Fig. 2. Mouse blastocyst morphology under various conditions. The initial cell aggregate (A) and the simulated blastocyst at t=2000 (B-F) are shown in cross-sectional views of xz-(left column) and yz-(right column) planes. (A) The initial cell aggregate, in which either a central (black circle) or peripheral (blue circle) vertex is replaced by a tetrahedron (t=0), followed by enlargement under various conditions specified in B-F. (B) An aggregate without zona pellucida (ZP) and with cavitation initiated from a central vertex. (C) An aggregate enclosed with a spherical ZP with cavitation initiated from a central point. (D) An aggregate enclosed with the ellipsoidal (long y-axis) ZP and cavitation from the center. (E) The ellipsoidal (long z-axis) ZP with cavitation initiated from a peripheral vertex. (F) The ellipsoidal (long y-axis) ZP with cavitation from a peripheral point.