Most of bryozoans are protandrous hermaphrodites. However, protogyny is also known among them, and there are variations within different populations of the same species. Bryozoan colony may be thought of as a dynamic system that regularly changes its sexual status with age. When protandrous, the colony starts to grow as sterile, continues as male, and finally becomes hermaphroditic. As testes complete their functioning earlier, it is possible that the colony may became female. In some species overwintered female colonies can develop new testes and become hermaphroditic once more. Bryozoan populations consist of the colonies of different ages, and it appears they are cross-fertilized in general. Self-fertilization, that was confirmed experimentally, can probably occur as a supplementary mechanism in extreme situations, and it never provides a reproduction.