i62 COLOUR IN NATURE chap, vii 



optical colours impossible ? The resemblance between 

 " mimicking " and " mimicked " forms is, of course, 

 not wholly explained by the small number of pig- 

 mental colours which can appear in a butterfly devoid 

 of optical colours, for the resemblance is often as 

 much in markings as in actual colour ; but if we deny 

 the " mimicry," we must, apparently, fall back upon 

 those " laws of growth " which many, perhaps justly, 

 find so unsatisfactory. 



