  Interplanetary coronal mass ejections (ICMEs) often consist of a shock wave,
sheath region, and ejecta region. The ejecta regions are divided into two broad
classes: magnetic clouds (MC) that exhibit the characteristics of magnetic flux
ropes and non-magnetic clouds (NMC) that do not. As CMEs result from eruption
of magnetic flux ropes, it is important to answer why NMCs do not have the flux
rope features. One claims that NMCs lose their original flux rope features due
to the interactions between ICMEs or ICMEs and other large scale structures
during their transit in the heliosphere. The other attributes this phenomenon
to the geometric selection effect, i.e., when an ICME has its nose (flank,
including leg and non-leg flanks) pass through the observing spacecraft, the MC
(NMC) features will be detected along the spacecraft trajectory within the
ejecta. In this Letter, we examine which explanation is more reasonable through
the geometric properties of ICMEs. If the selection effect leads to different
ejecta types, MCs should have narrower sheath region compared to NMCs from the
statistical point of view, which is confirmed by our statistics. Besides, we
find that NMCs have the similar size in solar cycles 23 and 24, and NMCs are
smaller than MCs in cycle 23 but larger than MCs in cycle 24. This suggests
that most NMCs have their leg flank pass through the spacecraft. Our geometric
analyses support that all ICMEs should have a magnetic flux rope structure near
1 AU.
