INTRODUCTORY. 19 



alone by other animals, which have got to know either by 

 painful personal experience or by hereditary experience that 

 the insect mimicked had better not be touched. This branch 

 of the subject will be treated of at length in the chapter re- 

 lating to " Protective Mimicry." 



The theory of Natural Selection is believed by most natural- 

 ists to furnish the key to all these problems. " Among the 

 numerous applications of the Darwinian theory," remarks Mr. 

 Wallace, " in the interpretation of the complex phenomena 



9 



presented by the organic world, none have been more successful, 

 or are more interesting, than those which deal with the colours 

 of animals and plants." 



Nevertheless, there are certain colour changes, which can be 

 produced by the direct action of external conditions such as 

 light, heat, cold, etc., and seem to be altogether independent of 

 any selective process. It is very possible that colour is more 

 largely affected by such causes than has hitherto been ad- 

 mitted. A few cases where these environmental effects appear 

 to have come into play will be discussed in the next chapter. 



Relation between Coloration and Structure. 



Among segmented animals we constantly find that the 

 pattern of coloration conforms to the segmentation. The 

 oblique stripes on the caterpillars of certain hawk moths are 

 repeated from segment to segment. Mr. Alfred Tylor* has 

 attempted to show that in the Mammalia there is an analogous 

 connection between deep-seated structures and superficial 

 markings. In the zebra, for instance, a dark longitudinal stripe 

 marks the whereabouts of the spinal column ; the striping on 

 the flanks roughly corresponds with the ribs. 



There is certainly evidence that coloration has some relation^ 



* " Coloration in Animals and Plants," London, li 



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