Two types of immature megakaryocytic series in the human fetal liver.

Megakaryocytes in the liver obtained from 185 human embryos and fetuses during the period from 28 days to 22 weeks of ovulation were investigated by light and electron microscopy. The early hepatic megakaryoblasts and the early hepatic promegakaryocytes at stage I observed in the intercellular spaces of the hepatocytes until 10 weeks of ovulation (early stage of hepatic hemopoiesis) were larger than the late hepatic megakaryoblasts and the late hepatic promegakaryocytes at stage I observed after 10 weeks of ovulation (late stage of hepatic hemopoiesis). The chromatin of the former two cells was finely dispersed, whereas that of the latter two showed moderate central and peripheral clumping. These findings seem to indicate that the progenitor cells of the magakaryoblasts and the hemopoietic stem cells in the liver in the early stage of hepatic hemopoiesis morphologically differ from those in the liver in the late stage, and that the megakaryocytes in the liver until 10 weeks of ovulation differ in maturation course from those after this ovulation stage.