ller. Many eggs display, in addition to the
strongly marked spots, more or fewer fainter spots embedded in a deeper
layer of the shell, and hence such eggs are said to be "double-spotted,"
e.g. rails and plovers.

Among some species, as in birds of prey, the intensity of this
coloration is said to increase with age up to a certain point, when it
as gradually decreases. Frequently, especially where but two eggs are
laid (Newton), all the dye will be deposited, sometimes on the first,
sometimes on the last laid, leaving the other colourless. But although
of a number of eggs in a "clutch"--as the full complement of eggs in a
nest is called--no two are exactly alike, they commonly bear a very
close resemblance. Among certain species, however, which lay several
eggs, one of the number invariably differs markedly from the rest, as
for example in the eggs of the house-sparrow or in those of the
sparrow-hawk, where, of a clutch of six, two generally differ
conspicuously from the rest. Differing though these eggs do from the
rest of the clutch, all yet present the characters common to the
species. But the eggs of some birds, such as the Australian swamp quail,
_Synoecus australis_, present a remarkably wide range of variation in
the matter of coloration, no two clutches being alike, the extremes
ranging from pure white to eggs having a greenish ground colour and
rufous spots or blotches. But a still more interesting illustration of
variation equally marked is furnished by the chikor partridge (_Caccabis
chukar_), since here the variation appears to be correlated with the
geographical distribution of the species. Thus eggs taken in Greece are
for the most part cream-coloured and unspotted; those from the Grecian
Archipelago are generally spotted and blotched; while more to the
eastward spots are invariably present, and the blotches attain their
maximum development.

But in variability the eggs of the guillemot (_Lomvia troile_) exceed
all others: both in the hue of the ground colour and in the form of the
superimposed markings, these eggs exhibit a wonderful range for which no
adequate explanation has yet been given.

Individual peculiarities of coloration are commonly reproduced, not only
with this species but also in others, year after year.

Significance of colour.

The coloration of the egg bears no sort of relation to the coloration of
the bird which lays it; but it bears on the other hand a more or less
direct rel