[Significance of the colonial components for the medusa formation and differentiation inPodocoryne carnea M. Sars].

1. All axial regions of the gonozoid and the medusa buds ofPodocaryne carnea M. Sars incorporate3H-thymidine. Medusa buds grow by mitosis and by migration of cells from the colony into the buds. 2. Stolonization inhibits the formation and differentiation of medusa buds: non stolonizing chimerae formed by a gonozoid and an autozoid produce more buds than stolonizing ones. 3. When isolated gonozoids and likewise isolated budding regions are not connected with an nutritive autozoid, the formation and differentiation of medusa buds are restricted. Young medusa buds (stage 3, Frey, 1968) transplanted onto autozoids may differentiate into medusae, while isolated buds of the same stage are transformed into stolons. 4. If the hypostome of the gonozoid is separated from the subhypostomal budding region by ligature and does not regenerate, the young buds already present are resorbed and no new ones are formed. 5. Heads of gonozoids transplanted onto cauli of adult autozoids may induce the formation of medusa buds in the subtentacular axial region. These buds differentiate into normal medusae. 6. Isolated adult autozoids, treated with extract taken from hypostomes of gonozoids, form medusa buds which complete normal differentiation. 7. Treatment of autozoid colonies with extract from gonozoids brings about a standstill of colony growth and resorption of autozoids. After transfer to normal sea-water a compensatory increase in growth and head formation takes place. 8. The results are discussed. It is suggested that an "activator" substance is produced in the hypostome of the gonozoid which induces and maintains the budding region in the subtentacular zone. Furthermore, budding would be dependent on the nutritional state of the gonozoid, food being supplied by the autozoid, and on the extent of inhibition by intensive stolonization.