  So far most studies on the structure of coronal mass ejections (CMEs) are
conducted through white-light coronagraphs, which demonstrate about one third
of CMEs exhibit the typical three-part structure in the high corona (e.g.,
beyond 2 Rs), i.e., the bright front, the dark cavity and the bright core. In
this paper, we address the CME structure in the low corona (e.g., below 1.3 Rs)
through extreme-ultraviolet (EUV) passbands and find that the three-part CMEs
in the white-light images can possess a similar three-part appearance in the
EUV images, i.e., a leading edge, a low-density zone, and a filament or hot
channel. The analyses identify that the leading edge and the filament or hot
channel in the EUV passbands evolve into the front and the core later within
several solar radii in the white-light passbands, respectively. What's more, we
find that the CMEs without obvious cavity in the white-light images can also
exhibit the clear three-part appearance in the EUV images, which means that the
low-density zone in the EUV images (observed as the cavity in white-light
images) can be compressed and/or transformed gradually by the expansion of the
bright core and/or the reconnection of magnetic field surrounding the core
during the CME propagation outward. Our study suggests that more CMEs can
possess the clear three-part structure in their early eruption stage. The
nature of the low-density zone between the leading edge and the filament or hot
channel is discussed.
