THE BEGINNINGS OF LIFE. 577 



direct agencies recognized by others, that he almost 

 neglects them as independent producers of variation 

 and gives to the special agency a general range and 

 applicability 1 . 



Influence of Change m External Conditions. 



If we take the three modes already referred to, or 

 any others, by which variations in the form or structure 

 of animals and plants are initiated, we find that in 

 each alike, if the change is to be a permanent one, 

 the principle of inheritance must come into play. It is 

 therefore only amongst the 'primary causes' of varia- 

 tion that any room for difference exists. Thus we 

 may have: (i) some altered incidence of external 

 forces directly bringing about an altered internal 

 action in the complex moving equilibrium which the 

 organism represents, and the perpetuation of such 

 alteration by inheritance, under the persistence of 

 similar conditions ; (2) the gradual induction of some 

 altered structure by modifications initiated in the func- 

 tional activity (indirect influence of conditions) of 

 some part of an organism, which alteration is similarly 

 perpetuated; and (3) the perpetuation and intensifi- 

 cation by inheritance, through several generations, of 

 some one or more out of the many individual differences 

 which are always manifesting themselves in the different 



1 Although of late Mr. Darwin has appeared more disposed to limit 

 the supposed influence of Natural Selection. (See note 3 of next page.) 

 VOL. II. P p 



