552 THE ZOOLOGIST. 



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 experi- 

 ence. 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 con- 

 spicuous 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 sur- 

 face did not afiford 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. 



io Tn ere 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, 



