362 
BIRDS. 
each side to the common membrane glued to the 
shell. Should a line be drawn from one ligament to 
the other, it would not exactly pass through the 
middle of the yolk, but above the centre, and would 
cut the yolk into two unequal parts, so that the 
smallest part of the yolk, which contains the seed, 
is of necessity raised towards the belly of the bird 
who performs the incubation ; and the other part, 
being more gross and weighty, always descends as 
near the bottom as the bands will permit; by 
which means, should the egg be displaced, the 
young could not receive any injury ; and whatever 
may happen, it enjoys a warmth that puts all about 
it in action, and by degrees completes the disen- 
gagement of its parts. As it is incapable of sliding 
down, it nourishes itself in ease, first with this 
liquid and delicate white, which is adapted to its 
condition, and afterwards with the yolk, which af- 
fords a more substantial food. By the time the 
bird has so far increased in size as to fill the shell, 
his beak is become sufficiently hardened to assist 
him in breaking through the walls of his prison. 
This he readily effects, and issues forth fully re- 
plenished with the yolk, which nourishes him a lit- 
tle longer, till he has strength enough to get on his 
feet and seek his own living, or until his parents 
come themselves to supply him. 
Some birds, when they leave the shell, are fed by 
their parents, while others seek their own provi- 
sion. The birds who nourish their young have 
commonly very few ; on the contrary, those whose 
