ation to the nature of the environment during incubation.

White eggs may generally be regarded as representing the primitive type
of egg, since they agree in this particular with the eggs of reptiles.
And it will generally be found that eggs of this hue are deposited in
holes or in domed nests. So long indeed as nesting-places of this kind
are used will the eggs be white. And this because coloured eggs would be
invisible in dimly lighted chambers of this description, and therefore
constantly exposed to the risk of being broken by the sitting bird, or
rolling out of reach where the chamber was large enough to admit of
this, whereas white eggs are visible so long as they can be reached by
the faintest rays of light. Pigeons invariably lay white eggs; and while
some deposit them in holes others build an open nest, a mere platform
of sticks. These exceptions to the rule show that the depredations of
egg-eating animals are sufficiently guarded against by the overhanging
foliage, as well as by the great distance from the ground at which the
nest is built. Birds which have reverted to the more ancient custom of
nesting in holes after having developed pigmented eggs, have adopted the
device of covering the shell with a layer of chalky matter (e.g.
puffins), or, to put the case more correctly, they have been enabled to
maintain survival after their return to the more ancient mode of
nidification, because this reversion was accompanied by the tendency to
cover the pigmented surface of the shell with this light-reflecting
chalky incrustation.

Eggs which are deposited on the bare ground, or in other exposed
situations, are usually protectively coloured: that is to say, the hue
of the shell more or less completely harmonizes with the ground on which
the egg is placed. The eggs of the plover tribe afford the most striking
examples of this fact.

But the majority of birds deposit their eggs in a more or less
elaborately constructed nest, and in such cases the egg, so far from
being protectively coloured, often displays tints that would appear
calculated rather to attract the attention of egg-stealing animals;
bright blue or blue spotted with black being commonly met with. It may
be, however, that coloration of this kind is less conspicuous than is
generally supposed, but in any case the safety of the egg depends not so
much on its coloration as on the character of the nest, which, where
protective devices are necessary, must harmo