72 



NATURE SKETCHES IN TEMPERATE AMERICA 



These colors are often produced by pigment and striae in the 

 same scales of butterflies. 



The laws which Wallace believed governed the production 

 of all cases of protective resemblance were rapid multiplication, 

 incessant, slight variation, and the survival of the fittest, in 

 other words, natural selection. Those cases which furnish 

 striking examples of protective resemblance, such as the walk- 

 ing-stick and leaf-like insects, represent instances in which the 

 process of modification has been going on during an immense 

 series of generations. The great majority of such species 

 occur in the tropics where the conditions of existence are most 

 favoral)le, and where climatic changes have for long periods 

 been hardly perceptible. 



The Tree To.\d 



^ 



CARCELY a week passed during 

 spring and summer that I did 

 not come across the tree-toad in 

 my walks afield. In April its 

 song was heard at twihght, 

 emanating from the lowlands at 

 the border of ponds, ditches, and 

 wet meadows, or from the shrubs 

 and trees nearby. During sum- 

 mer, one of its favorite places of 

 retreat in the daytime was in the 

 shade of the wooden rafters imder 

 the roof of a neighbor's porch. Again, 

 the little pockets on the trunks of beech 

 trees in the woods were especially attractive places 

 for them. In September, the openings into the old apple 

 trees often afforded choice locations in which they took up 



