On tlte Mechanical Conception of Nature. 685 



not merely the product of the physical constitu- 

 tion, but the resultant of this and of the quality 

 of the changing external conditions. Thus from 

 the first " species " there proceeded, through the 

 dissimilar influence of external conditions of life, 

 several new " species," and as this took place the 

 former physical nature of the organism at the 

 same time became changed, necessitating also a 

 new mode of reacting upon external influences, i. e. 

 another direction of variation. The difference 

 from the primary " species " must certainly be con- 

 ceived as having been very minute, but it must 

 have increased with each new transformation, and 

 must have proceeded exactly parallel with the 

 degree of physical change connected with each 

 transformation. Thus, hand in hand with the 

 modifications, the power of modification, or mode 

 of reaction of the organism to changing influences, 

 must have continually become re-modifie'd, and 

 we finally obtain an endless number of differently 

 constituted living forms, of which the variational 

 tendencies are different in exact proportion to 

 their physical divergence, so that nearly allied 

 forms respond similarly, and widely divergent 

 forms very differently, to the same inciting 

 causes. 



Individual variation arises, as I have at- 

 tempted to show, by each individual having been 

 continually affected by different, and indeed by 

 constantly changing, influences. Let us, how- 



Y y 2 



