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We address the question of the distribution of morphological types for faint galaxies in HST images taken with the Wide Field Camera as part of the Medium-Deep Survey, an HST key project. Especially for pre-refurbishment images, direct morphological classification is very difficult except for the brightest objects. Therefore we study the distribution of their axis ratios, which can be measured reliably down to $ V \sim 23 $. The distribution of both intrinsic and observed axis ratios is very different for early- and late-type galaxies, and we show that a good estimate of the fraction of early-type galaxies as a function of apparent magnitude can be obtained in this way. Preliminary results seem to indicate that the average axis ratio decreases with apparent luminosity, in qualitative agreement with simple models of the evolution of galaxies.
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