Abstract
Ultrastructure of the erythroblasts in mice splenic colonies was studied in contradistinction to that found in the normal mice spleen and bone marrow. Although the basic morphology of erythroblasts in those tissues was identical, most of the erythroblasts in splenic colonies were in the early stage, and those in normal mice were in the intermediate or late stage. A very few or no microtu-bules were seen in the erythroblasts in normal spleen and colonies, while they were often recognized in the marrow erythroblasts. The micropinocytic vesicles were often seen in the marrow erythroblasts. There was no distinct structure delimiting the erythroblasts colonies from the surrounding tissue cells. Further-more, macrophages were often recognized in the central part of colonies. Some macrophages engulfed and digested the erythroblasts. However, attachment apparatus such as desmosome, or the delivery of iron particles from macrophages to erythroblasts was never observed.
