64 



NATURE SKETCHES IN TEMPERATE AMERICA 



Lyell, "I always repeat to myself that we hardly know why 

 any one single species is rare or common in the best-known 

 countries," Whether a species is abundant in a given locality 

 is necessarily determined by natural causes. Chief among the 

 conditions favoring existence of a species are its adjustment to 

 its surroundings, that is, maintaining itself against competi- 

 tion with members of the same species and other enemies, and 

 the resistance to climatic conditions. I have attempted in 

 the foregoing account to exemplify by the polyphemus moth 

 some of its adaptations to these varied conditions. 



Protective resemblance in the .snout butterfly {IJbytlua back- 



vianni). The palpi project forward so as to resemble 



a stem, the underside of the 7vings simulate a 



dried leaf. This insect appears in May. 



