We have tracked the structural evolution of the monoolein bicontinuous cubic phase under in meso crystallogenesis conditions. Significantly, all measurements have been carried out in situ within a crystallisation plate reproducing the exact conditions during a crystallisation trial. The structure of the MO cubic phase, doped with a small concentration of amyloid-beta peptide, was measured 1 day, 5 days, 7 days and 21 days after addition of PACT crystallisation screen, which systematically varies cation, anion, pH and polyethylene glycol (PEG). The components of the screen had a significant impact on the structure of the cubic phase. We have rationalised the structural variation with respect to the effect of the individual screen components. Specifically addition of higher M w PEG effected a transition from a diamond cubic phase (Q II D) to a gyroid cubic phase (Q II G) across the majority of the plate and the Q II G phase became more prevalent with time. The effect of individual salts was correlated with their position in the Hofmeister series. Changes in pH and buffer system had a more minor effect on mesophase structure. We have discussed the implications of the observed structural changes with respect to the putative mechanism of protein crystal growth within a lipidic cubic phase.