We present in-situ observation studies of the directional solidification of transparent model eutectic alloys. On the basis of the thin-sample directional solidification method, original experimental devices have been developed in our laboratory for investigating fundamental aspects of the dynamics of coupled-growth front patterns in diffusive conditions. The most recent results concern: 1-the eutectic-grain dependency of coupled-growth microstructures, that is, the effects, of crystallographic origin, of the anisotropy of the free energy of the interphase boundaries, 2-the dynamics of lamellar and rod-like eutectic growth patterns in semi-bulk samples, and 3-the univariant growth of ternary eutectics (spiral eutectic dendrite). Quantitative comparison with time-resolved numerical simulations (phase-field) was also crucial. These studies, carried out on ground, are part of the preparation of the science-in-microgravity program Transparent Alloys (ISS/MSG ; ESA/NASA), which aims, in particular, at shedding new light on the lamella-to-rod transition in binary eutectics.