1 1 2 Studies in the Theory of Descent. 



this change being in a fixed direction which en- 

 tirely depends on the physical nature of the varying 

 organism, and is different in different species, or 

 even in the two sexes of the same species. 



I am so little disposed to speak in favour of an 

 unknown transforming power that I may here 

 again insist that the transformation of a species 

 only partly depends upon external influences, and 

 partly on the specific constitution of the particular 

 form. I designate this constitution ' specific/ 

 inasmuch as it responds to the same inciting cause 

 in a manner different to the constitution of another 

 species. We can generally form a clear concep- 

 tion why this should be the case ; for not only is 

 there in another species a different kind of latent 

 vital activity, but each species has also a different 

 developmental history. It must be admitted that, 

 from the earliest period of the formation of an or- 

 ganism, and throughout all its intermediate stages, 

 properties which have become established, such as 

 growth, nutrition, or tendency to development, 

 have been transferred to the species now existing, 

 each of which bears these tendencies in itself to 

 a certain extent. It is these innate tendencies 

 which determine the external and internal appear- 

 ance of the species at every period of its life, and 

 which, by their reaction to external factors, repre- 

 sent the life of the individual as well as that of the 

 species. Since the sum of these inherited ten- 

 dencies must vary more or less in every species, 



