154 CHILDHOOD OF ANIMALS 



these lay their eggs either actually on the ground or on low and 

 visible nests. 



The relation of coloured eggs to the environment is even more 

 difficult to interpret as an intelligible adjustment of condition to 

 environment. The colours of eggs are all due to pigments which 

 are derived from the blood and find their way to the outer surface 

 of the eggshell through the walls of the oviduct. If a bird with 

 an egg nearly ready to lay is frightened so that it rids itself of its 

 burden before the normal time, the premature egg is frequently 

 paler, or even colourless, and if more than one egg is laid, it frequently 

 happens that those which are deposited first are less brightly marked 

 or coloured than their successors. Many birds lay eggs which are 

 very different in appearance from each other. Guillemots and 

 cuckoos are well-known instances of this, and attempts, in my 

 opinion quite unsatisfactory, have been made to show that the 

 cuckoo chooses nests with eggs corresponding in colour to those 

 which she has laid, as the repositories for her own produce. Many 

 of the birds-of-prey, the secretary bird and some petrels, lay white 

 or very pale eggs with irregular blotches or spots of red, the latter 

 in holes, the former on rude heaps of twigs in the open. The South 

 American ostrich or rhea buries her eggs like her African relative, 

 but they are green or yellow at first and afterwards fade to a dirty 

 white. The cassowary and the emu deposit on open nests eggs 

 which are evenly coloured with bright or dark green. Tinamous 

 lay, on the bare ground, highly polished and lustrous eggs, self- 

 coloured with vivid shades which differ remarkably in the different 

 species, chocolate, purple, blue, blue-green or primrose. Turacos 

 lay green eggs on an open platform, the hoopoos green 

 eggs in holes, and the bustards greenish eggs with reddish 

 blotches in rude nests on the ground. Some ibises and spoonbills 

 lay blue eggs in nests on trees. There is rather more uniformity 

 in the case of spotted and blotched eggs, which in many cases are 

 laid on the open ground and may gain some protection from their 

 resemblance with pebbles, a protection which is most efficient in 

 shore-birds. The latter, most of the gulls, coursers, nightjars, 

 cranes and button-quails lay spotted or blotched eggs on the ground, 

 often with the merest scrape in the sand to serve as preparation. 

 Similar eggs are laid by auks in holes or on ledges, by cariamas on 

 the ground, in bushes or on trees, by divers on masses of grass and 

 herbage piled up near the edge of the water, by sun-bitterns on a 

 platform, and by hoatzins on tall trees. Finally, amongst passerine 



