An internally contradictory character of individual development may suggest a new periodization of the latter. Etagenesis is an age-associated development of an organism from the zygote to death. Ontogenesis is the period of realization of the genetic program of the organism's development under effects of exogenic factors, the period of growth and shaping of its main structure and functions, and the period of formation of its reproductive function. Mesogenesis is the period of the relatively stable state which is characterized by changing the balance between the processes of aging and antiaging, i.e. the vitauct. Gerontogenesis is the period during which destructive processes of aging prevail over antiaging processes. No strict borderlines between the above periods exist.