Adults of several species of both solitary and colonial ascidians are capable of slow crawling, involving the progressive formation of new attachments and tearing or dissolving the old ones. The ampullae play a leading part. A moving colony may divide into two, or two adjacent colonies may fuse: true fusion has been observed only once, inTrididemnum tenerum.BothCiona intestinalisandDiplosoma listerianummay metamorphose by attachment to the surface film and are capable of post‐metamorphic attachment to a solid surface for a prolonged period. In such attachment the ampullae play a leading role. A free‐swimming (unattached) colony ofDiplosomatakes on the form of aPyrosomacolony. Such colonies have been reared in the laboratory forming cigar‐shaped, jet‐propelled bodies up to 1 cm. long with as many as fifty