Electron microscopy of the formation of the cellular blastoderm in Drosophila melanogaster

Abstract

1. 1. The transition from the syncytial to the cellular blastoderm has been studied in Drosophila melanogaster embryos with the electron microscope. 2. 2. The ultrastructure of the syncytial blastoderm is described during the first stage of membrane growth. Before cell membranes form between the nuclei located at the surface of the embryo, the nuclei are spherical and lack nucleoli. Flattened cisternae of ER are present below the nuclei, but most of the basophilia of the cytoplasm is due to the presence of many unattached ribosomes. As the cell membranes form, a nucleolus appears in the nuclei which elongate and withdraw from the surface. 3. 3. Tubular extensions of the outer nuclear membrane occur near the membrane furrows, and these tubules, or vesicles from the tubules, may fuse with the furrow. However, rows of vesicles along the future site of the cell membranes are not found. 4. 4. The cytoplasmic side of the furrow bears filamentous material, 500 Å in thickness. This material is lacking on other membranes and it is possibly related to the formation of new cell membrane material.