and DM content is still questioned by some authors [@kro10] because of the large discrepancy of the number of objects really observed vs. expected from $\Lambda$CDM cosmology and because of their orbit concentration to the so-called disk-of-satellites, also found around M 31. This invokes the preference of their tidal-tail origin [@met09]. The observed large velocity dispersions, which are otherwise applied as representative to derive the M/L ratio is then caused by tidal effects.

3.  How is their evolution determined by the vicinity of the massive mature galaxy? Not only the tidal field must have a disruptive effect, but also a gaseous halo of the central galaxy will interact with the ISM of the dSphs [@may07]. That the relation of the gas fraction bound to the dSphs is increasing with distance from the MWG [@har01], points into that direction.

4.  Vice versa the question arises, how do the satellites influence the structure and evolution of the mature galaxy, here the MWG.

The first three questions also concern the morphological transition from gas-rich satellites to dSphs. Nevertheless, dSphs follow a mass-metallicity relation [@dek03; @gre03] and continue the total brightness vs. central surface-brightness relation from normal dEs to the faint end [@gre03].

As 