[Patterns of differentiation of medusae buds and medusae of podocoryne carnea M. Sars after isolation and dissociation].

1. The normal development of medusa ofPodocoryne carnea M.SARS is divided into 10 different stages according to morphological and anatomical criteria. 2. Medusa buds are viable and develop different patterns of differentiation when isolated early from the blastostyl. These patterns depend on type and frequency of the bud's age of development at the moment of isolation. 3. After isolation young medusa buds of the stages 1-4 are submitted to a process of dedifferentiation leading to a "Kugelstadium" (two-layered sphere). Out of this morphogenetically indifferent stage stolos can emerge. These often give rise to gasterozooids. This structural change, originating from young medusa buds, may be termed metaplasia. 4. Older medusa buds isolated in the stages 5-8 develop normally into medusae or medusa-like structures. The critical phase when the direction of development of the medusa is irreversibly fixed and out of which the differentiation of the medusa can autonomically emerge, lies between the bud-stages 4 and 5. 5. Aggregates of cells, obtained by dissociation of fully differenciated medusae, in a few cases produced stolos and structures of stolo-like shape. This means that at least part of the medusa cells has not irreversibly lost the ability to functional and structural metaplasia. 6. All the changes of structure, observed in the course of the investigations, led to a stolo to be designated as the most primitive stage of differentiation. Under favourable conditions the next higher stages (gasterozooids, blastostyls) can emerge.