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 ; l 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. 



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

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

 Protective Resemblance in insects will be found in it. 



