ILLUSTRATED AMONG PROTOZOA. 117 



newly added increase of internal complexity, will 

 be most effective in producing new features of 

 development. This explains the general fact in the 

 organic world that new variations of growth in 

 organisms appear, as a rule, about the time when 

 the individual completes its ontogenetic develop- 

 ment, — after the ancestral or generic characteristics 

 have developed. It would be difficult to determine 

 to what extent an unchanging environment can 

 produce changes of development in a long succes- 

 sion of generations, according to the principle under 

 discussion. Unless we disregard the most general 

 conclusions of Physics, Biology, and Psychology, 

 we must believe that some change, however small, 

 is produced in this manner in each generation — 

 just as we must believe that even the first revolu- 

 tion of a steel shaft contributes its share toward 

 causing the changes which, after many millions of 

 revolutions, become apparent in the crystallisation 

 and breaking of the shaft. 



While we might suppose a certain amount of 

 development to take place in an unchanging environ- 

 ment, yet, as a matter of fact, all environments change. 

 Carrying analysis to the farthest limit, we find that 

 a changeless environment does not exist ; the plane- 

 tary motions and the transmutations of solar energy 

 are factors of constant change, and from these and 



