UNIT-CHARACTERS OF RODENTS 127 



cordlngly the most constant feature produced by this varia- 

 tion. The dominant phase of this unit-character, which is 

 regularly found in all wild races, may be designated dark-eye, 

 D; its recessive allelomorph, pink-eye, d. The recessive varia- 

 tion, pink-eye, occurs in guinea-pigs, rats, and mice. It has 

 not been reported as yet for any other mammal. (See Fig. 

 55.) 



Another unit-character variation, which affects the pig- 

 mentation of rodents, occurs also in other mammals. This 

 consists in a reduced quantity of pigment and in such a 

 clumping of the pigment granules within the air spaces of the 

 hair as to produce a dilution of the pigmentation as a whole. 

 Black under these circumstances becomes a slaty blue, choco- 

 late becomes a dull muddy brown, and yellow acquires a pale 

 washed-out appearance. The best-known examples are found 

 in blue (Maltese) cats, blue rabbits and blue mice.'^ This 

 condition may be regarded as a recessive variation of a factor 

 for intense pigmentation normally found in wild rodents. We 

 may designate this intensity factor by I, its recessive allelo- 

 morph by i (dilution). 



In guinea-pigs and rabbits there has occurred a unit-char- 

 acter variation which affects, not the color, but the length 

 and texture of the hair, which in the so-called "angora" 

 variety is long and silky. This results from a failure of the 

 hair follicle to end its activity when the hair has attained its 

 normal length. In the angora variety the hair keeps on grow- 

 ing for an indefinitely long period. The long or angora coat 

 of guinea-pigs and rabbits is a recessive character in relation 

 to normal (short) coat. We may regard a normal and domi- 

 nant character for short coat, L, as having undergone varia- 

 tion to long coat, 1. (See Figs. 36, 37, and 41.) 



Among guinea-pigs alone of rodents has occurred another 

 morphological unit-character variation of the coat, which, 

 instead of being smooth and sloping uniformly from the nose 



' This variation probably does not occur in guinea-pigs; what was at one time 

 described as a variation of this sort having proved to be an alternative form of the 

 color factor. 



