The Collaborative International Dictionary of English v.0.48:

Heterogenesis \Het`er*o*gen"e*sis\, n. [Hetero- + genesis.]
   1. (Biol.) Spontaneous generation, so called.
      [1913 Webster]

   2. (Biol.) That method of reproduction in which the
      successive generations differ from each other, the parent
      organism producing offspring different in habit and
      structure from itself, the original form, however,
      reappearing after one or more generations; -- opposed to
      homogenesis, or gamogenesis.
      [1913 Webster]

WordNet (r) 3.0 (2006):

heterogenesis
    n 1: the alternation of two or more different forms in the life
         cycle of a plant or animal [syn: alternation of
         generations, heterogenesis, xenogenesis]