VARIOUS ANIMAL RESEMBLANCES 227 



from ordinary Warning Colours in that they are 

 common to two or more species : hence, as has been 

 already pointed out, the term Synapose7?tatic Colours, or 

 Common Warning Colours, may be conveniently applied 

 to them. 



The arguments in favour of Natural Selection as the 

 explanation of Protective Resemblance run entirely 

 parallel with those which favour it as the interpretation 

 of Mimetic Resemblance and Common Warning Colours. 

 By modifying the examples and, in some cases, the form 

 of the argument, nearly every section of this paper might 

 be converted into a defence of the former, and the argu- 

 ments which are strongest in support of the one are the 

 strongest in support of the other, viz. those contained in 

 Sections 4, 5, 6, 7, 11, and 12. 



Under the theory of Natural Selection all the resem- 

 blances among animals, mimetic and other, show the 

 clearest relationship, and (with the exception of the 

 debated Epigamic Colours) are to be explained by the 

 working of a common principle, viz., the selection of 

 variations which are useful in the struggle for existence. 

 Under the other theories mentioned above no such 

 grouping can be readily brought about, and Mimetic 

 Resemblance becomes due to one set of principles and 

 the other resemblances to another set. The majority of 

 those who look on Mimicry as due to External or to 

 Internal Causes, or to Sexual Selection, would probably 

 agree in explaining Protective Resemblance by Natural 

 Selection. And yet these latter cases, while far more 

 common, are often as detailed and as remarkable as those 

 of Mimicry. Those who adopt the most extreme form 

 of the theory of External Causes might perhaps maintain 

 that the resemblance to twigs, leaves, and bark is to be 

 explained in the same manner, and would thus bring 

 Protective and Mimetic Resemblance under the operation 

 of the same set of forces ; but few will be prepared to 

 carry the theory so far. Under the theory of Internal 

 Causes it is impossible to bring the two kinds of 

 resemblance together ; for while it is held by some that 

 two or more animals may independently and without 



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