  We construct three extreme different scenarios of the star formation
histories applicable to a sample of dwarf galaxies, based either on their
present metallicity or their luminosity. The three possible scenarios imply
different mechanical energy input rates and these we compare with the
theoretical lower limits established for the ejection of processed matter out
of dwarf galaxies. The comparison strongly points at the existence of extended
gaseous haloes in these galaxies, acting as the barrier that allows galaxies to
retain their metals and enhance their abundance. At the same time our findings
strongly point at a continuous star-forming process, rather than to coeval
bursts, as the main contributors to the overall metallicity in our galaxy
sample.
