i88 THE COURTSHIP OF ANIMALS 



coloured, it is difficult to believe that these different 

 postures and conspicuously different colours can have 

 been brought into existence solely by the action of Natural 

 Selection, which, it is generally contended, has brought 

 about the extinction of those individuals which neglected, 

 when resting, and therefore liable to be " caught napping," 

 to conceal their arresting colours. There is, indeed, nc 

 apparent reason why the female, which has nothing to 

 conceal, should depart from the custom common to 

 Butterflies, of resting with the wings closed and raised, 

 this position effectively protecting the male. The facts 

 seem to show that the coloration of the exposed surfaces 

 of the wings is determined primarily by some physiolo- 

 gical factor rather than by the incidence of Natural 

 Selection directly through external agencies. Thus, foi 

 example, the action of light on the surface of the wings 

 when in the resting posture may well inhibit the pro- 

 duction of vivid pigment owing to some inherent 

 physiological idiosyncrasy. But any individuals which 

 lack this inhibiting factor — as some species which, though 

 resting, are brightly coloured, appear to do — will be 

 eliminated, if they live in an environment harbouring 

 eliminating factors, which the exceptions to the rule we 

 must suppose do not. But on this interpretation the 

 fundamental factor in the determination of the coloration 

 is the action of light. Selection imposes a bar only to 

 certain types of coloration. 



Some Butterflies and Moths, it has just been hinted, 

 when resting exhibit bright colours. Our " Swallow-tail " 

 furnishes a good instance among the Butterflies. Here 

 the under surface of the wings is as brightly tinted as the 

 upper. Among the Moths may be cited many of the 

 gorgeous Atlas Moths, the Hawk Moths, the beautiful 



