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Two morphogenetic factors have been isolated from tissue of colonial hydroids. Both exert strong effects on pattern formation during metamorphosis, regeneration and colony development. Polyp-inhibiting factor (PIF) is a bivalent inhibitor which strongly affects head and bud formation but acts weakly on stolon branching. Proportion-altering factor (PAF) is a distalizing factor. It counteracts the formation of stolon and promotes the formation of head structures during metamorphosis and regeneration. PIF and PAF antagonistically influence the spatial arrangement of polyps within a colony. They are capable of dislocating structures and thus appear to interfere with or are even part of the pattern-controlling mechanism. Both factors are of low molecular size (about 500 daltons), hydrophilic and probably not peptides. [ABSTRACT FROM AUTHOR] more...