dorsal and ventral surfaces char- 

 acteristic of many mammals may be due largely to differences in 

 illumination. 



While my own investigations have not as yet been carried far 

 enough to warrant the formulation of an alternative hypothesis, 

 it nevertheless appears obvious that the theories advanced by 

 Dwight and Schultz are inadequate to account for some of the 

 phenomena observed in the moults and color patterns of mammals. 



Dwight's theory of the correlation between the distribution of 

 peripheral blood-vessels, and the points of origin and the sequence 

 of moult on different parts of the body of birds does not appear to 

 be applicable in the case of mice. We should scarcely expect to 

 find differences in the arrangement of superficial blood-vessels 

 sufficient to account for the differences in points of origin of the 

 moult observed in species of the same genus. But, more than this, 

 the fact that, in regeneration following removal of pelage, the 

 normal sequence is so markedly modified speaks against this 

 hypothesis. 



In no mammal are the differences in coloration of the dorsal 

 and ventral surfaces more marked, nor are the two regions more 

 sharply delimited than in some of the species of Peromyscus. 

 The sharpest contrast is seen on the tail. 



Whatever the role of light may have been in the evolution of 

 this color pattern, it appears to be a negligible factor in its 

 ontogenetic development. Since these animals are mainly 

 crepuscular or nocturnal in habit, the growth of the hair occurs 

 in. diffuse light. Differences in illumination of the dorsal and 



