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While we presented arguments against a simple cosmological building block scenario in the preceding paragraphs, there is clear evidence for ongoing harassment and accretion of dwarf galaxies. The most prominent examples of ongoing accretion are the tidal streams of the Sagittarius dSph galaxy (Ibata et al. 1994), and the giant stream of metal-rich giants around M31 (Ibata et al. 2001). Additional stellar overdensities have been detected in the Milky Way, e.g., the Monoceros feature (Newberg et al. 2002; Yanny et al. 2003), the Canis Major overdensity (Martin et al. 2004), the Triangulum-Andromeda feature (Rocha-Pinto et al. 2004) and more substructure near M31 (Zucker et al. 2004a). These may be parts of the tidal tails of disrupted dwarfs. The continuation of deep wide-field surveys and the addition of spectroscopic data for phase-space information will ultimately permit us to identify and constrain less pronounced accretion events and their number, providing an important observable for hierarchical structure formation.

Evidence for harassment is apparent in the S-shaped surface density profile of the Galactic dSph Ursa Minor (Palma et al. 2003) and in the twisted isophotes of the M31 dE companions M32 and NGC 205 (Choi et al. 2002). These and other dSphs may eventually be accreted as well. A crucial bit of information in this context is the knowledge of the orbits of dwarf companions - something the Gaia mission will help to establish.