Jake Harper
The development of a chick is a complex process that takes around 21 days. By the fifth day of incubation, the embryo has already undergone significant changes. The embryo's upper and lower beak are now completely differentiated, along with its legs and wings. The neck continues to lengthen, and the brain has settled into its cavity. The external opening of the ear has formed, and claws start to appear and grow. The allantois, which is responsible for gas exchange and waste management, grows larger, and the first feather follicles begin to appear. The embryo's heart, which began beating on the third day, continues to enlarge. The embryo's body turns 90 degrees, with its left side resting on the yolk, and its head and tail coming close together to form a C shape.
| Characteristics | Values |
|---|---|
| Embryo size | Sensible increase |
| Embryo shape | C shape |
| Head | Moves closer to the tail |
| Limbs | Extension |
| Fingers of the inferior limbs | Differentiation |
| Elbows and knees | Appearance |
| Beak | Development |
| Claws | Appearance |
| Allantois | Growth |
| Vitelline membrane | Surrounds the yolk |
| Chorio-allantoic membrane | Formation |
| Down | Covers the body |
| Internal organs | Development |
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What You'll Learn
The embryo has all the organs needed to sustain life after hatching
The development of a chick is a complex process that takes around three weeks, or 21 days, to complete. Embryonic development begins before the egg is laid, and once the egg is laid, development pauses until favourable conditions are met, either under a broody hen or in a controlled incubator.
By the end of the fourth day of incubation, the embryo has all the organs needed to sustain life after hatching. The embryo grows and develops rapidly, and by the seventh day, digits appear on the wings and feet, and the heart is completely enclosed in the thoracic cavity. The embryo starts to look more like a bird.
On the fifth day of development, there is a sensible increase in the embryo's size, and it takes on a C shape as the head moves closer to the tail. The limbs extend, and the fingers of the inferior limbs differentiate. The embryo's neck continues to lengthen, and the brain settles into its cavity. The external opening of the ear has formed, and claws begin to appear and grow. The embryo is starting to resemble a chick.
By the tenth day of incubation, feathers and feather tracts are visible, and the beak hardens. On day 11, the embryo has the aspect of a chick, and by day 14, the embryo is moving into position for hatching. After 20 days, the chick is in the hatching position, pulmonary respiration has begun, and the chick pierces the inner shell membrane to breathe the air in the cell. The chick is ready to hatch and begins to pierce the shell.
After 21 days of incubation, the chick finally hatches and emerges from the shell. The chick appears drenched and feeble but rapidly becomes lively.
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The embryo's upper and lower beak are now completely differentiated
The development of a chick embryo is a complex process that typically takes 21 days of favourable incubation conditions for the chicken to develop and hatch. The first signs of life begin just 5 hours after fertilisation, when cell division starts to create the new embryo. By the 44th hour of incubation, the heart and vascular systems join, and the heart begins to beat.
By the end of the fourth day of incubation, the embryo has all the organs it needs to sustain life after hatching, and most of its parts can be identified. On the fifth day, the embryo's head and tail come together to form a distinct C shape, and the fingers on the inferior limbs differentiate. This is also when sex differentiation occurs.
On the sixth day, the embryo's dark spot is the eye, and the beak has begun to form. By the seventh day, the digits appear on the wings and feet, and the heart is completely enclosed in the thoracic cavity. The embryo now looks more like a bird.
By the twelfth day, the first few feathers are visible, and by the fourteenth day, the claws are forming and the embryo is moving into position for hatching. After 20 days, the chick is in the hatching position, and the beak has pierced the air cell. Pulmonary respiration has begun, and the chick is ready to hatch.
On the topic of the embryo's beak differentiation, it is important to note that the beak is formed from the ectoderm layer of cells. The ectoderm also produces other important structures such as the nervous system, parts of the eyes, feathers, claws, and skin. By the time the embryo's upper and lower beak are completely differentiated, the neck will continue to lengthen, and the brain will have settled into its cavity. The embryo will also develop claws, and the allantois will grow larger, increasing vascularization. The very first feather follicles will begin to appear, and the embryo will start to resemble a chick.
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The embryo's brain has settled into its cavity
The development of a chick embryo is a complex process that cannot be fully understood without training in embryology. On the fifth day of incubation, the embryo takes on a C shape, with its head moving closer to its tail. There is also an increase in the embryo's size, and the limbs extend. The fingers of the inferior limbs also differentiate.
