2 THE STORY OF THE BIRDS. 
as soon as it was hatched or born; for we shall see 
later that a baby bird at once begins to look like his 
mother (Chapter IX). 
Perhaps we might set out at that parting of the 
ways between the reptiles and the mammals and_be- 
tween the reptiles and the amphibians, where the 
large egg comes in and the young are capable of being 
nourished for a long time independent of the parent 
or of position in the water; for the yolk of the bird’s 
ege feeds the young bird till hatched, and in some 
cases a short while after, and the hatching is inde- 
pendent of water. 
Then there is the region of better or more cellular 
lungs that we might begin at, or that of a better or 
more extensively chambered heart with warm blood 
pulsing through it; but that would be getting up 
within the realm of the bird itself almost—at least 
upon the border land. Yet the duckbill (with its kin) 
has all these traits and lays an egg and incubates it, 
but it is not a bird or in the line of the bird’s ancestry. 
Surely we may say that birdward tendencies were 
set up when Nature began by skin appendages to carry 
the lizards through the air; but the development of 
this might have missed the bird completely, for these 
lizards are certainly not the ancestors of the bird any 
more than bats are its fellows or descendants. They 
were only evolved out of the same conditions. 
Here, indeed, however, is the true region, for the 
dawning of bird life closely follows the dawning of 
vertebrate flight. Had there been no tendency to fly, 
the true bird could never have been developed. The 
