b, Extremity of penial seta of Acanthodrilus (after Horst).
c, Seta of Urochaeta (Perier).
In the vibraculum the part representing the zooecium is relatively smaller, and the mandible has become the "seta," an elongated chitinous lash which projects far beyond the zooecial portion of the structure.
archegonium, those surrounding the archegonia and base of the seta.
Frequently, also, a considerable differentiation of vegetative tissue occurs in the wall of the spore-capsule itself, and in some of the higher forms a special assimilating and transpiring organ situated just below the capsule at the top of the seta, with a richly lacunar chlorophyllous parenchyma and stomata like those of the wall of the capsule in the Anthocerotean liverworts.