202 ANIMAL LIFE 



advantage. Such an advantage may be swiftness of move- 

 ment, or unusual strength or capacity to withstand unfa- 

 vorable meteorological conditions, or the possession of such 

 color and markings or peculiar shape as tend to conceal the 

 animal from its enemies or from its prey. Eesemblances 

 may serve the purpose of aggression as well as protection. 

 In the case of the polar bears and other predaceous ani- 

 mals that show color likenesses to their surroundings, the 

 resemblance can better be called aggressive than protective. 

 The concealment afforded by the resemblance allows them 

 to steal unperceived on their prey. This, of course, is an 

 advantage to them as truly as escape from enemies would be. 



We have already seen that by the action of natural 

 selection and heredity those variations or conditions that 

 give animals advantages in the struggle for life are pre- 

 served and emphasized. And so it has come about that 

 advantageous protective resemblances are very widespread 

 among animals, and assume in many cases extraordinarily 

 striking and interesting forms. In fact, the explanation 

 of much of the coloring and patterning of animals depends 

 on this principle of protective resemblance. 



Before considering further the general conditions of 

 protective resemblances, it will be advisable to refer to 

 specific examples classified roughly into groups or special 

 kinds of advantageous colorings and markings. 



108. General protective or aggressive resemblance. As 

 examples of general protective resemblance that is, a gen- 

 eral color effect harmonizing with the usual surroundings 

 and tending to hide or render indistinguishable the animal 

 may be mentioned the hue of the green parrots of the 

 evergreen tropical forests ; of the green tree-frogs and' tree- 

 snakes which live habitually in the green foliage ; of the 

 mottled gray and tawny lizards, birds, and small mam- 

 mals of the deserts]; and of the white hares and foxes 

 and snowy owls and ptarmigans of the snow-covered arc- 

 tic regions. Of the same nature is the slaty blue of the 



