On the Mechanical Conception of Nature. 705 



series of generations until adaptation is luckily 

 reached through natural selection. Let us have 

 either natural selection or a phyletic force 

 both together are inconceivable. If there exists 

 a phyletic force, then it must itself bring about 

 adaptation. 



It might perhaps be here suggested that the 

 same objection applies to that process of modifi- 

 cation which is effected by small steps, but that 

 it does so only when the change occurs suddenly. 

 This, however, as I have already attempted to 

 show, but very rarely takes place ; in many cases 

 (mimicry) the conditions even change in the first 

 place through the change in form and therefore, 

 as is evident, as gradually as the latter. It must 

 be the same in all other cases where transforma- 

 tion of the existing form and not merely extinction 

 of the species concerned takes place. The 

 transmutation must always keep pace with the 

 change in the conditions of life, since if the latter 

 change more rapidly the species could not 

 compete with rival species \\. would become 

 extinct. 



The abrupt transformation of species implies 

 sudden change in the conditions of life, since a 

 Medusa does not live like a Polype, nor a Trema- 

 tode like its " nurse." For this reason it is im- 

 possible that natural selection can be an aiding 

 principle of " heterogeneous generation." If such 

 abrupt transformation takes place it must produce 



