Light microscopic observations of baboon femoral arterial endothelial cells (BFAECs, ID 2X0038) cultured to passage numbers 2, 4, 6, 8, 9, and 10, which are equivalent to cell population doublings of 6, 12, 18, 24, 27, and 30. The BFAECs were collected from a 2-year-old baboon (ID# 1 × 16715, Table 1). As shown on the figure, endothelial cells at the 9th or 10th passage had enlarged cytoplasmic volume, and diminished extent of characteristic cobble stone feature.