Day 1
Appearance of primitive streak and first somite
Day 2
Appearance of amniotic folds; heart beats; blood circulation
Day 3
Amnion completely encircles embryo; embryo rotates to
left side
Day 4
Eye pigmented; leg buds larger than wing
Day 5
Appearance of elbows and knees
Day 6
Appearance of beak; voluntary movement; demarcation
of digits and toes
Day 7
Comb growth begins; appearance of egg tooth
Day 8
Feather tracts prominent; upper and lower beak equal
in length
Day 9
Bird-like appearance; mouth opening appears
Day 10
Digits completely separated; toe nails
Day 11
Comb serrated clearly; tail feathers apparent; eye lid
oval
Day 12
Eyelids almost closed and elliptical
Day 13
Appearance of overlapping scales; embryo covered with
down; eye lid slit opening
Day 14
Embryo aligned with long axis
Day 15
Small intestines taken into abdomen
Day 16
Feathers cover body
Day 17
Head between legs
Day 18
Head under right wing
Day 19
Amniotic fluid disappears (embryo swallws it); yolk
sac half withdrawn
Day 20
Yolk sac completely drawn into body; beak pips into
air cell
Day 21
Shell pipping; normal hatching
