Results are presented of a very large-scale numerical experiment on two-dimensional gravitational clustering. The cloud in cell method is used for effective suppression of two-body effects. An initial perturbation spectrum with a lower cut-off in wavelength simulates conditions in the adiabatic theory of galaxy formation. The collisionless particles are appropriate to the hypothesis that hidden mass existed in the appropriate form (e.g. massive neutrinos or primordial black holes) prior to galaxy formation. In the case study presented (Ω = 1.07, H = 75 km s−1 Mpc−1, Zel'dovich spectrum of amplitudes) it is found that: (1) A cell structure forms at approximately the scale of the shortest wavelength perturbation, although larger voids exist. (2) There is no fragmentation or disruption of these large-scale inhomogeneities unless ad hoc (isothermal?) small-scale perturbations are added. (3) Although hierarchical clumping tends to progressively destroy the cell structure, such a structure can continue to exist to z = 0 in a closed (Ω > 1) model. Some new structure forms well after the primary era of pancaking.