Evidences of Theory of Natural Selection. 323 
Mr. Darwin’s thcory—namely, that the more perfect 
the resemblance is caused to become through the 
continuous influence of natural selection always picking 
out the best imitations, the more highly discriminative 
becomes the perception of those enemics against the 
depredations of which this peculiar kind of protection 
is developed; so that, in virtue of this action and 
re-action, eventually we have a degree of imitation 
which renders it almost impossible for a naturalist 
to detect the animal when living in its natural en- 
vironment. 
Warning Colours. 
In strange and glaring contrast to all these cases 
of protective colouring, stand other cases of conspic- 
uous colouring. Thus, for example, although there 
are numberless species of caterpillars which present 
in an astonishing degree the phenomena of pro- 
tective colouring, there are numberless other species 
which not only fail to present these phenomena in 
any degree, but actually go to the opposite extreme 
of presenting colours which appear to have been 
developed for the sake of their conspicuousness. At 
all events, these caterpillars are usually the most con- 
spicuous objects in their surroundings, and therefore 
in the early days of Darwinism they were regarded by 
Darwin himself as presenting a formidable difficulty 
in the way of his theory. To Mr. Wallace belongs 
the merit of having cleared up this difficulty in 
an extraordinarily successful manner. He virtually 
reasoned thus. If the ratson détre of protective 
colouring be that of concealing agreeably flavoured 
caterpillars from the eye-sight of birds, may not 
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