Fig. 6. Morphometric analysis of lumen formation. (A-D) Average normalized aggregate volume (A) does not change (P=0.06), whereas the average normalized cell volume (B) is reduced (P=0.02) in the window 60 minutes before and after lumen appearance. The average normalized sum of the apical and contact surfaces of individual cells (C) and normalized aggregates sphericities (D) remained constant (P=0.18 or 0.57, respectively). Individual data points (± s.e.m.) were normalized to the values at time 0 (only cells facing the lumen were measured in seven-cell aggregates; n=18). The indicated P-values were calculated by linear regression analysis (see Materials and Methods) (see also supplementary material Fig. S4D-H). (E) Luminal volume increases steadily after lumen initiation (P=6x10^–5). Coloured areas in the background of (A-E) define the morphogenetic stages shown in (A) (n=7). (F) Development of a luminal space (shaded 3D object) reconstructed from 4D images (aggregate of Fig. 5). Scale bar, 5 µm.