Preface to the English Edition. xix 



the extent of one of the transforming factors with 

 reference to a definite case. The experiments 

 upon which I base my views are not as numerous 

 as I could desire, and if I were now able to repeat 

 them they would be carried out more exactly than 

 was possible at that time, when an experimental 

 basis had first to be established. In spite of this, 

 the conclusions to which I was led appear to be 

 on the whole correct. That admirable and most 

 conscientious observer of the North American 

 butterflies, Mr. W. H. Edwards, has for many 

 years experimented with American species in a 

 manner similar to that which I employed for 

 European species, and his results, which are pub- 

 lished here in Appendix II. to the first essay, 

 contain nothing as far as I can see which is not 

 in harmony with my views. Many new questions 

 suggest themselves, however, and it would be a 

 grateful task if some entomologist would go 

 further into these investigations. 



The second essay directly attacks the main 

 problem above indicated. It treats of the "Origin 

 of the Markings of Caterpillars," and is to some 

 extent a test of the correctness and capabilities of 

 the Darwinian principles ; it attempts to trace the 

 differences in form in a definite although small 

 group entirely to known factors. 



Why the markings of caterpillars have particu- 

 larly been chosen for this purpose will appear for 

 two reasons. 



