ISOLATED PHENOMENA. 59 



feather-mark was properly considered a serious 

 difficulty to Darwin's theory because of its 

 remarkable character. But with consummate 

 ingenuity he undertook to connect it by a 

 series of less and less remarkable markings 

 with the ordinary feather-markings of the 

 group to which the peacock belongs. It is 

 impossible to exaggerate the importance of 

 studying phenomena in their quantitative and 

 qualitative variations, for on it depends the 

 establishment of continuity between phenom- 

 ena apparently widely separated, and it fre- 

 quently leads to results that can be reached in 

 no other way. 



