682 Studies in the Theory of Descent. 



element in the developmental processes of the or- 

 ganic world, and would always reproduce exact 

 copies of itself if the inequality of the external 

 influences did not affect the developmental course 

 of each new individual ; these influences are there- 

 fore the dynamical elements of the process. 



From this conception of variability two im- 

 portant empirically established facts can be 

 theoretically deduced, viz. the, limitability of 

 variation with respect to quality, which has already 

 been previously mentioned, and the origination of 

 transformations by the direct action of external 

 conditions of life. 



If the differences in individuals of the same origin 

 depend upon the action of unequal influences, 

 variation itself is nothing else than the reaction of 

 the organism to a definite external inciting cause, 

 the quality of the variation being determined by 

 the quality of the inciting cause and by that of 

 the organism. In the cases of individual variation 

 hitherto considered, the quality of the organism is 

 equal but that of the inciting cause is unequal, 

 and in this way there arise minute differences in 

 organisms of an equal physical constitution 

 variations of a different quality. 



The same result, viz., different qualities of 

 variation, may also arise in a reverse manner by 

 organisms of a different physical nature being 

 affected by equal external influences. The re- 

 sponse of the organism to the cause inciting 



