INTRODUCTION. Xxill 
Jackdaw, well provided with the requisite appliances for building an elabo- 
rate nest, rear their young in structures poorly fabricated in the holes of 
trees, rocks, banks, or buildings, or do not make a nest at all. From the 
above-mentioned facts I think that we are perfectly justified in drawing 
the inference that birds are in no way influenced by the appliances they 
possess in building their nests. We have seen that birds are capable, quite 
irrespective of the form of their bills and feet, of making elaborate nests of 
matchless beauty, or poorly fabricated and very plain in appearance, 
respectively, and according to circumstances ; and we may therefore 
‘rest assured that the nest-building capabilities of birds are not in any 
way subordinate to their natural appliances or tools for making their 
nests, but are regulated by, and subordinate to, the various conditions 
under which their young are produced, and especially by the colour of the 
eggs. Why does each species build a different kind of nest? Iam at 
present quite unable to say what influences birds in the choice of their 
materials. Mr. Wallace says that birds select those materials which are 
nearest to hand and easiest to obtain. He may be right; but when we find 
very differently constructed nests in the same localities, almost side by side, 
this explanation does not seem reasonable or sufficient. ‘The above re- 
marks on the nests of birds naturally draw our attention to 
Birds’ eggs studied in relation to their colour.—In these objects 
the chief peculiarity which claims our notice is their beautiful ground- 
colours and varied markings. Why, we naturally ask, do these eggs exhibit 
such diversity of colour? Why are some eggs white, whilst others are 
painted in tints rich and beautiful? or why are some spotless and others 
thickly marked? Some persons may urge that these colours are deve- 
loped for no object beyond that of adding to the beauty and harmony of 
Nature’s works, as they similarly urge the colours of the plumage of the 
birds themselves ; but let us see what an important part the colouring- 
matter of birds’ eggs plays in the economy of the birds—let us see how 
their complex and ever varying colours conform to the subtle influence of 
Law. ‘The colouring-matter of birds’ eggs is influenced by the bird’s 
mode of nidification, and is partly subordinated to the colours of the parents’ 
plumage. For convenience of treatment it is advisable to divide birds’ 
eggs into two great classes, quite irrespective of the affinities of the birds 
themselves, but solely in accordance with the fact of their being coloured 
or uncoloured, spotted or unspotted. Each of these great groups may be 
further subdivided into two subgroups which will include the exceptional 
cases to each. As regards white eggs, our first division will be 
White eggs laid in covered nests.—I think we must start with the 
very probable supposition that the eggs of the earliest forms of bird-life 
were white. Colour is a development for protective purposes, and to that 
cause alone must be ascribed all the wonderful and beautiful diversity of 