By the end of the fourth day of incubation, the embryo has all the organs it needs to sustain life after hatching. However, it is not until the fifth day that the embryo's brain settles into its cavity. The brain, along with the spinal cord, forms a hollow structure known as the neural cavity or neurocoel. These cavities are filled with fluid and play a crucial role in the development of the chick embryo's brain.
The neural tube, located dorsally in the median plane of the embryo, forms the basis of the central nervous system. The neural tube is formed from the neural ectoderm, which thickens and stratifies to create the neural plate. This process is known as neurulation and results in the fusion of the neural tube. As the neural folds come together, two subdivisions can be distinguished in the forming brain: the pros-encephalon (archencephalon) and the posterior deuteroencephalon.
The pros-encephalon is further subdivided into the anterior telencephalon and posterior diencephalon, while the rhomb-encephalon divides into the anterior metencephalon and posterior myelencephalon or medulla. These subdivisions create sharp angles in the long axis of the embryonic brain, accompanied by a general flexing of the entire head. The expansion of the brain cavity coincides with the completion of neural tube fusion.
The growth of the brain in the chick embryo is influenced by the accumulation of cerebrospinal fluid (CSF) in a closed neural tube. This pressure leads to a significant increase in brain size, with a 70% increase in cavity size and a 30% increase in tissue amount.
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The embryo's external ear opening has formed
The development of a chick embryo is a complex process that, in natural conditions, takes about three weeks. The transformation of an egg into a chick is considered one of the greatest miracles of nature.
On the fifth day of a chick's development, the embryo's external ear opening has formed. This is part of the wider development of the embryo's sensory organs, including the eyes, nose, and the rest of the ear. The embryo's upper and lower beak are now completely differentiated, as are its legs and wings. The neck continues to lengthen, and the brain has settled into its cavity. Claws are beginning to grow, and the first feather follicles are appearing.
The embryo's external ear opening is a critical part of the development of the auditory system. Studies have shown that prenatal music stimulation facilitates the postnatal functional development of the auditory system. The development of the inner ear is derived from a pair of surface sensory placodes (otic placodes) that appear in human development during week 4, lying in the head region behind the second pharyngeal arch. The otic placodes fold inwards, forming a depression, then pinch off from the surface, forming an epithelium surrounding a fluid-filled sac or vesicle (otic vesicle, otocyst, or auditory vesicle). The otocyst will differentiate to form all components of the membranous labyrinth.
The embryo's development of hearing is a gradual process. Hearing generally begins on incubation day 12 (E12) in the chicken embryo. However, little is known about the response properties of cochlear ganglion neurons for ages younger than E18.
By the end of the fourth day of incubation, the embryo has all the organs needed to sustain life after hatching. By the seventh day, digits appear on the wings and feet, and the heart is completely enclosed in the thoracic cavity. After the tenth day of incubation, feathers and feather tracts are visible, and the beak hardens. On the fourteenth day, the claws are forming and the embryo is moving into position for hatching. After 20 days, the chick is in the hatching position, and pulmonary respiration has begun. After 21 days of incubation, the chick finally begins to break out of the shell.
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Claws appear and begin to grow
On the fifth day of chick development, there is a noticeable increase in the embryo's size, and it takes on a C shape, with the head moving closer to the tail. There is also an extension of the limbs and the differentiation of the fingers of the inferior limbs.
By the ninth day, claws begin to appear and grow, along with the first feather follicles. The embryo's nostrils are present as narrow apertures, and the eyelids also start to grow. The distal portions of the limbs lengthen, and the vitelline membrane completely surrounds the yolk. The embryo is starting to resemble a chick.
On the tenth day, the embryo's eyelids continue to grow larger, covering more of its eyes. The allantois, which is the chick's connection to the chorion, reaches its maximum size. This structure is critical for exchanging gases and dealing with liquid waste.
By the twelfth day, the embryo's claws, toes, and ribs begin to harden due to the calcium intake from the egg shell. The embryo is covered in down feathers along its spine, upper eyelid, and around its ears.
By the thirteenth day, the embryo is almost fully formed, with leg scales growing more quickly and beginning to overlap. A few claws are completely formed, and the body is lightly covered all over with feathers.
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Frequently asked questions
The allantois. It helps the embryo exchange gases and deal with liquid waste.
The embryo's upper and lower beak are now completely differentiated. So are its legs and wings. The neck continues to lengthen. The brain has settled completely into its cavity.
The embryo grows and develops rapidly.
The embryo's entire body turns 90 degrees and lies down with its left side on the yolk. The head and tail come close together so the embryo forms a "C" shape.
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