What is ontogeny, what is its periodization?

Ontogenesis is a period of development of an organism that begins from the moment of fusion of parental gametes to the biological death of an individual. It includes several periods:
1. Embryonic – begins from the period of fertilization before the birth of the organism. Includes the stages of fragmentation, gastrulation and initial differentiation of organs and systems.
2. Postembryonic – from birth to the moment the reproductive function begins to function.
3. Reproductive – the period when an organism can reproduce sex cells to reproduce similar organisms.
4. Period of disappearance of reproductive function – aging of the organism occurs, followed by biological death.