554 



H. H. Newman 



might call such a condition hyper-dominance. Some examples of 

 this phenomenon follow: 



1 When all four strains of a series were subjected to the experi- 

 mental conditions of lack of oxygen or the presence of carbon 

 dioxide, it was found that the H hybrids were the most resist- 

 ant, the H pures next, the M pures next, and the M hybrids 

 the least resistant. The H hybrids then carry resistance to 

 an extreme while the M hybrids carry lack of resistance to an 

 extreme. 



2 A somewhat similar condition was seen in the degree of 

 depth of pigmentation of many of the H hybrids just before and 

 just after hatching. A considerable percentage of the latter become 

 more darkly pigmented than any of the H pures (the darker parent 

 species). 



3 After hatching it was found that the more successful type 

 o{ H hybrids grew faster and lived far longer, under the conditions 

 applied, than any of the H pures (the parent species that lives 

 the longer under these conditions). 



That there were all degrees of this dominance or hyperdomin- 

 ance cannot be denied, but the sarne can be said of practically all 

 cases of dominance described in the literature. There really 

 appears to be no valid reason why these cases just cited should not 

 be dealt with as examples of the phenomenon of dominance or 

 exclusive inheritance. I think, however, that I can demonstrate 

 that these cases of dominance are the secondary physiological 

 results of the interaction of two sorts of blended inheritance, viz: 

 in the time of establishment of the heart rhythm and in the rate 

 of heart-beat, both of which affect the general circulation. 



The heart rhythm of i^ pure, in accordance with the more rapid 

 development of this species, is established about 24 hours earlier 

 than in M pure. Both reciprocal crosses show an intermediate 

 condition, a blending more or less complete, with regard to this 

 character of time of establishment of heart rhythm. 



In the case of rate of heart-beat the following are the facts: the 

 rate of heart-beat in F. heteroclitus, after it has been well established, 

 is much slower than that of F. majalis, that of the former being on 

 the average about 135 beats per minute and that of the latter about 



