An amoeba's membrane as a mesh, in 3D and then in 4D. Its cortex pulls it in, its pressure holds its volume, and a signalling medium on the membrane fires: where it fires (cyan) actin pushes a pseudopod out; behind it myosin (warm) tightens and pulls back. On the floor it sticks, so the feet carry it. The mesh is remeshed as it flows: long edges split, short ones merge (in 3D edges also flip). In 4D the membrane is a mesh of tetrahedra, remeshed the same way, and what you see is your 3D slice through it: a foot leaving your slice through w shows as a piece cut off. The purple ball is the nucleus. Drag to turn, pinch or scroll to zoom. In 4D the pad twists your slice into w (J L, I K), the lever moves it ana and kata (R F), ⊞ or Z squares it up. how it works · CELL · kata