ORTHOGENESIS 305 



The idea of a conscious reaction is not associated in 

 Cope's mind with any mysterious conception of a vital 

 force ; it is merely a psychological generalisation. 



Other orthogenetic theories stray from the domain 

 of science and admit metaphysical entities as factors 

 of orthogenesis. Such is Naegeli's system which 

 seeks the main factor of evolution and the origin of 

 orthogenesis in an internal organic tendency towards 

 perfection, in a principle of progressive development. 

 Others have followed the same path and created sim- 

 ilar metaphysical entities to which they have given 

 various names. We shall not even mention them as 

 they have not contributed anything to science. 



