BY RAYMOND PEARL 



37 



This line is shown graphically in Fig. 2. 



Little comment on this pedigree line is necessary. We see a certain high 

 degree of fecundity faithfully reproduced generation after generation. 

 Different males were 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 either in homozygote or heterozygote condition. 



In marked contrast to the last example let us consider the low fecundity 

 line D61D168. It is a troublesome matter 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 D6iDi68 



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. 



This was the mutant referred to. Its progeny will be considered later. See p. 335. 



