96 KINSHIP OF BIRDS, AS SHOWN BY EGGS, 
It is possible, therefore, that birds may have themselves 
developed significant colors, protective and sexual, while 
the egg was yet untinted. 
Unfortunately for us there are no fossil colors; but the 
development of the egg in the oviduct hints embryologi- 
cally that color is comparatively a rather recent acquisition 
in the history of the egg. Far up in the oviduct, where the 
shell has just begun to form, the most boldly marked eggs 
are usually plain white, and the intenser colors are laid on 
last. The fact that young birds as a rule are said to lay 
paler eggs than the older ones indicates the same thing. 
‘There are colored eggs found among all groups of the lowest 
known birds now living, but these are comparatively young. 
The shell structure, egg shape and even the tint of yelk, 
as well as the surface color show traces of the various strains 
of kinship that come into it, as shown by hybrid eggs; 
and the usually much less distinctly marked shells of un- 
fertilized eggs show the very potent varying influence of the 
male here as elsewhere. 
The growth of the egg in the oviduct would seem to indi- 
cate that the first change from being white was a solid 
tinting of the whole surface. 
While among the low birds now a pinkish or reddish 
brown ground-color generally prevails (with exceptions), 
perhaps taking them all in all some shade of blue or green, 
or their combination, seems to have been the primary color. 
Since, however, shell-formation must be a highly congestive 
process, and since egg-stains seem so closely connected with 
blood-pigments, it would seem not improbable that pinkish 
or diluted blood-stains may have been the beginning of color. 
In this connection it is interesting to note that in some of 
the Megapodes (or Brush Turkey family), whose nesting is 
by burial either in the ground or in a mound—approaching 
very closely that of the crocodile—the eggs are a brickish- 
red often. If this form of nesting is primary, here is color 
before exposure—color it may be as an incident or accident 
