96 THE BREEDING OF ANIMALS 



In this investigation, Single Comb White Leghorns were 

 employed and a comparison of hens, pullets, two-year 

 and three-year-old hens was made. The important results 

 may be seen at a glance from the table (page 95). 



The records of this test show that the eggs laid by old 

 hens are heavier than those laid by pullets, that the num- 

 ber of chicks hatched was ten per cent greater, that the 

 initial weight at hatching time, and for several weeks 

 thereafter, was greater from the older hens, and finally 

 that the percentage of chicks dying from pullet's eggs 

 was three times greater than from the mature hens. 



In marked contrast to the above results are those 

 published by the Maine Experiment Station in Bulletin 

 168. The author (Pearl) of this publication states, 

 " The present statistics do not show any marked superi- 

 ority of hens over pullets in respect to breeding perform- 

 ance, so far as either fertility or hatching quality of eggs 

 are concerned." 



95. Age and fecundity. Duncan x distinguishes be- 

 tween the ability to bear children, which he calls fecundity, 

 from actual productiveness or the number of births, which 

 is designated as fertility. From Duncan's investigations 

 it is possible to formulate a general law which represents 

 a true statement of the relation of age to fecundity. This 

 general law has been stated by Marshall 2 as follows : 

 " The fecundity of the average individual woman may be 

 described, therefore, as forming a wave, which, starting 

 from sterility, rises somewhat rapidly to its highest point 

 and then gradually falls again to sterility." The results 

 discussed earlier in this chapter clearly indicate that in 



1 Duncan, "Fecundity, Fertility, Sterility and Allied Topics," 

 Edinburgh, 1866. 



2 Marshall, "The Physiology of Reproduction," p. 590. 



