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THE AMERICAN NATURALIST [Vol. L 



occur linked together (XY), i. e., they exhibit the kind of 

 relation which is now generally assumed as the interpreta- 

 tion of a widespread class of phenomena. 



3. That in the ever-sporting single this coupling or linkage is 



only partial so that X and T can occur dissociated. 



4. That in this type of single these two factors are distributed 



differently to the functional male and female germ cells. 

 The male germ cells are unable to carry either factor. The 

 female germ cells may contain both, or one or other, or 

 neither, the four different combinations occurring in the 

 ratio 7 : 1 : 1 : 7 or possibly 15 : 1 : 1 : 15. 

 These suppositions provide us with a working hypothesis which 

 covers the facts detailed above and enables us to form a concep- 

 tion of how it comes about that the two classes of singles behave 

 as they do. 



If 1 and 2 are true, and they postulate nothing beyond what is 

 held to be the probable explanation in the case of other charac- 

 ters studied by other observers, we must suppose that 3 is also. 

 Since were this not so, the offspring of an ever-sporting single 

 having X and Y linked together in any of its functional germ 

 cells, would some of them behave like F x cross-breds from the 

 cross no-d single 5 X d-single <$ and would yield only a small 

 proportion of doubles, whereas observation has shown that all 

 the offspring of ever-sporting singles give an excess of doubles 

 like the ever-sporting parents. Finally as to 4, the supposition 

 of a sex-limited distribution of factors finds also a parallel in 

 other cases : the special features in the present instance are that 

 a sex-limited distribution of factors should occur in an hermaph- 

 rodite organism, and that on the male side it should be complete. 



So much for the main points .of my scheme which are ac- 

 knowledged by Frost and clearly set forth by him. I now turn 

 to his criticisms. 



1. His first point is that I give no reason why singleness rather 

 than doubleness is eliminated on the male side, or why this elinn- 

 nation is uniform. This is true. But do we know the reason 

 "why" in any case where factors are lost or where they show a 

 sex-limited inheritance? Take, for example, such a case as the 

 red-flowered stock in illustration of the first point. We know 

 that the original wild form was purple-flowered, and we suppose 

 that at some point a mutant arose from which a certain factor B 

 capable of turning a red color blue, much as an alkali turns red 



