Ontogeny is the development of a being from conception (fertilisation) to the final adult form. Ontogenesis therefore includes the embryonic development and later growth of the body, and in the case of human beings, development of their psychology
It is sometimes said in evolutionary biology thatontogenesis is a summary of phylogenesis. This concept introduced by Ernest Haeckel in the XIXth century is an exaggeration but it highlights the fact that a person's ontogenesis provides considerable information about the phylogenesis of its species, i.e. about its evolutionary history.
Ontogeny is the study of the embryo (in this case the mouse) during its ontogenesis, providing information about the evolution of the species such as the development and disappearance of branchial clefts. © Ethan Hein CC by-nc-sa 2.0