This is a typical bird egg.This is a typical bird egg.

In the large end of the egg there is In the large end of the egg there is an air space. an air space.

Oxygen comes into the space Oxygen comes into the space through tiny holes, or pores, into through tiny holes, or pores, into the shell.the shell.

Of course the egg also Of course the egg also contains the yolk and the egg contains the yolk and the egg white.white.

The white spot on this yolk is called an The white spot on this yolk is called an “ovum.” This egg has been fertilized by a “ovum.” This egg has been fertilized by a rooster. If kept warm by a hen or in an rooster. If kept warm by a hen or in an incubator this ovum will grow into a chick.incubator this ovum will grow into a chick.

This ovum has been kept warm for 24 This ovum has been kept warm for 24 hours. The growing chick gets food and hours. The growing chick gets food and water from the yolk and oxygen from the water from the yolk and oxygen from the air through the shell’s air holes.air through the shell’s air holes.

After two days the white spot has changed. After two days the white spot has changed. The cells are forming what will be the The cells are forming what will be the chick’s body. Now the ovum is called an chick’s body. Now the ovum is called an “embryo.”“embryo.”

The top of the The top of the embryo will be the embryo will be the chick’s head. The chick’s head. The bottom will be its bottom will be its tail. The dark tail. The dark grains are the grains are the beginnings of beginnings of blood vessels.blood vessels.

By the third day, the By the third day, the embryo has grown embryo has grown into the shape of a into the shape of a backward question backward question mark. The top part mark. The top part of the question mark of the question mark is the head. is the head.

The dark spot in the The dark spot in the middle is the heart. middle is the heart. It is actually beating It is actually beating after three days!!after three days!!

A network of blood A network of blood vessels stretches over vessels stretches over the surface of the yolk. the surface of the yolk.

The heart pumps the The heart pumps the blood through the blood through the vessels. The blood vessels. The blood comes back to the comes back to the embryo, bringing food embryo, bringing food and water from the yolk. and water from the yolk. In this way the embryo In this way the embryo is nourished.is nourished.

After four days you After four days you can see the eye – can see the eye – the dark, round spot the dark, round spot on the head. The on the head. The embryo is growing embryo is growing fast and needs fast and needs more food. To more food. To bring this food from bring this food from the yolk, more and the yolk, more and more blood vessels more blood vessels have formed.have formed.

A clear pouch called A clear pouch called the “amniotic sac” the “amniotic sac” has grown around the has grown around the embryo. Inside the embryo. Inside the sac, the embryo sac, the embryo moves about in a moves about in a watery fluid.watery fluid.

The amniotic sac The amniotic sac protects the embryo protects the embryo and gives it a safe and gives it a safe place to develop.place to develop.

By the fifth day, the embryo By the fifth day, the embryo has changed even more. has changed even more. As the chick floats in the As the chick floats in the amniotic sac, you can see amniotic sac, you can see the little buds that will the little buds that will become its wings and legs.become its wings and legs.Another sac is growing – Another sac is growing – the “allantois membrane.:” the “allantois membrane.:” It is full of blood vessels It is full of blood vessels that take in oxygen from that take in oxygen from the air and carries away the air and carries away carbon dioxide. carbon dioxide. This is how the embryo This is how the embryo “breathes” even though it is “breathes” even though it is submerged in watery fluid. submerged in watery fluid. In time the allantois will In time the allantois will grow all around the yolk, grow all around the yolk, the albumen, and the the albumen, and the embryo.embryo.

The embryo has been kept warm for one week The embryo has been kept warm for one week now and is now called a “fetus.” The fetus has now and is now called a “fetus.” The fetus has the beginnings of a brain, a heart, and a the beginnings of a brain, a heart, and a stomach. It has eyes, ears, and a beak. Even stomach. It has eyes, ears, and a beak. Even its toes are all there.its toes are all there.

Notice how the blood vessels are growing Notice how the blood vessels are growing around the yolk.around the yolk.

At nine days the At nine days the fetus is starting to fetus is starting to look like a chick. look like a chick. The beak is The beak is formed. The wings formed. The wings are shaped like a are shaped like a chicken’s wings. chicken’s wings. Even the little Even the little stump of a tail it stump of a tail it there.there.

At eleven days At eleven days old the eyelids old the eyelids are formed. The are formed. The beak opens and beak opens and closes. The closes. The bumps on the bumps on the skin are the skin are the beginnings of beginnings of feathers.feathers.

When the fetus When the fetus is two weeks is two weeks old, it has old, it has feathers on its feathers on its body and claws body and claws on its toes. on its toes.

At 15 days At 15 days the fetus the fetus looks more looks more and more like and more like a chick. a chick. Notice how Notice how much of the much of the yolk has been yolk has been used up.used up.

By the 19By the 19thth day there day there is only a little bit of is only a little bit of yolk left. Before yolk left. Before hatching it too will be hatching it too will be drawn into the chick’s drawn into the chick’s body.body.

After hatching the After hatching the chick will not need to chick will not need to eat or drink for a few eat or drink for a few days. The last bit of days. The last bit of yolk will provide yolk will provide nourishment.nourishment.

The day before hatching the chick pokes a hole in the sac and The day before hatching the chick pokes a hole in the sac and takes a breath. The chick is still getting oxygen through blood takes a breath. The chick is still getting oxygen through blood vessels, but has to practice breathing before it hatches. Once its vessels, but has to practice breathing before it hatches. Once its head is in the air space, you can hear the chick peeping loudly head is in the air space, you can hear the chick peeping loudly inside the shell.inside the shell.

On the chick’s beak you can see the egg tooth. This tooth has a On the chick’s beak you can see the egg tooth. This tooth has a sharp little bump that will help the chick break the shell. A few sharp little bump that will help the chick break the shell. A few days after hatching the egg tooth will drop off.days after hatching the egg tooth will drop off.

Three weeks after the egg was first laid the Three weeks after the egg was first laid the chick pecks a small hole in the shell. It is chick pecks a small hole in the shell. It is hard work. After the hole is made the chick hard work. After the hole is made the chick seems to go to sleep. Nothing more is heard seems to go to sleep. Nothing more is heard from it for hours.from it for hours.

The chick begins pecking again. As it breaks the The chick begins pecking again. As it breaks the shell the chick turns around inside the egg. You can shell the chick turns around inside the egg. You can see how the egg rolls over as the chick pecks.see how the egg rolls over as the chick pecks.

The shell is broken almost all the The shell is broken almost all the way around.way around.

The chick gives a mighty kick with its big The chick gives a mighty kick with its big feet and…feet and…

……it bursts out of the shell.it bursts out of the shell.

Left behind in the shell is the Left behind in the shell is the allantois membrane with the allantois membrane with the waste matter inside it.waste matter inside it.

The chick tries to walk, but it is The chick tries to walk, but it is too weak. It hobbles about using too weak. It hobbles about using its wings as props.its wings as props.

Two days after Two days after hatching the chick is hatching the chick is on its own. It is not on its own. It is not finished growing yet! finished growing yet! Its downy feathers Its downy feathers will be replaced by will be replaced by larger ones.larger ones.

In about six months In about six months this baby chick will be this baby chick will be a full-gown chicken.a full-gown chicken.