[en] The distributions of quarks in the pion and nucleon are extracted from measurements of the reaction π^-N→μ⁺μ^-X at 253 GeV/c in a naive Drell-Yan analysis, as well as QCD-corrected analyses at leading-log and next-to-leading-log order. As x_π→1 the pion structure function shows a term that varies as 1/m_μμ⁴, which we interpret as a higher-twist effect. Additionally, the angular distribution of the μ⁺ in the muon-pair rest frame tends towards sin²θ as x_π→1 and as m_μμ→0 in a manner consistent with higher-twist effects. When the strongly mass-dependent higher-twist effects are included as part of the pion structure function, the nucleon structure function agrees well with leading-twist results from deeply inelastic lepton-hadron scattering. A significant advance of the present work is the extension of the analysis to low masses by the subtraction of the J/ψ and ψ' resonances from the continuum. Our analysis covers the kinematic range 0.4< x_π<1.0 and 0.02< x_N<0.33 with 3.0μμ<8.55 GeV/c². Cross sections for ψ' producton are presented in an appendix