Nos. 618-619] EGG PRODUCTION 



of 14.3 per cent., the 11-egg class a value of 9 per cent., 

 the 21-egg class a value of 11.4 and so on. Towards the 

 end of the season, say at 306 days, the value of the zero 

 class would be 13.3 per cent., and the 1-egg class would 

 have a value of 3.1 per cent., the 11-egg* class a value of 

 5.1 per cent., the 51-egg class a value of 14.3 and so on. 

 At the close of the season, 366 days, the zero class disap- 

 pears, while each egg class has the percentage values 

 given in Fig. 1, beginning at the extreme right and pro- 

 ceeding to the left, i. e., the egg curve is a mirror image 

 of the age at first egg curve. 



The first modifying factor, *. e., rate, tends to flatten 

 the theoretical egg curve by shifting individuals from 

 one side toward the other. Thus, an individual fall- 

 ing in the 56 class, on the 100 per cent, rate, would fall 

 into the 36 class at a 66| rate. If a 50 per cent, rate 

 were selected as the theoretical rate, the 66f rate hen 

 would be shoved over into the 76 class. If the date of the 

 first egg of a sufficiently large number of pullets all 

 hatched on the same day were plotted on a suitable cal- 

 endar, a duplicate of the age at first egg curve would be 

 obtained; but if several hatches are grouped together, 

 e. g. t the four hatches occurring in any one month, it is 

 evident that the curve plotted on the calendar would be 

 considerably flattened and in turn would flatten out the 

 theoretical curve of egg production as based on age at 

 first egg. . 



Selection.— Pearl's success in securing increased egg 

 production by breeding might be due to his methods of 

 selecting the breeders, regardless of all theoretical con- 

 siderations. Families that contained all high producers 

 were selected generation after generation to propagate 

 the high fecundity lines. Families in which true mediocre 

 producers appeared, i. e., where segregation took place, 

 were not used in breeding for increased egg production. 

 This type of selection could hardly fail to yield results, 

 provided that egg production is inherited. Nevertheless, 

 it is clear that fecundity is inherited in Mendelian fashion 



