The evolution of spiral galaxies and uncertainties in interpreting galaxy counts

Evolutionary models are discussed with respect to the interpretation of faint galaxy counts. The K-corrections are reviewed with available UV data, and the necessary assumptions and model input parameters. In particular the possibility that the bulges of spiral galaxies have evolved in a form similar to that expected for elliptical galaxies is explored. The inclusion of bulge evolution predicts significantly more galaxies and may be consistent with the steepening count-magnitude slope at faint magnitudes. A significant fraction of Bj = 23 galaxies could be luminous compact objects with redshifts greater than 1 seen during their epoch of rapid star formation.