Representative photographs of 1-μm thick plastic sections of E10.5 yolk sacs. (A) KLF2^+/+, (B) KLF2^+/-, and (C) KLF2^-/- embryos, stained with a solution of Toluidine Blue, Azure II, and Methylene Blue. EC indicates erythroid cells; BI, blood island; EL, epithelial layer; ML, mesothelial layer. Photographs were taken at 200 × magnification.