Learning Resources Chick Life Cycle Exploration Set Handbuch Seite 2

Chalazae: As the egg goes down through the
oviduct, it is continually rotating within the
spiraling tube. This movement twists the
structural fibers (called the chalazae), which
form rope-like strands that anchor the yolk in
the thick egg white. There are two chalazae
anchoring each yolk, on opposite ends of
the egg.
Eggshell: The eggshell is deposited around
the egg in the lower part of the oviduct of
the hen just before the egg is laid. The shell
is made of calcite, a crystalline form of
calcium carbonate. Chicken eggshells can
come in a variety of colors and sizes
depending on the type of chicken.
This entire trip through the oviduct takes
about one day.
Growth of the Embryo: The fertilized egg
(called the blastoderm) grows and becomes
the embryo. As the embryo grows, its primary
food source is the yolk. Waste products (like
urea) collect in a sack called the allantois. The
exchange of oxygen and carbon dioxide gas
occurs through the eggshell. The chorion lines
the inside surface of the egg and is connected
to the blood vessels of the embryo.
The Incubation Period: The embryo develops
inside the egg for 21 days until a chick pecks
its way out of its eggshell and is hatched.
The hen sits on the eggs until they hatch. The
hen only leaves the eggs briefly to eat and
drink, but returns quickly to keep them
warm. The chart below shows the stage of
the egg at each day of development. This
chart matches the artwork used on the cross-
section egg models.
Chicken eggs require 21 days to hatch, but
the incubation period for the eggs of other
species of poultry varies.
Definitions:
air cell an empty space located at the large
end of the egg, between the inner and outer
shell membranes
chalaza a spiral, rope-like strand that anchors
the yolk in the thick egg white; there are two
chalazae anchoring each yolk, one on the top
and one on the bottom (the plural of chalaza
is chalazae)
germinal disc or blastodisc a small circular
white spot (2–3 mm across) on the surface of
the yolk where the sperm enters the egg; the
nucleus of the egg is in the blastodisc
inner shell membrane the thin membrane
located between the outer shell membrane
and the albumin
outer shell membrane the thin membrane
located just inside the shell
shell made of calcium carbonate, it is the
hard, semi-permeable, protective coating
of the egg that lets gas exchange occur
and keeps other substances from entering
the egg.
thick albumin the stringy part of the egg
white (albumin) located nearest the yolk
thin albumin the watery part of the egg
white (albumin) located farthest from
the yolk
vitelline (yolk) membrane the membrane
that surrounds the yolk
yolk the yellow, inner part of the egg where
the embryo will form; contains the food that
will nourish the embryo as it grows