  The 3-part appearance of many CMEs arising from erupting filaments emerges
from a large magnetic flux tube structure, consistent with the form of the
erupting filament system. Other CMEs arising from erupting filaments lack a
clear 3-part structure and reasons for this have not been researched in detail.
This paper aims to further establish the link between CME structure and the
structure of the erupting filament system and to investigate whether CMEs which
lack a 3-part structure have different eruption characteristics. A survey is
made of 221 near-limb filament eruptions observed from 2013/05/03-2014/06/30 by
EUV imagers and coronagraphs. 92 filament eruptions are associated with 3-part
structured CMEs, 41 eruptions are associated with unstructured CMEs. The
remaining 88 are categorized as failed eruptions. For 34% of the 3-part CMEs,
processing applied to EUV images reveals the erupting front edge is a
pre-existing loop structure surrounding the filament, which subsequently erupts
with the filament to form the leading bright front edge of the CME. This
connection is confirmed by a flux-rope density model. Furthermore, the
unstructured CMEs have a narrower distribution of mass compared to structured
CMEs, with total mass comparable to the mass of 3-part CME cores. This study
supports the interpretation of 3-part CME leading fronts as the outer
boundaries of a large pre-existing flux tube. Unstructured (non 3-part) CMEs
are a different family to structured CMEs, arising from the eruption of
filaments which are compact flux tubes in the absence of a large system of
enclosing closed field.
