158 THE COLOUES OF ANIMALS 



vailing tint of the earth is* dark, as in peaty districts. 

 It is improbable that these are local races, and the 

 only other interpretation is that the colours can be 

 varied as the result of a stimulus. No experimental 

 proof of this has been as yet afforded. If the view 

 adopted here be correct, it will be of extreme interest 

 to define the susceptible period ; it will most probably 

 be found at the close of larval life. 



I have treated this part of the subject at some 

 length and have discussed many details. I have done 

 so because the inquiry is new, and will not be found 

 in other books on the colours of animals ; ^ and also 

 because I hope that some of my readers may be in- 

 duced to carry on investigations for themselves in a 

 field which is easily entered, and in which further 

 help is especially necessary. 



' Since this sentence was written, Mr. A. R. Wallace's most inter- 

 esting volume, Darwinism, has appeared. A short account of Variable 

 Protective Eesemblance in insects will be found in it. 



