PHILOSOPHICAL CONCLUSIONS. 381 



main factor in the case. The same force which is expressed 

 in the appearance of the new variation in the first place is 

 required to account for the appearance of the new generic, 

 the new ordinal, or the new class character. This force has 

 been distinguished as intrinsic evolution ; it is expressed in 

 variation itself, which is the chief factor assumed in the 

 theory of natural selection. The nature of the force is ex- 

 pressed in the term blastogenic of Weismann, and in the term 

 centrifugal, as used by Poulton ; but whatever it is called the 

 importance of the distinction lies in the fact that the selection, 

 the preservation, or the transmission of a character does not 

 account for its origin. 



Evolution is thus seen to be a process that is primarily 

 organic : it is expressed in the acquirement of new characters 

 in the course of growth by living organisms; and we may as 

 reasonably speak of evolution force, as of the growth force of 

 the individual, or the force of gravitation. As the normal 

 laws of growth of the individual are thwarted and diverted by 

 external conditions, so undoubtedly a greater or less modifica- 

 tion of the course of evolution has been produced by the 

 conditions of environment. 



When we attempt to explain the course of evolution by 

 tracing it backward from the differentiated, adjusted organ- 

 isms to their ancestors, it is natural to place great importance 

 upon the fact of the accomplished adjustment of the indi- 

 vidual to its particular environment; but when the point of 

 view is reversed and the organism is traced from the earlier 

 geological periods through the ages down to the present 

 time, the conviction becomes impressed upon the student that 

 environmental conditions are but the medium through which 

 the organic evolution has been determinately ploughing its 

 way. 



Differentiation of form and function has been the expres- 

 sion of vitality, and environment is never exhausted. With 

 the occupying of unexplored fields has come divergence and 

 the appearance of new form and structure ; progress has not 

 been made in overcrowded fields by the survival of the fittest. 

 The crowding of the field has led to division and co-ordina- 

 tion of labor. All die in due time, and thus end the struggle; 



