No. 534] FECUNDITY IN THE DOMESTIC FOWL 335 



Leaving this bird out of account because pathological, 

 the mean winter production of the family is 52.8 eggs, 

 very strikingly different from the average (9.67 eggs) of 

 the birds of the same generation in the main low line in 

 which the mutation appeared. 



Two other daughters of the mutant E248 were mated 

 to <£D31, a bird known not only to belong to a genotype 

 of mediocre to low fecundity, but to be remarkably pre- 

 potent in respect to this character, so that practically 

 regardless of the females with which he has been mated 

 the get has been uniformly poor in respect to egg pro- 

 duction. Four adult females resulted from the two 

 matings under discussion. They have an average winter 

 production of 23.75 eggs. There are several possible 

 explanations of this result, but the most probable is that 

 we have here simply one more instance of the extraordi- 

 nary prepotency of JD31. 



The last of the daughters of the mutant was mated to 

 a cross-bred male, no. 578, and consequently the progeny 

 can not fairly be compared with the pure Barred Bocks 

 in respect to fecundity. 



The facts here briefly discussed are shown in the fol- 

 lowing table and graphically in Fig. 4. 



It is apparent from the table and the diagram that the 

 main line and the "mutant" line are entirely distinct. 

 Indeed they do not overlap in their ranges even except- 

 ing only the pathological individual G495. The "mu- 

 tant" pullet E248, for some reason or other, possessed 

 the capacity both to lay a relatively large number of 

 e ?gs, and the genes necessary to make this quality ap- 

 pear in her progeny. Whether this individual is to be 

 regarded as a true "mutation" would appear to be 

 largely a question of definition. In the writer's opinion 

 the most probable explanation is that E248 is a Men- 

 delian segregation product. That is, let it be supposed 

 that both D168 and D61 were heterozygous with respect 

 to degree of fecundity, and were producing in some (un- 

 known) ratio both "high fecundity" and "low fecun- 



