evergreens, as holly or ivy, or surrounded by the delicate green
tints of our early spring vegetation, and may thus harmonise very well
with the colours around them. The great majority of the eggs of our
smaller birds are so spotted or streaked with brown or black on
variously tinted grounds that, when lying in the shadow of the nest and
surrounded by the many colours and tints of bark and moss, of purple
buds and tender green or yellow foliage, with all the complex glittering
lights and mottled shades produced among these by the spring sunshine
and by sparkling raindrops, they must have a quite different aspect from
that which they possess when we observe them torn from their natural
surroundings. We have here, probably, a similar case of general
protective harmony to that of the green caterpillars with beautiful
white or purple bands and spots, which, though gaudily conspicuous when
seen alone, become practically invisible among the complex lights and
shadows of the foliage they feed upon.

In the case of the cuckoo, which lays its eggs in the nests of a variety
of other birds, the eggs themselves are subject to considerable
variations of colour, the most common type, however, resembling those of
the pipits, wagtails, or warblers, in whose nests they are most
frequently laid. It also often lays in the nest of the hedge-sparrow,
whose bright blue eggs are usually not at all nearly matched, although
they are sometimes said to be so on the Continent. It is the opinion of
many ornithologists that each female cuckoo lays the same coloured eggs,
and that it usually chooses a nest the owners of which lay somewhat
similar eggs, though this is by no means universally the case. Although
birds which have cuckoos' eggs imposed upon them do not seem to neglect
them on account of any difference of colour, yet they probably do so
occasionally; and if, as seems probable, each bird's eggs are to some
extent protected by their harmony of colour with their surroundings, the
presence of a larger and very differently coloured egg in the nest might
be dangerous, and lead to the destruction of the whole set. Those
cuckoos, therefore, which most frequently placed their eggs among the
kinds which they resembled, would in the long run leave most progeny,
and thus the very frequent accord in colour might have been brought
about.

Some writers have suggested that the varied colours of birds' eggs are
primarily due to the effect of surrounding