266 THE THEORIES OF EVOLUTION 



now kill a second sheep more easily than the first. 

 When a bacillus insufficiently virulent for sheep ac- 

 quires the necessary virulence by passing successively 

 through several animals, the increase is due to the 

 gradual development of that organ through its func- 

 tioning. 



We may describe the facts in any way we desire; 

 the result will be the same — increase in virulence, that 

 is, adaptation. 



It is now perfectly clear that what Le Dantec crit- 

 icises mostly is the Darwinian method. As far as 

 the basic thought of Darwinism is concerned, Le Dan- 

 tec recognises all the importance of natural selection, 

 although he objects to the fortuitous characters of the 

 variations on which it bears. "Those variations," he 

 writes, "are directly determined by the environment 

 and are adaptative." 



Roux's theory of the struggle between parts has ex- 

 erted a certain influence on Le Dantec; we find traces 

 of it in his monograph on plastidia, or elementary liv- 

 ing units. "They compete," he writes, "for better 

 conditions of assimilation, as the environment does not 

 act upon them uniformly and only the fittest survive." 



This natural selection bears upon the primary con- 

 stituents of the organism and results in the direct 

 adaptation of the organism to its environment. The 

 Darwinian idea applied to internal tissues leads ulti- 

 mately to Lamarckian conclusions. 



