Megakaryocytes in the yolk sac, liver and bone marrow of the mouse: a cytometrical analysis by semithin light microscopy.

Megakaryocytes of the yolk sac, liver and bone marrow were cytometrically observed by light microscopy using semithin plastic sections. In the yolk sac at 10 and 11 days of gestation, megakaryocytes contained an irregularly round nucleus and clearly stained short lines corresponding to the demarcation membranes. All yolk sac megakaryocytes were less than 10 microns in diameter. Large megakaryocytes appeared in the fetal liver at 12 days and increased in number thereafter. Megakaryocytes in the fetal liver changed in their size between 12 and 15 days of gestation. Liver megakaryocytes at 15 days of gestation and during the neonatal period showed similar distribution profiles in cell size and nuclear-cytoplasmic ratio as adult bone marrow megakaryocytes.