Terminal Motility in Elongating Stolons of Proboscidactyla flavicirrata

Proboscidactyla flavircirrata is a commensal hydroid whose stolonselongate rapidly in the absence of its host. Growth pulsationscomparable to those of other hydroids originate endogenouslyin each stolon tip, although influenced by the to and fro movementsof the hydroplasm. Neither growth pulsations nor elongationappear to depend upon cellular proliferation, because the distalends of stolons lacked mitotic figures and since irradiationsufficient to halt mitosis failed to stop stolon elongation.Cellular migration is also apparently unessential for elongationbecause severed stolon tips, isolated from potential sourcesof reusable cells, nevertheless elongated. Marking experimentssuggested that cells changed shape rather than location as severedtips advanced. In old preparations the stolons became attenuatedbecause the tips continued to progress without adequate recruitmentof cells. Stolons deprived of their tips failed to elongatealthough they were still connected to the remainder of the colonyand contained mitotic cells. Cytochalasin B simultaneously haltedgrowth pulsations and stolon elongation in a reversable manner.Apparently stolon tip locomotion in Proboscidactyla is essentialto the elongation process.