No. 534] FECUNDITY IN THE DOMESTIC FOWL 331 



used with different females, but in every case the males 

 used were from high fecundity lines and were believed 

 to carry this quality in their germ cells cither in homo- 

 zygote or heterozygote condition. 



In marked contrast to the last example let us consider 

 the low fecundity line D61D168. It is a troublesome mat- 

 ter to propagate the low fecundity lines, because of the 

 difficulty of getting a sufficient number of eggs during 

 the early part of the breeding season. The line D61D168 

 is of interest not alone as an illustration of a typical low 

 line, but also because there appeared in it a mutation, or 

 something very like one. We will consider here only the 

 main line and not the mutant. 



Pedigree Line D61D168 

 ■9ES»l(*5)Xc?o"5* 9im(St)X<?573-0 



419 {9)X<?m 9 F165 (7)* <?669 J ' 4»(lf j 



This line is shown graphically in Fig. 4, in which the 

 mutant and its progeny are also shown. 



A low line in which no mutant has appeared, but in 

 which also the mean production is not so low as in line 

 D61D168 is D65D366. Since the egg production has not 

 been so low in the early part of the breeding season with 

 this line it has been easier to propagate it. 



