PROTECTIVE COLORATION. 119 



investigation by those who wish to collect evidence in favour of 

 modification due to natural selection. 



Specific Characters retained even in Insects which imitate the same 



Environment. 



In referring to the changes of' colour undergone by flat fishes 

 in order to assimilate to the ground upon which they happen 

 to be resting, Mr. Cunningham remarks:* "A large number 

 of different species belonging to different genera lies within the 

 same area or ground of uniform colour ; to this colour they 

 all have to assimilate their general tint, but each species has 

 its own permanent characteristic marking. As these markings 

 are all different, they cannot all aid equally in the protective 

 resemblance; some of them, at least, must either be indifferent 

 or disadvantageous to the attainment of the useful result. As 

 far as we can judge, all the specific markings are indifferent." 

 This is equally true of other animals besides fishes. There are 

 a large number of moths which habitually settle upon lichen- 

 covered trees: for instance, Biston betularia, Cleora glabraria, 

 l^jin(l(f lichfiiaria, etc.; all these insects have white or brownish 

 wings dusted or marked with black. But not even the veriest 

 tyro among entomologists would fail to recognise the specific 

 distinctness. It may be (I am not aware if it is so) that 

 one species resembles more closely a particular lichen than 

 another does, which is more like a second species; but in this 

 there is not much advantage, for I can say from personal 

 experience that the insects are found upon different tree trunks 

 and among various kinds of lichen, to most of which they have 

 a certain likeness. 



Protective resemblance, therefore, even if due entirely to 

 natural selection, has its limits; and we must regard as an 



' Preface to his Translation of Elmer's work, p. xiii. 



