Critical experimental studies in a model transparent organic system have been carried out to establish the interlamellar spacing selection criterion for directionally solidified eutectic alloys. It is shown that the spacing selection is not very sharp and a finite distribution of spacing is observed for a given velocity. The width of the distribution is found to increase as the velocity is decreased. This band of spacings is shown to lie within the stable zone predicted by the lamellar stability theory, and the average spacing lies slightly above the value which corresponds to the minimum undercooling condition. A number of velocity change experiments were also carried out in which the initial spacing was either larger or smaller than the final spacing. For both these conditions, the average eutectic spacing is found to drift toward the spacing value which is slightly larger than the smallest stable spacing for the final velocity. All experimental results show that the stable range of eutectic spacings is much smaller than that discussed by Jackson and Hunt.