The Collaborative International Dictionary of English v.0.48:

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]

The Collaborative International Dictionary of English v.0.48:

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]

WordNet (r) 3.0 (2006):

kenogenesis
    n 1: 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) [syn: cenogenesis,
         kenogenesis, caenogenesis, cainogenesis,
         kainogenesis] [ant: palingenesis, recapitulation]