Saturday, July 22, 2006

The ontogenesis

Ontogenesis (from the Greek. on, born case ontos - real and... genesis), the individual development of organism, the totality of the sequential morphological, physiological and biochemical conversions, undergone with organism from the moment of its origin to the end of the life. Ontogenesis includes increase, increase in the mass of body, its sizes, differentiation. Term "O." it is introduced by 3. Haeckel (1866) with the formulation to them biogenetical law. In animals and plants, which are multiplied through sex, the origin of new organism is achieved in the process of fertilization, and O. begins from the impregnated egg cell, or the zygote. In organisms, of which the characteristically sexless multiplication, O. begin from the formation of new organism by dividing of maternal body or specialized cell, via budding, and also from the rhizome, the tuber, the bulb and the like (see vegetative multiplication). In the course of O. each organism regularly passes sequential phases, stages or development periods, from which basic in the organisms, which are multiplied through sex, they be: embryonic (embryonic, or prenatal), poslezarodyshevyy (postembryonal, or post-natal) and the development period of adult organism. At the basis of ontogenesis lies the complex process of realization on the different stages of the development of the organism of the hereditary information, placed in each of its cells. The caused by heredity program O. is achieved under the effect of many factors (condition of environment, intercellular and intertissue interactions, humoral- hormonal and nervous regulations) and is evinced by the interconnected processes of multiplying of cells, their increase and differentiation. Laws governing the ontogenesis, causal mechanisms and factors of cellular, woven and organ differentiation are studied by complex science - biology of development, which uses, besides the traditional approaches of experimental embryology and morphology, the methods of molecular biology, cytology and genetics. Ontogenesis and the historical development of organisms - phylogenesis - the indissoluble and mutually caused sides of the united process of the development of living nature. The first attempt at the historical substantiation O. made i. f. of mekkel'. The problem of relationship O. and phylogenesis was set By ch. Darwin and was developed By f. Mueller, 3. Haeckel and all other connected with the change heredities, new in evolutionary sense signs appear in the O., but only those of them, which contribute to the best adaptation of organism to the condition for existences, they remain in the process of natural selection and are transferred to the subsequent generations, i.e. they are attached in the evolution. The knowledge of regularities, reasons and factors O. serves as scientific basis for finding the means of influence on the development of plants, animals and man, which has important significance for the practice of plant growing and stock raising, and also for medicine.