THE BUTT KB FLY 



35 



conditions, especially heat, under which they have developed. 

 Mr. W. H. Edwards in this countr}', and Weismann and others 

 in Europe, have shown that, when the summer brood is kept 

 during development in a refrigerator, the butterfly has the color 

 of the winter form. 



Protective Resemblance and Mimicry. — Every one who has 

 visited a natural history museum must have noticed that the 

 polar mammals are apt to be more or less white, while those 



Fig. 37. — Cafocala ilia, the underwing. Upper wings, l)ark color; lower 

 wings, black with orange l^ands. 



which live in tropical forests are dark. It is ea.sy to under- 

 stand that these colors in their proper surroundings make the 

 animals which wear them hard to see. This may be of advan- 

 tage in enabling them to escape the observation of their 

 enemies, which are seeking for them, or to avoid being seen 

 by their pre^^ as thej^ approach. This general resemblance 

 to their background is seen even in some caterpillars, e.g. the 

 tomato-worm, which is colored so exactly like the leaf on which 

 it feeds that it is hard to find. Other caterpillars, belonging 

 to the family of " measuring worms," have the color of the 



