118 THE STORY OF THE BIRDS. 
Usually such birds as have long built in holes have 
their eggs white. But there are many hole builders 
that lay beautifully marked eggs, as the sparrow hawks 
and others. The case here is perhaps similar. The 
egos were originally marked in keeping with an ex- 
posed nest, and they retain in their hieroglyphics the 
history of the family, if we could only read it. Doubt- 
less every marked bird’s egg is a palimpsest story of 
the bird, with pedigree after pedigree written over it. 
Some of the white eggs of hole builders have perhaps 
never been colored or marked, but others doubtless 
may be blank by losing their family record. Among 
the colored eggs of many birds to-day there are tend- 
encies toward an occasional white egg, and in the 
bluebirds these are rather frequently found. It is 
possible that, since their eggs are no longer more use- 
ful when colored than when plain, the bluebird of 
the very far future may lay a white egg, if it persist 
in hole building. 
If we had space some evidences could be cited 
that the coloring and marking of eggs are compara- 
tively recent. It is shown by the deposit of color in - 
the oviduct, occurring usually when the egg is low 
down only, and then upon the outer layers of the 
shell chiefly. In some grouses and ptarmigans the 
color can be readily rubbed off when the egg is first 
laid. 
On the other hand, in a few birds there is evi- 
dence which seems to show that there is a tendency 
toward losing color. In the cormorants and similar 
forms, in cuckoos and others, the outer layer of the 
