After the body was born, it starts postembryonic development, which can last from 1-2 days to a few hundred years - it all depends on the species.This implies that the duration of a vital sign of the species of organisms, whether such level of organization.Postembryonic ontogenesis consists of these periods: juvenile, puberty and senile, which ends in death.All multicellular organisms are subject to the direct or indirect type of development.
principles of direct
post-embryonic development explicitly peculiar to mammals, reptiles, birds, insects and some, of course, man.In the development of such periods last note:
- childhood;
- adolescence;
- young people;
- phase of his youth;
- stage of maturity;
- old age.
Each period is accompanied by certain changes that eventually lead to the aging and death of the organism.It should be noted that the senile period, there is a lot of physiological and morphological processes that lead to a lowering of vitality and resistance to the adverse effects of external and internal factors.Such mechanisms are, unfortunately, still not fully explored, so they can not be prevented by artificial means.
Death completes postembryonic not only development, but also the existence of an individual organism.It may have a physiological nature, i.e. occur due to aging, and also occur as a result of pathological changes that result often serve a variety of diseases or injuries.
Features indirect development
Indirect postembryonic development occurs exclusively in multicellular animals and is characterized by the emergence of the larvae from the egg - the embryo, which is significantly different in structure from the adults, but already able to eat on their own.Externally, the larva, of course, can have a distant resemblance to their ancestors, but its structure is much easier and the size is much smaller.At present special embryo internal organs, allowing him to live a life different from the one that led the adults of the same species.However, the larva completely absent rudimentary sexual characteristics, so at this stage it is impossible to determine to whom it will become - in male or female.
Indirect postembryonic development implies a profound transformation of the body that occur throughout the whole period.In animals, these processes do not affect only certain parts of the body, but the whole body as a whole.Over time, the authorities larvae disappear and in their place there are bodies, which are peculiar to the adult animal.Post-embryonic development of animals can be of two types: complete and incomplete metamorphosis.In the first case, the insect passes these stages: egg, larva, imago, and the second - the transformation of the larvae into a full adult state is through pupal stage.
