No. 578] MULTIPLE ALLELOMORPHS 89 



given rise to black, chocolate and albino varieties of rab- 

 bits and other rodents, but a hypothesis of this sort will 

 not fit the present case. No factorial loss can be detected, 

 but only a change in that genetic factor which has been 

 called the agouti or gray factor. Under the influence of 

 this factor, what would otherwise be a black variety be- 

 comes gray, and what would otherwise be sooty yellow 

 ("tortoise" of the fanciers) becomes clear yellow ("fawn" 

 of the fanciers). This same factor converts chocolate 

 into cinnamon (Punnett, 1912). In every way. accord- 

 ingly, its influence on the coloration of rabbits is similar 

 to that of the agouti factor in guinea-pigs and mice. 



ButinmiceCuenot (1909) showed that the agouti factor 

 may assume three distinct forms allelomorphic to each 

 other, the effects of which are seen respectively in gray, 

 light-bellied gray, and in yellow mice. Entire absence of 

 agouti marking from the fur (non-agouti) forms a fourth 

 allelomorph in the series. 



In guinea-pigs the agouti factor assumes two alterna- 

 tive conditions, the effects of which are seen in ordinary 

 (light-bellied) agoutis and in agoutis with "ticked" bel- 

 lies, respectively (Detlefsen, 1914). These two conditions 

 correspond closely in appearance and in order of domi- 

 nance to the light-bellied gray and the ordinary gray of 

 mice, the former being dominant in both cases. Non- 

 agouti is an allelomorph to both, as in mice. 



The peculiarity of the agouti seen in black-and-tan rab- 

 bits is that it produces less extensive ticking of the fur 

 than does ordinary agouti. In a typical black-and-tan 

 rabbit the light-colored (yellowish) bands on the hairs, 

 which constitute the "ticking," occur only sparingly on 

 the sides of the body, and not at all on the back or the 

 head. But the under side of the body, including the 

 throat and under surface of the tail, are light (yellowish 

 or whitish) and the back of the neck and inside of the ears 

 bear reddish or yellowish pigment, as in gray rabbits. 

 The typical black-and-tan rabbit of the fanciers has very 

 intense pigmentation which deepens the shade of the 

 "tan" (yellow) found on belly, sides, etc. But this inten- 



