COLOURS OF ANIMALS. 177 



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 discussed in the work already referred to. 



Sexual Colours. 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 

 comparatively rare, and not great in amount, whereas 

 among birds they are very frequent and very largely 

 developed. So among insects, they are abundant in 

 butterflies, while they are comparatively uncommon in 

 beetles, wasps, and hemiptera. 



The phenomena of sexual variations of colour, as 

 well as of colour generally, are wonderfully similar in 

 the two analogous yet totally unrelated groups of birds 

 and butterflies ; and as they both offer ample materials, 

 we shall confine our study of the subject chiefly to 

 them. The most common case of difference of colour 

 between the sexes, is for the male to have the same 

 general hue as the females, but deeper and more 



