1877.] The Colors of Animals and Plants. 653 
the colors of the two sexes differ. This difference is very gen- 
eral, 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 compara- 
tively rare and not great in amount, whereas among birds they 
are very frequent and very largely developed. So among in- 
sects, they are abundant in butterflies, while they are compara- 
tively uncommon in beetles, wasps, and hemiptera. 
The phenomena of sexual variations of color, as well as of color 
generally, are wonderfully similar in the two analogous yet to- 
tally unrelated groups of birds and butterflies ; and, as they both 
otter ample materials, we shall confine our study of the subject 
chiefly to them. The most common case of difference of color be- 
tween the sexes is for the male to have the same general hue as 
the females, but deeper and more intensified, as in many thrushes, 
finches, and hawks, and among butterflies in the majority of our 
British species. In cases where the male is smaller the intensi- 
fieation of color is especially well pronounced, as in many of the 
hawks and falcons, and in most butterflies and moths in which 
the coloration does not materially differ. In another extensive 
series we have spots or patches of vivid color in the male which 
are represented in the female by far less brilliant tints, or are al- 
_ together wanting, as exemplified in the gold-crest warbler, the 
green woodpecker, and most of the orange-tip butterflies (Antho- 
charis).. Proceeding with our survey we find greater and greater 
differences of color in the sexes, till we arrive at such extreme 
Canes as some of the pheasants, the chatterers, tanagers, and 
birds-of-paradise, in which the male is adorned with the most 
gorgeous and vivid colors, while the female is usually dull brown 
or olive-green, and often shows no approximation whatever to 
the varied tints of her partner. Similar phenomena occur among 
utterflies ; and in both these classes there are also a considera- 
ble number of cases in which both sexes are highly colored in a 
different way. Thus many woodpeckers have the head in the 
male red, in the female yellow; while some parrots have red 
Spots in the male, replaced by blue in the female, as in Psittac- 
wla diopthalma. In many South American papilios green spots 
ae the male are represented by red on the female ; and in several 
Species of the genus Epicalia orange bands in the male are re- 
Placed by blue in the female, a similar change of color as in the 
