290 



SCIENCE 



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



COLOE VARIETIES OF THE GUINEA-PIG 



Series 1 Series 2 



Agouti, BBrTA. Black, BBrY, 



Chocolate, BrY. 

 Yellow (black-eyed). Yellow (black-eyed), 

 YA (BBr in eyes Y (BBr in eyes and 



and skin only), gives skin on'y), does not 



agouti in crosses with give agouti in crosses 



black. with black. 



Yellow ( brown-eyed ) , 

 Y (Br in eyes and 

 skin only ) . 



As in rabbits, the color varieties fall into 

 two parallel series, in one of whieb the factor 

 A is present, while in the other it is wanting. 



The chocolate variety was first obtained, in 

 the experiments under discussion, from ani- 

 mals of other colors. Later, with the kindly 

 assistance of Mr. Bateson, a chocolate male 

 was obtained in England, where the variety 

 has apparently originated recently. It is not 

 mentioned by Cumberland (see bibliography) 

 in his well-known work on the cavy. 



The brown-eyed yellow variety I have ob- 

 tained only recently in the second generation 

 (i^„) from a cross between black-eyed yellow 

 and chocolate. Its existence elsewhere is un- 

 known to me. 



We may confidently expect the production 

 by appropriate matings of two varieties which 

 will fall into series 1, opposite the newly ob- 

 tained varieties of series 2, chocolate and 

 brown-eyed yellow, from which varieties they 

 will differ only by the addition of the factor, 

 A. 



The coat pigments of mice are similar to 

 those of guinea-pigs, viz., black, brown and 

 yellow. All three are probably present to- 

 gether- in the coat of the gray house-mouse, 

 along with a barring factor, A. Loss of A 

 produces the black variety, precisely as in 

 rabbits and guinea-pigs; loss of B produces 

 the cinnamon agouti variety (a combination 

 unknown as yet in guinea-pigs, as already 

 stated) ; loss of both B and A produces, as in 

 guinea-pigs, the chocolate variety. The yel- 

 low variety, we must believe, results from the 

 suppression in the coat of both black and 

 brown pigment, but this loss-condition, curi- 

 ously enough, is dominant in crosses over the 



more inclusive combinations which contain B 

 and Br. 



Davenport (1904) and Cuenot (1906) have 

 recorded observations upon yellow mice which 

 manifestly bore the factor A, since they gave 

 reversion in crosses with black and with 

 chocolate individuals; but it is evident that 

 the yellow mice used in my own experiments 

 (Castle, 1906) lacked this factor completely, 

 for neither grays nor cinnamon agoutis were 

 obtained in crosses with black or with choco- 

 late individuals. Further, Cuenot's black- 

 eyed yellow mice were heterozygous, bearing 

 black as a recessive character; my own, like- 

 wise heterozygous, so far as tested, bore in 

 most cases chocolate as a recessive character. 

 The yellow mice of Steer (mentioned by Bate- 

 son, 1903), which gave chocolate young, were 

 evidently of this same sort. I have examined 

 the eye pigments of one of the chocolate-pro- 

 ducing yellow mice and find it to be brown, 

 as in chocolate guinea-pigs, not black, as 

 Cuenot states the eyes of his yellow mice to 

 have been. 



From these scattered observations we may 

 infer that the gametic formula of yellow mice 

 is varied; sometimes they lack B, sometimes 

 they lack A, sometimes they lack both B and 

 A ; sometimes still other modifications seem to 

 be involved which cause absence of pigmenta- 

 tion from the eyes, or eyes and belly both. 



The wild rat doubtless has the same three 

 factors involved in the production of its gray 

 coat, as do the other rodents already discussed, 

 those factors being B, Y and A ; but the only 

 one of these which has yet been lost so as to 

 produce a self-colored variety is the barring 

 factor, A. Loss of this produces the well- 

 known black variety. 



For the sake of simplicity, no reference has 

 been made in the foregoing discussion to 

 albino individuals, which may occur in any 

 or all color-varieties. They are individuals 

 which lack some activating substance neces- 

 sary to make pigments visible. They carry 

 color potentialities precisely as pigmented in- 

 dividuals do, as is clearly shown by the results 

 of crosses between albinos and pigmented in- 

 dividuals. Further, they are differentiated. 



