(a) Distribution of spot types in ST slices sampled from three different developmental stage. (b) Coordinate alignment result of ST slices from 4.5 to 5 PCW and 6.5 PCW. (c) Coordinate alignment result of ST slices from 6.5 PCW to 9 PCW. (d) The alignment of three ST slices (4.5–5 PCW, 6.5 PCW, 9 PCW) in a 3D coordinate framework.