EVENTS IN EMBRYONIC DEVELOPMENT
i) Before Laying & Incubation
• Fertilization, cell division, and segregation into tissues occur before laying.
Early cleavage 3.5-4.5 hr The shell membrane of the egg is formed in the
isthmus of the oviduct
During cleavage The germ wall is formed from the marginal
periblast.
Late cleavage 4.5-24 hr Shell egg is formed in the uterus
ii) Between laying and incubation
• There is no growth (inactive embryonic life)
iii) During Incubation
Day 1:
• 16 hours- first sign of resemblance to a chick embryo
• 18 hours- appearance of the alimentary tract
• 20 hours- appearance of vertebral column
• 21 hours- beginning of the nervous system
• 22 hours- beginning of head
• 24 hours- beginning of eye
On day one, the yolk sac starts to develop. In addition, the blastoderm develops to the size of a
quarter and contains the start of the chick’s head (with brain and eyes), spine, and blood vessels,
including the nervous and digestive systems. By the end of the first day of incubation, blood
islands appear.
Day 2:
• 25 hours- beginning of heart
• 35 hours- beginning ear
• Circulation of blood begins after about 40 hours of incubation.
, • 42 hours- Heart beats
The amniotic and chorionic membranes begin to develop; faint blood vessels (the vitelline
vessels) appear on the surface of the yolk, along with the start of the heart and ear; by the end of
the day, the heart (the spot in the corner) begins to beat.
Day 3:
• 60 hours- beginning of nose
• 62 hours- beginning of legs
• 64 hours- beginning of wings
• The embryo, shaped like a question mark
• begins to take shape as the lungs, nose, legs, wings, and tail
• allantois form, and the amniotic sac grows to surround it
• blood vessels become visible.
Day 4:
• Beginning of tongue
The embryo separates from the yolk sac, rises on the yolk, turns onto its left side, and begins to
curve at the tail; the tongue begins to develop; it starts to take colour.
Day 5:
• formation of reproductive organs and differentiation of sex.
• leg bones, crop, and circulatory system begin to develop
• chorion and allantois begin fusing
• the start of the beak appears
• The eye is now clearly visible.
Day 6:
• The beak begins to form.
i) Before Laying & Incubation
• Fertilization, cell division, and segregation into tissues occur before laying.
Early cleavage 3.5-4.5 hr The shell membrane of the egg is formed in the
isthmus of the oviduct
During cleavage The germ wall is formed from the marginal
periblast.
Late cleavage 4.5-24 hr Shell egg is formed in the uterus
ii) Between laying and incubation
• There is no growth (inactive embryonic life)
iii) During Incubation
Day 1:
• 16 hours- first sign of resemblance to a chick embryo
• 18 hours- appearance of the alimentary tract
• 20 hours- appearance of vertebral column
• 21 hours- beginning of the nervous system
• 22 hours- beginning of head
• 24 hours- beginning of eye
On day one, the yolk sac starts to develop. In addition, the blastoderm develops to the size of a
quarter and contains the start of the chick’s head (with brain and eyes), spine, and blood vessels,
including the nervous and digestive systems. By the end of the first day of incubation, blood
islands appear.
Day 2:
• 25 hours- beginning of heart
• 35 hours- beginning ear
• Circulation of blood begins after about 40 hours of incubation.
, • 42 hours- Heart beats
The amniotic and chorionic membranes begin to develop; faint blood vessels (the vitelline
vessels) appear on the surface of the yolk, along with the start of the heart and ear; by the end of
the day, the heart (the spot in the corner) begins to beat.
Day 3:
• 60 hours- beginning of nose
• 62 hours- beginning of legs
• 64 hours- beginning of wings
• The embryo, shaped like a question mark
• begins to take shape as the lungs, nose, legs, wings, and tail
• allantois form, and the amniotic sac grows to surround it
• blood vessels become visible.
Day 4:
• Beginning of tongue
The embryo separates from the yolk sac, rises on the yolk, turns onto its left side, and begins to
curve at the tail; the tongue begins to develop; it starts to take colour.
Day 5:
• formation of reproductive organs and differentiation of sex.
• leg bones, crop, and circulatory system begin to develop
• chorion and allantois begin fusing
• the start of the beak appears
• The eye is now clearly visible.
Day 6:
• The beak begins to form.
