A simple model for the manifold of galaxies.

The authors assume an initial protogalaxy to consist of a few independently moving clouds. As driving process of its early evolution they have the collisions of clouds. This process dissipates energy, but slowly enough such that the evolution can be considered as quasi-static. The retarding process is star formation which the authors model with a phenomenological formula depending on the density and the random velocities of the clouds. Star formation diminishes the substrate of the driving process and therefore may bring the evolution to a "halt" if there is not new delivery. If this condition does not act, then a further "halt" occurs if the energetically deepest state permitted under conservation of angular momentum is arrived at. The authors' semi-quantitative model permits to understand besides of other details: 1. The fact that the observed number of dimensions of the manifold of galaxies is two (amongst other possibilities, one may choose mass and angular momentum as two independent parameters). 2. The appearance of galaxies of different morphological type at constant mass. Here the authors identify the Hubble sequence by the axis ratio and by the fraction of nonstellar mass left at the end of the early evolution. 3. The occurrence of an extremal oblateness at an intermediate type - due to the competition of the driving and the retarding processes. 4. The formation of the type scale at varying masses within an acceptable time scale - due to the scaling laws inherent to the model.