Fig. 5b 24 FIG. 5: Alternative representation of the NHCD. ( a ) The horizontal axis measures the shortest path from each cell type to the fertilized egg along the network, ℓ $_{N$_{1}$}$. ( b ) The horizontal axis denotes the appearance time of a given cell type, T $_{a}$. For simplicity we do not plot the links leading to loops. The colors of the branches denote the functional classes as in Fig. 1.