  The present paper presents a discussion of classification systems for
galaxies, with special emphasis on possible modifications of the Hubble "tuning
fork" diagram, and on galaxy types not included in Hubble's original scheme.
Hubble's morphological types were defined in terms of standards observed at
small look-back times that were mostly located in the field, or in poor
clusters. It is pointed out that it is often difficult to shoehorn galaxies
located in the cores of rich clusters, or objects viewed at large look-back
times, into the Hubble classification system. The evolutionary relationships
between E, S0 and dSph galaxies are presently still controversial and poorly
understood. It is suggested that S0 galaxies may have arrived at their present
morphology along various evolutionary tracks. Late-type barred spirals are
found to be systematically less luminous than normal late-type galaxies. This
suggests that the dichotomy between normal and barred spirals may reflect
significant differences in their evolutionary histories. Such differences might
be explored by searching for systematic differences between the [O/Fe] values
in normal and barred spirals. Finally it is pointed out that the Large
Magellanic Cloud may have been a low surface brightness galaxy for an ~8 Gyr
period that ended 3-5 Gyr ago. This suggests that some galaxies can jump from
one morphological classification type to another.
