Page 72 - Design in Nature

Air space
Outer layer of
A Necessary Loss
thin albumin
Dense albumin During incubation, the egg
loses 16% of its water content in
Chalazae
Inner layer of the form of evaporation. Scientists
thin albumin
long believed this to be harmful
Latebra
Yellow yolk and due to the porous structure of
the eggshell. However, the most
recent research shows this loss to
Shell be necessary for the chick to emerge

from the egg. The chick needs oxygen
Germinal disc and space to be able to move its head
just enough to crack the shell while
Section of egg
hatching. The evaporation of water creates the
room and oxygen required.
Furthermore, water loss ratio is adjusted to vary between 15 to 20% for

ideal conditions depending on the type of eggshell. For instance, water loss
in the eggs of loons is a few times higher than in others that incubate under
dryer conditions.

Chicks have a special "egg tooth" that they
use only to hatch the egg. This tooth is
formed just before hatching and,
amazingly, disappears after hatching.
The eggshell is strong enough to
protect the embryo during twenty
days of incubation. However, it is
also easily breakable so that the
chick can emerge.