GENERAL HABITS 199 



one concerning which but comparatively little 

 is known. For our present purpose we cannot 

 do better than give the general substance of 

 what we have already written in a volume to 

 which the present may aptly serve as a supple- 

 ment.i Of all forms of protective modification 

 of plumage that of Mimicry — a weak and de- 

 fenceless bird imitating the colour of a stronger 

 and more favoured one — is certainly the most 

 curious and remarkable. Two facts, however, 

 must be kept in mind ; the first, that this re- 

 semblance between distantly related species is 

 apparently unconscious on the part of the 

 species practising it ; the second, that all in- 

 stances of similarity of colour in different species 

 are not necessarily cases of Mimicry. These 

 must fulfil certain conditions, admirably laid 

 down by Dr. Wallace, as follows. The imitative 

 species must inhabit precisely the same locali- 

 ties, the imitators must be the more defence- 

 less or labour under some other disadvantage, 

 be least numerous individually, and present 

 marked differences from the majority of their 

 allies. In every true case of mimicry the points 

 of imitation are external and visible only. Some 

 of the most interesting instances of avine 



^ Curiosities of Bird Lifc^ pp. 235-241. 



