76 HEREDITARY CHARACTERS 



the non-mutants. Yet mutants, according to de Vries, are 

 " elementary species." 



Whatever view we take of what constitutes a species, 

 we have to face the fact that there are some considerably 

 divergent forms, related to each other but having no con- 

 necting links, and we have to judge whether it is more 

 probable that such cases are due to the intermediate links 

 having died out ; or whether in cases where so-called species 

 merge into each other, the intermediate links have been 

 "formed after the species to which they are theoretically 

 supposed to give rise." l 



1 J. A. Thomson, op. cit., p. 82. 



