August 30, 1907] 



SCIENCE 



289 



uals of the varieties named. In accordance 

 ■with the general principles of Mendelian in- 

 heritance, it is found in these two series that 

 any variety, which contains a dominant char- 

 acter, may be, as regards that character, either 

 homozygous or heterozygous. Thus, hetero- 

 zygous gray animals might produce any of the 

 forms included in either series; indeed, in our 

 experiments, all the forms eseept blue were so 

 obtained, and blues were obtained in the fol- 

 lowing generation from the blue-grays. 



Blue-grays, bred inter se, may, when hetero- 

 zygous, be expected to produce also blue, white- 

 bellied yellow and sooty yellow; blacks may 

 give blue, as well as sooty yellow; blues and 

 white-bellied yellows may each give sooty 

 yellow; but sooty yellow is apparently in- 

 capable of producing any other variety enu- 

 merated in either series; it is recessive with 

 respect to those varieties. 



Accordingly, as regards breeding capacity 

 {i. e., gametic formula), we may distinguish 

 six different sorts of gray rabbits, three of 

 black ones, three of blue-gray ones, two each 

 of white-bellied yellow and blue ones, but of 

 sooty yellow one sort only, if we disregard 

 qualitative differences in the traces of black 

 pigment borne by sooty yellow individuals. 

 An enumeration follows of these various 

 sorts of individuals, most of which, as will 

 be seen, have already been identified. In 

 the enumeration, B will be used for black pig- 

 ment, B' for the same in minute quantities 

 only, Y for yellow pigment and A for the 

 barring factor. 

 Qraj/ 



1. BYA ■ BYA breeds true. Found in wild rab- 

 bits and in the " Belgian hare " used in our ex- 

 periments. 



2. BYA ■ BY gives also black. This condition is 

 often found in Belgian hares supposed to be pure, 

 but really not pure as regards color characters. 

 Produced in our experiments. 



3. BYA-B (dilute) YA should give only gray 

 and blue-gray. Not certainly known. 



4. BYA ■ B ( dilute ) Y gives, in addition to 

 gray, black, blue-gray and blue. Observed except 

 as regards the production of blue young; observa- 

 tions not very extensive. 



5. BYA ■ B'YA gives, in addition to gray, white- 

 bellied yellow only. Observed. 



6. BYA ■ B'Y gives, in addition to gray, black, 

 white-bellied yellow and sooty yellow. Observed. 

 Black 



1. BY ■ BY breeds true. Known to exist. 



2. BY B (dilute) Y gives black and blue. Ob- 

 served. 



3. BY ■ B'Y gives black and sooty yellow. Ob- 

 served. 



Blue-Oray 



1. B (dilute) YA-B (dilute) YA should breed 

 true. Not yet obtained. 



2. B (dilute) YAB (dilute) T gives also blue. 

 Observed. 



3. B (dilute) YA-B'Y should give blue-gray, 

 blue, white-bellied yellow and sooty yellow. Not 

 observed. 



White-lellied Yellow 



1. B'YA ■ B'YA breeds true. Observed. 



2. B'YA ■ B'Y gives white-bellied yellow and 

 sooty yellow. Observed. 



Blue 



1. B (dilute) YB (dilute) Y should breed 

 true. Not yet certainly known. 



2. B (dilute) Y ■ B' (dilute) Y gives blue and 

 sooty yellow. Observed. 



Sooty Yellow 



B'Y ■ B'Y breeds true, so far as tested. 



All of the numerous color varieties men- 

 tioned have arisen by loss, partial or com- 

 plete, of one or more of the three independent 

 factors which contribute to the production of 

 the gray coat of wild rabbits. 



It may be of interest to compare with the 

 case of the rabbit, the evolution of color 

 varieties among guinea-pigs, mice and rats, 

 which, like the rabbit, are rodents more or 

 less completely domesticated. 



The agouti (or wild) type of coat of the 

 guinea-pig is produced by the same three fac- 

 tors as the gray coat of rabbits, viz., black 

 pigment (B), yellow pigment (F), and a bar- 

 ring factor (A). But in guinea-pigs there 

 occurs also a third pigment of a chocolate- 

 brown color, which is usually associated with 

 black pigment, but has in recent years been 

 obtained entirely separate from black pigment 

 in the variety known as " chocolate." For 

 this factor of the pigmented coat we may use 

 the symbol Br, signifying brown. The homo- 

 zygous color varieties of the guinea-pig may 

 then be designated as follows: 



