Phillip Postier, age 11, of Skiatook, Okla., for his question:

CAN AN UNBORN CHICK BREATHE INSIDE ITS SHELL?

Hens lay eggs all year around, although their egg production is highest during the spring months. Today's hen had ancestors who only laid eggs during the spring, however. Almost all wild birds lay only in the spring. The bird's pituitary gland, located at the base of the brain, secretes hormones when the amount of daylight increases, and this speeds the development of eggs.

It isn't necessary for a female chicken to be mated with a rooster to have her lay eggs. However, her eggs will not hatch into chicks unless the eggs are fertilized.

Hens start laying eggs at about 5 months old, and continue in their prime laying between 250 and 350 eggs each year until they are about 14 months old. Commercial egg farms usually sell their hens for meat when production drops.

Most eggs that go to market are unfertile, but those that are, must be kept at relatively low temperatures to prevent embryonic development.

Fertilization of the hen's egg takes place in the upper part of the oviduct. The union of male and female reproductive cells causes the development of the embryo. The fertilized cell starts to divide almost immediately, and many cell divisions are completed before the egg is laid.

For a chick to hatch, the egg must be incubated under a hen or in an incubator for 21 days with a temperature between 99 and 100 degrees Fahrenheit. The egg white provides nourishment for the embryo for the first two weeks, and then during the third week the new baby receives the necessary nourishment from the yolk.

Much like babies develop in their mother's bodies before they are born, a baby chick has no need to breathe air until he enters the world on his own. The baby chick's breathing organs go into action when it pecks its way out of the shell.

Farmers buy about nine out of 10 chickens they raise from breeder hatcheries or commercial hatcheries. Hatcheries produce more than 3.75 billion baby chicks each year to fill the huge demand for both egg laying chickens and meat chickens.

There are about 325 million egg laying chickens in the United States today. They lay about 72 billion eggs each year.

Leading egg producing state in the United States is California, where more than 8.75 billion eggs go to market each year. Producing more than 5.5 billion each year is Georgia, and Pennsylvania, North Carolina, Arkansas and Indiana each turn out more than 3 billion annually. More than 2 billion eggs are produced each year in Iowa, Alabama, Florida and Texas.

Leading broiler raising state is Georgia followed (in order) by Arkansas, Alabama, North Carolina, Mississippi, Maryland, Texas, Delaware, California and Maine.