46 F. B. SUMNER AND R. R. HUESTIS. 



hairs, a character in respect to which the parent races differ but 

 slightly. 



From the standpoint of current genetic theories, the figures of 

 chief interest in this table are those relating to the relative vari- 

 ability of the F l and Fo generations of hybrids. It will be noted 

 that in all of the seven cases under comparison the standard devia- 

 tion is larger for the second generation than for the first, al- 

 though in some cases the difference is not statistically significant. 

 The probability quotient ( difference -:- probable error) ranges 

 from 0.3 to 7.2, the mean of the seven figures being 3.3. It is 

 to be remarked that the increase of variability is most certain 

 (D/E- = 7.2) in respect to one of the characters (agouti band) 

 which differ most widely in the two parent races. But it must 

 likewise be noted that the increase is quite non-significant 

 (/}/- = 0.3) in the case of the other most distinctive racial dif- 

 ference (percentage of B hairs.) 



It is of interest to compare the evidence for segregation (so 

 far as this may be inferred from the F 2 variability), as shown by 

 this series of determinations and by those made with the tint 

 photometer. Omitting the figure for total length of hair, which 



has little to do with pelage color, we have the following- quo- 

 tients for the " characters " thus far considered : 



B hairs 0.3 White 3.8 



1.9 Black 5.4 



2.2 Tip 5.5 



A 2.8 Agouti -.^ 



Color 3.6 



Here it will be seen that the mean of the quotients for the four 

 classes of hairs is 1.8, that for black, white and color being 4.3, 

 and that for the two measured segments of the individual hairs 

 being 6.3. So far as may be judged from the foregoing figures, 

 it can hardly be said that these microscopic hair characters show, 

 on the whole, any greater evidence of segregation than do the 

 color values for the aggregate pelage. The figure for black is 

 exceeded (significantly) by only one other figure, that for the 

 agouti band, while the figures based upon the hair counts arc the 



