Spontaneous generation refers both to the supposed processes in which different types of life might repeatedly emerge from specific sources other than seeds, eggs or parents, and also to the theoretical principles which were presented in support of any such phenomena.
Another version of spontaneous generation is variously termed univocal generation, heterogenesis or xenogenesis, in which one form of life has been supposed to arise from a different form, such as tapeworms from the bodies of their hosts [REF].