COLOUR IN BIRDS’ EGGS. 207 
interest per se, and which will be of still higher value if we can 
discern their bearing on biological problems. 
We take it that the natural or original colour of birds’ egos 
is the pure white of the mineral substance (carbonate of lime) of 
which they are composed, just as the natural colour of bone is 
white, and that, too, of the shells of mollusca, &c. All shells 
are secreted by animal membranes. In the mollusca, an external 
layer of membrane usually remains free from admixture of 
mineral matter, as an animal epidermis, which can be peeled 
off. But this is not the case with birds’ eggs; they possess a 
membranous lining, generally white, occasionally brownish or 
bluish, but outside this the animal substance and mineral matter 
are intimately commingled to the very surface. Colour, if pro- 
duced, is then, in almost all eggs, ingrained. Often it can be 
detected incorporated in the inner layers of the shell, as blotches 
beneath the surface. 
Birds’ eggs have many foes. Even where man has not 
appeared upon the scene, a number of systematic nest-robbers 
exist. Snakes, the great Lace-Lizard (Hydrosaurus or Varanus 
varius), which takes such liberties with the settlers’ hen roosts, 
the ‘native cats” (Dasyurus viverrinus and D. maculatus we 
perhaps the Bush Rats, and last, but by no means least, other 
birds, and especially the crows, are very destructive of our 
native birds’ eggs, and of the young birds in the nest. To such 
intruders pure white eggs would be a conspicuous and gratuitous 
advertisement, and the birds would be exposed to undue danger 
while in the egg. As has been remarked hundreds of times 
before, we accordingly find that white eggs, and especially eggs 
of shining or pearly whiteness, are almost always found in nests 
which either conceal the eggs completely, or which are them- 
Selves completely concealed. Thus the cookatoos, parrots, 
parrakeets, and other members of the family, in almost all 
cases, build in holes of trees, usually high up and quite out of 
reach. Owls build in holes of large gum trees; Kingfishers, 
including the Laughing Jackass /Dacelo gigas) in holes of trees 
or banks ; the Diamond Birds, the Roller, and Bee-eater, in holes 
in trees or in burrows. The Penguins and many of the Petrels 
lay their eggs at the extremities of long burrows in the ground, 
facing the sea. The eggs of all of these birds are white. 
The eggs of the doves, pigeons, and podarguses, are 
