344 EVOLUTION, OLD AND NEW. 



the swvival of the fittest hy mecms of mmute fortuitous 

 indefinite va/riaiions. 



"Among many other obligations whioli the author 

 has to acknowledge to Professor Huxley, are the point- 

 ing out of this very difficulty, and the calling his at- 

 tention to the striking resemblance between certain 

 teeth of the dog, and of the thylacine, as one instance, 

 and certain ornithic peculiarities of pterodactyles as 

 another." * 



In brief then, changed distributioh of use and disuse 

 in consequence of changed conditions of the environ- 

 ment is with Lamarck the main C9,use of modification. 

 According to Mr. Darwin natural selection, or the sur- 

 vival of favourable but accidental variations, is the 

 most important means of modification. In a word, 

 with Lamarck the variations are definite; with Mr. 

 Darwin indefinite. 



• ' Genesis of Species,' p. 76, ed. 1871. 



