There are some species which, having no hydroid or strobila state, mature without alternation of generation (metagenesis).
A third way in which metagenesis might originate is through polymorphosis.
The term Nurse (German Amme), employed for the asexual generations in metagenesis, may advantageously be dropped altogether.
metagenesis met·a·gen·e·sis (mět'ə-jěn'ĭ-sĭs)
See alternation of generations.