viii ORIGIN AXD USES OF COLOUR IX AXIMALS 213 



great divisions ; those Avhich are M'hite 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 pro- 

 A'ails 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. Xoav, 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 pufhns, which nest in holes in the 

 ground ; Anth 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, A\Tens, 

 willow- warblers, and Australian finches, Ijuild 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 aftbrd some very in- 

 teresting examples of the varied modes by Avhich 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 gTound pigeons, 

 lay their Avhite 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 Avhite and 

 shining ; yet it is a difficult matter to discover, from beneath, 

 Avhether there are eggs in the nest or not, while they are Avell 

 hidden l)y the thick foliage above. The Australian podargi — 



