INHERITANCE OF FECUNDITY 249 



these are relatively unimportant as compared with the differential 

 embryonic mortality. The proportion of embryos which start 

 to develop, but lack the power to complete development is uni- 

 formly much greater for some hereditary combinations than for 

 others, regardless of the particular individuals used as parents, 

 and under uniform conditions of incubation and of housing and 

 feeding the parent stock. 



It is in this direction that I am inclined to look for the explana- 

 tion of the discordant results of cf 578's matings with barred Fi 

 females. The records give one the impression that the potency 

 or absolute fecundity value of the several gametic factors had, 

 because of the super-normal physiological condition, been bodily 

 raised considerably above the normal for the strains used in these 

 experiments. One cannot escape the feeling that all these birds 

 were making higher records than individuals of the same gametic 

 constitution but of more ordinary physiological character in gen- 

 eral would have done. The scale of fecundity values has appar- 

 ently shifted in an upward direction; in other words something 

 similar to what occurs when two inbred strains of maize are 

 crossed happened here. 



Along this line is the only explanation for the outcome of these 

 four matings that I am able to suggest. It is quite possible that 

 it may have no bearing, and that the results are due to some peculi- 

 arity of gamete formation which can be suggested by some one. 

 Personally, however, I am more inclined to keep to the solid 

 ground of the observed physiological peculiarities of these mat- 

 ings rather than to 'juggle the genes.' Even in the hands of an 

 adept the latter procedure runs some risk of taking one a great 

 way from any solid ground of fact whatever. 



Regarding these four matings 699-702 the following facts are 

 definitely known: 



1. High fertility of eggs. 



2. Smallest embryonic (pre-natal) mortality of any particular 

 gametic combination yet experienced in the work of this labora- 

 tory. 



3. Great vigor and vitality of chicks at hatching and during 

 growth. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 13, NO. 2 



