cenogenesis, kenogenesis, caenogenesis, cainogenesis, kainogenesis(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)

Kenogenesis(noun)

modified evolution, in which nonprimitive characters make their appearance in consequence of a secondary adaptation of the embryo to the peculiar conditions of its environment; -- distinguished from palingenesis