These have been described as giant cells with budding nuclei (Bizzozero [2]); but it seems to me that they are worthy of a more distinctive name. I shall speak of them hereafter as megakaryocytes, or large nucleated giant cells, while the first class might be named polykaryocytes, or multinucleated giant cells.
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The evidence of formation of blood platelets from the megakaryocyte is conclusive. Except for the origin of platelets in the early embryo from a forerunner of the megakaryocyte, Wright recognizes no other source for blood platelets in mammals.
Source: wiktionary
Under appropriate culture conditions, the megakaryocyte burst-forming cell can develop into 40 to 500 megakaryocytes within 1 week.
Source: wiktionary