Postembryonic development and laws of ontogenesis

Postembryonic development lasts from birth or hatching to the end of the organism’s life. In direct development the young organism resembles the adult and mainly grows: birds, mammals and lizards develop this way. In development with metamorphosis a larva hatches from the egg; it differs from the adult in structure and habitat and later turns into the adult form through metamorphosis. For example, when a tadpole becomes a frog the tail disappears and lungs and legs appear; this change is controlled by the thyroid hormone thyroxine. The importance of metamorphosis is that the larva and the adult feed on different food and so do not compete with each other; in some insects the larva only feeds and grows, and in many there is also a pupal stage.