Fig. 2. Spontaneous differentiation of human ES cells. (A) Micrograph of a Hematoxylin and Eosin-stained section of a typical teratoma following the grafting of human ES cells into the testis capsule of immunodeficient mice, showing the presence of cartilage (1), primitive neural cells (2), stratified squamous epithelium (3), glandular epithelium (4), muscle (5) and other cell types. (B) Histological section of a human ES cell embryoid body. Scale bars: A, 800 µM; B, 100 µM.