368 
TROPICAL NATURE 
v 
running to its burrow, is made conspicuous to the sportsman, 
and no doubt to all beasts of prey, by its upturned white tail. 
But this very conspicuousness while running away, may be 
useful as a signal and guide to the young, who are thus 
enabled to escape danger by following the older rabbits, 
directly and without hesitation, to the safety of the burrow ; 
and this may be the more important from the semi-nocturnal 
habits of the animal. If this explanation is correct, and it 
certainly seems probable, it may serve as a warning of how 
impossible it is, without exact knowledge of the habits of an 
animal and a full consideration of all the circumstances, to 
decide that any particular coloration cannot be protective or 
in any way useful. Mr. Darwin himself is not free from such 
assumptions. Thus, he says : — “ The zebra is conspicuously 
striped, and stripes cannot afford any protection on the open 
plains of South Africa.” But the zebra is a very swift 
animal, and, when in herds, by no means void of means of 
defence. The stripes therefore may be of use by enabling 
stragglers to distinguish their fellows at a distance, and they 
may be even protective when the animal is at rest among 
herbage — the only time when it would need protective colour- 
ing. Until the habits of the zebra have been observed with 
special reference to these points, it is surely somewhat hasty 
to declare that the stripes “cannot afford any protection .” 1 
Colour proportionate to Integumentary Development 
The wonderful display and endless variety of colour in 
which butterflies and birds so far exceed all other animals, 
seems primarily due to the excessive development and endless 
variations of the integumentary structures of these two 
groups. No insects have such widely expanded wings in pro- 
portion to their bodies as butterflies and moths ; in none do 
the wings vary so much in size and form, and in none are they 
clothed with such a beautiful and highly-organised coating of 
scales. According to the general principles of the production 
of colour already explained, these long continued expansions of 
membranes and developments of surface-structures must have 
led to numerous colour-changes, which have been sometimes 
checked, sometimes fixed and utilised, sometimes intensified, 
1 For further information on this point, see Darwinism , p. 220. 
