BREWSTER. 



RANGE OF VARIABILITY. 



277 



remaining columns give the relative variability of the several dimensions 

 in individuals of the two species. The numbers at the bottom of the table 

 — " Cases of Agreement " and " Cases of Disagreement " — are found as 

 in Table A. Table C is much less satisfactory than Table A, because 

 the differences in variability between different dimensions are here small, 

 and therefore the relative sizes of the coefficients are more at the mercy 

 of accident. Even here, however, there is a decided preponderance of 

 cases in which individual variation is directly correlated with specific 

 difference. 



TABLE D. 



C. V. OP Four Measurements of Two Genera of Rodents. 

 (Based on Miller, '93 and '93*.) 



Table D is computed from the measurements given with the descrip- 

 tion of two new s{)ecies of rodents.* Zapus insignis and Z. hudsonius 

 are reported to resemble each other closely, but to differ in the length of 

 the ear. Sitomys americanus and S. americanus canadensis are described 

 as nearly alike except in the length of the tail. Table D shows that, of 

 the four dimensions which are recorded for these species, the mean C. V. 

 of the ear is greatest in Zapus, and of the tail greatest in Sitoinys. The 

 0. V. in each single species, too, is greatest for the characteristic dimen- 

 sion, except in the case of Z. insignis. Possibly Z. insignis is the con- 



* Miller ('93), pp. 1-8 and 55-70. 



