5O F. B. SUMNER AND R. R. HUESTJS. 



quantitative relations which are merely due to mathematical 

 necessity. 



The point of chief interest, perhaps, is to learn whether two 

 characters, both of which differ in the two races here dealt with, 

 tend to be correlated within the single race. Thus, among other 

 differences, the subspecies eremicits is paler and more highly 

 colored than fraterculus, has more hairs belonging to the " D " 

 class, and less belonging to the " D " class, has somewhat longer 

 pelage, a longer subterminal band in the agouti hairs, and a 

 shorter dark segment distal to this, and considerably less pigment 

 in the soles of the feet. To what extent are these character dif- 

 ferences associated together within the single race ? 



Attention has already been called to the fact that in various sub- 

 species of Peromyscus nianiculatus, as well as in hybrids between 

 these, there seems to be little or no correlation between the dark- 

 ness of the pelage and the depth of pigmentation of the feet. 1 

 This is true despite the existence of a marked tendency for darker 

 races to have darker feet. 



The present studies bear out this conclusion. Separate coeffi- 

 cients have been computed for the males and females of the 

 erenriciis and fraterculus series, as well as for the F 1 and F., hy- 

 brids. Of these eight coefficients, five are positive, two negative 

 and one o. The figures range from - .067 to 4- .253, the 

 weighted mean of the series being 4- .056. The only figures in 

 the series which are of possible significance are those for frater- 

 culus. In any case, we believe that the slight correlation some- 

 times shown between these two characters is due to heterogeneity 

 in age. Younger mice (even when the pelage is " adult ") tend 

 to have slightly darker pelages and slightly darker feet, a circum- 

 stance which would insure a certain amount of correlation in a 

 series of mixed age. 



In some other cases, however, characters which are associated 

 together as racial attributes have been found to be correlated with- 

 in the individuls of a race. Thus, positive correlations were 

 found in each of the four groups 2 between the maximum length 



1 Sumner, American Naturalist, May-June, 1923. 



-Ereinicus, fraterculus. F and F o hybrids. Here the sexes have been com- 

 bined in the case of each group. 



