THE GENERAL SIGNIFICANCE OF AMPHIMIXIS 209 



determined by other factors also, namely, l)y germinal and personal 

 selection and by the directive control which these exert on variations. 



The e(}iializing effect of amphigony may perhaps be expressed 

 thus : In the case of every new adaptation tliere is at first a large 

 area of variation, but this gradually decreases owing to a continual 

 restriction on the part of natural selection, until ultimately — when 

 the highest degree of constancy of the character or species has been 

 attained — it only extends very little beyond the ' adaptation-play- 

 ground ' or the ' area of exemption.' 



One of the effects of amphimixis is thus to bring about an 

 increasing restriction of the area of variation, or, as we usually say, 

 a constancy of the facies of a given form, a condensation into 

 a species. How far this result is necessary or useful, and therefore 

 how far it may be regarded as accounting for the persistence of 

 amphimixis, we shall discuss in the chapter on the formation of 

 species. My own view is that even the fact that new^ adaptations 

 are rendered possible through amphimixis and amphigony, the 

 mode of reproduction associated w^ith it, affords in itself a sufficient 

 reason wdiy amphimixis should have been retained when once it 

 had been introduced. 



II. 



