358 



THE STRUGGLE FOR EXISTENCE 



animal. This resemblance is a protection, because the 

 weaker animal is taken by its enemies for the animal which 

 it resembles, and consequently goes unharmed by them. 

 The succeeding generations of the weaker animal come 

 more and more to imitate the stronger, until, finally, we 

 ourselves have difficulty in distinguishing one from the 



other. A butterfly, 

 known as the vice- 

 roy, imitates another 

 and larger butterfly, 

 known as the mon- 

 arch. The monarch 

 has reddish brown 

 wings, two inches 

 long, with black 

 veins. It also has a 

 peculiar odor which 

 is very much disliked 

 by birds, hence it is 

 let alone by them. 

 Now, if another but- 

 terfly should grow to 

 look like the mon- 

 arch, even though it 

 had no pecuHar odor, it would be less liable to be eaten by 

 birds, because the birds, having grown to know the monarch, 

 would think that this other butterfly was also a monarch 

 and would let it alone. Exactly this thing has happened. 

 The viceroy has grown to resemble the monarch so closely 

 that only a very observant person can tell them apart, 

 and probably birds do not know one from the other, hence 

 See Figure 237. 



Fig. 237. — Monarch butterfly above and vice- 

 roy below. Note the resemblance. 



touch neither. 



