Key points are not available for this paper at this time.
The relation between spiral and S0 galaxies is considered in the light of recent data on the colors and morphology of disk systems and on the content of clusters at different redshifts. It is suggested that S0's may be disk systems that lost their gas-rich envelopes at an early stage and consumed their remaining gas by star formation. The fact that S0's have smaller disk-to-bulge ratios than spirals is consistent with this picture, as are the colors of S0's if most of their star formation stopped at least a few gigayears ago.
Larson et al. (Thu,) studied this question.