  The integrable systems associated with Seiberg-Witten geometry are considered
both from the Hitchin-Donagi-Witten gauge model and in terms of intermediate
Jacobians of Calabi-Yau threefolds. Dual pairs and enhancement of gauge
symmetries are discussed on the basis of a map from the Donagi-Witten
``moduli'' into the moduli of complex structures of the Calabi-Yau threefold.
