Parthenogenesis is of normal occurrence in the life-cycle of many Hymenoptera.
Generally the larval is the feeding, the imaginal the breeding, stage of the life-cycle.
In one of the best-known species, Cicada septemdecim, from North America, the life-cycle is said to extend over seventeen years.
The difficulty of tracing the relationships of algae is largely due to the inadequacy of our knowledge of the conditions under which they pass through the critical stages of their life-cycle.
In fresh-water Hydromedusae the life-cycle is usually secondarily simplified, but in marine forms the life-cycle may be extremely complicated, and a given species often passes in the course of its history through widely different forms adapted to different habitats and modes of life.