The Process of Heredity 557 



M pures, and having an equal amount of material to assimilate, 

 succumb more readily to accumulations of carbon dioxide than do 

 the M pures. 



No physiological explanation is offered for the dominance of 

 F. heteroclitus in the matter of color pattern at the time of hatching. 

 This seems to be a case of dominance much like many that have 

 been described in other forms in connection with definitive char- 

 acters. 



Dominance and Survival 



Is dominance the equivalent of survival ? This is a question 

 difficult to answer with assurance. It appears, however, that the 

 H hybrid individuals showing the highest degree of dominance in 

 characters that are of vital significance, such as time of establish- 

 ment of heart rhythm and rate of heart-beat, produce at one end 

 of the series individuals that survive and outlive the best of the 

 pure bred individuals of either species; and at the other extreme 

 of the series, individuals that fail to survive, perishing during the 

 developmental process. Thus dominance of certain good com- 

 binations of characters means survival, and recessiveness of these 

 same combinations means early death. 



In a sense then the dominants, those with the most nearly 

 perfect resemblance to one parent in a certain set of vital characters 

 are the only ones that survive; the recessives, those with the least 

 perfect resemblance, perish early in the developmental process. 

 All the survivors show dominance with regard to certain combina- 

 tions of characters, and, if we were dealing only with end results 

 we would probably be deceived into considering that we had 

 a typical case of exclusive inheritance. But we have the advan- 

 tage of having seen the elimination of the recessives. 



We may conclude, then, that the dominance of good combina- 

 tions of characters is the equivalent of survival, while the recessive- 

 ness of these same combinations of characters is the equivalent of 

 failure to survive. In this sense our question "Is dominance the 

 equivalent of survival V is answered in the affirmative. 



The dominance of superficial, non-vital characters, such as 

 color pattern, intensity of pigmentation, etc., may be definitely 



