Melody Gillespie, age 14, of Stacy, Minn., for her question:
HOW DOES A CHICKEN LAY AN EGG?
The chicken., producer of both eggs and flesh, is probably the farm world's favorite animal. She has been tamed and domesticated for more than 3,000 years. Today more than 100 different varieties can be found of this animal that probably developed from a wild jungle fowl in Southwest Asia.
Through selection and crossing, man has changed the shape, size, color and habits of the chicken. Originally a jungle fowl laid a dozen eggs, hatched them and reared the brood. Some years she would lay a second batch. Vow, however, for generation after generation only the eggs from the best layers have been allowed to hatch and we now have hens that lay more than 300 eggs a year and make no attempt to hatch their own eggs.
Poultry men have also selected other types of fowl that were especially suited to meat production those that grow large and fast.
The hen's egg is one of man's most important foods. Its production is almost a miracle as it builds within the hen's body and is delivered in its delicate container.
The hen's yolk is really the whole egg. In the surface of the yolk is the fertilized ovum. The surrounding yolk is white and yellow and is laid down in alternating, concentric rings around the ovum. Finally the entire yolk mass is enclosed in a thin, elastic membrane.
As the yolky egg passes down the hen's oviduct, it revolves with the heaviest or most dense portion of the white (,the albumen)) being secreted around the yolky mass in spiral sheets. The ends of these sheets form short, twisted cords of white called chalazae.
Next a less dense layer of albumen is deposited and finally two thin shell membranes are laid down around the albumens. The oviduct secretes a fluid albumen which passes through the shell membranes and surrounds the denser albumens.
When the egg reaches the uterus, a shell made of calcium and magnesium phosphates and carbonates is added. At the rounded end of the egg, the two shell membranes separate to form an air space.
The entire movement of the egg through the reproductive tract of the hen takes between 16 and 20 hours.
Bird eggshells are rarely spherical. They are usually oval, cone shaped or cylindrical. The egg shape can actually serve as a protective function. Some birds, for example, nest on rocky ledges or bare ground and round eggs would roll away. This isn't a problem with the hen who has been bred to help fill man's food basket, however