  Duality in the integrable systems arising in the context of Seiberg-Witten
theory shows that their tau-functions indeed can be seen as generating
functions for the mutually Poisson-commuting hamiltonians of the {\em dual}
systems. We demonstrate that the $\Theta$-function coefficients of their
expansion can be expressed entirely in terms of the co-ordinates of the
Seiberg-Witten integrable system, being, thus, some set of hamiltonians for a
dual system.
