Abstract The nature of secondary multiplication in the Digenea, especially in the molluscan host is reviewed. The concepts of alternation of generations and polyembryony are examined and discarded as unhelpful. In the absence of both meiosis and recognizable ovaries in miracidia, sporocysts and rediae, there are no criteria for distinguishing diploid ameiotic ‘eggs’ from other diploid cells, and thus no clear distinction is possible between ameiotic parthenogenesis and budding from a single cell. Comparison with other groups, especially the coelenterates, suggests budding and metamorphosis of larval stages as the explanation of digenean life histories. Functional equivalents of the digenean larval stages are indicated in other groups. The germinal lineage possibly preserves a line of totipotential cells, which by avoiding differentiation retain an unrestricted range of phenotypic responses. By dividing as infrequently as possible, consistent with the production of an adequate number of germinal cells, the lineage is, to a degree, preserved from the creation and incorporation of molecular errors, and thus the subsequent life history stages are protected from the incorporation of ‘senescence’ acquired at an earlier stage in the life history. Restriction of sexuality to the fluke stage usually promotes outbreeding between genetically diverse adults, each with the proven capacity to complete successfully all life history phases.