Practice question

Drosophila oocytes are centrolecithal, containing abundant central yolk surrounded by a thin peripheral cytoplasmic layer. This yolk mass prevents formation of complete cleavage furrows, so early mitoses proceed without cytokinesis, producing multiple nuclei sharing common cytoplasm in a syncytium. These nuclei migrate outward to the cortex, establishing syncytial blastoderm. Later, plasma membranes ingress simultaneously to cellularize surface nuclei while central yolk remains uncleaved. Because only the peripheral cytoplasm divides over undivided yolk, the pattern is classified as superficial meroblastic cleavage, characteristic of insects and distinct from holoblastic patterns.