Postembryonic Development

Postembryonic Development 

the period in the ontogenesis of multicellular animals that follows the period of embryonic development and usually ends with the onset of sexual maturity and, in most animals, the cessation of growth. Postembryonic development begins after the emergence of the embryo from the egg and embryonic membranes, when the organism becomes capable of active feeding and locomotion. Upon transition to the postembryonic state the organism either immediately possesses the principal pubertal morphological characteristics (direct development) or essentially differs from the pubertal form, in which case the larva that hatches out of the egg must undergo a metamorphosis before it reaches its adult state. Growth continues during the period of postembryonic development and further organogenesis and histogenesis occur. The functions of the developing organism become more complex; establishment of the final proportions of the body is especially characteristic.

In some animals postembryonic development constitutes the greater part of their life span. Among insects, in a number of cicadas the larva lives 17 years, while the pubertal insect lives one summer; the mayfly larva lives to three years, but often in its pubertal form the mayfly lives only one day.

The necessity for defense against enemies and active food procurement are ensured during postembryonic development by a number of adaptations that make the animal self-sufficient, sometimes for its entire life span. With indirect, or larval, development, the animal, having larval organs, is self-sufficient only during the postembryonic period.

A. V. IVANOV