Morgan [127, 128, 129, 130] has produced a system for classifying the central concentration of light in a galaxy to give population groups which apparently correlate with the stellar content of the inner parts of the galaxy  as judged by integrated spectral types. These population groups a, af, f, fg, g, gk, and k imply early and late spectral-type stars, respectively, as contributing most of the light from the nucleus; however, the designation is found by inspecting the central concentration of monochromatic light: a galaxies have little or no central concentration while k galaxies are highly concentrated. In addition, Morgan identifies form families, which are explained in below; these correspond to the most basic classification, see above. A recent application of this classification system to southern galaxies is given in .
|D||Galaxies with rotational symmetry but showing neither spiral structure nor ellipticity|
|cD||Supergiant D galaxies, predominantly found in clusters  and embedded in an extensive halo|
|Ep||Peculiar ellipticals containing conspicuous absorbtion patches|
|N||High-luminosity nucleus superimposed on a considerably fainter outer envelope, see also |
According to  dumb-bell galaxies are a group of objects allied to the D galaxies, in which two, separated, approximately equal nuclei are observed in a common envelope. They may well be related to galaxies that have one or more fainter components in their envelopes. Dumb-bell galaxies are then the extreme cases of very close multiple galaxies in which there are only two, but equal, components. A catalogue of dumb-bell galaxies can be found in .