730 .General and Applied Biology 



Some of the most striking adaptations in animals are the various colors 

 and patterns which characterize certain species. Colors may be due to 

 roughs reflecting, physical structures which scatter (diffuse) light into its 

 various colored rays, or they may be due to the deflection of rays of light 

 from the straight paths as they pass obliquely from one medium to an- 

 other through the process of refraction. Hence, the physical structure 

 of the bodies of insects, the scales of fish, the feathers of birds, etc., are 

 responsible for many bright colors. Other colors in animals are due to 

 chemical pigments which frequently are in special cells called chromato- 

 phores (kro' ma to for) (Gr. chroma, color; phoreo, to bear) . The latter 

 contain pigments such as black, brown, yellow, orange, red, etc., which 

 vary with the species and may even change size and shape in individual 

 organisms, thereby altering the coloration (Fig. 209). In general, the 

 coloration of an or2:anism which blends with its environment renders it 

 more or less inconspicuous in that particular habitat, while the same 

 coloration in a different habitat may make it conspicuous. The colora- 

 tions in animals may serve such natural purposes as protection (conceal- 

 ment) or aggression, warning or signaling, assisting in courtship and selec- 

 tion of mates, etc. Certain species seem to change colors rather quickly 

 to more or less blend with the environment, as shown by the changing 

 colors of certain fish, chameleons, etc. Others change colors with the 

 seasons (seasonal coloration), thereby securing protection or being sup- 

 plied with characters which conceal them for aggressive purposes. The 

 weasel and ptarmigan (bird) change to white in the autumn and to dark 

 colors in the spring. 



Some organisms are so constructed as to resemble other organisms or 

 even nonliving objects [protective resemblance) , thereby being protected 

 somewhat. The walking stick (an insect, order Orthoptera) structurally 

 resembles a dead twig. The underside of the wings of the "deadleaf" 

 butterfly [Kallima) of India resembles a dead leaf when folded at rest. 

 The caterpillars of certain insects also resemble sticks. The viceroy but- 

 terfly [Basilar chia) greatly resembles the disagreeably tasting Monarch 

 butterfly [Danaus) so the former may be somewhat immune from attack 

 by birds. Such a phenomenon involving a model and mimic is called 

 mimicry. Some animals may not use their colorations or special struc- 

 tures for protection but for aggression. This seems to be true for tigers, 

 lions, tree frogs, praying mantes, etc., in which they may blend into their 

 surroundings, thus permitting them to approach their prey more easily. 



