1 1 o Studies in the Theory of Descent. 



results because the different variations which, for 

 the time being, constitute the variability of the 

 species, would alw r ays be in a different numerical 

 proportion in the isolated district as compared with 

 other regions ; and further, because constancy is 

 produced by the crossing of these (isolated) 

 varieties among themselves ; so that the resultant 

 of the various components is (local) variation. If 

 the components are dissimilar the resultant would 

 also be different, and thus, from a theoretical 

 point of view, there seems to me no obstacle in 

 the way of the production of such local forms by 

 the process of ' amixia.' I believe that I have 

 further shown that numerous local forms can 

 be conceived to have arisen through this process 

 of preventive crossing, whilst they cannot be ex- 

 plained by the action of climatic influences. 



That I do not deny the existence of true climatic 

 forms in admitting this principle of ' amixia/ as 

 has been frequently imagined, appears suffi- 

 ciently from the treatise in question. The ques- 

 tion arises, however, whether climatic influences 

 may not also originate forms by ' amixia ' by 

 making a species variable. It would be difficult 

 at present to decide finally upon this subject. 

 If, however, in all cases a variation in a certain 

 fixed direction occurred through climatic influences, 

 a form could not arise by ' amixia ' from such a 

 variability, since the components could then pro- 

 duce resultants different only in degree and not 



