304 F. B. SUMNER AND H. H. COLLINS 



In a previous paper several peculiarities were pointed out in 

 the microscopic appearance of the individual hairs: 1) A consid- 

 erable proportion of these are practically devoid of pigment in 

 the zone which is ordinarily yellow, the rest being normal in this 

 respect; 2) the normally dark surface pigment of the terminal 

 portion of the hairs is nearly or quite invisible; 3) in the basal 

 zone, the normal black pigment bodies are represented by groups 

 of small irregular granules or flocculent dark masses. 



While the range of variation in the pallids is not as great 

 as that of wild mice belonging to some of the natural 

 subspecies, well-marked individual differences are none the less 

 present. Some specimens have, a considerably greater amount 

 of yellow in their pelage than others, presenting a richer color 

 on this account. These are perhaps intermediate between the 

 'cinnamon' and 'cinnamon buff' of Ridgway. On the other hand, 

 specimens have appeared in which the pelage is noticeably darker 

 than the average. Between these two extremes all gradations 

 may be found. 



Even wider variations have been met with in respect to the 

 eye color of the pallid mice. In some individuals this is scarcely 

 darker than that of the eyes of true albinos. In at least two 

 specimens, on the other hand, it is nearly as dark as in normal 

 animals of the wild type, though even here careful comparison 

 reveals an undoubted difference. In the great majority the eyes 

 may be characterized as dark red. 



Whether or not these individual differences in coat color or eye 

 color are hereditary has not been determined. ^^ It is of possible 

 significance that both of the dark-eyed variants arose as 'ex- 

 tracted recessives,' after a cross with other mutants (albino and 

 yellow). One of them possesses, in addition to dark eyes, the 

 darkest pelage of any pallid yet noted. 



Aside from the occurrence of these variations of a possibly 

 genetic nature, the pallid mutation has behaved, in every respect, 

 as a simple monohybrid, recessive character. Despite the ex- 

 istence of plainly darker specimens, no true 'intermediates' or 



^^ One of the two dark-eyed individuals referred to is apparently sterile; the 

 other is not j'^et old enough for breeding purposes. 



