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 "’ (‘ Proce. Boston Soe. 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). 
* 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 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. 
® Or the numberless examples of insects which fall motionless when 
their food-plant is shaken. 
© 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, 
