VIII 
ORIGIN AND USES OF COLOUR IN ANIMALS 
213 
great divisions ; those which are white or nearly so, and those 
which are distinctly coloured or spotted. Egg-shells being com¬ 
posed mainly of carbonate of lime, we may assume that the 
primitive colour of birds’ eggs was white, a colour that pre¬ 
vails now among the other egg-bearing vertebrates — lizards, 
crocodiles, turtles, and snakes ; and we might, therefore, expect 
that this colour would continue where its presence had no 
disadvantages. Now, as a matter of fact, we find that in all 
the groups of birds which lay their eggs in concealed places, 
whether in holes of trees or in the ground, or in domed or 
covered nests, the eggs are either pure white or of very pale 
uniform coloration. Such is the case with kingfishers, bee- 
eaters, penguins, and puffins, which nest in holes in the 
ground; with the great parrot family, the woodpeckers, the 
rollers, hoopoes, trogons, owls, and some others, which build in 
holes in trees or other concealed places; while martins, wrens, 
■willow-warblers, and Australian finches, build domed or covered 
nests, and usually have white eggs. 
There are, however, many other birds which lay their 
white eggs in open nests; and these afford some very in¬ 
teresting examples of the varied modes by which concealment 
may be obtained. All the duck tribe, the grebes, and the 
pheasants belong to this class; but these birds all have the 
habit of covering their eggs with dead leaves or other material 
whenever they leave the nest, so as effectually to conceal 
them. Other birds, as the short-eared owl, the goatsucker, 
the partridge, and some of the Australian ground pigeons, 
lay their white or pale eggs on the bare soil; but in these 
cases the birds themselves are protectively coloured, so that, 
when sitting, they are almost invisible; and they have the 
habit of sitting close and almost continuously, thus effectually 
concealing; their eggs. 
Pigeons and doves offer a very curious case of the protec¬ 
tion of exposed eggs. They usually build very slight and 
loose nests of sticks and twigs, so open that light can be 
seen through them from below, while they are generally well 
concealed by foliage above. Their eggs are white and 
shining; yet it is a difficult matter to discover, from beneath, 
whether there are eggs in the nest or not, while they are well 
hidden by the thick foliage above. The Australian podargi— 
