324 Darwin, and after Darwin. 
the raison @étre of conspicuous colouring be that 
of protecting disagreeably flavoured caterpillars 
from any possibility of being mistaken by birds? 
Should this be the case, of course the more con- 
spicuous the colouring the better would it be for 
the caterpillars presenting it. Now as soon as this 
suggestion was acted upon experimentally, it was 
found to be borne out by facts. Birds could not be 
induced to eat caterpillars of the kinds in question; 
and there is now no longer any doubt that their con- 
spicuous colouring is correlated with their distasteful- 
ness to birds, in the same way as the inconspicuous or 
imitative colouring of other caterpillars is correlated 
with their tastefulness to birds. Here then is yet 
another instance, added to those already given, of 
the verification yielded to the theory of natural 
selection by its proved competency as a guide to facts 
in nature; for assuredly this particular class of facts 
would never have been suspected but for its suggestive 
agency. 
As in the case of protective imitation, so in this 
case of warning conspicuousness, not only colour, but 
structure may be greatly modified for the purpose 
of securing immunity from attack. Here, of course, 
the object is to assume, as far as possible, a touch- 
me-not appearance; so that, although destitute of 
any real means of offence, the creatures in question 
present a fictitiously dangerous aspect. As the 
Devil’s-coach-horse turns up his stingless tail when 
threatened by an enemy, so in numberless ways do 
many harmless animals of all classes pretend to be 
formidable. But the point now is that these instincts 
of self-defence are often helped out by structural 
