They formed a separate system (the Rete Sicula) until in 1906, like the rest of the railways of Italy, they passed into the hands of the state, with the exception of the line round Mount Etna and the line from Palermo to Corleone.
A Monograptus makes its first appearance as a minute dagger-like body (the sicula), which represents the flattened covering of the primary or embryonic zooid of the colony.
This sicula, which had originally the shape of a hollow cone, is formed of two portions or regions - an upper and smaller (apical or embryonic) portion, marked by delicate longitudinal lines, and having a fine tabular thread (the nema) proceeding from its apex; and a lower (thecal or apertural) portion, marked by transverse lines of growth and widening in the direction of the mouth, the lip or apertural margin of which forms the broad end of the sicula.
A bud is given off from the sicula at a variable distance along its length.
This theca grows in the direction of the apex of the sicula, to which it adheres by its dorsal wall.