Mass dependence of the HBT radii observed in e+e- annihilation

It is shown that the recently established strong mass- dependence of the radii of the hadron sources, as observed in HBT analyses of the $e^+e^-$ annihilation, can be explained by assuming a generalized inside-outside cascade, i.e. that (i) the four-momenta and the space-time position four-vectors of the produced particles are approximately proportional to each other and (ii) the "freeze-out"times are distributed along the hyperbola $t^2 - z^2 = \tau_0^2$.