Intraspecific tissue incompatibility can also be found in some lower organisms, for example the Cnidariae. It is shown how a colony of Hydractinia echinata attains full growth and how it behaves when it comes in stolonal contact with compatible respectively incompatible members of their own species. If the colonies are histologically compatible they will fuse, if they are incompatible special nettle cells will be lanced against the competitor at the point of contact. The poison can lead to paralysation. Persisting contact of two competitors causes massive degeneration symptoms.