Fried, scrambled, boiled, poached, or raw, eggs are eaten and enjoyed by almost everyone. Used in deserts, breads, and all sorts of recipes these little beauties are a staple of kitchens all over the world.

How do we get them? How are they made?

The Formation of an Egg: The Yolk: The chicken egg starts as an egg yolk inside a hen. A yolk (called an oocyte at this point) is produced by the hen's ovary in a process called ovulation. Fertilization: The yolk is released into the oviduct (a long, spiraling tube in the hen's reproductive system), where it can be fertilized internally (inside the hen) by a sperm. The Egg White (albumin) : The yolk continues down the oviduct (whether or not it is fertilized) and is covered with a membrane (called the vitelline membrane), structural fibers, and layers of albumin (the egg white). This part of the oviduct is called the magnus. The Chalazae : As the egg goes down through the oviduct, it is continually rotating within the spiraling tube. This movement twists the structural fibers (called the chalazae), which form rope-like strands that anchor the yolk in the thick egg white. There are two chalazae anchoring each yolk, on opposite ends of the egg. The Eggshell : The eggshell is deposited around the egg in the lower part of the oviduct of the hen, just before it is laid. The shell is made of calcite, a crystalline form of calcium carbonate. This entire trip through the oviduct takes about one day. Growth of the Embryo: The fertilized blastodisc (now called the blastoderm) grows and becomes the embryo. As the embryo grows, its primary food source is the yolk. Waste products (like urea) collect in a sack called the allantois. The exchange of oxygen and carbon dioxide gas occurs through the eggshell; the chorion lines the inside surface of the egg and is connected to the blood vessels of the embryo.

Internal Structure of the EGG Definitions : air cell - an empty space located at the large end of the egg; it is between the inner and outer shell membranes. chalaza - a spiral, rope-like strand that anchors the yolk in the thick egg white. There are two chalazae anchoring each yolk, one on the top and one on the bottom. (The plural of chalaza is chalazae.) germinal disc or blastodisc - a small, circular, white spot (2-3 mm across) on the surface of the yolk; it is where the sperm enters the egg. The nucleus of the egg is in the blastodisc. inner shell membrane - the thin membrane located between the outer shell membrane and the albumin. outer shell membrane - the thin membrane located just inside the shell. shell - the hard, protective coating of the egg. It is semi-permeable; it lets gas exchange occur, but keeps other substances from entering the egg. The shell is made of calcium carbonate. thick albumin - the stringy part of the egg white (albumin) located nearest the yolk. thin albumin - the watery part of the egg white (albumin) located farthest from the yolk. vitelline (yolk) membrane - the membrane that surrounds the yolk. yolk - the yellow, inner part of the egg where the embryo will form. The yolk contains the food that will nourish the embryo as it grows.

The Incubation Period: The embryo develops inside the egg for 21 days (the incubation period), until a chick pecks its way out of its eggshell and is hatched.)

CHICKEN EMBRYO AT 72 HOURS. CHICKEN EMBRYO AT 10 DAYS.

Not all eggs come out normal. These eggs are not only unproductive but inedible in most cases.

DOUBLE YOLKERS APPEAR WHEN OVULATION OCCURS TOO RAPIDLY, OR WHEN ONE YOLK SOMEHOW GETS "LOST" AND IS JOINED BY THE NEXT YOLK. DOUBLE YOLKERS MAY BE BY A PULLET WHOSE PRODUCTIVE CYCLE IS NOT YET WELL SYNCHRONIZED. THEY'RE OCCASIONALLY LAID BY A HEAVY-BREED HEN, OFTEN AS AN INHERITED TRAIT. THE PHOTOS SHOW A DOUBLE YOLK EGG LAID BY EITHER A BARRED ROCK OR RHODE ISLAND RED HEN OWNED BY SHELLEY MADDEN-KEMP, NEAR FORT WORTH, TEXAS ON JANUARY 29, SHELLEY MADDEN-KEMP OCCASIONALLY, AN EGG CONTAINS MORE THAN TWO YOLKS. THE GUINNESS BOOK OF RECORDS LISTS THE WORLD'S LARGEST [CHICKEN] EGG (WITH A DIAMETER OF 9 INCHES/22.5 CM) AS HAVING FIVE YOLKS AND THE HEAVIEST EGG (1 POUND/0.45 KG) AS HAVING A DOUBLE YOLK AND A DOUBLE SHELL. THIS PHOTO SHOWS THE SIZE OF THE DOUBLE YOLKER NEXT TO A REGULAR SIZED BR/RIR EGG.

