INTRODUCTORY. 17 



be set down in the case of many animals to a similar need 

 which has produced a similar effect. We can find, in fact, in 

 this group, and for the matter of that in others, examples of 

 most of the remarkable phenomena of coloration believed to 

 owe their existence to natural selection, which yet cannot, at 

 least so far as we can see, have that significance. 



The Same Plan of Coloration often found in Distantly Related 



Animals. 



Just as the same pigments may occur in animals that are 

 not nearly related, so the same plan of coloration distinguishes 

 animals that are occasionally quite distantly placed in the 

 scheme of classification. Green butterflies, moths, beetles, 

 birds, lizards and frogs are numerous ; the transverse stripes 

 of the tiger are seen in the zebras and in the marsupial wolf 

 Tltt/'lacinus ; a spotted coat distinguishes a considerable 

 number of mammals belonging to different orders. The raven, 

 the American Ani, the Molothrus, agree in having a uniform 

 black covering of feathers ; the colours and patterns upon the 

 wings of the butterflies belonging to the genus Leptalis are 

 exactly repeated in butterflies of the genus Heliconius a re- 

 presentative of an entirely distinct family. Eye-like markings 

 are found in caterpillars, moths, butterflies and shrimps. In 

 fact, it is not too much to say that hardly any animal has a 

 general plan of coloration which is distinctly its own, and is 

 not even closely paralleled in some other animal or animals 

 belonging to a different group. The reasons for these resem- 

 blances will be discussed in the following chapters ; they may 

 be roughly classified under three principal heads, which are 

 however not trenchantly marked off from each other. Animals 

 which resemble each other in having a uniform green colora- 

 tion, such as the iguana, the tree frog, certain caterpillars and 



