30 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



accentuated, or be lost. In the early generations of hybrids it acted 

 in no uniform manner, but seemed to vacillate. The majority of the 

 hybrids tended toward the very dark type. This can not be held to be 

 the ultimate course for all the progeny, because no light-bellied hybrids 

 were bred after the i wUd. Had such occurred and been bred, it is 

 possible that some progeny might have remained of the practically 

 unchanged wild agouti pattern, to which some j wild animals had 

 reverted. 



(2) When one crosses the modified, dark, ticked-bellied agouti with 

 tame, Hght-bellied agouti, the latter is epistatic and both forms segre- 

 gate from each other in the Fa generation. Both sorts of agouti are 

 allelomorphic to their absence, and also to each other.^ 



NON-AGOUTIS MATED INTER SE. 



Extracted non-agouti hybrids appeared in the F2 generation (see 

 table 6). Other similar, extracted recessives appeared in seven sub- 

 sequent generations. They have all bred true when mated to recessive 

 mates and have given, up to the time of tabulation, about 400 non- 

 agouti offspring. This agrees with the experience of other observers, 

 that extracted non-agoutis breed true to the non-agouti character. 

 This applies to matings of hybrid females and hybrid males, and hybrid 

 males with guinea-pigs, as well as hybrid females to guinea-pigs. The 

 cumbersome tables for this class of matings are not given, inasmuch as 

 the result is fairly obvious and any deviation would mean an unexpected 

 reversal of dominance. 



5. BLACK AND BROWN. 

 HOMOZYGOUS BLACKS IN CROSSES. 



Black, in guinea-pigs and mice, is epistatic to brown. Wild gray mice 

 and ordinary agouti guinea-pigs are homozygous in black. Rabbits 

 and rats are likewise homozygous in this factor, but we know of no brown 

 in the latter two. The wild Cavia rufescens as bred in the laboratory 

 (table 1) acted just as a wild mouse or pure strain of agouti guinea-pig. 

 All the offspring were black-pigmented and agouti-marked. Among 

 the later generations of hybrids not all black-pigmented young were 

 agouti-marked, but for our present purpose the two are included in a 

 single classification, since both bore black pigmentation. 



When a wild male was mated with female guinea-pigs of any color 

 or of no color, the offspring were black pigmented. This result shows 

 that the wild males are homozygous in black. Matings of this sort, 

 summarized in table 2, produced 37 young, all of which were black 

 agouti. These | wild individuals produced 83 black-pigmented off- 

 spring when mated with guinea-pigs of various colors (see table 6). 



'It should be added that the wild modified agouti could be recombined with brown, giving 

 ticked-bellied cinnamon agoutis. The formula would be presumably A'A'bb or A'abb. 



