190 



E. C. MACDOWELL 



With assistance from Mr. S. Wright standard deviations were 

 calculated for the total first generation and back cross frequencies, 

 as classified in relation to the parents, for each measurement 

 (table 3) . These constants do not give actual deviations because 

 the totals are classified in a purely relative manner. However 

 for purposes of comparing the two generations these standard 

 deviations are permissible because the frequencies in both gen- 

 erations are classified in relation to the same parental classes. 



TABLE 3 



Means and standard deviations of the first generation (Fi) and back cross (B.C.) 

 based on classifications in relation to the parents, similar to those given in table 2 

 and expressed in terms of those classes. 



Six measurements show significant increase in the back cross 

 over the first generation, three show decrease in the back cross, 

 and four lie within the probable error, meaning practically no 

 change. This is a mathematical demonstration that there is 

 enough lack of correlation between the bone measurements for 

 different characters to give different results. Since twice as many 

 characters show increase as decrease, it can be concluded that 

 there is greater variability in the back cross offspring than in 

 the offspring of the first generation. 



