MULTIPLE FACTORS IN MENDELIAN INHERITANCE 187 



is slightly smaller than that of the first generation. In families 

 1443, 1531, 1532 and 1537 there were not enough Fi individ- 

 uals to use in determining coefficients of size. The back crosses 

 of these families are given for comparison with the first genera- 

 tions and back crosses of other families. In family 1491 the 

 standard deviation of the back cross is the same as the highest 

 first generation standard deviation, namely, that in family 2011. 

 In 1493 and 1537 the back cross standard deviations are very 

 nearly as low as the highest first generation standard deviations, 

 but the standard deviation of the first generation of family 1493 

 is much lower than that of the back cross of the same family. 

 This is the largest family obtained. 



b. Classification in relation to the parents 



The data were next treated in a way to show graphically the 

 size relations between the parents, the first, and back cross gen- 

 erations, considering one character at a time. This method of 

 treatment also shows the relative variability of the first and back 

 cross generations and offers another method for combining differ- 

 ent families. This method may be called classification in rela- 

 tion to the parents. For each family 15 classes were formed be- 

 tween the parental classes. Each parental measurement is taken 

 as the middle of a parental class; the extent, or range of each class 

 equals one-sixteenth the difference between the parental measure- 

 ments. Into classes so formed the first and back cross genera- 

 tions were separated. This was done for all characters in all 

 families. From these classifications the number of animals of 

 all families that fall half way between their parents in regard to 

 any measurement is readily found by adding the frequencies in 

 the middle column; likewise the sums in other columns show the 

 distribution of animals in other relations to their parents. The 

 male parent in all families was the same animal. The female 

 parents differed in size to some extent. This means that in the 

 various families and in the totals, individuals are put together 

 that are not exactly similar as to size. They are, however, sim- 

 ilar as to their relative positions between their respective parents. 



