352 TROPICAL NATURE v. 
The universal avoidance by carnivorous animals of all 
these specially protected groups, which are thus entirely free 
from the constant persecution suffered by other creatures not 
so protected, would evidently render it advantageous for 
any of these latter which were subjected to extreme persecu- 
tion to be mistaken for the former; and for this purpose it 
would be necessary that they should have the same colours, 
form, and habits. Now, strange to say, wherever there is 
a large group of directly-protected forms (division a of animals 
with warning colours), there are sure to be found a few other- 
wise defenceless creatures which resemble them externally so 
as to be mistaken for them, and which thus gain protection, 
as it were, on false pretences (division b of animals with 
warning colours). This is what is called “mimicry,” and it 
has already been very fully treated of by Mr. Bates (its dis- 
coverer), by myself, by Mr. Trimen, and others. Here it is 
only necessary to state that the uneatable Danaide and 
Acreide are accompanied by a few species of other groups 
of butterflies (Leptalide, Papilios, Diademas, and Moths), 
which are all really eatable, but which escape attack by their 
close resemblance to some species of the uneatable groups 
found in the same locality. In like manner there are a few 
eatable beetles which exactly resemble species of uneatable ° 
groups; and others, which are soft, imitate those which are 
uneatable through their hardness. For the same reason 
wasps are imitated by moths, and ants by beetles; and even 
poisonous snakes are mimicked by harmless snakes, and 
dangerous hawks by defenceless cuckoos. How these curious 
imitations have been brought about, and the laws which 
govern them, have been already discussed. (See p. 54.) 
Sexual Colowrs 
The third class comprises all cases in which the colours of 
the two sexes differ. This difference is very general, and 
varies greatly in amount, from a slight divergence of tint up 
to a radical change of coloration. Differences of this kind 
are found among all classes of animals in which the sexes are 
separated, but they are much more frequent in some groups 
than in others. In mammalia, reptiles, and fishes, they are 
