EXPERIMENTAL. 37 



Classification in Relation to Parents. 



Using coefficients of size gives no information as to the relative sizes 

 of the parents and the two following generations. To show this and 

 to indicate the comparative distributions of the frequencies of the two 

 generations based on actual measurements, a table has been formed in 

 which the rabbits are classified one character at a time in regard to their 

 size as compared with their two parents. See table 7, pages 40 and 41. 

 Only crosses with ^2319 and the subsequent back-crosses have been used 

 in this tabulation. The difference between a pair of parents in the size of 

 a character was divided by 16. This gave the width of one class for 

 this character in this family. By calling the parents the means of two 

 extreme parental classes there remained fifteen equal classes between 

 them. The measurements of the same character in all the Fi and back- 

 cross animals from these parents were arranged in classes, whose limits 

 were determined in this way. Similarly each family was classified for 

 this character. From tables so formed the number of animals in all 

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

 character is readily found by adding the frequencies in the middle 

 column; and so the sums of the frequencies in the other columns 

 show the distribution of animals in other relations to their parents. 

 The sums of all the Fi animals in the various classes were plotted in a 

 frequency curve; the sums of the back-cross classes were plotted in a 

 comparable curve. By this same method the other characters were clas- 

 sified and curves plotted, showing the positions of the Fi and back-cross 

 animals in relation to their parents or grandparents (see fig. 9, page 42). 

 In table 7 the offspring are grouped with reference to the measure- 

 ments of the parents of the family; the measurement of the father falls 

 in the middle of class 1 in every case, and that of the mother in the 

 middle of class 17. Between these two classes lie fifteen classes in which 

 a majority of the offspring occur, though it will be observed that some 

 of the offspring exceed the mother's measurement (class 17), falling in 

 classes 18 to 25, while others fall below the father's measurement 

 (class 1) and so are found in classes — 1 to — 13. The correspondng 

 generations of the several families are combined, class by class, to form 

 grand totals as regards each measurement taken.* 



In general it may be said of all the characters that the intermediate 

 size of the greater number of the first generation is very apparent. If 

 they occupied an exact middle position between their parents, their mean 

 would in every case fall in class 9. In two measurements, Na. and M 2 , 

 this condition is practically realized (see table 6) ; in one measurement, 

 Za., the mean lies nearer to class 8 than class 9 — that is, the Fx offspring 

 fall slightly below the intermediate class ; but in all the other measure- 

 ments, they are from one to three classes higher than the intermediate 



*With the assistance of Mr. S. Wright means and standard deviations were calculated 

 for the F x offspring and the offspring from the back cross with the father, as given in table 0. 



