Factors effecting manubrium-regeneration in hydromedusae (Coelenterata)

1. Umbrellar fragments of the leptomedusaCampanularia johnstoni with or without parts of the radial canal demonstrate a gradient in the potential for manubrium regeneration and in regeneration time. 2. Implantation experiments exclude the manubrium as a source of inhibition or induction in the regeneration of another manubrium. One special case of inhibition appears to be due to competition for a common substrate. 3. Medusa fragments consisting of only peripheral umbrella (C-fragments) undergo a considerably different restitution process as compared with fragments including a central portion of the umbrella (A-fragments). Vital stain is seen to disperse in the subumbrellar tissues during this process in C-fragments, whereas vital stain in A-fragments is observed to accumulate and later on is incorporated into the regenerating manubrium. 4. The mesogloea of different-sized A-fragments retains a stable form when freed of its adhering cellular components, after a 12-24 h regeneration period; for C-fragments, however, the same result is not observed until 72 to 96 h after their excision. 5. InPodocoryne carnea the observed gradients in manubrium regeneration can be abolished when the subumbrellar tissues are separated from the mesogloea by collagenase treatment. 6. A model for manubrium regeneration in interradial fragments, based on the influence of tension exerted by the cicatrization process and the counteracting mesogloeal force, is presented and discussed.