WARNING COLOEATION. 171 



^lace in many cases. The pigments themselves must be 

 altered, not only in their amount and distribution, but in 

 their nature and chemical composition. Assuming that there 

 is no change of habit (of diet, for instance), it is almost im- 

 possible to conceive of such important physiological changes 

 •evoked by what is, after all, so small a need. 



There are so many other easier ways of defence, and one 

 would imagine that the action of natural selection would 

 proceed along the line of least resistance. To take a par- 

 ticular instance, — Mr. Poulton suggests that the larva of the 

 Cinnabar Moth caterpillar was originally entirely orange- 

 •coloured, like the flowers of the ragwort upon which it 

 feeds. In this case, what is the need for any change ? 

 Why should the insect, so to speak, tempt fortune when it 

 is well off? Mr. Poulton, however, partially disposes of this 

 •difficulty by the suggestion that the black bands have been 

 ■only accentuated by natural selection ; they stood in the 

 way, it may be assumed, of a perfect protective coloration, 

 and were increased so as to produce a warning coloration. 

 The suggestion is ingenious, but it is of course purely hypo- 

 thetical. It might be imagined with equal reason that the 

 •caterpillar was originally almost black (like the Fox Moth 

 larva), and is now gradually acquiring a protective instead 

 ■of a warning coloration, by the increase of the yellow and the 

 diminution of the black. The most probable suggestion of all 

 (based, be it observed, like most theories of animal colour, 

 upon absolute ignorance of the pigments) is that the cater- 

 pillar owes its yellow coloration to the yellow pigment of 

 the flowers of the ragwort — the black being possibly a denser 

 •deposit of the same, or due to the chlorophyll in the leaves, or 

 formed anew. If the caterpillar took to the leaves more than 

 the flowers it might lead to the production of the black 