SUCH AN EGG IS MOST OFTEN A PULLET'S FIRST EFFORT, PRODUCED BEFORE HER LAYING MECHANISM IS FULLY GEARED UP. IN A MATURE HEN, A WIND EGG IS UNLIKELY, BUT CAN OCCUR IF A BIT OF REPRODUCTIVE TISSUE BREAKS AWAY, STIMULATING THE EGG PRODUCING GLANDS TO TREAT IT LIKE A YOLK AND WRAP IT IN ALBUMEN, MEMBRANES AND A SHELL AS IT TRAVELS THROUGH THE EGG TUBE. YOU CAN TELL THIS HAS OCCURRED IF, INSTEAD OF A YOLK, THE EGG CONTAINS A SMALL PARTICLE OF GRAYISH TISSUE. THE PHOTOS BELOW SHOW A BARRED PLYMOUTH ROCK FART EGG LAID DURING THE FIRST WEEK OF APRIL, 2004.

NO SHELL: This is another accident of the hen's reproductive system and is not necessarily an indication of any problem. The membrane was placed on the yolk and white, but it somehow slipped past the "shell mechanism" and the shell wasn't deposited.

AN EGG WITHIN AN EGG, OR A DOUBLE SHELLED EGG APPEARS WHEN AN EGG THAT IS NEARLY READY TO BE LAID REVERSES DIRECTION AND GETS A NEW LAYER OF ALBUMEN COVERED BY A SECOND SHELL. SOMETIMES THE REVERSED EGG JOINS UP WITH THE NEXT EGG AND THE TWO ARE ENCASED TOGETHER WITHIN A NEW SHELL. THE EGG ON THE LEFT WAS LAID EITHER BY A BUFF ORPINGTON OR A BLACK AUSTRALORP IN EARLY THE EGG FOUND INSIDE THE OTHER HAD NO YOLK (FART EGG).

This happens from time to time and is just an "accident". The long, thin egg below was laid by one of our Barred Rock hens in June, It is over 2 1/2 inches long and less than 1 1/4 inches across the middle.

A CHINESE HEN HAS PRODUCED A SPOON-SHAPED EGG. AN EGG IN CHINA HAS BEEN FOUND WITH A TAIL. THE EGG, FOUND BY CHEF WANG AT HIS RESTAURANT IN ANYANG CITY, HENAN PROVINCE, IS NORMAL SIZE, BUT HAS A TAIL THAT IS 3 CM LONG.

This is fairly common and occurs most often in brown eggs. The pigment is sometimes deposited on the egg unevenly during production resulting in one end being a light tan and the other a darker brown. The large end usually has the darker color. The deposit of the pigment rarely forms a recognizable pattern (like seeing shapes in clouds), but here is a happy face egg found August 6, 2000.

 BLOOD SPOTS: Blood spots occur when blood or a bit of tissue is released along with a yolk. Each developing yolk in a hen's ovary is enclosed in a sack containing blood vessels that supply yolk building substances. When the yolk is mature, it is normally released from the only area of the yolk sac, called the "stigma" or "suture line", that is free of blood vessels. Occasionally, the yolk sac ruptures at some other point, causing blood vessels to break and blood to appear on the yolk or in the white. As an egg ages, the blood spot becomes paler, so a bright blood spot is a sign that the egg is fresh. MEAT SPOTS: Meat spots are even less common than blood spots. They appear as brown, reddish brown, tan, gray or white spots in an egg, usually on or near the yolk. Such a spot may have started out as a blood spot that changed color due to chemical reaction, or it may be a bit of reproductive tissue. WORMY EGGS: Wormy eggs are extremely rare, occurring only in hens with a high parasite load. Finding a worm in an egg is not only unappetizing, but is a clear indication that you are not doing a good job in keeping your hens healthy and parasite-free.

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