kenogenesis

Kenogenesis \Ken`o*gen"e*sis\, n. [Gr. ? new + E. genesis.] (Biol.) 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. [Written also cenogenesis and c[ae]nogenesis.] [1913 Webster]

cenogenesis \cen`o*gen"e*sis\ n. [Gr. ? new + E. genesis.] (Biol.) The introduction during embryonic development of characters or structure not present in the earlier evolutionary history of the strain or species (as addition of the placenta in mammalian evolution); a 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. [Also spelled caenogenesis and formerly kenogenesis.] [WordNet 1.5 + 1913 Webster]