Supplementary Movie 4
Requirement of outward movement in air sac-like structure. Cell division probability was set at p=0.8×10−5 until t=24×104, and p=0.8×10−6 afterwards. The degree of apical constriction was set as ka=5 initially, increased by 0.0012 at each time step to ka=293 until t=24×104, and reduced by 0.0035 until ka reached to 0.5. The cell numbers increased from 40 (t=0) to 153 (t=34×104).