MUTATION 321 



which is sufficient to account for the most complex 

 structures, the most perfect cases of adaptation. 

 Interspecific selection chooses from several mutations, 

 and consequently from the various new species, those 

 that are to survive. Natural selection and artificial 

 selection are absolutely similar in this respect and it is 

 perfectly legitimate, all statements to the contrary 

 notwithstanding, to draw a parallel between them. 



The external environment influences the evolution 

 of individuals through interspecific selection ; it is also 

 in all probability the environment which determines 

 the appearance of a period of mutation; but the ac- 

 tion of the environment can not accomplish more 

 than this. The nature of mutations is in no way de- 

 termined by external factors; their origin is germinal, 

 congenital, and depends upon changes taking place 

 within the sexual cells. The appearance of new char- 

 acters, the awakening of latent characters or their 

 passing into latency, are due to unknown internal 

 causes acting within the germ cells. 



This view, which minimises the influence of ex- 

 ternal factors, is a connecting link between De Vries 

 and the Weismannians, in spite of the stand De Vries 

 takes against the classical theory of natural selection. 

 On the other hand, it separates De Vries distinctly 

 from the Lamarckians. 



Among the naturalists who have been converted to 

 the mutation theory we may mention T. H. Morgan, 



