Morphology and growth kinetics of fibroblastoid adherent cells (FACs) derived from human AoM, UGRs, and YS. Representative morphologies of FACs derived from AoM (A,D), UGRs (B,E), and YS (C,F) are shown at lower and higher densities. Cumulative population-doubling assay reveals that the FACs from AoM (G) proliferate more rapid than those from UGRs (H) and YS (I). Original magnification: (A-F) × 100. AoM indicates aorta with its surrounding mesenchyme; UGRs, urogenital ridges; and YS, yolk sac.