288 



SCIENCE 



[N. S. Vol. XXVI. No. 661 



point out that the same general explanation 

 which was given for the color varieties of the 

 guinea-pig is applicable likewise to the rabbit, 

 but with certain interesting differences. 



The gray coat of wild rabbits contains (1) 

 black pigment and (2) yellow pigment (3) 

 arranged upon the hair in bands, most con- 

 spicuous of which is a subapical band of yel- 

 low. The belly and under surface of the tail 

 are white, due to entire absence of pigment 

 from the terminal portions of the hair in those 

 body regions. Whenever in rabbits the fur 

 above is barred, the belly and lower surface 

 of the tail are white. Three separately herit- 

 able factors, which conform with Mendel's 

 law of heredity, are involved in the gray coat. 

 These are B, black pigment; Y, yellow pig- 

 ment, and A, the barring arrangement of the 

 pigments, which includes absence of pigment 

 from the hair-tips of the belly, as already ex- 

 plained. 



Color varieties other than gray lack one or 

 more of these factors more or less completely. 



Varieties which lack the factor A have un- 

 barred hair, in which the black and yellow 

 pigments are intimately mingled together. 

 Several different shades of color are produced 

 by such combinations of the two pigments, in 

 different proportions. In llach individuals 

 black pigment is in excess, in sooiy yellow 

 individuals yellow pigment is in excess, in 

 Hue individuals the black pigment exists in 

 a dilute form, while the yellow apparently re- 

 mains scanty in amount. But all three varie- 

 ties alike, namely, black, sooty yeUow and 

 blue, have unbarred hairs and lack the white 

 belly and tail found in wild rabbits. What 

 they all in common have lost, as compared 

 with wild rabbits, is the barring factor, A. 



Rabbits which retain this factor are readily 

 recognized by the white belly and tail. Such 

 of them as have little or no black pigment in 

 their fur are known as yellow; such as have 

 black pigment of the dilute sort found in blue 

 individuals are known as hlue-gray, and such 

 as have abundant black pigment of the ordi- 

 nary intense sort are known as gray; their 

 coat corresponds in every respect with that of 

 wild rabbits. 



Accordingly we can recognize among rab- 

 bits two parallel series of color varieties, 

 which differ only in this respect, that in one 

 series the factor A is present, while in the 

 other series it is absent. 



COLOR VARIETIES OF THE RABBIT 



Series 1 Series 2 



Gray, BYA Black, BY 



Blue-gray, B (dilute) Blue, B (dilute) Y 



YA 



White-bellied yellow, B Sooty yellow, B (traces 



(traces only) YA only) Y 



Any member of series 1 is dominant in 

 heredity over the corresponding member of 

 series 2, as might be expected; since series 

 2 is derivable from series 1 by loss of a single 

 unit-character, A. 



Within series 1, gray is dominant over blue- 

 gray as well as over white-bellied yellow, both 

 these conditions being derivable from gray by 

 modification of the black pigment, iu one case 

 in quality, in the other case in quantity. 



Similar relations exist between the corre- 

 sponding members of series 2, black being 

 dominant over its derived conditions, blue and 

 sooty yellow. 



Knowing the unit-characters borne by each 

 variety (its gametic formula), one can readily 

 predict the result of crosses between the sev- 

 eral varieties. Any cross which brings to- 

 gether the three factors, B, Y and A, will give 

 reversion, i. e., a return to the wild type of 

 coat, gray. 



Thus, grays are obtained from mating white- 

 bellied yellow or blue-gray with black. White- 

 bellied yellow mated with blue gives some- 

 times gray, sometimes blue-gray, depending 

 on the quality of the black pigment trans- 

 mitted (in traces) by the yellow parent. 



Similarly, sooty yellow mated with blue- 

 gray may give either gray or blue-gray. But 

 a mating of sooty yellow with homozygous 

 white-bellied yellow produces nothing but the 

 last named sort, since the black pigment trans- 

 mitted in traces only by both parents is in- 

 sufficient in amount to produce the gray coat. 



The foregoing statements apply, of course, 

 only to crosses between homozygous Individ- 



