i 62 
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. 
