COAT-COLOR IX HYBRIDS OF PEROMYSCUS EREMICUS. 47 



lowest of the series. If we accept the degree of segregation ^ as 

 a safe index of the number of genetic factors underlying a given 

 character, we must conclude that only one of the foregoing char- 

 acters (agouti band) is more elementary, genetically speaking, 

 than the crude value for " black " in the pelage. While the data at 

 hand do not warrant any such simple inference, we may safely af- 

 firm that micr<>-oipic analysis has thus far helped us little in the 

 search for unit factors underlying the coat color of Peromyscus.- 



That we arc here dealing in part with genetic differences is 

 plain from a consideration of parent-offspring and fraternal cor- 

 relation- ba-cd ujKjn these characters. The following figures are 

 the means for vix of the characters, the coefficients for "tip" not 

 havim; been computed: 



Parent-offspring 



:tS F ...................................... + -302 



.ilits F ................ ..................... + .267 



' 



+.254 

 +.205 



I lie mean of these figures is 0.257, being thus somewhat greater 

 than tin- iiu-an of the figures (0.238) for black, white and color. 

 n latioii is not equally strong for all of these characters. The 

 in of tlu- hi; 'I res for the . /. />'. C, and /'. hairs is 0.227, tnat f r 

 total length being 0.314, and that for the agouti band 0.319. These 

 -iiL^est that the proportion of non-genetic variability is 

 i(l< rably greater in the case of the hair counts than in the 

 case "i the linear measurements, a fact of possible significance in 

 rnnnertinii with the inferior evidence for segregation shown .by the 

 former characters. 



It is to be noted that the mean correlation between the pure-race 

 parenN and their F, offspring (0.284) is somewhat greater than 



i Sirutlx ~|x.iking. these quotients indicate the probability of the existence of 



; tu-. nit litYi-rences, rather than the amount of such differences. With equal 

 mimlirrs ;m.l r.|iial variability, however, they are proportional to the magnitude of 

 thi % iliiu-rrtK-es. 



\ circumstance tending to diminish the validity of these comparisons is the 

 \;ir-. -i-e of accuracy of the technique upon which the measurement of the 



various cliaracters rests. The greater the observational error, the greater, of 



. \\ ill he the proportion of the total variability which is due to non-genetic 

 r..iu-1-rning the relative magnitude of this factor in the different cases, 

 \vi- li.i\c littlr basis for opinion. 



4 



