202 The Field Naturalist's Quarterly August 



scarcely be able to identify a perfectly fresh egg. Other 

 birds which lay an almost white egg with thick shell in 

 open nests are the cormorants, gannets, swans, and harriers. 

 These are large and powerful birds, all well able to protect 

 their treasures. 



Where eggs are laid in holes of the earth, trees, or 

 buildings, entirely concealed from the light, there we should 

 expect to find least colouring matter in the shells ; whilst, on 

 the other hand, the more the nesting habits of the bird 

 expose the eggs to the noonday glare, and so to passers-by, 

 the more darkly are they coloured. Light, too, is inimical 

 to protoplasm and the growth of germ life generally, and so 

 unconcealed eggs are usually dark in colour or thick in 

 texture of shell. Purely white eggs are always by some 

 means protected both from the direct rays of the sun and 

 prying eyes. The eggs of the house-sparrow, with its 

 double nesting habits, sometimes building in a tree, at 

 others in holes, vary immensely even in one and the same 

 nest, in the density of their surface markings, and may be 

 in a transition stage. This is a bold and hardy bird, and 

 a careless architect : but evidence of a process of evolution 

 being at work may be discovered in the one unusually 

 light-coloured egg which nearly every clutch of the tree- 

 sparrow contains. 



Tinted eggs, or eggs with a uniformly coloured shell 

 without any darker surface markings, are produced by those 

 birds which build chiefly in holes, and as with those birds 

 which lay clear white eggs with red spots, in similar situ- 

 ations, so here, those which make the most elaborate nest 

 in larger or more open holes, these lay eggs more highly 

 coloured in their ground tint, and also with more conspicu- 

 ous superficial markings, and vice versa. For example, 

 starlings' eggs are sometimes almost white, and their shell is 

 comparatively thin and clear : these birds make but a poor 

 nest, and the eggs are generally well hidden from the light ; 

 whilst the handsome eggs of the jackdaw are laid in a far 

 better nest and are more or less exposed to daylight — in 

 fact, several instances are on record of the jackdaw building 

 an open nest. It has been suggested that birds nesting 

 in comparative darkness require white eggs in order that 



