Fitness in the Living World 3 1 I 



2. Adaptations for Defense and Offense 

 Every principle of defense known and used by man has 

 been employed by lower animals for uncounted millions of 

 years. Among these are thorns, spines, ancf armor, camou- 

 flage, the false flag, and that most effective means of defense 

 a strong offense. Thorns and spines, frequently barbed 

 and poisonous, are of wide occurrence among animals and 

 plants. The cactus and bramble, the sea-urchin and porcu- 

 pine, ward off enemies by their bristling surfaces. Mollusks, 

 Crustacea, armored fishes, dinosaurs, tortoises and arma- 

 dillos are veritable armored cruisers or land tanks. 



Nowhere has the principle of camouflage been carried to 

 such extent or perfection as among certain animals. The 

 principle of protective coloration is of very general occur- 

 rence in the animal world. The polar bear and fox, the lion 

 and antelope, the dark upper and light under surfaces of 

 birds, resemble the backgrounds against which they are usu- 

 ally seen. Even the tiger and zebra are protectively colored 

 to match the lights and shades of their natural habitats, a 

 thing which can be readily believed by anyone who has seen 

 the bizarre bars and patterns on camouflaged ships. When 

 the background changes, as from winter to summer, some 

 animals change their colors, as in the case of the ptarmigan 

 and arctic hare, which are white in winter and gray or brown 

 in summer. Other animals change colors and patterns very 

 rapidly to match corresponding changes of the background, 

 as in the case of cephalopods and fishes (especially floun- 

 ders), amphibians and reptiles (notably chameleons). 



Animal camouflage includes not only colors and color 

 patterns, like those of the background against which the 

 animal is seen, but also shapes and outlines like those of sur- 

 rounding objects. Some fishes, crustaceans, mollusks, and 

 worms which live in sea-weed are covered with streamers, 



