The final stage of the nucleated, immature erythrocyte, before nuclear loss. Typically the cytoplasm is described as acidophilic, but it still shows a faint polychromatic tint. The nucleus is small and initially may still have coarse, clumped chromatin, as in its precursor, the polychromatophilic erythroblast, but ultimately it becomes pyknotic, and appears as a deeply staining, blue-black, homogeneous structureless mass. The nucleus is often eccentric and sometimes lobulated. [ http://openisbn.com/search.php?q=0721601464&isbn=1/ ]