  An analysis of the Dalitz plots for the decays $D^+\to K^-\pi^+\pi^+$ and
$D^+\to\pi^-\pi^+\pi^+$ indicates that structure with significant phase
variation is required in the s-wave $K^-\pi^+$ and $\pi^-\pi^+$ systems in the
region below 1 GeV/c$^2$ effective mass. A constant, non resonant "contact"
term, together with a simple s-wave Breit Wigner amplitude with $M_{0}=797\pm
19\pm 43, \Gamma_{0}= 175\pm 12\pm 12$ MeV/c$^2$ for the $\Km\pip$ system and
$M_{0}=478^{+24}_{-23}\pm 17, \Gamma_{0}=324^{+42}_{-40}\pm 21$ MeV/c$^2$ for
the $\pi^-\pi^+$ system provide good fits to the data in this region.
