Electron micrographs of several bone marrow late erythroblasts.

Multinucleate erythroblasts showing striking “double membranes” with partial dilatation of the intramembranous space (A). Erythroblasts revealing nondilated cisternae (B,C). Late erythroblast depicting spongy heterochromatin with numerous “punched out” areas (B). Binucleate erythroblasts showing large areas of nuclear membrane without attached heterochromatin (C). Uranyl acetate and lead citrate stain. Original magnification: A, × 10 600; B and C, × 18 000).