EGG PRODUCTION. 6l 



sary that the correlation between mothers and daughters in 

 respect to egg production be actually measured. From such 

 measurement it can be told whether on the average the excep- 

 tional mother produces the exceptional daughter or whether the 

 exceptional daughter is as likely as not to be the daughter of 

 the mediocre or poor mother. 



In the second place if the results of an experiment in which 

 the mothers are especially selected are to be used in the discus- 

 sion of inheritance of egg producing ability it is necessary that 

 the daughters' average production be compared not merely with 

 the mothers' average, but also with the average of other birds 

 of the same age as the daughters and kept under the same 

 environmental conditions but not of selected ancestry. 



THE CORRELATION BETWEEN MOTHERS AND DAUGHTERS IN 

 RESPECT TO EGG PRODUCTION. 

 Taking up first the question of the correlation between the 

 egg production of the mothers and the daughters it is necessary 

 to answer the following question. Did the exceptionally good 

 mother in this experiment on the average produce daughters 

 above the average of daughters or not? Some general indica- 

 tion as to the answer which the data give to this question is 

 afforded in Figs. lo and ii. The plan on which these figures are 

 constructed is as follows : The upper of the two horizontal 

 zigzag lines in each figure represents the egg production of the 

 31 mothers included in the experiment. This upper zigzag line 

 in Fig. 10 is the graph of the data given in the sixth column of 

 Table I. The lower zigzag line in each figure is the graph of 

 the average egg production of each of the groups of daughters 

 associated with the 31 mothers. In Fig. 10 the lower zigzag line 

 is the graph of the data given in the seventh column of Table I. 

 In general any plotted point in the upper of the two zigzag lines 

 shows the mother's performance during a given period of the 

 year and the plotted point directly below it on the lower zigzag 

 line shows the average performance of this mother's daughters. 

 Fig. 10 gives the data for the winter (November i to March 

 i) ^SS production and Fig. 11 the spring (March i to June i) 

 egg production. 



