EVOLUTION IN NATURAL SCIENCE 9 



direct and indirect. The direct proofs are those 

 faint traces of transformation of species, as they 

 may still be discovered; such, for instance, as the 

 botanist Hugo de Vries has described in support 

 of his theory of mutation. He shows that in the 

 botanical genus (Enothera, mullein, new forms are 

 still being developed, which behave like real species. 

 Against this theory of mutation it has been urged 

 with some reason that the mutation is less important 

 than de Vries believed. Standfuss has established, 

 by means of numerous experiments in breeding 

 butterflies, that mutation has scarcely any sig- 

 nificance as a factor in the formation of species. 

 Standfuss is of opinion that it is scarcely possible 

 for species to be formed by fluctuating variation 

 (which includes Darwin's accidental modifications). 

 He regards as of real importance only the adaptive 

 variations, i.e. modifications due to accommodation, 

 which are caused by definite external causes and 

 are transmitted to succeeding generations. What 

 we mean by modifications, due to accommodation, 

 and how they can produce new species and genera, 

 I hope to show you later on by means of photographs 

 from my own special department. 



I need only say a few words about the indirect 

 proofs. With regard to them the scientist, who 

 wishes to arrive at a conclusion on evolution of 

 species, behaves like a skilful public prosecutor, 

 who wishes to secure the conviction of a prisoner 

 charged with committing an offence which was 



