Kenogenesis and Palingenesis

Kenogenesis noun - Introduction during embryonic development of characters or structure not present in the earlier evolutionary history of the strain or species (such as the addition of the placenta in mammalian evolution).

Palingenesis is an antonym for kenogenesis.

Palingenesis noun - Emergence during embryonic development of various characters or structures that appeared during the evolutionary history of the strain or species.

Kenogenesis is an antonym for palingenesis.