Homozygous females produce embryos that arrest prior to cellularisation. Embryos derived from cnn^mfs8/Df(2R)cnn females have severe defects in nuclear division and distribution. The defects become more dramatic as cleavage progresses. Large areas of the cortex are devoid of nuclei. Nuclei which do migrate to the surface mostly continue to undergo DNA replication but fail to segregate their chromosomes. Consequently, more nuclei appear large and polyploid. Some of these drop back into the interior of the embryo, while others remain and form large chromosome aggregates at the embryonic cortex. Chromosomes are seen spread along the length of spindles, and monopolar and multipolar spindles are seen. The embryos never achieve cellularisation.