Chicken embryos subjected to incubation at certain durations
excellent sources of information for actual scrutiny of the early embryonic development at the macroscopic level.
The different hours of incubation used in this activity
chosen to distinctively show the highlight of the macroscopic changes in the early development of the said embryo.
Incubate six (6) chicken eggs at 37°C but at varying durations - two eggs at 13, 17 and 21 hours, respectively.
After each of the desired incubation periods have been attained, crack the eggs and observe the macroscopic structures of the embryo.
Point of reference in observation
Cranial to caudal
Dorsal to ventral
Left to right
Point of reference in observation
Cranial to caudal
Dorsal to ventral
Left to right
Dorsal to ventral
Observe the positioning of the body structures.
Cranial to caudal
Observe from the head to the tail.
Left to right
Observe the angle of the body and the head.
Observable embryonic structures
Egg membrane systems
Positioning of the head
Size of the head
Size of the body
Weight of the embryo
Amount of the amniotic fluid
Egg membrane systems
These structures include all egg coverings such as vitelline membrane, chorion and tertiary membranes.
Membrane systems present at 13th hour
area opaca
area pellucida
also, early signs of gastrulation
Membrane systems present at 17th hour
Formation of primitive streak
Initial formation of the following membranes: yolk sac, amnion. allantois, and chorion
Membrane systems present at the 21st hour:
differentiation of primitive streak to neural tube
further development of membranes (heart and blood vessels are visible)
POSITIONS OF THE HEAD (13 hour)
Head is positioned ventrally; positioned towards the belly side or underside of the embryo
POSITIONS OF THE HEAD (17 hour)
Head rotates dorsally; with similar orientation at 13 hours
POSITIONS OF THE HEAD (21 hour)
Head continues to develop dorsally, facing towards the back or posterior direction
OTHER CHARACTERISTICS OF EMBRYO
13th: visible blood vessel formation, the presence of an initial primitive streak, and signs of intermediate development
17th: alimentary tract starts to form
21st: network of blood vessels radiating outwards,developing heart or a concentration of blood cells
What are some properties of an amniote egg?
Albumin, or egg white
Egg yolk
Three extra-embryonic membranes
Inner amniotic membrane
Three extra-embryonic membrane
Chorion
Amnion
Allantois
CHARACTERISTICS OF AMNIOTES
reptiles, birds, and mammals
terrestrially-adapted egg, which is protected by amniotic membranes
Amniotic membranes
Meant that the embryos of amniotes were now provided with their own aquatic environment, which led to less dependence on water for development, allowing the amniotes to branch out into drier environments.
Bird eggs
Composed of calcium carbonate
Reptile eggs
leathery and require a moist environment
Mammals
Do not lay eggs (except for monotremes). Instead, the embryo grows within the mother’s body; however, even with this internal gestation, amniotic membranes are still present
Bird eggs
Composed of calcium carbonate
Reptile eggs
leathery and require a moist environment
Mammals
Do not lay eggs (except for monotremes). Instead, the embryo grows within the mother’s body; however, even with this internal gestation, amniotic membranes are still present
Bird eggs
Composed of calcium carbonate
Reptile eggs
leathery and require a moist environment
Mammals
Do not lay eggs (except for monotremes). Instead, the embryo grows within the mother’s body; however, even with this internal gestation, amniotic membranes are still present
Shell
Allow retention of water
provides protection for the developing embryo while being permeable enough to allow for the exchange of carbon dioxide and oxygen
Albumin, or egg white
provides the embryo with water and protein
Egg yolk
energy supply for the embryo, as is the case with the eggs of many other animals, such as amphibians
Extra-embryonic membrane
those present in amniotic eggs that are not a part of the body of the developing embryo
Inner amniotic membrane
surrounds the embryo itself
Chorion
Surrounds the embryo and yolk sac
facilitates exchange of oxygen and carbon dioxide between the embryo and the egg’s external environment
Amnion
protects the embryo from mechanical shock and supports hydration
Allantois
stores nitrogenous wastes produced by the embryo and also facilitates respiration
Air space
found at the blunt end of the chick egg
Air space function/s
initial source of oxygen when it begins to break through the eggshell
allows egg's content to expand and contract with temp changes
act as a protective barrier, shielding from sudden movements
Cleavage pattern in the chick egg
partial and discoidal cleavage
Term for the cleavage pattern
Meroblastic
Describe the cleavage pattern
partial and discoidal cleavage
Term of cleavage pattern
Meroblastic
Describe the cleavage pattern
partial and discoidal cleavage
Term of cleavage pattern
Meroblastic
Discoidal
involves the protoplasm, located as a cap over the yolk mass, during the early to mid-cleavage stage.
Meroblastic cleavage
characteristic of eggs with a significant amount of yolk, such as those of birds and reptiles, and allows for the formation of a blastoderm for embryo development, utilizing the yolk as a nutrient reserve for the developing chick.