The number of mitotic cells per hemi-neuromere in Borr^unspecified mutant embryos is reduced significantly to approximately 50% of the wild-type at stage 12, and to approximately 20% of the wild-type at stage 14. In addition, the overall number of cells per hemi-neuromere is also lower than normal in Borr^unspecified cells. The percentages of prophase and prometaphase cells are higher in Borr^unspecified mutants compared with the wild-type, whereas anaphases and telophases are underrepresented in the mutants. This profile shift of the mitotic stages appears to be progressive during embryonic development, and becomes more pronounced by stage 14 when telophases have become exceedingly rare, maybe as a result of cumulative defects during consecutive abnormal cell divisions. Many of the rare anaphases detected at stage 12 appear to be abnormal, exhibiting uneven segregation of chromatin.