The air space between the two shell membranes, usually in the large end of the egg.
Allantois
A sac-like organ of an embryo that obtains oxygen, nourishment, and calcium from the egg; and in which is deposited the embryo's waste products.
Amnion
A sac filled with fluid that surrounds the embryo and protects it from injury.
Avian
Of, relating to, or characteristic to birds.
Avian egg
A bird egg composed of the shell, shell membranes, albumen, and yolk containing the true egg or ovum.
Blastoderm
A fertilized true egg.
Blastodisc
A true egg that has not been fertilized.
Chalazae
The two whitish cords attached to the yolk of an egg which hold the yolk in the center of the albumen.
Chick tooth
The tiny, horny projection on the top of the chick's beak which it uses to peck holes in the shell when hatching.
Chorion
A membrane surrounding both the yolk sac and the amnion.
Cloaca
The vent or common opening in birds through which the digestive, urinary, and reproductive tracts empty.
Down
Soft, fine, hair-like feathers on young birds.
Egg
The microscopic reproductive cell of the female; the true egg or ovum. Also see Avian egg.
Embryo
The early stage in development of the chick within the egg.
Embryology
The study of the formation and development of embryos.
Extraembryonic membranes
Membranes outside the embryo's body that provide respiration, nutrition, excretion, and protection. They include the yolk sac, amnion, allantois, and chorion.
Fertilization
The union of a male reproductive cell with a female reproductive cell.
Fetus
The chick during the later development stages in the egg.
Follicle
The sac in which an ovum and its yolk are held until the yolk matures and is released.
Humidity
Moisture in the air.
Incubation
The process of applying heat to eggs and causing them to hatch.
Infundibulum
The upper, funnel end of the oviduct that picks up the yolk after its release from the ovary.
Isthmus
The section of the oviduct following the magnum; it forms the inner and outer shell membranes of the egg.
Magnum
The section of the oviduct between the infundibulum and isthmus where the thick white of an egg is formed.
Ovary
The female organ that holds the true eggs cells and produces the yolks.
Oviduct
The female bird organ which puts the albumen, shell membranes, and shell around the yolk.
Oviposition
The release of an avian egg from the oviduct.
Ovulation
The release of a true egg or ovum from a follicle in the ovary.
Ovum
The female germ cell or true egg; plural form is ova.
Pip
To break through or peck holes in the shell by the chick.
Primitive streak
A vertical, opaque line where the embryo begins to grow and develop.
Sperm
The microscopic reproductive cell of a male; the male germ cell.
Uterus
The section of the oviduct next to the isthmus that secretes a portion of the albumen and all of the shell and shell pigment.
Vagina
The final section of the oviduct connected to the cloaca. The cuticle or "bloom" on an egg is added here before lay.
Yolk sac
The portion of the unused yolk drawn into the chick before hatching.
