52 The Action of Light upon the [January, 
pupae, either in the earth, in the trunks of trees, or other 
localities where neither beauty can betray them nor its lack 
screen them from the pursuit of any enemy. 
As the first among the causes of colouration he places the 
need of protection. He points out that browns and other 
tertiary colours, being most readily produced by “ an irre- 
gular mixture of many kinds of solar rays, are most likely 
to occur when the need of protection is slight, or even when 
it does not exist at all, always supposing that bright colours 
are not in any way useful to the species.” Hence browns, 
olives, and other dirty colours may naturally be expected to 
predominate. 
Brilliant colours, again, often serve as a sign that their 
wearer possesses some unpleasant or dangerous property, 
and hence warn possible enemies to pass on and seek some 
less nauseous prey. The number of apparently feeble and 
defenceless species which are clad in the most conspicuous 
colours, and which are avoided and refused by birds, 
monkeys, spiders, &c., is astonishing. The present writer, 
in a paper read before the Entomological Society (Trans. 
Ent. Soc., 1877, ^ art HI., p. 205) has shown that, in a 
great number of cases at least, the most showy and 
conspicuous caterpillars feed upon plants either absolutely 
poisonous or possessing offensive flavours and odours, 
whence the rejection of such larvae by insectivorous animals. 
Their brilliant colouration is therefore simply a danger- 
signal. 
The theory of “ Sexual Selection,” upon which Mr. Darwin 
lays great weight, Mr. Wallace finds himself unable to 
accept as in any way an explanation of the distribution of 
colour in animals. He remarks that “ whilst male butter- 
flies rival, or even excel, the most gorgeous male birds in 
bright colours and elegant patterns, there is literally not 
one particle of evidence that the female is influenced by 
colour, or even that she has any power of choice, whilst 
there is much direCt evidence to the contrary.” In the case 
of the silk-moth Mr. Darwin admits that “ the females 
appear not to evince the least choice in regard to their 
partners.” On the principle of natural selection among a 
number of rival male butterflies, “ the most vigorous and 
energetic ” will probably be successful, and, as these pro- 
perties are very generally correlated with intensity of colour, 
natural selection “ becomes a preserver and intensifier of 
colour.” Very similar is the case among birds. We know 
that in many species the male displays his colours and 
ornaments, but, as Mr. Wallace contends, there is a tota 
