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552 this time a chrysalis, and of course has no opportunity of improving the cocoon. The selective test is applied long after the operation has been performed, and when there is no possibility of gaining by experience. We are thrown back, then, solely upon natural selection, which acts on the nervous system of the caterpillar, and thus compels it to make the cocoon in a certain way. In other words, those caterpillars which are impelled by their nervous system to make ill-formed conspicuous cocoons have no chance of living, and, in future stages, producing offspring. Hence the selection caused by the keen sight of foes first raises, and then maintains at a high level, the standard of cocoon-making."

"This contention as to the uselessness and danger of experience applies to the whole of those smaller defenceless animals which have no chance of fighting with their enemies, or of escaping when once they have been detected" ('Proc. Boston Soc. Nat. Hist.' vol. xxvi. p. 391). It would be a most gratuitous indulgence in unnecessary hypothesis to insist that the appropriate attitude which gives a meaning to form and colour, and itself receives a meaning from these, originated in one way in the caterpillar, and in another and totally different way in the imago which develops from it.

7 See note (3).

8 The observation does not prove more than that the fox seeks cover and hides when he sees that he is observed by man. The burnt surface did not afford cover, and the fox sought it elsewhere. It would be very rash to assume from the observation that the fox knew anything about his own protective colouring.

9 Or the numberless examples of insects which fall motionless when their food-plant is shaken.

10 There are many reasons for considering that colours and patterns change very rapidly when no longer sustained by natural selection. When animals become cave-dwellers, or inhabit the greatest depths of the ocean, their colours are profoundly modified and often tend to disappear. This happens in forms closely allied to others which still retain the normal colouring and live in the light.

The majority of domestic animals have been immensely modified in this respect in a measurable number of years. In some cases these changes have been brought about without the aid of specially directed artificial selection. Thus a large proportion of our fowls produce white eggs instead of the brown of the ancestral species.

Again, the enormous difference between the colours and patterns of certain closely-allied species is evidence for ease and rapidity of change rather than stability in this element of structure. The argument becomes stronger when we consider the cases of sexual and seasonal,