"The growth of the rhabdosome from the initial prosicula is described for two species of Monograptus. Sections of the metasicula have shown the nature of the 'Stillstandsguertel' first described by Kraft, and in both species evidence about the structure of the interthecal septum is given. It appears that there are two forms of Monograptus dubius which have the same external appearance but differ in the details of early development."