28 CHELTENHAM COLLEGE NATURAL HISTORY SOCIETY, 
while the cock has been more free to vary. What proofs have we 
that the duller colour was the original one? Well, we know the life 
of every young animal is, as it were, an epitome of the history of the 
class to which it belongs, that in its early youth it resembles its more 
remote ancestors, and as it grows older develops the characters of the 
more immediate ones. For instance, young rooks have, like other 
birds of the family of the Corvida, feathers at the base of the beak, 
but after the first moult they lose these feathers and have a bare 
patch, which fits them for the peculiar life of rooks, that is, for digging 
in the moist soil for grubs, etc. 
Now we find that the plumage of young birds generally approxi- 
mates to that of the hens, whereas, later the young cocks get their 
brighter feathers, and in this way we get a peep at the ancestral 
plumage. Whilst speaking of this theory that colouring in birds is 
often protective, let us see how far the theory is borne out in the case 
of eggs. 
First let us notice a law that is of equally wide application, which 
is, that the eggs of closely allied birds, that is, of birds who are 
descended from a common ancestor, are, as we should expect, some- 
what similar. For instance, here I have examples of eggs of different 
gulls, which you see are very much alike ; here, examples of the 
family Corvide—the rook, the carrion crow, the jackdaw, the magpie, 
and the jay—and they again are similar, and here you have the same 
thing in some of the finch family. But as well as the fact of the 
similarity of the eggs of allied birds, we do get a great number 
of instances of protective colouring. For instance, eggs laid on the 
ground or on slight nests on the ground are commonly mottled 
browns or light olive browns, as the lapwing and the pheasant ; when 
among stones the colouris buff or stone-coloured, as in the eggs of 
gulls or terns. When the eggs are laid in trees or bushes the ground 
colour of the egg is commonly blue or green, so that they are not 
very obvious among the surrounding foliage. If, like the blackbird’s, 
the nest is in an evergreen or in a very thick bush where little light 
penetrates the eggs are duller in colouring. The chaffinch’s eggs 
are not very conspicuous, for the hen lines the nest with lichen and 
moss very like them in colour. 
But how are we to account for the existence of white eggs,—these 
may be laid under several conditions, by birds that lay their eggs in 
holes, in banks, or trees, as the sand-martin, and the wood-owl. We 
find white eggs laid by birds who make dome-shaped nests, as the 
wrens and chiff-chaff, or they may be white in those cases in which 
