Complex sentence: William M. Springer challenged the constitutionality of the 1864 Act based on the contention that the tax imposed by the statute was a direct tax not apportioned among the states according to the population of each state.
Split into simpler sentences: William M. Springer challenged the constitutionality of the 1864 Act. Springer's challenged was based on the contention that the tax imposed by the statute was a direct tax not apportioned among the states according to the population of each state.