The Collaborative International Dictionary of English v.0.48:

Metagenesis \Met`a*gen"e*sis\, n. [Pref. meta- + genesis.]
   1. (Biol.) The change of form which one animal species
      undergoes in a series of successively produced
      individuals, extending from the one developed from the
      ovum to the final perfected individual. Hence, metagenesis
      involves the production of sexual individuals by nonsexual
      means, either directly or through intervening sexless
      generations. Opposed to monogenesis. See Alternate
      generation, under Generation.
      [1913 Webster]

   2. (Biol.) Alternation of sexual and asexual or gemmiparous
      generations; -- in distinction from heterogamy.
      [1913 Webster]

WordNet (r) 3.0 (2006):

metagenesis
    n 1: alternation of sexual and asexual generations [syn:
         metagenesis, digenesis]