478 



The Journal of Heredity- 



agouti of another wild species C. citilcri 

 and the Kuinea-i)ig aj^'outi. Carta rnfes- 

 cens itself does not differ as much from 

 the agouti guinea-pig or C. cutleri as do 

 its hybrids. It has, however, a some- 

 what darker appearance OAving to narrow 

 yellow hands in the hair. In the hybrids 

 with the guinea-])ig the distinction 

 between the agouti of ('. rnfescens and 

 that of the guinea-])ig in inost cases 

 increased as the amount of guinea-pig 

 blood was increased. In many cases the 

 young were almost indistinguishable 

 from blacks which is never the case 

 with the yellow-bellied guinea-] )ig 

 agoutis. This effect was especially 

 noticeable when the guinea-pig parents 

 were of a certain exceedingly intense 

 black stock. The fact that all stocks of 

 guinea-pigs with factor C show a more 

 intense black than the pale slaty color 

 of the wild s]jecies (which also can be 

 shown to possess factor C) suggests that 

 guinea-pigs have acquired through selec- 

 tion a much higher level of factors in 

 class 2a3. Thus C. rufescens, with a 

 lower level of both the agouti factor and 

 the density of black, shows about the 

 same net result in pattern as the 

 guinea-pig agouti. As noted above, 

 the Peruvian cavy, C. cutleri. apparently 

 possesses the same agouti factor as 

 guinea-pigs. It follows that the dark 

 gray of C. rufescens and the light gra\- of 

 C. cutleri differ by a unit Mendelian 

 factor, a thing not demonstrated for 

 many specific differences among animals. 

 It should be added, however, that there 

 is considerable variation within C. 

 rufescens and both allelomorphs may be 

 present as suggested by Castle. 



TORTOISIv SKRIRS OF ALLELOMORPHS 



Self red or yellow differs from the 

 cf)lors which show black or brown in the 

 fur (except the sooty reds) by a unit 

 factor as shown by Castle,^" and 

 confirmed by later workers." Castle 

 showed that reds might be homozygous 

 or heterozygous for the agouti factor 

 or not transmit it at all (EyEyAA, 

 EyEyAAb and EyEyAbAb) a point 



which differentiates the red and >-ellow 

 of guinea-pigs completely from red and 

 yellow in mice. Recently Ibsen'- has 

 announced that the common tortoise- 

 shells (black and red spotted) contain an 

 allelomorph between complete extension 

 of dark colors and the complete restric- 

 tion found in reds and yellow^s. While 

 he has not yet published the evidence, 

 his series, E, Ep and lily, is adojited 

 here provisionally. The writer has ob- 

 tained results, in experiments made to 

 test the hypothesis, which seem to bear 

 it out although not yet demonstrating 

 it exhaustively. The tortoise-shell pat- 

 tern like the ])iebald may vary from a 

 very small amount of red to nearly self 

 red and it is very ])robable that animals 

 with formula EpEp may occasionally 

 overstep both limits. As in piebalds, 

 asymmetry is very common and much 

 of the variation is doubtless merely 

 developmental. There are not only 

 variations in the extent and localization 

 but also in the intensity of the black 

 spots. Areas of the fur on the same 

 animal may be wholly intense black (or 

 agouti, brown, etc.) or wholly red or 

 intermediate, a brindle of black and 

 red, in which the black is of reduced 

 density. In some cases, instead of a 

 brindle, the black and red become so 

 thoroughly blended in the hairs that 

 a brown spot results. In this way 

 animals which are both tortoise and 

 piel)ald are occasionalh' not merely 

 tri-colorcd but four-colored with solid 

 spots of black, brown and red on a 

 white ground. 



PIEBALD AND TORTOISIi: PATTERNS 



There is some similarity in the 

 jiat terns of ])iebald and tortoise guinea- 

 pigs. The differences, however, are no 

 less striking so that even in red-eyed 

 dilutes (CrCr) in which l)oth i)at terns 

 are in white, they can often be distin- 

 guished. In jiiebalds the ])attern is 

 typically one of large sjjots or blotches 

 of color on a white ground. There are 

 certain more or less definite spot centers 

 as the eves and ears, as noted bv Castle" 



'"Castle. W. E. 19().S. Ihid., 1907. Inc. cil. 



" See for example. Sollasj. I. ]i. J. l')()<>. Rcpi. Evol. Com. R. Soc. Loudon, ^M 79. 



'Mbsen, H. L. 1916. Genetics, \:2\^l-im. 



" Castle, W. E. 1905. Loc. cil. 



