COLOR AND COAT CHARACTERS. 17 



different sorts, one sort resembling the agouti of C. rufescens, the other 

 that of the guinea-pig. If we designate the tame agouti as A and the 

 wild agouti as A', then these five parents had a zygotic formula of AA'. 

 It is evident, then, that they must have produced certain gametes which 

 bore A, the powerful tame agouti factor, and others which bore A', the 

 weak wild agouti factor. The young accordingly were of two sorts, 

 wild and tame agouti. This subject will receive consideration in a 

 later part of this paper. For the present, all kinds of agouti will be 

 considered as one, irrespective of their source. 



Summary. — The wild Cavia rufescens is homozygous in agouti. This 

 condition is epistatic to the non-agouti condition of the tame guinea- 

 pig. The agouti of the tame is likewise epistatic to the non-agouti 

 condition of the hybrids. Hybrids may be produced which are homo- 

 zygous in agouti. In table 5 the summary of tables 2, 3, and 4 shows 

 that 85 agouti offspring were produced from matings of pure agouti 

 animals. Therefore the agouti factor is epistatic, whether found in the 

 wild, the tame, or the hybrid. This agrees with Nehring's results on 

 Cavia aperea, though his interpretation was different. To make data 

 plain and not suppress any facts, it should be stated that a few albinos 

 enter into some of the tables. Such albinos, we know, carry all color 

 factors in the same proportions as their colored brothers and sisters, 

 with the exception of the basic color factor itself. It may therefore be 

 understood that albinos have been omitted from the tables, unless a 

 thorough breeding test has demonstrated to what color class each albino 

 belongs, in which case it has been included in the corresponding colored 

 class. 



HETEROZYGOUS AGOUTIS MATED TO NON-AGOUTIS. 



All the I wild hybrids derived from the cross (table 2) of a Cavia 

 rufescens male with female guinea-pigs w^ere supposedly heterozygous 

 in agouti ; 9 female ^ wild hybrids w^ere mated with male guinea-pigs. 

 The sterility of the male hybrids prevented a breeding test in their case. 

 The female ^ wild all bore the agouti coat and had received the agouti 

 factor from the wild parent. A priori, they should have been hetero- 

 zj^gous in this factor, having received it from one parent only. Such 

 they proved themselves to be in their matings with the non-agouti 

 guinea-pig males. They gave offspring of two sorts, agouti and non- 

 agouti (in this case all were black) in approximately equal numbers; 

 83 such offspring (table 6) were obtained, of which 47 were agouti 

 (also heterozygous) and 36 were non-agouti. To strengthen the case, 

 it may be pointed out that each female | wild should prove her hetero- 

 zygous condition by giving both sorts of young, provided the numbers 

 are large enough; 7 of the 9 females gave both sorts of young. One 

 female (9 75) gave 4 agoutis only, and another female (? 72) gave 4 non- 

 agoutis. Presumably these last two females would have yielded both 



