Although both hatch from eggs, chickens and frogs experience different life cycles. Chicken eggs are fertilised internally and laid individually, while frog eggs are laid by the thousands and fertilised externally. Also, frogs endure stages of metamorphosis between hatching and maturity, while chickens do not.
A hen lays about one egg per day. If the hen has not mated with a rooster before she lays the egg, the egg has not been fertilised and will never hatch. If she has mated and the sperm is still stored in the hen's body, the egg may be fertilised before its hard outer shell forms. After the shell is hard, the hen lays the egg in her dry nest and sits on it to keep it warm. A fertilised egg must be incubated constantly or it will never hatch. Inside the hard shell, a yolk nourishes the embryo until the egg hatches after 21 days.
Unlike chickens, frogs lay eggs in water by the thousands. Prior to mating, a female's belly fills with still-unfertilised eggs and she looks for water where she will mate and lay her eggs. The male frog climbs onto her back and fertilises the eggs as they emerge from the female frog's body. These eggs, called frog spawn, have jellylike outer shells. They cling together in a slippery clump that floats on water. Depending on the breed of frog, the female may leave her eggs or she may stay or return frequently to watch over them. Although frogs lay thousands of eggs, few survive predators to hatch six to 21 days later.
Chick to Chicken
When the chicken egg is ready to hatch, the baby inside uses a special egg tooth on top of its beak to break free of the shell. When it finally emerges--a process that can take many hours--the newly hatched chick roughly resembles the adult chicken but smaller. Its feathers are soft and yellow instead of white. The chick lacks the distinctive red flaps below the beak and on top of the head. As the chick grows, it develops a wattle and comb and true feathers replace the chick's yellow down. The chicken reaches maturity after about six months and can live for seven to 15 years, depending on breed.
Tadpole to Frog
A frog egg hatches to release not a frog, but an embryo, which attaches itself to a reed in the water and quickly becomes a tadpole. After a few days or weeks, depending on the breed, the tadpole breaks away from the weed and swims freely in the water, eating small insects and algae. The tadpole looks nothing like its parents. More like a fish than a frog, it breathes through gills and has a long tail that propels it through the water. After about five weeks, the frog begins to change, with skin gradually growing over the gills until they disappear. Legs begin to sprout sometime between six to nine weeks and the tail begins to shrink until it disappears. At 12 to 16 weeks, the air-breathing adult frog leaves the water and may live another four to 15 years, depending on breed.