EGGS OF BIRDS. 
169 
though the kingfisher, for example, hides her shining- white eggs in a 
hole, yet that will not conceal them from the piercing eyes of their 
chief enemy, — the water-rat, — which, like all burrowing animals, can 
see with the least possible light. Many birds, also, which lay bright- 
coloured eggs, make open nests : the thrush, for example, whose clear 
blue eggs, with a few black blotches, are far from being concealed by 
the plastering of clay and cow-dung, upon which they are deposited. 
The green-bird {Frmgilla chloris, Temminck) again, which builds 
an open nest of green moss, lined with horse-hair, black or white, as it 
can be had, lays clear white eggs, with red spots, precisely like those of 
the common wren and the hay-bird, (^Sylvia trochilus^ which build 
covered nests, with a small side entrance ; while the house-sparrow 
{Passer domesticus, Ray) lays eggs of a dull dirty green, streaked 
with dull black, and always builds in holes, or under cover. These 
objections will render it unnecessary for me to follow Darwin into his 
fanciful account of the origin of the colour of eggs, which he ascribes to 
the colour of the objects amongst which the mother bird chiefly lives, 
acting upon the shell through the medium of the nerves of the eye ; for 
if this were correct, we should have the green-bird and the red-breast, 
instead of their white eggs, laying blue ones, like the hedge-sparrow 
and the redstart.* 
With respect to the eggs of birds, it has been remarked by Mr. 
Knapp,^ that in those of one hue, the colouring matter resides in the 
calcareous part ; but where there are markings, these are rather extra- 
neous to it than mixed with it. The elegant blue that distinguishes 
the eggs of the firetail {Sylvia phcenicurusj Lath.) and of the hedge- 
sparrow, though corroded away, is not destroyed by muriatic acid. 
The blue calcareous coating of the thrush’s egg is consumed ; but the 
dark spots, hke the markings on the eggs of the yellow-hammer, house- 
sparrow, magpie, &c., still preserve their stations on the film, though 
loosened and rendered mucilaginous by this calcareous matter, which is 
partly taken up during incubation, the markings upon these eggs remain 
little injured, even to the last, and are almost as strongly defined as when 
the eggs are first laid. These circumstances seem to imply that the 
colouring matter on the shells of eggs does not contribute to the various 
hues of the plumage, but it is reasonable to conclude, are designed to 
answer some particular object not obvious to us ; for though the marks 
are so variable, yet the shadings and spottings of one species never 
wander so as to become exactly figured like those of another family, 
but preserve year after year a certain characteristic figuring. 
* Insect Transformations, p. 35. 
^ Journal of a Naturalist, p. 230. 
